東台灣蛇綠岩中尖晶石橄欖岩及角閃石輝長岩之礦物化學及全岩化學研究

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(1)國立臺灣師範大學理學院地球科學研究所碩士論文 Department of Earth Sciences College of Science. National Taiwan Normal University Master Thesis. 東台灣蛇綠岩中尖晶石橄欖岩及角閃石輝長岩之礦物化學及全岩化學研究 Mineral and whole rock geochemistry of the spinel peridotite and hornblende gabbro from the East Taiwan Ophiolite, Southeast Taiwan.. 謝伯杰 Bor-Jie, Hsieh. 指導教授：. 謝奈特. 博士. Adviser : J. Gregory Shellnutt, Ph.D. 中華民國一○四年六月 June, 2015.

(2) Abstract The South China Sea is one of the youngest marginal ocean basins and is an important feature for reconstructing the tectonic evolution of Southeast Asia. The opening of South China Sea is primarily based on the magnetic anomaly record and is thought to have been active between 32 and 15.5 Ma. The East Taiwan Ophiolite (ETO) is one of the few preserved remnants of South China Sea. The age of ETO is obtained by LA-ICP-MS in situ zircon U/Pb methods and yielded an age of 14.1 ± 0.4 Ma, suggesting that magmatic activity lasted an additional 1.5 million years. New mineral chemistry and bulk rock geochemical data indicate the ETO formed at an oceanic ridge setting. Cr-spinel data (Cr# = 42 – 54) and depleted εNd(t) values (i.e. +9.1) from the peridotites plus the depleted εNd(t) values (i.e. +11.4) and LREE depleted pattern (La/Yb ≦ 1) of the ETO gabbro are consistent with a ridge setting (i.e. N-MORB composition). The East Taiwan Ophiolite is likely a portion of the terminal part of the spreading ridge of South China Sea prior to subduction beneath the Luzon arc.. Key words: ophiolite, geochemistry, East Taiwan Ophiolite, peridotite, Taiwan, South China Sea. I.

(3) Acknowledgement Three years as a master student not only did I progress on the academic field but also make some differences in me. I have to give my best thanks to professor Shellnutt for giving me this opportunity working on this master thesis and supporting and accompanying me from the slow beginning till the harsh end. I also need to give my gratitude to a bunch of people for their kindness help through my three year work. Thanks to Dr. Mary Yeh and Dr. George Ma for taking me to and helping me with the field work. Thanks to Dr. Yoshiyuki Iizuka and his assistants Mr. Wang and Miss Hsieh for all the help on the SEM and EPMA experiments. Thanks to Dr. Kuo-Long Wang and Dr. Typhoon Lee and their assistants Mr. Lin and Mr. Hsu for all the help on the isotopic, trace elements and REEs analysis. Thanks to Dr. Sun-Lin Chung and Dr. Yuan-Hsi Lee and their assistants Miss Tang and Miss Tsai for the U-Pb age dating. I want to give my special thanks to all the members in professor Shellnutt’s group. Carol Chuang is always a good and reliable consultant when I have questions either on academic or personal life. Wen-Yu Hsia gives me some useful messages and share me good news from time to time. Thuy Pham Thanh and Duyên Trần usually share some interesting Vietnam things and expand my vision. You made my master student life wonderful and unforgettable. Last but not least, I want to express my love to my lovely family. My parents, brother and sister are my best support whenever I need help. I would not accomplish this thesis without their fully support and I would like to dedicate this thesis to my family. II.

(4) Table of Contents Abstract. ............................................................................................................................ I. Acknowledgement ................................................................................................................ II Table of Contents ................................................................................................................ III List of Figures ...................................................................................................................... V List of Pictures .................................................................................................................... VI List of tables ...................................................................................................................... VIII Chapter 1 Introduction ..................................................................................................... 1 1.1 Introduction .......................................................................................................... 1 1.2 Introduction of the Ophiolite .............................................................................. 3 1.2.1. Historical background of ophiolite complexes .................................................. 3. 1.2.2. Types of ophiolite .............................................................................................. 9. 1.2.3. Global distribution of ophiolite ....................................................................... 12. 1.2.4. Ophiolite of circum-Pacific ............................................................................. 17. 1.3 Geological Background ...................................................................................... 18 1.3.1. Geological setting and tectonic evolution of the South China Sea .................. 18. 1.3.2. General Geology of Taiwan............................................................................. 23. 1.3.3. Geological setting of Costal Range ................................................................. 26. 1.4 East Taiwan Ophiolite and sample collection .................................................. 30 1.4.1. Previous researches of the East Taiwan Ophiolite........................................... 30. 1.4.2. Sample collection ............................................................................................ 32. Chapter 2 Research Methods.......................................................................................... 37 2.1 Petrography Description.................................................................................... 37 2.2 Scanning Electron Microscope (SEM)/ Energy Dispersive Spectrometry ........ (EDS) ............................................................................................................... 40 2.3 Electron Probe Micro Analyzer (EPMA) ......................................................... 43 2.4 In situ zircon Laser Ablation Inductively Coupled Plasma Mass ...................... Spectrometry (LA-ICP-MS) ......................................................................... 45 2.5 Thermal Ionization Mass Spectrometer (TIMS) ............................................. 48 2.6 Inductively coupled plasma-mass spectrometry (ICP-MS) ............................ 52 2.7 X-Ray Fluorescence Spectrometry (XRF) ....................................................... 53 Chapter 3 Petrography .................................................................................................... 56 3.1 Petrography ........................................................................................................ 56 III.

(5) 3.2 SEM/EDS images................................................................................................ 62 Chapter 4 Results ............................................................................................................. 68 4.1 Mineral Chemistry ............................................................................................. 68 4.1.1. Spinel from the ETO peridotites ...................................................................... 68. 4.1.2. Gabbro Mineral Chemistry .............................................................................. 69. 4.2 In situ zircon U/Pb age dating result ................................................................ 70 4.3 Trace elements, Rare Earth Elements (REEs) and Sr/Nd isotopes ............... 76 4.4 Whole rock geochemistry .................................................................................. 83 Chapter 5 Discussion ....................................................................................................... 85 5.1 Age of the East Taiwan Ophiolite ..................................................................... 85 5.2 Rare earth elements, trace elements and isotopic composition of the ETO ...... mantle ............................................................................................................. 88 5.3 The tectonic setting of the East Taiwan Ophiolite ........................................... 93 5.4 Implications for the South China Sea ............................................................. 100 Chapter 6 Conclusion ....................................................................................................106 References .......................................................................................................................107 Appendixes .......................................................................................................................115 Appendix 1.. EPMA Data ......................................................................................... 115. Appendix 1.. EPMA Data ......................................................................................... 130. Appendix 2.. U - Pb age data ................................................................................... 136. IV.

(6) List of Figures Figure 1.. Typical ophiolite sequence. ............................................................................... 7. Figure 2.. Suprasubduction zone (SSZ) type ophilite. ....................................................... 8. Figure 3.. Global distribution of some major ophiolites. ................................................. 15. Figure 4.. Map of Southeast Asia. .................................................................................... 22. Figure 5.. Geologic framework of Taiwan. ...................................................................... 25. Figure 6.. Geological setting of Coastal Range region. ................................................... 28. Figure 7.. Different geological stratigraphy of the Coastal Range. .................................. 29. Figure 8.. Map of Guanshan area and Chiawu creek and the sample collecting spots. ... 33. Figure 9.. SEM structure. ................................................................................................. 41. Figure 10.. TIMS structure. ................................................................................................ 49. Figure 11.. 206. Pb/238U - 207Pb/235U concordia plot. ............................................................. 74. Figure 12.. 206. Pb/238U mean age. ........................................................................................ 75. Figure 13.. Sample REE concentration spider diagram. .................................................... 80. Figure 14.. Sample trace elements spider diagram. ........................................................... 81. Figure 15.. The foraminifera timescale NN2 to NN6 correspond to the geological ................... timescale. .......................................................................................................... 87. Figure 16.. REE pattern of the peridotites.......................................................................... 89. Figure 17.. Hornblende gabbro TD01014 REE pattern. .................................................... 90. Figure 18.. Initial 87Sr/86Sr vs. εNd value. .......................................................................... 92. Figure 19.. Rock sequence of East Taiwan Ophiolite. ....................................................... 96. Figure 20.. Whole rock Mg number. .................................................................................. 97. Figure 21.. Whole rock aluminum content......................................................................... 98. Figure 22.. Spinel chrome number. .................................................................................... 99. Figure 23.. South China Sea spreading ridge and magnetic anomalies. .......................... 101. Figure 24.. Tectonic development of the East Taiwan Ophiolite at 15 Ma. .................... 105. V.

(7) List of Pictures Picture 1.. Serpentinite blocks. ......................................................................................... 34. Picture 2.. Glassy basalt. ................................................................................................... 34. Picture 3.. Pillow basalt. ................................................................................................... 35. Picture 4.. Gabbro. ............................................................................................................ 35. Picture 5.. Fallen block of peridotite and landslide. .......................................................... 36. Picture 6.. Peridotite. ......................................................................................................... 36. Picture 7.. A finished thin section. .................................................................................... 38. Picture 8.. Carl Zeiss Axioplan 7082 polarizing optical microscope. ............................... 39. Picture 9.. JEOL USA JSM-7100F Analytical Field Emission SEM. .............................. 42. Picture 10. JEOL W-EPMA JXA8900-R electron probe microanalyzer. .......................... 44 Picture 11. UP-213 laser ablation system. ......................................................................... 46 Picture 12. Agilent 7500cx ICP-MS. ................................................................................. 47 Picture 13. Thermo Finnigan Mat GmbH MAT262Q thermal ionization mass spectrometer. 50 Picture 14. Thermo ScientificTM Triton Plus multicollector thermal ionization mass........................ spectrometer....................................................................................................... 51. Picture 15. Panalytical AxiosmAX WDXRF. ....................................................................... 54 Picture 16. Melting the powder and flux by Claisse® M4 Fluxer. ..................................... 55 Picture 17. Finished glass beads. ....................................................................................... 55 Picture 18. Optical microscope image of sample TD01001. ............................................. 58 Picture 19. Optical microscope image of sample TD01001. ............................................. 59 Picture 20. Optical microscope image of sample TD01002. ............................................. 60 Picture 21. Optical microscope image of sample TD010014. ........................................... 61 Picture 22. Back-scattered electron (BSE) image of sample TD01001. ............................ 63 Picture 23. BSE image of sample TD01001. ..................................................................... 63 Picture 24. BSE image of sample TD01002. ..................................................................... 64 Picture 25. BSE image of sample TD01003. ..................................................................... 64 Picture 26. BSE image of sample TD01004. ..................................................................... 65 Picture 27. BSE image of sample TD01007. ..................................................................... 65 Picture 28. BSE image of sample TD01008. ..................................................................... 66 Picture 29. BSE image of sample TD01013. ..................................................................... 66 Picture 30. BSE image of sample TD01014. ..................................................................... 67 Picture 31. BSE image of sample TD01014. ..................................................................... 67 VI.

(8) Picture 32. Zircon sample CL image and LA-ICP-MS testing spot................................... 71 Picture 33. Zircon sample CL image and LA-ICP-MS testing spot................................... 72 Picture 34. Zircon sample CL image and LA-ICP-MS testing spot................................... 73. VII.

(9) List of tables Table 1.. Simple information of important ophiolite around the world. ......................... 16. Table 2.. Trace elements concentration of the East Taiwan Ophiolite. .......................... 78. Table 3.. REE elements concentration of the East Taiwan Ophiolite. ............................ 79. Table 4.. Sr-Nd isotopic ratio of the peridotite and gabbro. ........................................... 82. Table 5.. Bulk rock composition of the serpentinized peridotites and hornblende .............. gabbro sample. ..................................................................................................................... 84 Table 6.. Various Age Estimates of the South China Sea (SCS) basin from previous ........ studies.. ....................................................................................................................... 104. VIII.

(10) Chapter 1 Introduction 1.1 Introduction Ophiolite is a suite of ultramafic, mafic and sedimentary rocks that have been obducted onto land and are interpreted to as remnants of oceanic lithosphere. The study of ophiolites is one of the most direct ways to study the oceanic lithosphere composition and is an important feature for scientists who are interested in the birth and evolution of Earth’s lithosphere. Ophiolites are also sources of ore deposits rich in chromite (i.e. podiform chromite), iron and copper (i.e. massive volcanic sulfide) and other associated minerals (eg. laterites, asbestos). The South China Sea is one of the youngest marginal ocean basins and is an important feature for reconstructing the tectonic evolution of Southeast Asia and is the focus of numerous geological, geophysical, tectonic and geodynamic studies. The East Taiwan Ophiolite (ETO) is possibly one of the few preserved remnants of South China Sea and thus could be an important suite for studying chemical composition and evolution history of the South China Sea. Understanding the tectonic development of the South China Sea can help to constrain the regional paleogeography and locations of oil and gas reservoirs within the basin. This purpose of this thesis is to provide new geochemical data from the East Taiwan Ophiolite (ETO) and attempt to connect the ETO with the terminal stages of South China Sea spreading. This thesis consists of six chapters, including introduction, research method, petrography description, research result, discussion, and conclusion. The first part of the introduction chapter will give some brief introduction to the history, the classification and distribution of ophiolite around the 1.

(11) world. The second part is the geological background of the studying area, including the South China Sea, Taiwan, and the Coastal Range. The third part will give a quick review of the previous research on the East Taiwan Ophiolite and a short paragraph of the field work conducted for this study. The second chapter describes the sample preparation and research methods used in this research. The third chapter focuses on the sample description and the characteristics under optical microscope and scanning electron microscope (SEM). The fourth chapter presents the mineral chemistry, geochronology and whole rock geochemical results. The fifth chapter interprets the new data in conjunction with previous study in order to present a comprehensive interpretation of the age of the East Taiwan Ophiolite (ETO), the relationship and tectonic origination of the ETO and interpretation of emplacement of the ETO as a fragment from the South China Sea. The final chapter outlines the salient points derived from this study followed by the references and appendices.. 2.

(12) 1.2. Introduction of the Ophiolite. 1.2.1. Historical background of ophiolite complexes Ophiolite is a suite of rocks that is interpreted to represent oceanic crust and. the upper mantle lithological sequence. The rock suite is usually preserved to varying degrees within continental-continental, arc-continental collision, ridge-trench interaction and/or subduction-accretion setting (Miyashiro, 1977; Pearce et al. 1983; Bodinier and Godard, 2003;, Dilek and Furnes, 2011).). The name of ophiolite is derived from the Greek root “ophi”, which means snake skin or serpent, and “lite” means stone from the Greek root “lithos”. This word was first used by a French mineralogist Alexandre Brongniart in 1813 to describe some serpentinite mélanges as the sheared rock surface has a dark greenish shiny appearance similar to some snakes (Coleman, 1977; Dilek, 2003). The definition of an ophiolite was refined to include a suite of magmatic rocks (i.e. ultramafic rocks, gabbro, diabase, and volcanic rocks) occurring in the Apennines region (Brongniart, 1827). Mineralogists and petrologists in late 19th and early 20th centuries, however, arbitrarily changed, extended or limited the definition of an ophiolite to meet their requirements. The German petrologist Gustuv Steinmann introduced a new concept known as the “Steinmann Trinity”, which included serpentinite, diabase-spilite (spilite is a kind of albitized, vesicular basaltic lava rock) and radiolarian chert found in the Alps. He further constrained the definition of ophiolite in his 1927 publication to include peridotite (serpentinite), gabbro, diabase, spilite and some associated deep-sea sedimentary rocks (Steinmann, 1927; Coleman, 1977; Dilek 2003). The important conceptual break-through was recognizing that the rock suite could share a common. 3.

(13) petrogenetic evolution and was one of the earliest systematical descriptions of the magmatic evolution of ophiolite. Interest in ophiolite waned between the 1930s and 1960s but was still investigated by Hess (1955) in “Crust of the Earth” and argued in favour of the relationship proposed by Steinmann (1927). Hess (1955) insinuated that serpentinite and other mafic and ultramafic rocks of alpine-type could be derived from an island arc orogenic system. Years later he discussed the formation of oceanic basins in which he used seismic velocity to distinguish the boundary of oceanic crust and upper mantle and constrain the thickness of oceanic crust (Hess, 1962). Hess’s (1962) article laid the foundation for the study of the slow-spreading oceanic crust found at mid-ocean ridge settings and ophiolite studies. It was not until 1967 that a modern view of ophiolite began to develop when a collection of 33 papers was published in a special volume edited by Wyllie (1967) entitled “Ultramafic and Related Rocks”. The collection of papers provided new and interesting facts about the mafic and ultramafic rocks and the compositions of the rocks within an ophiolite were further discussed. Alpine-type peridotite (i.e. peridotites and serpentinite occurrences in mountain belts as plutonic intrusions into folded geosynclinal sedimentary rocks of orogenic systems) was, for the first time, separated from other kinds of ultramafic rocks (e.g. ultramafic rocks in layered intrusion, zoned ultramafic complexes, alkalic ultramafic rocks, ultramafic nodules, kimberlites) as an independent group being discussed (Wyllie, 1967). Thayer (1967) discussed the petrogenetic relationship between the mafic and ultramafic rocks from Alpine-type ophiolite and their same origination of the ultramafic magma evolution. In this article, Thayer (1967). 4.

(14) interpreted how the gabbro, diabase, and other leucocratic rocks in alpine-type peridotites could have originated from a single primary peridotitic magma. Jackson and Thayer (1972) classified the peridotites into: 1) harzburgite-type alpine peridotite and 2) lherzolite-type alpine peridotite. The classification was used as the basis for categorizing different types of ophiolite and inferring their petrogenetic development. In their study, Jackson and Thayer (1972) pointed out that harzburgite-type alpine peridotite is more depleted and represented the uppermost mantle, whereas the lherzolite-type alpine peridotite was initiated from less depleted and represented the characteristics of subcontinental mantle or deeper oceanic mantle. Nineteen seventytwo was a watershed moment in ophiolite studies as a consensus was reached at the first Geological Society of America Penrose Conference on ophiolites (1972), in which the complete ophiolite sequence was defined (Anonymous, 1972; Dilek, 2003 ). The definition included tectonized peridotite, cumulated peridotite, intrusive isotropic gabbro, layered gabbro, sheeted dikes, pillow lava, and pelagic sediments (Fig 1). The Penrose Conference definition is still widely used today and is the basis of modern ophiolite studies (Anonymous, 1972). In the early 1970s Japanese geochemist Miyashiro (1973) pointed out that a suite of pillow basalt and sheeted dike rocks from Troodos ophiolite showed calcalkaline characteristics and suggested that some ophiolites are created at a volcanic island arc setting rather than a mid-ocean ridge setting. Miyashiro (1973) was the first to propose the ophiolite-subduction zone relationship and this hypothesis led to tremendous debate and re-evaluation of the tectonic setting of many ophiolites. Pearce (1975) suggested a marginal basin origin for the Troodos massif, which he. 5.

(15) considered to have formed at the beginning of a submarine island arc suite. A few years later Pearce et al. (1984) introduced the concept of “suprasubduction zone (SSZ) type ophiolite” in which oceanic crust could form above a subduction zone setting as the overriding plate is extended (Fig. 2). This is one of the most important conceptual evolution of the ophiolite study. The SSZ type ophiolite concept led to a series of on land and marine geological and geophysical investigations within modern oceanic convergent margin setting, in particular drilling programs, seismic experiments and deep-water investigations were initiated around the Izu-Bonin-Mariana arc-trench system, which is one of the best documented suprasubduction zones in the world. Nowadays more than 75% of the ophioolite is classified as SSZ type ophiolite or subduction related.. 6.

(16) Figure 1. Typical ophiolite sequence (revised from Coleman, 1977).. 7.

(17) 8. Figure 2. Suprasubduction Zone (SSZ) type ophilite (revised from Dilek and Furnes, 2011)..

(18) 1.2.2. Types of ophiolite The Ophiolite was studied as a whole issue and was not being detailed. classified. However, it is clear that there are a variety of ophiolite with different structural architecture, chemical fingerprints, and evolutionary paths, suggesting different tectonic environments of origin. A Japanese geologist Miyashiro (1975) proposed a classification by the rock series of the ophiolite, 1) ophiolite complexes containing both calc-akalic (CA) type and tholeiite (TH) type volcanic rocks, 2) Ophiolite complexes containing only TH type rocks, and 3) ophiolite complexes containing TH type and alkalic series rocks (Miyashiro, 1975). Moores (1982) classified ophiolite as Tethyan type and Cordilleran type based upon the presence or absence of a continental substrate (i.e. passive margin of a continental plate or fragment), arc volcanic edifices, and/or accretionary mélanges and is still a widely recognized concept of ophiolite classification. Nicolas (1989) proposed another classification based on the tectonic setting of the ophiolite emplacements. The three main categories are: 1) ophiolite tectonically resting on continental passive margins (e.g. Semail ophiolite in Oman, Papuan ophiolite in Papua-New Guinea), 2) ophiolite incorporated into the active continental margins of the Circum-Pacific belt (i.e. ophiolitic occurrences in the Franciscan Complex in California), and 3) suture zone ophiolite occurring in continent-continent or arc-continent collision zones (i.e. ophiolites in the AlpineHimalayan orogenic system, Caledonian ophiolites, Hercynian and Uralian ophiolites).. 9.

(19) Dilek and Furnes (2011) proposed a new classification partially based on the criteria of Nicholas (1989) and Dilek (2003) that divided ophiolite into two major groups and some subgroups: 1) subduction unrelated group and 2) subduction related group, which are in parallel with the Tethyan-type and Cordilleran-type of Moores (1982) (Moores, 1982; Dilek, 2003; Wakabayashi and Dilek, 2003; Dilek and Furnes, 2011). The subduction unrelated group, which was the basis of earlier work, is further subdivided by Dilek and Furnes (2011) into continental-margin type (CM type), midocean ridge type (MOR type) and plume type (P type). The CM type ophiolite is derived from the Ligurian type ophiolite of Dilek (2003) and can be traced back to the Class-III type of Miyashiro (1975) (Miyashiro, 1975; Dilek, 2003; Wakabayashi and Dilek, 2003; Dilek and Furnes, 2011). It was formed during the early stage of the ocean basin evolution and is characterized by the widespread existence of largely serpentinized peridotites that are intruded and/or covered by small to moderate volumes of gabbros, local dikes, and pillow lavas. The MOR type ophiolite is close to the Class-II or Class-III type of Miyashiro (1975) based on the presence of tholeiitic and alkaline volcanic rocks (Miyashiro, 1975; Dilek, 2003; Dilek and Furnes, 2011). It generally represents the stratigraphy of the Panrose conference and shows N-MORB, E-MORB and/or contaminated(C) MORB geochemical characteristics (Dilek and Furnes, 2011). P type ophiolite is characterized for having thick plutonic and volcanic sequences and is subdivided into plume-proximal ridge and oceanic plateau subtypes (Dilek and Furnes, 2011). On the other hand, the subduction related group, which representing ~75% of all ophiolites, is subdivided into suprasubduction zone type (SSZ type) and volcanic. 10.

(20) arc type (VA type). The SSZ type is subdivided into three subtypes: 1) backarc to forearc environment, 2) forearc setting, and 3) oceanic/continental backarc subtype (Dilek, 2011). The SSZ type ophiolite may correspond to the Class-I type of Miyashiro (1975) and the combination of Mediterranean type and Chilean type of Dilek (2003), which are the products of high degrees of melting of depleted, harzburgitic mantle (Miyashiro, 1975; Dilek, 2003; Dilek, 2011). In general, the SSZ type ophiolite structurally have a complete Penrose sequence, and it represents the mid-ocean ridge basalt (MORB), island arc tholeiite (IAT) and boninite geochemical characteristics (Dilek, 2003; Dilek, 2011). VA type ophiolite is similar to SSZ type but differ for having thicker and more developed arc crust which is representing tholeiitic to calc-alkaline composition (Dilek, 2003; Dilek, 2011).. 11.

(21) 1.2.3. Global distribution of ophiolite There are many exposed ophiolite outcrops around the world, and they are. usually distributed near major collisional zones or accretionary orogenic belts (Fig. 3). There are three major orogenic belts which preserved ophiolite: 1) Alpine Himalayan Orogenic Belt, 2) Appalachian - Caledonian - Hercynian - Uralian and Central Asian belts and 3) Western Pacific and Cordilleran Orogenic Belts. The earliest studied ophiolites are around the Mediterranean Sea, which is a part of the Alpine - Himalayan Orogenic Belt. The Alpine - Himalayan Orogenic Belt stretches nearly half of the globe, from East Australia, Indochina, through Tibet, South Central Asia all the way west through the Arabian Peninsula, Turkey, Mediterranean and Alps, and even across the Atlantic Ocean into the eastern Caribbean. Some very well-known ophiolite occurrences in this belt includes: Ligurian Ophiolite (Apennines, Italy), Troodos Ophiolite (Troodos, Cyprus) and Semail Ophiolite (Oman and The United Arab Emirates). The Internal Ligurian Ophiolite of the Apennines Mountains was the first ophiolite described by Brongniart (1827) in which he used the term “ophiolite” and later was the inspiration of the “Steinmann Trinity”. The Jurassic Ligurian Ophiolite is interpreted as a continental margin type ophiolite, which consists of exhumed subcontinental lherzolite overlain by basaltic lava and intruded by some small gabbroic plutons and mafic dikes (Dilek and Furnes, 2011). A part of the same Alpine - Himalayan belt, the Late Cretaceous Troodos ophiolite of Cyprus is considered to be one of the best known ophiolite complex in the world. The Troodos ophiolite is thought to be a preserved portion of oceanic crust that formed during the Mesozoic development of the Tethyan Seaway 12.

(22) at a SSZ (Coleman, 1977; Staudigel et al., 1999; Dilek and Furnes, 2009). The Late Cretaceous Semail ophiolite is located along the eastern margin of the Arabian Peninsula and is the largest ophiolite complex (30,000 km3) and the best exposed ancient oceanic section in the world (Coleman, 1977; Searle and Cox, 1999). These three ophiolites are amongst the best studied and most complete ophiolites in the world. The second orogenic belt is Appalachian-Caledonian-Hercynian-Uralian and Central Asian belts, which preserved ophiolite in Norway (Solund-Stavfjord), Greenland (Isua), Newfoundland (Bay of Islands) and New York State (Stark's Knob). The most famous ophiolite in the Appalachians is the Bay of Islands Ophiolite in western Newfoundland. The Bay of Islands ophiolite was originally interpreted to be the remnants of the proto-Atlantic oceanic lithosphere generated at a spreading center or marginal basin (Coleman, 1977; Pearce et al., 1984; ), but is now classified as a supra subduction zone forearc type (Varfalvy et al., 1997; Dilek and Furnes, 2011). The third orogenic belt is the Western Pacific and Cordilleran Orogenic Belts, or also known as the circum-Pacific orogenic belt. The two orogenic belts cover the largest area and stretch along the Circum-Pacific Seismic Belt (Fig. 3). The best preserved ophiolites around the Circum-Pacific belt include: Papuan Ophiolite (Papua New Guinea), Zambales Ophiolite (west Luzon, Philippines), Coast Range Ophiolite (California, United States), Olivos Ophiolite (Chihuahua, Mexico), Rocas Verdes Ophiolite (Patagonian Andes, Chile) and the East Taiwan Ophiolite (Taiwan). The ophiolites in the Circum-Pacific orogenic belt are mostly suprasubduction zone (SSZ) type or volcanic arc (VA) type ophiolite. The Papuan ophiolite extends ~400 13.

(23) km discontinuously along the Owen Stanley mountain range in Papua New Guinea. And the Izu-Bonin-Mariana belt (I-B-M belt) is the most famous supra-subduction zone ophiolite belt, which extends from Japan to Guam, a distance of ~2800 km, and includes the Izu Islands, Bonin Islands, and Mariana Islands (Stern et al., 2003, Plank et al., 2007).. 14.

(24) Figure 3. Global distribution of some major ophiolites. The information of the ophiolite is listed in Table 1 (revised from Yakubchuk et al., 1994; Dilek, 2003; Dilek and Furnes, 2011).. 15.

(25) Table 1. Simple information of important ophiolite around the world. The location of the ophiolites list here are shown in Figure 3. No.. Ophiolite name. Location. Age (Ma). Type. 1. Ligurian. Italy. 200. Continental Margin. 2. Tihama. Red Sea, Saudi Arabia. 20. Continental Margin. 3. Macquarie Island. Australia. 10. Mid Ocean Ridge. 4. Taitao. S. Chile. 10. Mid Ocean Ridge. 5. Peri-Caribbean. Caribbean Sea. 105. Plume. 6. Zambales. Philippines. 40-44. SSZ. 7. Troodos. Cyprus. 92-94. SSZ. 8. Semail. Oman. 92-95. SSZ. 9. Kizildag. Turkey. 92-94. SSZ. 10. Xigaze. Tibet, China. 120-126. SSZ. 11. Yakuno. Japan. 270-280. SSZ. 12. Magnitogorsk. S. Urals, Russia. 385-400. SSZ. 13. Bay of Islands. Canada. 484. SSZ. 14. Itogon. Philippines. 30. Volcanic-arc. 15. Coast Range. California, US. 140. Volcanic-arc. 16.

(26) 1.2.4. Ophiolite of circum-Pacific The circum-Pacific orogenic belt is referred here as the western Pacific island. belts (e.g. Japan islands, Ryukyu islands, Taiwan island, Philippine islands, Indonesian islands, Papua New Guinea islands, east Australia and New Zealand islands), the Cordilleran belts of western North America, and the western South America which extends along a great circle for more than 25,000 km in the Pacific Rim (Ishitawari, 1991, 1994; Dilek, 2003; Furnes et al., 2014). Ophiolites of the circum-Pacific belts are characterized by a ranges of ages that cover the entire Phanerozoic (Ishitawari, 1994; Dilek, 2003). The circum-Pacific ophiolites are usually suprasubduction zone type or volcanic arc type ophiolite and commonly show the supra-subduction zone type ophiolite characteristics (i.e. structurally and/or geochemically heterogeneous to the crustal components attesting to the progressive evolution of their mantle melt sources) (Ishitawari, 1994; Dilek, 2003; Dilek and Polat, 2008). The circum-Pacific ophiolites are found mostly on or among the accreted oceanic and trench sediments that characterizing active continental margin , and thus it contrasts with the Tethyan ophiolite occurrence, where ophiolites are mostly emplaced on passive continental margins through continental collision events (Ishitawari, 1994). The East Taiwan Ophiolite, on the other hand, is unusual amongst the circum-Pacific ophiolites as it represent a highly depleted mantle composition that differs from the suprasubduction zone type ophiolite and is more similar to a mid-ocean ridge origin and the opening of a marginal sea basin.. 17.

(27) 1.3 Geological Background 1.3.1. Geological setting and tectonic evolution of the South China Sea South China Sea is a marginal sea of Eurasia and borders the South China. Block, Indochina Block, Luzon arc, Palawan. The opening of South China Sea is considered to have occurred during the Oligocene and is one of the youngest ocean basins in the world (Ludwig, 1970; Ben-Avraham and Uyeda, 1973; Briais et al., 1993; Lee and Lawver, 1995,). Based on the magnetic anomaly mapping in 1979 (anomalies 11 to 5d, Taylor and Hayes, 1980, 1983; revised to anomalies 11 to 5c, Briais et al., 1993), the opening lasted from the late Oligocene to the early Middle Miocene (32 to 15 Ma). The tectonic process responsible for the opening of the South China Sea is debated. There are three principal models which describe the formation of the South China Sea. 1) The South China Sea is an inactive marginal basin and opened as a consequence of back-arc extension due to eastward subduction of the Eurasia plate (Karig, 1971; Ben-Avraham and Uyeda, 1973, Zhang, 1984). 2) The South China Sea is opened mainly due to the mantle lateral flow or mantle plume (Watanabe et al., 1977; Taylor and Hayes, 1980; Flower et al., 1998; Zhang et al., 2001). 3) The South China Sea opened as a consequence of regional displacement in SE Asia due to the collision of India-Eurasia at ~50 Ma (Tapponnier et al., 1982, 1986, 1990; Lee and Lawver, 1995). Karig (1971) proposed that the South China Sea is perhaps an inactive marginal basin with higher than normal heat flow value than traditional marginal basin. Ben-Avraham and Uyeda (1973) mentioned the opening of the South China 18.

(28) Sea may be related to the subduction of the Pacific plate and the compression of the China Sea basin. Zhang (1984) proposed that South China Sea as well as East China Sea are the continental margin under tension and the subduction of the plate led to the consequence of post-arc pull-apart basin. This interpretation was challenged when Taylor interpreted the magnetic anomalies. The magnetic anomalies reveal the E-W direction expansion axis of the South China Sea, which is unreasonable to be a backarc basin of the Luzon arc with the nearly N-S direction subduction axis (Taylor and Hayes, 1980). Watanabe et al. (1977) published the heat flow of the South China Sea with the value 85 ± 8 mW/m2 at north and 112 ± 16 mW/m2 at south of the basin. In this paper (Watanabe et al., 1977), they also predicted an age of 14-36 Ma (lower Miocene to lower Oligocene) for the South China Basin. Taylor and Hayes (1980, 1983) proposed the magnetic anomaly of the spreading axis of South China Sea, and interpreted the spreading of the South China Sea between ~32 Ma and ~17 Ma (mid Oligocene through early Miocene). Flower et al. (1998) proposed a model explaining the dispersed volcanism and DUPAL-like asthenosphere in East Asia and West Pacific. Zhang et al. (2001) discussed the mantle lateral flow and the tectonic regime relationship and suggested that the lateral flow was the dominant factor of the thinning of the lithosphere and the expansion of the South China Sea. However, Cui et al. (2005) and Xia (2005) remodeled the convection of the mantle flow and suggested that the upwelling of the hot mantle material had an impact on the thinning of the lower lithosphere but less influence on the crust thinning and thus taking much longer time for the opening.. 19.

(29) Tapponnier et al. (1982, 1986, 1990) proposed that the collision of the India block and Eurasia had a large impact on the East China, South China and Indochina blocks. The collision pushed out the East China and South China block and dominated the left-lateral shearing of the Ailao Shan-Red River metamorphic belt. They proposed that the penetration of India block into the Eurasian continent pushed Indochina southeastward with clockwise rotation, and the over 500 km left-lateral movement directly influenced the Oligocene-Miocene opening of the South China Sea. Lee and Lawver (1995) used the pole of rotation to reconstruct the position of tectonic block of the Southeast China. Xia (2005) suggested that this tectonic pull apart by the rotation of Indochina should be supported by the mantle upwelling mentioned previously. The tectonic evolution of the Southeast China and South China Sea began at the early Cenozoic (~60 Ma), at when Indochina was about 500 km NW of its present position. During the early Eocene (about 55-50 Ma), the northeastward moving Greater India began to collide with the southern margin of Eurasia and closed the Tethys Ocean. The collision of India and Eurasia forced the Indochina peninsula southeastwards along the left-lateral Ailao Shan-Red River fault and induced clockwise rotation of ~25° between 40 Ma and 22 Ma (Tapponnier et al., 1982, 1990, Lee and Lawver, 1995). The rotation of the Indochina peninsula led to the stretching and thinning of the continental shelf of South China block. The opening of the South China Sea started at the northwest part of the basin at ~32 Ma. The rheology of the South China block, Indochina and Sundaland blocks permitted the initial N-S directed extension of the South China Sea. The spreading direction changed during. 20.

(30) the early Miocene between magnetic anomaly 7 and 6b from predominately N-S to NW-SE direction. The directional change is thought to be related to ridge jump, which Barckhausen and Roeser (2004) suggests was due to the onset of a second spreading ridge in the southwestern part of the South China Sea basin however it remains uncertain (Hayes, 1988; Barckhausen and Roeser, 2004). The South China Sea expansion ceased at ~17 Ma due to the collision of the Kalimantan terrain and the North Palawan block (Holloway, 1982; Taylor and Hayes, 1983).. 21.

(31) Figure 4. Map of Southeast Asia.. 22.

(32) 1.3.2. General Geology of Taiwan The island of Taiwan is situated along the boundary of the Eurasian plate to. the west and Philippine Sea plate to the east and is important location for understanding the geological and tectonic evolution of East and Southeast Asia. Taiwan is ~385 km in length and ~143 km in width and has a total area of 35,960 km2 and consists of six geological domains: Central Mountain Range, Tananao metamorphic complexes, Hsuehshan Range, Western foothills, Coastal Range and the Coastal Plain. The collision of the Eurasia plate and Philippine Sea plate occurred during the Late Jurassic and created the central Mountain Range that reaches a maximum elevation of ~4000 meters. According to Seno (1977) and Suppe (1981), the collision rate of Philippine Sea plate with the Eurasian plate is about 7 cm/yr in a northwestsoutheast direction (ω = 1.2°/ m.y., 45.5°N, 150.2°E) and causes the island to move ~3-4 cm/yr to the northwest and 1-2 cm/yr in vertical growth. Taiwan is located at the junction between the Ryukyu island arc and Luzon island arc thus there are characteristics of an island arc, accretionary wedge, continental plate and oceanic lithosphere. (Bowin et al. 1978; Chai, 1972; Suppe, 1984; Tsai, 1986; Kao et al., 1998) Proto-Taiwan was formed during late Jurassic to early Cretaceous, about 150 million years ago, when the Eurasia plate and Pacific plate collided. The Pacific plate subducted westward beneath the Eurasia plate and created the Zhejiang-Fujian magmatic arc and proto-Taiwan. During the early Cenozoic, subduction slowed and eventually stopped allowing sediments to accumulate in the forearc basin. At the 23.

(33) same time, the Philippine Sea Plate started to migrate northwestward and rotate clockwise from an E-W direct to its current N-S orientation (Lee and Lawver, 1995). During the mid to late Miocene (~ 15-12Ma), the Luzon arc along a rightlateral transform fault pushes the continental shelf of the Eurasia plate whereas the other side of Philippine Sea Plate subducted under the extended Ryukyu arc (Teng, 1990; Huang et al., 2006). During the mid-Pliocene (~3-5 Ma), the continental shelf of Eurasia continually subducted under Luzon arc and consumed the accretionary wedge, which uplifted as a small island and rapidly produced a high mountain range (the proto-Central Mountain Range) during the late Pliocene (Teng, 1990; Huang et al., 2006). From the late Pliocene, the Luzon arc reached its current position off the coast of Hualien and the margin of the arc obliquely collided with Eurasia. Concurrent with the Luzon-Eurasia collision, the tectonic setting of northeast Taiwan transformed from compression and collision to extension which caused the collapse of the Ilan terrain and the formation of the Ilan plain after a long period of orogenesis (Suppe, 1984; Lee and Wang, 1987; Teng, 1990, 1996, 2007). The volcanic rocks of the Luzon arc accreted to the uplifted Pliocene-Pleistocene passive margin sediments of Euraisa and became the Coastal Range whereas the uplifted sedimentary rocks developed into the Central Range. The northeast side of the Philippine Sea plate subducted beneath the Ryukyu Arc and induced backarc extension and the opening of the Okinawa Trough (Teng, 1990, 2007; Kao et al., 1998; Gao et al., 2008).. 24.

(34) Figure 5. Geologic Framework of Taiwan (revised from Teng, 1990).. 25.

(35) 1.3.3. Geological setting of Costal Range The Coastal Range is located in eastern Taiwan and is one of the five main. mountain ranges of the island. It stretches ~140 km north starting from the estuary of the Hualien River and ends at Beinan Mountain, Taitung. The Coastal Range is separated into a north part and a south part, bounded by Siouguluan River. The north part is slightly higher than the south part but is no longer being uplifted (Chen et al., 1991). River terraces are more abundant south of the Siouguluan River suggesting the area is still being uplifted. The Longitudinal Valley, between the Central Range and Coastal Range, is the boundary between Eurasia and the Philippine Sea plate. The Central Range is underlain by deformed rocks of the Eurasia continental margin while the Coastal Range is underlain by island arc volcanic rocks from the Luzon arc (Page and Suppe, 1981). Hsu (1956) divided the Costal Range into five formations by rock type, which from oldest to youngest are: Tuluanshan formation, Takangkou formation, Chimei volcanic complex formation, Lichi formation and Beinanshan conglomerate formation (Hsu, 1956, 1976). Biq (1969) suggested that the Takangkou formation and Chimei formation are a continuous sequence and named it after Takangkou formation. According to the petrographic differences, Teng (1979, 1980) added two new formations, the Baliwan formation and the Fanshuliao formation, into the original sequence described by Biq (1969). Teng and Wang (1981) proposed that Tuluanshan, Fanshuliao and Lichi formation belong to the pre-collision arc facies whereas the post-collision Baliwan and Beinanshan formations are continental facies. In the paper by Teng and Lo (1985), they further classified the Tuluanshan formation 26.

(36) as arc facies, the Takangkou formation as a fringing reef carbonate facies, the Fanshuliao formation as forearc basin deposition, and the Lichi formation as trench mixing facies. The Luzon arc was actively moving along a right-lateral transform fault during mid and late Miocene (~ 15-12 Ma) and collided with the continental margin during the mid-Pliocene (~ 5-3 Ma) followed by the formation of the Baliwan formation and Beinanshan conglomerate formation (Teng and Lo, 1985; Teng, 1990; Huang et al., 2006).. 27.

(37) Figure 6. Geological setting of Coastal Range region (revised from Liou, 1979).. 28.

(38) 29. Figure 7. Different geological stratigraphy of the Coastal Range. (Stratigraphy definition from Hsu, 1976; Chang, 1975; Chi et al., 1981; Teng and Wang, 1981; and Teng and Lo, 1985).

(39) 1.4 East Taiwan Ophiolite and sample collection 1.4.1. Previous researches of the East Taiwan Ophiolite The East Taiwan Ophiolite sporadically exposed along the southeastern part. of the Coastal Range, from Taitung City to Hualien County, and considered to be a remnant of the South China Sea (Liou et al. 1977; Suppe and Liou, 1979; Liou, 1979; Suppe et al., 1981; Jahn, 1986; Chung and Sun, 1992). The East Taiwan Ophiolite was first geologically mapped by Juan et al. (1953), and, at that time, was referred to as “Taiwanite” due to the large irregular shaped intrusion of glassy basalt (up to 95% glassy texture). The geological mapping of the Coastal Range by Hsu (1956) outlined the full distribution of “Taiwanite”. Chen et al. (1976), Juan et al. (1976) and Chou et al. (1978) studied the mafic and ultramafic rocks and suggested that the “Taiwanite” represented differentiated of a primitive melt. Chen et al. (1976) provided some mineral chemistry data and compared the crystallizing temperature of the olivine in “Taiwanite”. Juan et al. (1976) performed the quenching experiment and EPMA, and discussed the characteristics of the alkali olivine basalt magma and olivine tholeiite magma from the “Taiwanite”. Chou et al. (1978) discussed the rare earth element pattern and ended up with the conclusion that the serpentinized peridotites may probably be the residua of mantle. The book “The East Taiwan Ophiolite” written by Liou et al. in 1977 is an important progress of research of the ETO, in which they provided not only detailed reconnaissance record of the distribution and the rock sequence of the ETO but also new geochemical data and interpreting the ocean ridge origin of the ETO. Liou (1979) and Liou and Ernst (1979) were both discussing the metamorphism of the ETO and 30.

(40) suggesting that the ETO experienced two stage of metamorphism, 1) pre-brecciation ridge-type metamorphism and 2) off-axis metamorphism. Suppe and Liou, (1979), Suppe et al. (1981), Jahn, (1986) and Chung and Sun, (1992) constrained the framework model of a mid-ocean ridge setting of the East Taiwan Ophiolite. Suppe and Liou (1979) summarized some previous studies (e.g. Page and Suppe, 1980; Suppe et al. 1981) and suggested the concept of the tectonic model of the ETO. Suppe et al. (1981) reexamined the ophiolitic stratigraphy of the ETO and analyzed the serpentinized peridotite, gabbro, plagiogranite, diabase and basaltic rocks with XRF analysis. They also suggest the plausible mid-ocean ridge origination of the ETO and a displacement of 700-1000 km distance. Jahn (1986) provided some new major and trace elements data, REE data and isotopic data and agreed with the ETO ocean-ridge interpretation. Radioisotopic age dating of the ETO and nanofossil studies (i.e. NN5) indicates that the ETO is ~14.6 ± 0.4 Ma. Chung and Sun (1992) presented new major and trace elemental data, REE data and isotopic data and proposed that the ETO was formed at a normal slowspreading axis environment. Shao et al. (2014) published new U-Pb age dates that shows the gabbroic rock of the ETO formed at ~17.5 Ma whereas the diorite and plagiogranite rocks were formed at ~14 Ma.. 31.

(41) 1.4.2. Sample collection For this study samples were collected at Dianguang, Guanshan Township,. along the Chia Wu Creek which is the largest exposed outcrop of the ETO. Rocks were collected along a 1.6 km traverse from midstream to upstream and ranged in size from pebble to boulder. The rock size generally increased from the midstream to upstream with some boulders as large as an automobile. The rock type also changed from midstream to upstream. The midstream rocks consisted of serpentinite, glassy basalt and pillow basalt outcroppings. Larger boulders of gabbro were found within the stream. Large boulders of gabbro and outcrops of peridotite were found near the headwater of the stream. Peridotite samples used in this research were collected around this spot. Subsequent to this fieldwork the outcrop was buried (summer, 2013) and cannot easily be reached.. 32.

(42) 33. Figure 8. Map of Guanshan area and Chiawu creek and the sample collecting spots..

(43) Picture 1. Serpentinite blocks.. Picture 2. Glassy basalt.. 34.

(44) Picture 3. Pillow basalt.. Picture 4. Gabbro.. 35.

(45) Picture 5. Fallen block of peridotite and landslide (behind).. Picture 6. Peridotite.. 36.

(46) Chapter 2 Research Methods 2.1 Petrography Description Rock chips for thin sectioning were cut using a masonry saw to a size of ~3 x 2 cm. The pieces were pasted onto a glass slide (5 x 2.5 cm) with epoxy and placed on a hot plate for at least 24 hours until the epoxy solidified. The affixed sample was further cut to reduce thickness before polishing. The rock was polished using 200, 600 and 1000 mesh silicon carbide emery to grind the sample until proper thickness under microscope (~30 μm). Aluminum oxide powder (3 μm) was used for final polishing. An example of a finished thin section is found in picture 7. A Carl Zeiss Axioplan 7082 polarizing optical microscope (Pic. 8) was used for the observation of 8 polished sections at the Department of Earth Science, National Taiwan Normal University. Individual minerals were identified using standard petrographic techniques (i.e. shape, color, cleavage, interference color, relief, extinction angle) and mineral modes were determined using a point-counter and visual estimation.. 37.

(47) 38. Picture 7. A finished thin section..

(48) Picture 8. Carl Zeiss Axioplan 7082 polarizing optical microscope.. 39.

(49) 2.2 Scanning Electron Microscope (SEM)/ Energy Dispersive Spectrometry (EDS) Small rock pieces (< 25 mm in diameter) were mounted in epoxy and subsequently ground and polish. The sample mounts were loaded into a JEOL USA JSM-7100F Analytical Field Emission SEM (Pic. 9) at the Laboratory of Electron Probe Micro-Analyses, Institute of Earth Science, Academia Sinica. The standard settings of this machine used for this study are: vacuum setting of the machine was set at 25 Pa, acceleration voltage at 15 kV, probe current at 0.18 nA, and working distance 10 mm. The focus, brightness and contrast of the field were adjusted for maximum clarity so that back scattered electron image pictures can be taken. The Oxford Instrument INCA-300 energy dispersive spectrometer (EDS) is attached on the SEM and was used to analyze the energy peak of targeted minerals. The duration of a single EDS analysis was 60 seconds, and the predicted mineral was judged depending on the energy magnitude of different elements.. 40.

(50) Figure 9. SEM structure.. 41.

(51) Picture 9. JEOL USA JSM-7100F Analytical Field Emission SEM.. 42.

(52) 2.3 Electron Probe Micro Analyzer (EPMA) The electron probe micro analyzer (EPMA) was used to determine the major element composition of the targeted mineral. The EPMA detects the characteristic wavelength of different elements and quantifies the mineral composition. For the analyses, the sample mounts were coated with carbon using a Quorum Technology Q150TE high vacuum carbon coater and loaded into the EPMA. For this study, a JEOL W-EPMA model JXA-8900-R with 4 wavelength dispersive spectrometers (WDS) (Pic. 10) at the Laboratory of Electron Probe Micro-Analyses, Institute of Earth Science, Academia Sinica was used. The electron beam was defocused at an interval of approximately 10 mm on an area of about 5 µm diameter by beam conditions of 15 kV and 12 nA. Back-scattered electron images were used to guide the analysis on target positions of minerals. The measurements were corrected by using chemical-known standard minerals as listed: wollastonite for Si with TAP crystal and Ca with PET crystal, rutile for Ti (PET), corundum for Al (TAP), chrome oxide for Cr (PET), hematite for Fe with LiF crystal, tephroite for Mn (PET), pyrope for Mg (TAP), nickel olivine for Ni (LiF), albite for Na (TAP), and adularia for K (PET). Peak counting for each element and both upper and lower baselines are counted for 10 s and 5 s, respectively. Relative standard deviations (RSD) for all elements were less than 1%.. 43.

(53) Picture 10. JEOL W-EPMA JXA8900-R electron probe microanalyzer.. 44.

(54) 2.4 In situ zircon Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) Zircons were mechanically separated at the Yu-Neng Rock and Mineral Separation Co., Lanfang, Hubei province, China using a steel jaw crusher, magnetic separation and heavy liquids and purified by hand-picking under binocular microscope. Zircons were linearly mounted on a glass slide over a circle diameter of 1.5 cm. A mold was placed over the zircons and epoxy was poured over the zircons to ensure transfer of the minerals to the epoxy. The mount was polished to approximately half the mean grain thickness. A panchromatic CL imaging system (Gatan Mini-CL) attached to a scanning electron microscope (JOEL JSM-6360LV) was used to capture cathodoluminescence images (CL image) of the individual zircons to examine their internal structure. The epoxy zircon grain mount was loaded into a New Wave UP-213 laser attached to an Agilent 7500cx ICP-MS (Pic. 11 and 12) in the Tectonics and Low-temperature Heat Dating Laboratory, Department of Earth and Environmental Sciences, National Chung-Cheng University. Individual zircons were ablated using a beam diameter of 40 μm and frequency of 10 Hz. Helium gas was used as the carrier gas and supported by Argon gas. A single analysis takes 130 seconds, including 60 seconds preheating the tube and 70 seconds acquiring data. The measurements were corrected by using age-known standards: GJ (600 ± 5 Ma) and Plešovice (337 ± 10 Ma).. 45.

(55) Picture 11. UP-213 laser ablation system.. 46.

(56) Picture 12. Agilent 7500cx ICP-MS.. 47.

(57) 2.5 Thermal Ionization Mass Spectrometer (TIMS) The collected samples are crushed into powder for better solvation. Hydrofluoric acid (HF), nitric acid (HNO3), and hydrochloric acid (HCl) were used to dissolve the rock powders of the samples used for this experiment. The sample solutions were passed through three columns with cation exchange resin. The first cation exchange column was used to concentrate and collect Sr and trace elements separately. The second column was used to further concentrate Sr, and the third column was used to concentrate and collect Nd. The concentrates were loaded on a double rhenium filament. In this research, a Thermo FinniganTM Mat GmbH MAT262Q thermal ionization mass spectrometer (Pic. 13) was used for Sr isotope analysis and a Thermo ScientificTM Triton Plus multicollector thermal ionization mass spectrometer (Pic. 14) was used for Nd isotope analysis. The TIMS would charge and ionize the Sr and Nd particles in the steam that evaporates from the filament, then the ionized particles were accelerated by magnetic field and captured by different Faraday cups with different weight so that the machine can identify the different isotopes from each other. These two TIMS are placed in Mass Spectrometer Lab, Institute of Earth Science, Academia Sinica. The standard settings of MAT262Q are as follows: the vacuum setting of the machine sets at below 10-9 mbar; the high voltage at 9975 V; two current settings for evaporation and ionization, 0.8A and 4.1A when preheating, and increase to about 1.8A and 4.45A when analyzing (the current could be changeable depending on the signal intensity).. 48.

(58) Figure 10. TIMS structure.. 49.

(59) Picture 13. Thermo Finnigan Mat GmbH MAT262Q thermal ionization mass spectrometer.. 50.

(60) Picture 14. Thermo ScientificTM Triton Plus multicollector thermal ionization mass spectrometer.. 51.

(61) 2.6 Inductively coupled plasma-mass spectrometry (ICP-MS) The bulk rock trace elements analysis was determined using quadrupole inductively coupled plasma mass spectrometry (Q-ICP-MS, model Agilent 7500s) at the Geochemistry and Petrogenesis Lab, Department of Geosciences, National Taiwan University. The sample liquids used for ICP-MS were extracted using the procedure for extracting Sr and Nd isotopes. The measurements of the ICP-MS is corrected with standards AGV-1, AGV-2, GSP-1, JB-1 and JG-1, and the precision was generally better than 5% (2σ) for most trace elements.. 52.

(62) 2.7 X-Ray Fluorescence Spectrometry (XRF) Approximately 3 grams of rock powder from each sample was heated to 100°C for 3 hours to release ambient water from the sample and then heated to 900°C for 6 hours to oxidize and release molecular water. The net change of weight was recorded at each step and used to calculate the loss on ignition (LOI). 0.6 grams of rock powder was thoroughly mixed with 6 grams of Claisse® lithium borates with lithium bromide flux (49.75% Li2B4O7, 49.75% LiBO2 with 0.5% LiBr). The mixed powder and flux was added to platinum (95%) and gold (5%) crucibles and fused at ~1200°C to make a glass bead using a Claisse® M4 Fluxer (Pic. 16). The glass bead was loaded in the Panalytical AxiosmAX (Pic. 15) at the XRF Laboratory, Department of Earth Sciences, National Taiwan Normal University used for analysis. The calibration standards are United States Geological Survey (USGS) AGV-2 (andesite), BCR-2 (basalt, Columbia River), BHVO-2 (basalt, Hawaiian Volcanic Observatory), BIR-1a (Icelandic basalt), COQ-1 (carbonatite), DNC-1a (dolerite), DTS-2b (dunite, Twin Sisters Mountain), GSP-2 (granodiorite, Silver Plume, Colorado), SDC-1 (Mica Schist), SGR-1b (Green River Shale) and W-2a (diabase).. 53.

(63) Picture 15. Panalytical AxiosmAX WDXRF.. 54.

(64) Picture 16. Melting the powder and flux by Claisse® M4 Fluxer.. Picture 17. Finished glass beads.. 55.

(65) Chapter 3 Petrography 3.1 Petrography The samples of this research were collected along Chia-Wu creek near Kuanshan, Taitung County. The collected specimen are several centimeters to 20 cm in diameter, and 8 out of 15 samples are used, including 7 peridotites and 1 gabbro. The peridotites are darkish green in color with some olive green spots and composed primarily of serpentine. Most of the olive green spots are less than 0.5 cm in diameter. Sample TD01001, TD01002, TD01003, TD01004 have some dark red color intermingled between the darkish green region whereas TD01007, TD01008 and TD01013 do not. Calcite veins cut through some rock samples (i.e. TD01001, TD01002, TD01003, TD01004 and TD01008). The gabbro sample (TD01014) is composed of ~55% mafic minerals (hornblende and oxide) and ~45% plagioclase and has an intergranular texture. The peridotite samples are comprised mostly (≥ 90 vol%) of serpentine with minor amounts of orthopyroxene pseudomorphs (≥ 3 vol%) and spinel (≥ 1 vol%). The original texture of the rock has been replaced but the serpentine suggests the rock was poikilitic. Small iron-oxide minerals form anastomosing bands which give the appearance of former grain boundaries. The oxide minerals are likely due to serpentinization of olivine. There are rare occurrences of party-altered (i.e. pseudomorphic?) olivine which range in size from 0.5 mm to ~1 mm and still have discernable hexagonal to rounded shapes. Orthopyroxene pseudomorphs ranging in size from 0.5 mm to 3.5mm represent ~3% of the rock mode. The orthopyroxene pseudomorphs are commonly round and larger than the pseudomorphic olivine, 56.

(66) display a different relief from the serpentine and still have cleavage visible which makes them relatively easy to identify. Sub-hedral to anhedral spinel is probably the only preserved unaltered mineral in the rock. The spinel is between 0.5 and 2 mm in length and dark red in plain polarized light. Megnetite- and calcite-rich veins are common and likely the result of hydrothermal alteration of the original olivine and pyroxene. Samples TD01007 and TD01008 are relatively less altered than other peridotite samples and have slightly larger orthopyroxene pseudomorphs. The gabbro is coarse grained and granular and consists of ~55% hornblende and ~45% of plagioclase with accessory quantities (i.e. < 1 vol%) of ilmenite and/or magnetite. The hornblende is light green under plain polarized light with second order interference colors under crossed polars (Pic. 21). The hornblende crystals are euhedral to sub-hedral and tend to be smaller (i.e. 0.1 mm) than the sub- to an-hedral plagioclase crystals (i.e. > 0.5 mm). The oxide minerals are small (i.e. < 0.05 mm), sub- to anhedral and commonly bordering plagioclase rather hornblende.. 57.

(67) Picture 18. Optical microscope image of sample TD01001. Orthopyroxene pseudomorph with chrome spinel, iron oxide and serpentine in TD01001. (a) Plane polarized light (PPL), (b): Crossed-polars.. 58.

(68) Picture 19. Optical microscope image of sample TD01001. Calcite vein and orthopyroxene pseudomorph with iron oxide and serpentine in TD01001. (a) Plane polarized light (PPL), (b): Crossed-polars.. 59.

(69) Picture 20. Optical microscope image of sample TD01002. Chromium spinel, calcite vein and serpentine in TD01002. (a) Plane polarized light (PPL), (b): Crossed-polars.. 60.

(70) Picture 21. Optical microscope image of sample TD010014. Amphibole, plagioclase in TD01014. (a) Plane polarized light (PPL), (b) Crossed-polars.. 61.

(71) 3.2 SEM/EDS images SEM images of the peridotites (i.e. TD01001-004, 007, 008 and 013) and gabbro (i.e. TD01014) are shown in picture 22 to 31. The serpentinized peridotites generally have similar textures (i.e. filled with ~95% of serpentine) but there are some differences in the level of alteration and formation of oxide minerals and calcite veins. Picture 22 and 23 are images of sample TD01001, which is mostly composed with serpentine (pale gray) but also with some Cr-spinel (white grains), iron oxide (thin white veinlet) and calcite (thick white vein in Pic. 23). Picture 24 shows the image of TD01002, which shows the same minerals as TD01001 but is much more enriched in calcite (light gray veinlet). The images of TD01003 (Pic. 25), TD01004 (Pic. 26), TD01007 (Pic. 27) are similar, with serpentine (pale gray), Cr-spinel (white grains) and little iron oxide (thin white veinlet). Sample TD01004 and TD01007 have fewer Cr-spinels than other samples. The images of TD01008 (Pic. 28) and TD01013 (Pic. 29) have more iron oxide than sample TD01001. The Cr-spinel grains in the peridotites are tens to few hundreds micrometers in length, and the bigger sized grains are euhedral or subhedral, while the middle and smaller sized crystals are subhedral or anhedral shape. Picture 30 shows the textures of the gabbro sample TD01014, which is composed with about ~55% of hornblende and ~45% of plagioclase, and picture 31 shows the ilmenite in the sample.. 62.

(72) Picture 22. Back-scattered electron (BSE) image of sample TD01001. (serp. = serpentine, spl. = Cr-spinel, oxide = Fe oxide, same below.). Picture 23. BSE image of sample TD01001. (cal. = calcite, same below.). 63.

(73) Picture 24. BSE image of sample TD01002.. Picture 25. BSE image of sample TD01003.. 64.



(76) Picture 30. BSE image of sample TD01014. (Pl. = plagioclase, Hbl. = hornblende, same below.). Picture 31. BSE image of sample TD01014. (Ilm. = ilmenite).. 67.

(77) Chapter 4 Results 4.1 Mineral Chemistry 4.1.1. Spinel from the ETO peridotites The results of EPMA analysis are listed in appendix 1. The spinels are Cr-. rich and classify as Cr-spinel. The Cr2O3 content ranges from a relatively low concentration of 35 wt% for TD01001, to an intermediate range between 38 and 41 wt% for TD01002, TD01003 and TD01004 and increases to a slightly higher concentration of 41 to 46 wt% for sample TD01007, TD01008 and TD01013. The mean Cr2O3 value is ~42 wt%. The mean aluminum content of all samples is ~26.5 wt%, while samples TD01001 and TD01003 have higher concentrations (31 and 29 wt%) and TD01008 and TD01013 has lower (25 wt%). The Cr and Al contents are used to calculate the Cr# (100Cr/ (Cr+Al)). The mean Cr number of all samples is ~51.6. Sample TD01001 has the lowest Cr number value (Cr# = 43), whereas all other samples have values >47. The highest Cr# is 54 from TD01008. The MgO content of the spinels are relatively constant at ~15% but their overall range is from 12% to 17%. TD01001 and TD01003 have higher values than average, mostly above 15.5 wt% and up to 16.5 wt%. Except few analyses, the value of TD01004 and TD01007 concentrate at 14 to 15.5 wt%. The value of sample TD01008 and TD01013 are slightly lower than others, between 12.5 and 14.5 wt%. Total iron content (detected as FeO) counts for all samples between 13 and 17 wt%. The ratio of Mg and Fe, calculated as the Mg# (100Mg/ (Mg+Fe)) ranges between. 68.

(78) 60 and 66. The concentration of other elements in the analysis (SiO2, TiO2, MnO, NiO, CaO, Na2O and K2O) are lower than 0.5 wt%. 4.1.2. Gabbro Mineral Chemistry The gabbro mainly consists of three minerals, hornblende, plagioclase and. ilmenite. The EPMA results of hornblende give the SiO2 content between 44 and 49 wt%, FeO content between 16.5 and 19 wt%, MgO content between 10.5 and 14 wt%, CaO content between 9.5 and 11 wt%, Al2O3 content between 4.5 and 7.5 wt%, TiO2 content and Na2O content below 2 wt% and MnO and K2O under 0.2 wt%. The SiO2 content in plagioclase composition range between 64 and 68 wt%, Al2O3 between 19.5 and 20.5 wt%, CaO around 1 wt%. There is around 10 to 11 wt% Na2O in the plagioclase, while there’s merely no K2O in it (less than 0.2 wt%). And other elements are also close to detection limits. The ilmenite have ~47.5 to 50.7 wt % FeO and 47.9 to 49.3 wt% TiO2 with other element concentrations < 1 wt%.. 69.

(79) 4.2 In situ zircon U/Pb age dating result Picture 32 to 34 show the CL images of the 20 zircons separated from the gabbro TD01014 used for LA-ICP-MS analysis. The grain size of the zircons are ~100 to ~250 μm in diameter, and most of the grains are broken. Some of the zircons have obvious zoning while some are more complicated. The full U/Pb analysis data are shown in appendix 2. The average detection ratio is 0.0022 ± 0.00014, while the average. 207. 206. Pb/238U. Pb/235U detection ratio is. 0.0134 ± 0.00361. The Concordia diagram, constructed using Isoplot 3.0 (Ludwig, 2003), is shown in figure 11 with 2 error ellipses of the individual spot analyses. The weighted mean 206Pb/238U age is 14.1 ± 0.4 Ma on 20 individual zircon crystals and the MSWD (i.e. mean square of weighted deviation) is 4.2. Due to the young age of these zircons, the 207Pb/235U age has a larger uncertainty and thus is less meaning in this research.. 70.

(80) Picture 32. Zircon sample CL image and LA-ICP-MS testing spot. (The individual zircon age is listed in the picture, same below.). 71.

(81) Picture 33. Zircon sample CL image and LA-ICP-MS testing spot.. 72.

(82) Picture 34. Zircon sample CL image and LA-ICP-MS testing spot.. 73.

(83) U-Pb Concordia Age 0.005 data-point error ellipses are 2. 30 26. 0.004. 74. 206Pb/238U. 22 0.003. 18 14. 0.002 10 0.001. 14.1 ± 0.4 Ma. 6 2. 0.000 0.000. 0.004. 0.008. 0.012. 0.016. 0.020. 207Pb/235U. Figure 11. 206Pb/238U - 207Pb/235U concordia plot.. 0.024. 0.028.

(84) 206Pb/238U 18. Age. data-point error symbols are 2. 17 16 15 14 75. 13 12 11 10. Mean = 14.13 ± 0.37, 95% conf. N = 20. 9. Figure 12. 206Pb/238U mean age..

(85) 4.3 Trace elements, Rare Earth Elements (REEs) and Sr/Nd isotopes The trace elements in the peridotite samples are quite depleted except the transitional metals (i.e. Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Zn). The concentration of the transition metals range from several ppm (e.g. Sc) to tens ppm (e.g. Ti, V, Zn) to hundreds ppm (Mn, Co) to thousands ppm (e.g. Cr, Ni). Sr concentration in TD01002 (~219 ppm) is several times higher than other samples (0 ~ 43 ppm). Sample TD01004, though still quite depleted (< 3 ppm), is more abundant in other trace elements (i.e. Ga, Rb, Y, Zr, Nb, Cs, Ba, Hf, Ta, W, Pb, Th) than other samples (< 1 ppm or under detection). The rare earth elements (REEs) of all serpentinized peridotites except TD01004 are quite depleted (< 0.1 ppm). TD01004 has much higher concentration in REEs than other samples (~ 10 times). These serpentinized peridotites have a slight U-shape pattern (i.e. slightly higher LREE and HREE) and a negative Eu anomaly. If normalized to chondrite values (McDonough and Sun, 1995), the REEs concentration except TD01004 are about 0.1 times of C1 chondrite concentration, while TD01004 is 1 to 2 times chondrite concentration. The measurement of. 87. Sr/86Sr isotope ratio of four peridotite samples (i.e.. TD1001, TD01002, TD01003, and TD01004) ranges between 0.70883 and 0.70908. The initial 87Sr/86Sr values cannot be calculated due to the extremely low Rb content (i.e. below detection limit) but given their likely age (i.e. ~14 Ma) the measured value will not be significantly different from the initial values (i.e. ± 0.00001). The Sm and Nd concentration of most peridotites is too low to measure the. 143. Nd/144Nd ratio;. however, sample TD1004 has sufficient concentration and has a measured 76.

(86) 143. Nd/144Nd ratio of 0.513106. The initial ratio based on the age of the gabbro is. 0.513083 and corresponds to an Nd(T) value of +9.1 using a CHURtoday value of 0.512638. Gabbro sample TD01014 has a wide range of transitional metals, which is abundant in Ti (~15040 ppm) and V (~860 ppm) while depleted in Cr (~6 ppm) and Cu (~8 ppm). The REEs concentrations in TD01014 are generally about 10 times more abundant to the chondrite concentration, and it has a similar pattern as N-type (normal) MORB. The measured 87Sr/86Sr isotope ratio of 0.70503 corresponds to an ISr value of 0.70501. The measured 143Nd/144Nd isotope ratio is 0.513226 with an Nd(T) value of +11.4.. 77.