Geochemical Constraints for the Genesis of
Post-collisional Magmatism and the
Geodynamic Evolution of the Northern
Taiwan Region
KUO-LUNG WANG
1,2*, SUN-LIN CHUNG
1, SUZANNE Y. O’REILLY
2,
SHEN-SU SUN
3, RYUICHI SHINJO
4AND CHANG-HWA CHEN
51
DEPARTMENT OF GEOSCIENCES, NATIONAL TAIWAN UNIVERSITY, PO BOX 13-318, TAIPEI 106, TAIWAN
2
ARC NATIONAL KEY CENTRE FOR THE GEOCHEMICAL EVOLUTION AND METALLOGENY OF CONTINENTS (GEMOC), DEPARTMENT OF EARTH AND PLANETARY SCIENCES, MACQUARIE UNIVERSITY, SYDNEY, N.S.W. 2109, AUSTRALIA
3
16 GIFFEN CLOSE, HOLT, CANBERRA, A.C.T. 2615, AUSTRALIA
4
DEPARTMENT OF PHYSICS AND EARTH SCIENCES, UNIVERSITY OF THE RYUKYUS, OKINAWA, JAPAN
5
INSTITUTE OF EARTH SCIENCES, ACADEMIA SINICA, PO BOX 1-55, NANKANG, TAIPEI, TAIWAN
RECEIVED NOVEMBER 14, 2002; ACCEPTED OCTOBER 21, 2003
Taiwan is an active mountain belt created by the oblique collision of the northern Luzon arc with Asia. Late Pliocene extensional collapse of the northern Taiwan mountain belt (NTMB) was accompanied by magmatism that formed the Northern Taiwan Volcanic Zone (NTVZ; 28---02 Ma). The geochemical characteristics of the NTVZ magmas can thus provide constraints both for the mantle source composition and the geodynamic processes operating in the late orogenic stage of the region. The NTVZ volcanic rocks consist dominantly of calc-alkaline andesites and basalts, along with sub-ordinate but heterogeneous lavas including low-K, shoshonitic and ultrapotassic magmas. From the NE to the SW in the NTVZ, the magmas show systematic compositional variations from low-K to calc-alkaline and then shoshonitic. This spatial geochemical varia-tion, characterized by southwesterly increase in potassium and incompatible trace elements, appears to be subparallel to the south-western part of the modern Ryukyu subduction system. Sr---Nd isotope ratios of the NTVZ volcanic rocks (87Sr/86Sr
070376---070551; 143Nd/144Nd 051259---051301)
suggest that two mantle source components are involved in the magma generation, the asthenosphere and metasomatized subconti-nental lithospheric mantle. These two components are represented by the 26 Ma Mienhuayu high-Mg basaltic andesites and the 02 Ma
Tsaolingshan high-Mg potassic lavas, respectively. The latter are interpreted to be the products of small-degree melting of a phlogopite-bearing, harzburgite lithospheric mantle source metasomatized recently by the nearby Ryukyu subduction zone processes. The Sr---Nd---Pb isotope systematics and specific trace-element ratios of the NTVZ volcanic rocks suggest that melts derived from subducted sediments and fluids released from slab dehydration reactions were both involved in metasomatizing this mantle source. The unique spatial geochemical variation of the NTVZ volcanic rocks can be successfully modelled using variable degrees of partial melting of the mantle source regions, coupled with mixing of different melt components from depleted asthenospheric and metasomatized lithospheric mantle components beneath individual volcanic fields. It is inferred that mixing of melts from specific mantle components and the degree of partial melting are spatially and temporally related to the tectonic evolution of the northern Taiwan region, and not simply due directly to subduction zone processes. The overall NTVZ geochemical characteristics can be explained by various degrees of melting within an ascending region of the asthenospheric mantle, triggered by extensional collapse of the NTMB, and interaction of these melts with overlying fluid- and sediment-modified lithospheric mantle.
KEY WORDS: Northern Taiwan Volcanic Zone; post-collisional magmatism; Pb isotopes; subduction components; geodynamics of basalt genesis
INTR OD UCT ION
The tectonic evolution of orogenic belts is typically marked by changes in the composition of the associated magmatism (e.g. Harris et al., 1986). Post-collisional mag-matism is one of the common features of many orogens around the world, and may indicate that the orogen is in the process of collapsing (Dewey, 1988). Petrogenetic studies of post-collisional magmatism not only provide constraints on the geodynamic processes responsible for the cessation of collision and onset of extensional col-lapse, but also reveal changes in magma source regions associated with such processes. In addition, one of the prevailing characteristics of post-collisional magmatism is its subduction-related geochemical characteristics despite subduction processes having been terminated as a result of continental collision. The subduction-related signa-tures are attributed to metasomatism by slab-derived fluids of the mantle lithosphere prior to collision (Pearce et al., 1990; Turner et al., 1992, 1993, 1996; Platt & England, 1993). Thus, the geochemical characteristics of calc-alkaline post-collisional magmatism allow the evaluation of subduction-related metasomatism of their mantle source.
Taiwan is an active mountain belt created by the oblique collision between the northern Luzon arc and the Asian continent (see Teng, 1990). Despite continuing plate convergence in central and southern Taiwan, extensional collapse has occurred in the northern part of the mountain belt since Plio-Pleistocene times. Accord-ingly, Teng (1996) proposed a model for the orogenic evolution of northern Taiwan, from mountain building induced by collision to subsequent extensional collapse, lasting only a few million years. Wang et al. (1999) proposed that post-collisional extension in the northern Taiwan mountain belt (NTMB) caused the magmatism of the Northern Taiwan Volcanic Zone (NTVZ) (Fig. 1). Compared with other collision orogens also character-ized by extensional collapse (Dewey, 1988; Platt & Visser, 1989; Malavielle, 1993), northern Taiwan may provide one of the most active examples of such a tectonic pro-cess. In this study, we aim to: (1) investigate the petrogen-esis of the post-collisional magmatism, which displays distinctive spatial and temporal geochemical variations indicative of changes in magma source region; (2) explore metasomatism of the mantle source by different subduc-tion components, e.g. hydrous fluids and subducted sedi-ments; (3) track the evolution of the mantle source region during the late orogenic stage; (4) show how the geo-chemical trends within individual magmatic episodes can constrain the nature of geodynamic processes.
R EGIONAL GE OLOGY : THE N TVZ
Located at the Asian continental margin at the boundary of the Philippine Sea plate, the island of Taiwan is not only a collision zone but also a transform region between the opposing Luzon and Ryukyu subduction systems (Fig. 1). The Ryukyu subduction and the resultant Ryukyu arc---trench system, active since the Paleogene, are associated with the development of a back-arc basin, the Okinawa Trough, which has a distinct topography (42000 m below sea level; Fig. 1) and a strong curvature. Driven by the NW movement of the Philippine Sea plate, the northern segment of the Luzon arc is generally believed to have collided with the Asian continental mar-gin at 10 Ma (Teng, 1990). The Taiwan mountain belt, composed of deformed strata of both the Asian continent and the Luzon arc, reaches a maximum altitude near 4000 m in its central part (Fig. 1). Whereas collisional tectonism is still continuing, as evidenced by the promi-nent crustal shortening in central and southern Taiwan (e.g. Angelier et al., 1986; Yu & Chen, 1994), structural and seismological data demonstrate that the northern part of the Taiwan mountain belt has been subjected to extensional deformation in the Quaternary (Suppe, 1984; Lee & Wang, 1988; Yeh et al., 1991). Thus, Teng (1996) proposed that extensional collapse of the NTMB took place in Plio-Pleistocene times. Consequently, the topo-graphic elevation of the orogen reduces from near 4000 m in central Taiwan to rolling hills in the north-eastern part and eventually becomes submerged in the offshore area farther to the NE (Fig. 1).The NTVZ comprises two major onshore volcanic fields, the Tatun and Keelung Volcano Groups (TTVG and KLVG), and several offshore volcanoes (Fig. 1). The NTVZ volcanic rocks consist dominantly of andesites with calc-alkaline geochemical characteristics, similar to those commonly observed in convergent-margin lavas (e.g. Gill, 1981). Thus, they have conventionally been regarded as the westernmost part of the Ryukyu volcanic arc (Chen, 1990; Juang, 1993; Chung et al., 1995b; Teng, 1996). The conventional view was first questioned by Chen (1997), who suggested an extensional rather than a subduction-related tectonic regime for magma genera-tion. To accommodate available geophysical and geo-logical evidence, Wang et al. (1999) proposed that the NTVZ resulted from post-collisional extension related to the late Pliocene orogenic collapse of the NTMB. This extension may also account for the reactivation of the opening of the Okinawa Trough that commenced in the middle Miocene (Sibuet et al., 1995) but became inactive after the arc---continent collision in Taiwan. Reactivated rifting in the Okinawa Trough started pro-pagating to the SW from 15 Ma, with accompanying development of the westernmost part of the Ryukyu subduction system towards Taiwan (Chung et al., 2000).
Radiometric age data show that the NTVZ volcanism commenced at 28---26 Ma and lasted throughout the Quaternary. Figure 2 summarizes existing age data for the NTVZ volcanic rocks, carried out by various dating
methods including fission track, K---Ar and Ar---Ar. The age data suggest that the earliest eruptions occurred in the Sekibisho (SBS) and Mienhuayu (MHY) islets and the TTVG around 28---26 Ma, with the youngest ages
25°N 130°E 120° 130° 140°E 10° 20° 30° 40°N 25° 26°N
Fig. 1. Maps showing the regional tectonic setting of Taiwan and the volcanic fields of the NTVZ, modified from Wang et al. (1999, 2002). WBP indicates the western boundary of the subducting Philippine plate. It should be noted that the NTVZ is currently located 200 km above the Wadati---Benioff zone. Stippled area represents the Taiwan orogen basement characterized by folded and tilted Tertiary strata (Wageman et al., 1970; also named southern Taiwan---Sinzi Folded Zone). Lower right inset: tectonic setting of Taiwan. OT, Okinawa Trough; RT, Ryukyu Trench. Upper left inset: detailed bathymetric map showing the location of the NTVZ. Bold black line indicates the surface projection of the 100 km contour of the depth to the Wadati---Benioff zone (Sibuet et al., 1998).
around 02 Ma in most of volcanic fields. In some local-ities, however, the volcanic ages might be younger than 02 Ma, as dating results are close to or even smaller than the limit of the dating methods. The age spectrum in Figure 2 shows a generally random distribution in space and time, distinct from the southwesterly younging trend of the NTVZ volcanism argued by some workers (e.g. Teng et al., 1992; Teng, 1996). This trend, based on limited geochronological data, was ascribed to south-westerly propagation of the Ryukyu subduction system (Teng et al., 1992). However, when more recent age data ( Juang, 1993; Tsao, 1994; Lee, 1996; Wang et al., 2000; Chung et al., 2001b) are included, the alleged trend disappears (Fig. 2) so that the argument by Teng et al. (1992) and Teng (1996) is problematic.
SAMPLE S A ND ANA LYTICAL
ME THO DS
Samples and major-, trace-element and
Nd---Sr isotope methods
Representative volcanic samples were collected from different localities in the NTVZ for detailed geochemical investigation, including whole-rock major- and trace-element, and Sr---Nd---Pb isotope determinations. Geo-chemical data for the SBS and Kobisho (KBS) volcanic rocks from Shinjo (1998, and unpublished Pb data, 2003) and some Nd---Sr isotope data from Chen (1989) are also included in this paper for comparison. All NTVZ volca-nic rocks are microscopically porphyritic. Lithology and phenocryst assemblages are (1) plagioclase þ olivine titanomagnetite for SBS basalts; (2) plagioclase þ olivineþ augite for KBS basalts; (3) olivine þ bronzite þ
plagioclase for MHY basaltic andesites; (4) plagioclaseþ olivine þ bronzite for Pengchiayu (PCY) basalts; (5) plagioclase þ augite þ hornblende þ biotite for KLVG dacites; (6) plagioclase þ augite þ olivine for TTVG basalts and plagioclaseþ augite þ hypersthene þ hornblende for andesites; (7) olivineþ augite þ plagioclase for Kuanyinshan (KYS) basalts and plagioclaseþ augite þ hypersthene þ hornblende olivine for andesites; (8) olivine þ diopside þ phlogopite þ Fe---Ti oxide leucite for TLS absarokites. Detailed petrographic descrip-tions and mineral chemical data have been reported in a number of publications (Chen, 1990; Juang, 1993; Shinjo, 1998; Wang et al., 2000, 2002; Chung et al., 2001b), and so in this paper we focus only on the whole-rock geochemistry of the NTVZ volcanic rocks.
Powder samples were prepared using a jaw crusher and a corundum mill. Major-element compositions were determined by X-ray fluorescence (XRF) using a Rigaku1
RIX 2000 spectrometer at the Department of Geosciences, National Taiwan University. The analytical uncertainties are generally better than 5% for all ele-ments (Lee et al., 1997). Loss on ignition was determined by routine procedures. Powdered samples weighing about 50 mg were dissolved using a HF---HNO3 (10:1) mixture in screw-top Teflon Savillex1
for 7 days at 100C, followed by evaporation to dryness, refluxing
in 7N HNO3and drying again, and then dissolving the sample cake in 2% HNO3. An internal standard solution of 10 ppb Re was added and the spiked dissolutions were diluted with 2% HNO3to a sample/solution weight ratio of 1/1000. The internal standard was used for monitor-ing the signal shift durmonitor-ing inductively coupled plasma-mass spectrometry (ICP-MS) measurements using a Perkin Elmer1 Elan-6000 spectrometer at Guangzhou 0 1 2 3 2.6 2.6 0.2 0.5 0.4 2.1 0.3 1.0 1.4 0.9 0.3 1.0 2.8 1.5 0.2 0.2 0.4 0.7 1.1 0.5 0.6 0.2 0.5 0.2 0.3 0.2 FTD K-Ar Ar-Ar NE SW
TLS KYS TTVG KLVG PCY MHY KBS SBS
Age (Ma)
Fig. 2. Radiometric age data for each volcanic field in the NTVZ. Data sources include: fission-track dating (FTD) from Liu et al. (1986), Liu (1987) and Wang & Chen (1990); K---Ar ages from Juang (1988, 1993), Shinjo et al. (1991) and Tsao (1994); Ar---Ar ages from Lee (1996), Wang et al. (2000) and Chung et al. (2001b). It should be noted that eruption ages of the NTVZ display random distribution relative to their geographical locations. Abbreviations of individual volcanic fields: TLS, Tsaolingshan; KYS, Kuanyinshan; TTVG, Tatun Volcanic Group; KLVG, Keelung Volcanic Group; PCY, Pengchiayu; MHY, Mienhuayu; SBS, Sekibisho; KBS, Kobisho.
Institute of Geochemistry, the Chinese Academy of Sciences, China, which has a good stability range within 10% variation (Liu et al., 1996; Li, 1997). Values recommended for the USGS rock standard BCR-1 (Govindaraju, 1994) were used for data calibrations; the analytical errors are generally better than 5% for most trace elements. The samples were dissolved for Sr and Nd separation using routine cation-exchange column techni-ques. Sr and Nd isotope ratios were measured using VG3541and Finnigan MAT 2621mass spectrometers, respectively, at the Institute of Earth Sciences, Academia Sinica, Taiwan. Detailed chemical and mass spectro-metric procedures were described by Chen et al. (1990). The isotopic ratios were corrected for mass fractionation by normalizing to86Sr/88Sr¼ 01194 and146Nd/144Nd¼
07219. Long-term laboratory measurements for SRM 987 Sr and La Jolla (UCSD) Nd standards yield 071024 000004 (2s) and 051187 000003 (2s), respectively. During the period of the study, measurements for the NIST standard SRM 987 gave 86Sr/88Sr ¼ 071023 000001 (2s; n ¼ 3), and for the La Jolla (UCSD) Nd standards gave 0511867 0000006 (2s; n ¼ 3). The overall blank contributions were 08 ng Sr for about 20 mg Sr and 03 ng Nd for about 06 mg Nd in the samples.
Double-spike Pb method
Chemical separation of Pb for isotope analysis was undertaken at the National Taiwan University, Taiwan and the University of the Ryukyus, Japan. Rock chips and/or powders were leached with 6N HCl at 80
C for 30 min. Then they were rinsed with distilled water before being decomposed with HF and HNO3. The Pb was separated using standard HBr anion exchange proce-dures in Teflon columns and the sample solution passed through the columns twice for purification. All chemical processes resulted in loss of about 50% of the Pb in chip samples and 90% in powders, respectively. Two small aliquots of the purified Pb sample were loaded onto two single Re filaments used for natural and double-spiked sample runs separately. A small drop of 207Pb---204Pb
double-spike solution and Pb emitter silica gel---H3PO4 solution, prepared according to Gerstenberger & Haase (1997), were then added to the aliquot on the mix run filament. Repeated sucking back and release of the mixture with the loading pipette ensured a good sample---spike mixture. Lead isotope measurements were made on a Finnigan MAT2621mass spectrometer using static multi-collector mode at the University of the Ryukyus, Japan. Data acquisition was usually performed at a filament temperature of about 1050---1150C and consisted of four blocks of data per run, with each block comprising ten 16 s integrations (thus, 160 s integration time per block). Lead isotope ratios were corrected for mass fractionation by the use of a 207Pb---204Pb
double-spike method. A new 207Pb---204Pb double-spike
solution was prepared and calibrated in this study. The spike calibration is briefly described as follows.
The isotope composition of the newly prepared
207Pb---204Pb double spike was calibrated with NIST Pb
standard SRM 982. The standard had been measured in separate natural and mix runs with the new double spike for calibrating the isotopic compositions of the double spike. The isotopic compositions of SRM 982 in the natural runs (n¼ 22 in the period of analysis) were normalized to 208Pb/206Pb ¼ 100016, a value
recom-mended by Cameron et al. (1969) and accepted in other Pb double-spike and triple-spike studies (e.g. Galer & Abouchami, 1998; Thirlwall, 2000). Data from these SRM 982 analyses and from double-spiked SRM 982 mix runs (n ¼ 8) were then used to correct for mass fractionation effect and to determine the isotopic com-position of the double spike. All calculations were performed by an iterative technique using an Excel spreadsheet (Woodhead et al., 1995). The 204Pb/207Pb was determined to be 09921 in the newly prepared double-spike solution. Once the double-spike composi-tion was calibrated it was tested by obtaining the isotope composition of NIST Pb Standard SRM 981 with the double-spike method. All mixed samples measured (n¼ 54) had Q 07---09 [Q ¼ 204Pb
spike/(204Pbspike þ
204Pb
sample)]. The double-spike calibrated SRM 981 has the following composition:206Pb/204Pb¼ 169411 42, 207Pb/204Pb¼ 154978 52 and208Pb/204Pb¼ 367185
142 (2s), which agrees well with values recently reported by Galer & Abouchami (1998) and Thirlwall (2000) using triple-spike and double-spike methods, respectively. The external reproducibility of the SRM 981 (2SD, 54 ana-lyses in the period of this study) is 124 ppm for 206Pb/ 204Pb, 112 ppm for207Pb/204Pb and 96 ppm for208Pb/ 204Pb. The overall blank contributions were 04 ng Pb for
about 02 mg Pb in the samples. Accordingly, high-quality Pb isotope data were produced for this study using the double-spike method.
The major- and trace-element and Sr---Nd---Pb isotopic compositions of the NTVZ volcanic rocks are presented in Tables 1 and 2, respectively.
WHOLE-ROCK GE OC HEMICAL
COMPOSITION
Major-element compositions
In a plot of K2O vs SiO2(Fig. 3a), most of the NTVZ volcanic rocks display calc-alkaline characteristics except for the SBS and MHY magmas, which are low-K, and the TLS magmas, which are shoshonitic. Volcanic rocks from the offshore volcanoes are principally mafic to mediate, whereas the onshore volcano groups are inter-mediate to felsic. The mafic rocks (SiO255 wt %) from
Table
1
:
Whole-rock
major-and
trace-element
compositions
for
the
N
T
VZ
volcanic
rocks
Volcanic field: Sekibisho (SBS) 1 Kobisho (KBS) Mienhuayu (MHY) Sample no.: SBS-1 SBS-2 SBS-7 KBS-1 1 KBS-3 1 KO-3 KO-4 KO-5 MHH-01 MHY-1 MHY-2 MHY-3 MHY-4 MHY-5 MHY-7 MHY-8 MHY-9 MHY-2-1 MHY-2-2 Major element (wt %) SiO 2 49 . 91 53 . 02 50 . 15 50 . 66 50 . 21 49 . 30 50 . 02 48 . 65 54 . 50 53 . 30 53 . 70 53 . 28 49 . 44 49 . 99 53 . 41 53 . 56 52 . 82 53 . 45 54 . 21 TiO 2 0 . 88 0 . 83 1 . 02 0 . 85 0 . 85 0 . 76 0 . 83 0 . 85 1 . 44 1 . 56 1 . 64 1 . 50 1 . 68 1 . 61 1 . 53 1 . 52 1 . 48 1 . 54 1 . 41 Al 2 O3 20 . 27 17 . 39 18 . 84 16 . 12 16 . 97 17 . 20 17 . 49 17 . 13 14 . 60 14 . 52 15 . 01 14 . 35 14 . 26 14 . 81 14 . 35 14 . 50 14 . 58 14 . 49 14 . 24 Fe 2 O3 * 10 . 60 10 . 58 11 . 52 9 . 52 9 . 28 9 . 11 9 . 13 9 . 79 10 . 39 10 . 79 10 . 19 10 . 65 11 . 46 11 . 10 10 . 58 10 . 55 10 . 63 10 . 69 10 . 34 MnO 0 . 17 0 . 22 0 . 18 0 . 16 0 . 16 0 . 15 0 . 16 0 . 16 0 . 14 0 . 14 0 . 13 0 . 14 0 . 13 0 . 13 0 . 13 0 . 14 0 . 13 0 . 14 0 . 14 MgO 4 . 38 5 . 09 4 . 73 6 . 60 6 . 66 7 . 08 5 . 95 6 . 85 7 . 38 7 . 80 5 . 90 8 . 08 6 . 46 6 . 69 7 . 82 7 . 87 7 . 05 7 . 48 8 . 08 CaO 10 . 44 9 . 61 10 . 16 11 . 42 11 . 26 12 . 59 11 . 81 11 . 66 8 . 48 8 . 22 8 . 05 8 . 00 7 . 28 7 . 91 8 . 22 8 . 03 7 . 88 8 . 44 8 . 27 Na 2 O2 . 97 2 . 67 2 . 88 2 . 60 2 . 55 1 . 82 2 . 11 1 . 87 2 . 14 2 . 47 2 . 66 2 . 72 2 . 47 2 . 53 2 . 67 2 . 66 2 . 73 2 . 45 2 . 34 K2 O0 . 26 0 . 43 0 . 36 1 . 67 1 . 64 1 . 48 1 . 74 1 . 66 0 . 40 0 . 41 0 . 47 0 . 42 0 . 55 0 . 45 0 . 43 0 . 42 0 . 53 0 . 42 0 . 59 P2 O5 0 . 10 0 . 16 0 . 15 0 . 39 0 . 41 0 . 36 0 . 42 0 . 43 0 . 13 0 . 54 0 . 69 0 . 23 3 . 41 2 . 06 0 . 14 0 . 14 0 . 65 0 . 51 0 . 29 LOI 1 . 67 1 . 11 1 . 17 1 . 63 0 . 99 0 . 00 0 . 62 0 . 38 1 . 51 0 . 48 0 . 93 0 . 09 1 . 87 1 . 60 0 . 00 0 . 08 0 . 54 0 . 45 0 . 76 Total 99 . 98 100 . 00 99 . 99 99 . 99 99 . 99 99 . 85 100 . 28 99 . 43 101 . 10 100 . 22 99 . 38 99 . 46 99 . 02 98 . 87 99 . 27 99 . 47 99 . 01 100 . 06 100 . 67 Mg no. 0 . 47 0 . 51 0 . 47 0 . 60 0 . 61 0 . 63 0 . 59 0 . 60 0 . 61 0 . 61 0 . 56 0 . 62 0 . 55 0 . 57 0 . 62 0 . 62 0 . 59 0 . 60 0 . 63 Trace e lement (ppm) Sc 32 . 83 4 . 03 0 . 03 7 . 33 6 . 62 4 . 33 2 . 62 2 . 42 1 . 5 n .d. n .d. n .d. 2 1 . 86 0 . 66 7 . 91 8 . 85 4 . 42 1 . 11 3 . 5 V 297 276 281 254 251 230 263 2 79 170 8 3 8 9 1 42 137 1 49 141 143 1 41 143 1 39 Cr 41 28 27 96 93 127 144 9 2 3 71 241 188 4 11 422 4 24 425 434 4 29 381 4 14 Co 29 . 02 9 . 03 1 . 03 6 . 03 6 . 03 8 . 73 5 . 03 9 . 74 2 . 02 4 . 22 1 . 04 2 . 43 7 . 03 7 . 24 1 . 54 5 . 64 0 . 63 0 . 83 1 . 4 Ni 19 . 01 3 . 01 6 . 03 5 . 03 5 . 04 0 . 26 4 . 73 5 . 91 3 8 . 28 2 . 55 1 . 51 4 1 . 39 4 . 41 0 2 . 0 139 . 81 4 3 . 51 5 4 . 01 3 2 . 81 7 8 . 1 Cu n.d. n.d. n.d. n.d. n.d. 72 . 88 3 . 07 7 . 33 9 . 31 8 . 31 2 . 73 6 . 23 8 . 93 6 . 73 0 . 13 6 . 54 7 . 33 2 . 15 4 . 3 Zn n.d. n.d. n.d. n.d. n.d. 65 . 27 0 . 07 4 . 11 1 0 . 06 4 . 87 2 . 21 0 2 . 01 1 6 . 51 0 6 . 6 103 . 11 1 7 . 09 6 . 71 3 5 . 31 1 7 . 0 Ga n.d. n.d. n.d. n.d. n.d. 16 . 41 8 . 31 7 . 21 8 . 71 0 . 71 1 . 31 9 . 12 0 . 12 0 . 82 0 . 01 9 . 11 9 . 71 9 . 11 7 . 6 R b 6 9 6 7 06 74 46 4 4 61 6 1 0 1 21 51 4 1 51 61 61 9 1 7 2 2 Sr 268 265 392 433 436 421 419 4 92 187 139 110 1 78 334 2 22 195 190 2 16 212 2 22 Y2 0 . 72 4 . 52 5 . 41 9 . 21 9 . 51 7 . 71 8 . 42 0 . 22 2 . 21 2 . 31 3 . 61 9 . 41 3 . 82 1 . 92 0 . 21 9 . 72 3 . 42 0 . 51 8 . 4 Zr 47 . 05 4 . 06 7 . 08 1 . 08 2 . 07 4 . 48 8 . 18 9 . 19 2 . 05 0 . 85 6 . 98 2 . 99 0 . 49 0 . 78 5 . 08 4 . 68 3 . 68 3 . 58 0 . 6 Nb 1 . 92 . 02 . 53 . 73 . 73 . 54 . 24 . 16 . 53 . 54 . 45 . 35 . 86 . 05 . 45 . 36 . 45 . 67 . 9 Cs 0 . 28 0 . 44 0 . 30 1 . 41 1 . 34 0 . 72 1 . 26 0 . 66 0 . 50 0 . 26 0 . 27 0 . 53 0 . 49 0 . 48 0 . 51 0 . 51 0 . 64 0 . 38 0 . 52 Ba 87 110 137 234 241 215 232 2 54 137 102 91 131 1 51 140 139 136 1 72 94 124 La 3 . 83 4 . 77 7 . 16 7 . 96 8 . 23 7 . 27 7 . 87 8 . 63 5 . 58 3 . 72 4 . 22 5 . 03 4 . 75 5 . 23 4 . 57 4 . 86 6 . 18 4 . 90 7 . 10 Ce 9 . 71 1 . 61 7 . 51 7 . 71 8 . 21 6 . 61 7 . 81 9 . 71 2 . 46 . 87 . 61 1 . 31 1 . 41 2 . 01 0 . 61 0 . 91 3 . 61 1 . 01 5 . 3 Pr 1 . 46 1 . 70 2 . 54 2 . 35 2 . 43 2 . 18 2 . 41 2 . 56 1 . 73 1 . 13 1 . 26 1 . 63 1 . 63 1 . 81 1 . 59 1 . 64 1 . 99 1 . 59 2 . 15Volcanic field: Sekibisho (SBS) 1 Kobisho (KBS) Mienhuayu (MHY) Sample no.: SBS-1 SBS-2 SBS-7 KBS-1 1 KBS-3 1 KO-3 KO-4 KO-5 MHH-01 MHY-1 MHY-2 MHY-3 MHY-4 MHY-5 MHY-7 MHY-8 MHY-9 MHY-2-1 MHY-2-2 Nd 7 . 16 8 . 26 12 . 03 10 . 48 10 . 80 9 . 88 10 . 66 11 . 55 8 . 85 6 . 30 7 . 06 8 . 25 8 . 24 9 . 12 8 . 05 8 . 27 9 . 48 8 . 36 9 . 99 Sm 2 . 24 2 . 52 3 . 36 2 . 81 2 . 87 2 . 55 2 . 85 2 . 92 3 . 15 2 . 10 2 . 32 3 . 15 2 . 96 3 . 39 3 . 04 3 . 09 3 . 27 2 . 94 3 . 05 Eu 0 . 834 0 . 912 1 . 152 0 . 981 0 . 998 0 . 920 1 . 008 1 . 020 1 . 217 0 . 830 0 . 880 1 . 240 1 . 170 1 . 380 1 . 260 1 . 270 1 . 300 1 . 061 1 . 028 Gd 2 . 74 3 . 03 3 . 79 3 . 11 3 . 17 2 . 99 3 . 41 3 . 46 4 . 07 2 . 64 2 . 81 3 . 57 3 . 25 3 . 78 3 . 41 3 . 56 3 . 73 3 . 45 3 . 31 Tb 0 . 494 0 . 537 0 . 641 0 . 507 0 . 521 0 . 490 0 . 545 0 . 560 0 . 657 0 . 440 0 . 470 0 . 690 0 . 640 0 . 750 0 . 690 0 . 690 0 . 700 0 . 646 0 . 593 Dy 3 . 33 3 . 63 4 . 19 3 . 16 3 . 26 2 . 90 3 . 32 3 . 25 3 . 90 2 . 60 2 . 86 3 . 89 3 . 48 4 . 26 3 . 87 3 . 85 3 . 98 3 . 80 3 . 57 Ho 0 . 736 0 . 812 0 . 912 0 . 661 0 . 678 0 . 620 0 . 702 0 . 700 0 . 752 0 . 480 0 . 530 0 . 780 0 . 700 0 . 830 0 . 780 0 . 770 0 . 800 0 . 663 0 . 622 Er 2 . 16 2 . 42 2 . 67 1 . 88 1 . 93 1 . 80 2 . 03 2 . 08 1 . 95 1 . 30 1 . 45 2 . 02 1 . 79 2 . 18 2 . 04 2 . 04 2 . 10 1 . 76 1 . 66 Tm 0 . 335 0 . 377 0 . 413 0 . 286 0 . 294 0 . 260 0 . 293 0 . 290 0 . 285 0 . 180 0 . 200 0 . 280 0 . 240 0 . 300 0 . 280 0 . 270 0 . 290 0 . 243 0 . 230 Yb 2 . 15 2 . 42 2 . 62 1 . 80 1 . 85 1 . 70 1 . 87 1 . 93 1 . 69 1 . 11 1 . 23 1 . 68 1 . 42 1 . 84 1 . 72 1 . 71 1 . 76 1 . 49 1 . 40 Lu 0 . 319 0 . 367 0 . 387 0 . 264 0 . 270 0 . 240 0 . 284 0 . 280 0 . 245 0 . 160 0 . 170 0 . 250 0 . 210 0 . 270 0 . 270 0 . 250 0 . 260 0 . 214 0 . 205 Hf 1 . 35 1 . 53 1 . 86 2 . 08 2 . 13 1 . 73 2 . 19 1 . 97 2 . 61 1 . 63 1 . 77 2 . 21 2 . 40 2 . 48 2 . 36 2 . 25 2 . 18 2 . 56 2 . 36 Ta 0 . 150 0 . 160 0 . 190 0 . 300 0 . 290 0 . 200 0 . 228 0 . 240 0 . 375 0 . 210 0 . 260 0 . 330 0 . 360 0 . 380 0 . 350 0 . 330 0 . 400 0 . 324 0 . 446 Pb 2 . 18 2 . 77 2 . 38 3 . 13 3 . 19 2 . 45 3 . 01 3 . 74 2 . 24 1 . 93 1 . 21 4 . 77 6 . 49 6 . 47 2 . 78 2 . 43 3 . 12 2 . 45 5 . 98 Th 0 . 57 0 . 65 0 . 99 1 . 69 1 . 72 1 . 64 1 . 80 1 . 93 1 . 15 0 . 86 0 . 88 1 . 26 0 . 80 1 . 47 1 . 44 1 . 21 1 . 66 0 . 84 0 . 93 U0 . 20 0 . 31 0 . 31 0 . 53 0 . 53 0 . 26 0 . 53 0 . 35 0 . 32 0 . 21 0 . 21 0 . 40 0 . 68 0 . 46 0 . 35 0 . 33 0 . 41 0 . 29 0 . 31 Volcanic field: M ienhuayu (MHY) Pengchiayu (PCY) Keelung Volcanic G roup (KLVG) Sample no.: MHY-2-3 MHY-2-4 MHY-2-5 MHY-2-6 MHY-2-7 MHY-2-8 MHY-2-9 Pen-17 Pen-20 PGU-03 PGU-04 PGU-05 PGU-07 TS-3 GML CKS5-1 L -2 L-15 L-25 CH-7 Major element (wt %) SiO 2 52 . 76 52 . 66 52 . 32 54 . 20 54 . 04 53 . 37 52 . 96 49 . 46 51 . 18 53 . 12 50 . 74 53 . 54 52 . 84 54 . 96 56 . 24 56 . 25 56 . 15 57 . 62 57 . 11 58 . 13 TiO 2 1 . 50 1 . 43 1 . 40 1 . 45 1 . 46 1 . 44 1 . 51 1 . 12 1 . 19 1 . 12 1 . 09 1 . 19 1 . 09 0 . 58 0 . 56 0 . 57 0 . 54 0 . 50 0 . 55 0 . 46 Al 2 O3 14 . 48 14 . 26 13 . 89 14 . 43 14 . 57 14 . 35 14 . 16 17 . 78 17 . 24 16 . 74 16 . 13 15 . 40 16 . 45 17 . 79 18 . 20 18 . 12 17 . 10 18 . 13 17 . 69 17 . 80 Fe 2 O3 * 10 . 77 10 . 07 10 . 26 10 . 56 10 . 57 10 . 69 10 . 76 10 . 23 9 . 49 9 . 45 9 . 30 9 . 87 9 . 54 6 . 90 6 . 11 5 . 88 6 . 27 6 . 00 5 . 72 6 . 44 MnO 0 . 14 0 . 13 0 . 14 0 . 14 0 . 13 0 . 14 0 . 14 0 . 16 0 . 15 0 . 14 0 . 14 0 . 14 0 . 14 0 . 12 0 . 11 0 . 12 0 . 12 0 . 12 0 . 13 0 . 12 MgO 7 . 71 7 . 01 7 . 67 7 . 89 7 . 65 7 . 81 7 . 44 5 . 44 5 . 45 4 . 83 5 . 03 6 . 47 4 . 99 4 . 63 4 . 62 4 . 35 4 . 73 3 . 75 4 . 06 3 . 65 CaO 8 . 51 8 . 69 8 . 91 8 . 20 8 . 17 7 . 92 7 . 87 10 . 37 10 . 33 10 . 13 10 . 36 9 . 19 10 . 22 8 . 75 7 . 84 7 . 28 8 . 44 7 . 83 7 . 39 7 . 90 Na 2 O2 . 29 2 . 48 2 . 54 2 . 52 2 . 57 2 . 45 2 . 31 2 . 28 2 . 43 1 . 86 1 . 87 1 . 77 1 . 82 2 . 55 2 . 57 2 . 71 2 . 68 2 . 87 2 . 68 3 . 12 K2 O0 . 45 0 . 61 0 . 49 0 . 50 0 . 56 0 . 56 0 . 54 1 . 41 1 . 46 1 . 52 1 . 34 0 . 95 1 . 43 1 . 87 1 . 60 1 . 62 1 . 68 1 . 65 1 . 80 1 . 62 P2 O5 1 . 01 0 . 93 0 . 88 0 . 25 0 . 32 0 . 48 0 . 76 0 . 45 0 . 39 0 . 38 0 . 36 0 . 28 0 . 37 0 . 31 0 . 21 0 . 37 0 . 20 0 . 27 0 . 33 0 . 23 LOI 0 . 52 1 . 26 1 . 27 0 . 12 0 . 09 0 . 31 0 . 87 n.d. 1 . 23 n.d. n.d. n.d. n.d. n.d. n.d. 3 . 07 n.d. n.d. n .d. n.d. Total 100 . 14 99 . 53 99 . 77 100 . 26 100 . 13 99 . 52 99 . 32 98 . 70 100 . 54 99 . 29 96 . 37 98 . 80 98 . 89 98 . 44 98 . 06 100 . 34 97 . 90 98 . 74 97 . 45 99 . 48 Mg no. 0 . 61 0 . 60 0 . 62 0 . 62 0 . 61 0 . 61 0 . 60 0 . 54 0 . 56 0 . 53 0 . 54 0 . 59 0 . 53 0 . 59 0 . 62 0 . 62 0 . 62 0 . 58 0 . 61 0 . 55
Volcanic field: M ienhuayu (MHY) Pengchiayu (PCY) Keelung Volcanic G roup (KLVG) Sample no.: MHY-2-3 MHY-2-4 MHY-2-5 MHY-2-6 MHY-2-7 MHY-2-8 MHY-2-9 Pen-17 Pen-20 PGU-03 PGU-04 PGU-05 PGU-07 TS-3 GML CKS5-1 L -2 L-15 L-25 CH-7 Trace element (ppm) Sc 21 . 72 0 . 12 0 . 12 0 . 82 1 . 22 1 . 52 1 . 73 5 . 54 4 . 02 7 . 22 7 . 12 4 . 32 8 . 24 6 . 62 6 . 92 0 . 42 9 . 62 4 . 32 6 . 82 4 . 4 V 142 138 127 139 144 142 145 249 232 234 224 174 231 251 221 210 2 30 222 1 85 242 Cr 401 346 365 397 408 421 386 40 42 32 38 n.d. 37 60 128 53 126 3 2 6 8 2 6 Co 31 . 22 8 . 93 0 . 93 1 . 53 0 . 63 0 . 63 0 . 73 4 . 24 1 . 72 9 . 12 8 . 83 3 . 92 9 . 72 1 . 31 8 . 81 6 . 15 5 . 45 7 . 41 6 . 63 4 . 0 Ni 174 . 4 150 . 9 174 . 9 179 . 2 166 . 0 171 . 2 168 . 32 0 . 02 1 . 61 5 . 21 6 . 96 6 . 41 7 . 12 6 . 62 8 . 11 7 . 22 9 . 91 4 . 72 2 . 71 0 . 9 Cu 39 . 74 9 . 83 8 . 03 8 . 53 3 . 84 1 . 03 2 . 9 n.d. n .d. 3 2 . 81 7 . 73 6 . 43 0 . 6 n .d. n .d. n .d. n .d. n.d. n .d. n.d. Zn 186 . 8 166 . 9 217 . 8 127 . 2 130 . 8 129 . 4 152 . 28 2 . 79 0 . 58 2 . 57 7 . 38 1 . 57 8 . 6 178 . 35 4 . 94 8 . 94 8 . 94 6 . 74 9 . 74 6 . 7 Ga 19 . 21 8 . 21 7 . 81 8 . 51 9 . 01 8 . 91 9 . 5 n.d. n .d. 1 9 . 11 8 . 31 8 . 11 8 . 4 n .d. n .d. n .d. n .d. n.d. n .d. n.d. Rb 16 19 17 18 20 20 18 28 42 46 41 29 42 128 78 58 80 76 89 57 Sr 251 228 339 187 157 209 211 540 524 530 510 342 517 391 296 412 3 21 399 4 04 403 Y2 1 . 92 3 . 72 0 . 82 0 . 71 9 . 81 9 . 41 9 . 12 1 . 42 6 . 62 2 . 72 1 . 52 2 . 12 1 . 82 2 . 52 1 . 41 5 . 21 7 . 91 5 . 91 9 . 41 2 . 5 Zr 80 . 07 8 . 97 7 . 68 0 . 18 2 . 48 0 . 98 2 . 29 3 . 09 2 . 29 0 . 98 5 . 28 2 . 48 6 . 5 110 . 15 3 . 12 3 . 45 3 . 83 7 . 05 0 . 94 2 . 3 Nb 6 . 46 . 26 . 06 . 37 . 06 . 96 . 56 . 26 . 36 . 46 . 04 . 76 . 07 . 46 . 61 0 . 16 . 87 . 69 . 03 . 9 Cs 0 . 37 0 . 43 0 . 39 0 . 43 0 . 49 0 . 46 0 . 41 0 . 55 0 . 92 1 . 03 0 . 98 0 . 68 0 . 88 7 . 60 4 . 91 6 . 36 5 . 55 7 . 67 8 . 85 3 . 40 Ba 112 110 107 116 124 116 110 444 371 355 342 232 340 564 475 564 4 44 513 6 31 387 La 6 . 32 7 . 26 5 . 66 6 . 08 6 . 26 6 . 16 5 . 42 9 . 22 10 . 97 10 . 25 9 . 68 7 . 68 9 . 71 16 . 58 17 . 61 18 . 87 14 . 65 16 . 45 20 . 90 9 . 97 Ce 13 . 71 4 . 51 2 . 11 3 . 41 3 . 31 3 . 21 1 . 92 1 . 12 2 . 32 3 . 02 1 . 91 7 . 42 1 . 82 9 . 92 8 . 03 6 . 92 7 . 03 1 . 43 7 . 41 9 . 7 Pr 2 . 01 2 . 13 1 . 79 1 . 93 1 . 89 1 . 87 1 . 75 2 . 90 3 . 25 3 . 19 3 . 00 2 . 45 3 . 00 3 . 92 3 . 99 4 . 17 3 . 32 3 . 56 4 . 55 2 . 33 Nd 9 . 70 10 . 44 8 . 76 9 . 41 9 . 06 9 . 11 8 . 56 13 . 46 15 . 15 14 . 85 14 . 05 11 . 79 14 . 16 15 . 54 15 . 51 15 . 54 12 . 90 13 . 42 17 . 01 9 . 22 Sm 3 . 11 3 . 39 2 . 91 3 . 10 2 . 92 2 . 93 2 . 87 3 . 75 4 . 11 4 . 15 3 . 93 3 . 68 3 . 98 3 . 19 3 . 09 2 . 92 2 . 80 2 . 77 3 . 45 2 . 10 Eu 1 . 124 1 . 176 1 . 044 1 . 083 1 . 035 1 . 062 1 . 009 1 . 270 1 . 401 1 . 510 1 . 470 1 . 380 1 . 440 0 . 854 0 . 870 0 . 812 0 . 836 0 . 772 0 . 993 0 . 672 Gd 3 . 63 3 . 89 3 . 33 3 . 54 3 . 37 3 . 31 3 . 27 3 . 99 4 . 53 4 . 32 4 . 10 4 . 09 4 . 10 3 . 13 3 . 21 2 . 76 2 . 65 2 . 47 3 . 03 2 . 01 Tb 0 . 670 0 . 709 0 . 639 0 . 661 0 . 626 0 . 612 0 . 613 0 . 652 0 . 744 0 . 750 0 . 710 0 . 730 0 . 710 0 . 517 0 . 486 0 . 421 0 . 482 0 . 442 0 . 547 0 . 352 Dy 3 . 94 4 . 21 3 . 73 3 . 95 3 . 76 3 . 63 3 . 65 3 . 87 4 . 43 4 . 34 4 . 13 4 . 35 4 . 16 3 . 26 2 . 97 2 . 51 2 . 62 2 . 36 2 . 92 1 . 87 Ho 0 . 707 0 . 739 0 . 654 0 . 689 0 . 658 0 . 637 0 . 640 0 . 786 0 . 902 0 . 870 0 . 830 0 . 860 0 . 830 0 . 707 0 . 636 0 . 520 0 . 638 0 . 570 0 . 714 0 . 455 Er 1 . 87 1 . 93 1 . 70 1 . 79 1 . 72 1 . 68 1 . 69 2 . 14 2 . 45 2 . 33 2 . 19 2 . 26 2 . 23 2 . 10 1 . 85 1 . 52 1 . 65 1 . 49 1 . 88 1 . 17 Tm 0 . 259 0 . 262 0 . 228 0 . 241 0 . 233 0 . 230 0 . 233 0 . 296 0 . 335 0 . 340 0 . 320 0 . 330 0 . 330 0 . 342 0 . 295 0 . 244 0 . 288 0 . 260 0 . 340 0 . 204 Yb 1 . 56 1 . 62 1 . 46 1 . 54 1 . 47 1 . 43 1 . 43 1 . 88 2 . 09 2 . 07 1 . 97 1 . 99 2 . 00 2 . 21 1 . 88 1 . 59 1 . 74 1 . 58 2 . 12 1 . 25 Lu 0 . 224 0 . 234 0 . 213 0 . 217 0 . 210 0 . 209 0 . 211 0 . 279 0 . 319 0 . 300 0 . 280 0 . 280 0 . 290 0 . 351 0 . 301 0 . 247 0 . 276 0 . 253 0 . 347 0 . 199 Hf 2 . 50 2 . 41 2 . 37 2 . 46 2 . 52 2 . 52 2 . 52 2 . 48 2 . 50 2 . 67 2 . 51 2 . 55 2 . 53 3 . 08 1 . 56 0 . 90 1 . 53 1 . 14 1 . 48 1 . 21
Table
1:
continued
Volcanic field: M ienhuayu (MHY) Pengchiayu (PCY) Keelung Volcanic G roup (KLVG) Sample no.: MHY-2-3 MHY-2-4 MHY-2-5 MHY-2-6 MHY-2-7 MHY-2-8 MHY-2-9 Pen-17 Pen-20 PGU-03 PGU-04 PGU-05 PGU-07 TS-3 GML CKS5-1 L-2 L -15 L-25 CH-7 Ta 0 . 376 0 . 359 0 . 346 0 . 365 0 . 399 0 . 387 0 . 375 0 . 366 0 . 473 0 . 380 0 . 360 0 . 290 0 . 360 0 . 645 0 . 419 0 . 612 0 . 641 0 . 619 0 . 542 0 . 394 Pb 1 . 86 1 . 70 0 . 76 1 . 65 1 . 61 6 . 72 1 . 17 4 . 93 5 . 61 3 . 23 3 . 31 2 . 06 4 . 89 45 . 16 7 . 72 12 . 86 7 . 44 10 . 21 12 . 55 6 . 28 Th 0 . 98 0 . 91 0 . 87 0 . 94 1 . 09 1 . 02 0 . 95 1 . 64 1 . 74 1 . 75 1 . 66 1 . 42 1 . 67 7 . 10 5 . 42 6 . 04 6 . 90 8 . 06 8 . 93 4 . 06 U0 . 27 0 . 31 0 . 33 0 . 29 0 . 27 0 . 26 0 . 26 0 . 50 0 . 50 0 . 54 0 . 52 0 . 42 0 . 53 2 . 82 2 . 05 2 . 15 2 . 56 2 . 65 3 . 09 1 . 42 Volcanic field: KLVG Tatun Volcanic Group (TTVG) Kuanyinshan (KYS) Tsaolingshan (TLS) Sample no.: CH-14 A-3 A -4 A-10 A-18 A-31 A-99 A-129 H-B-1 B -2 K-41 K-57 K-60 K-64 K-99 K-108 TLS-1 TLS-3 TLS-8 TLS-12 Major element (wt %) SiO 2 57 . 07 58 . 22 55 . 20 56 . 01 54 . 95 56 . 65 52 . 61 49 . 27 51 . 94 50 . 10 51 . 43 51 . 26 54 . 52 50 . 42 59 . 98 64 . 20 48 . 29 47 . 65 48 . 36 47 . 64 TiO 2 0 . 49 0 . 54 0 . 60 0 . 52 0 . 75 0 . 54 0 . 81 1 . 54 1 . 33 1 . 54 0 . 85 1 . 12 0 . 79 1 . 07 0 . 49 0 . 35 0 . 81 0 . 80 0 . 81 0 . 82 Al 2 O3 17 . 73 18 . 52 19 . 68 18 . 01 19 . 35 17 . 95 18 . 86 17 . 38 17 . 17 17 . 26 17 . 08 15 . 59 16 . 98 14 . 85 18 . 22 18 . 89 11 . 80 12 . 75 12 . 20 11 . 44 Fe 2 O3 * 6 . 69 6 . 83 7 . 30 7 . 12 7 . 74 7 . 47 8 . 05 9 . 54 9 . 32 9 . 38 8 . 27 8 . 68 7 . 23 8 . 33 4 . 29 3 . 28 7 . 36 7 . 24 7 . 25 7 . 40 MnO 0 . 13 0 . 14 0 . 14 0 . 14 0 . 14 0 . 14 0 . 14 0 . 17 0 . 16 0 . 16 0 . 17 0 . 16 0 . 15 0 . 15 0 . 10 0 . 09 0 . 13 0 . 13 0 . 13 0 . 13 MgO 3 . 90 2 . 92 3 . 46 4 . 42 3 . 73 3 . 22 4 . 55 5 . 95 6 . 13 5 . 80 7 . 71 7 . 96 6 . 67 8 . 40 3 . 38 2 . 22 15 . 51 14 . 72 14 . 83 16 . 07 CaO 7 . 72 7 . 26 8 . 09 8 . 27 8 . 19 6 . 55 9 . 15 10 . 64 10 . 21 10 . 42 9 . 29 10 . 12 8 . 91 10 . 43 6 . 01 4 . 71 7 . 29 7 . 24 7 . 27 7 . 16 Na 2 O3 . 05 2 . 94 2 . 87 2 . 66 2 . 79 2 . 37 2 . 50 2 . 23 2 . 40 2 . 38 2 . 72 2 . 56 2 . 80 2 . 17 3 . 50 4 . 68 1 . 80 1 . 91 1 . 89 1 . 74 K2 O1 . 65 1 . 54 1 . 48 1 . 76 1 . 84 1 . 60 1 . 70 1 . 42 1 . 36 1 . 53 1 . 69 1 . 86 1 . 72 1 . 72 2 . 04 1 . 91 4 . 84 4 . 58 4 . 82 5 . 13 P2 O5 0 . 24 0 . 20 0 . 22 0 . 26 0 . 26 0 . 25 0 . 20 0 . 25 0 . 23 0 . 25 0 . 48 0 . 37 0 . 47 0 . 34 0 . 31 0 . 27 1 . 56 1 . 54 1 . 55 1 . 60 LOI n.d. 1 . 17 0 . 63 0 . 85 1 . 05 3 . 68 0 . 21 0 . 18 n.d. n.d. 0 . 08 n.d. n.d. 2 . 41 1 . 53 n.d. n.d. n.d. 0 . 01 n.d. Total 98 . 66 100 . 28 99 . 67 100 . 02 100 . 43 100 . 42 98 . 78 98 . 57 100 . 24 98 . 82 99 . 75 99 . 68 100 . 23 100 . 29 99 . 85 100 . 60 99 . 39 98 . 56 99 . 12 99 . 13 Mg no. 0 . 56 0 . 48 0 . 51 0 . 57 0 . 51 0 . 48 0 . 55 0 . 58 0 . 59 0 . 57 0 . 67 0 . 67 0 . 67 0 . 69 0 . 63 0 . 60 0 . 82 0 . 82 0 . 82 0 . 83 Trace element (ppm) Sc 22 . 91 4 . 41 2 . 32 9 . 52 9 . 02 1 . 72 1 . 22 4 . 62 5 . 22 4 . 23 4 . 54 7 . 43 0 . 54 8 . 52 4 . 01 5 . 92 8 . 52 5 . 62 9 . 52 5 . 8 V 2 38 182 177 273 262 206 281 299 323 3 19 257 287 2 19 309 1 35 59 191 1 39 190 141 Cr 27 4 3 69 5 1 4 1 7 8 4 1 12 99 249 282 2 12 292 6 3 2 3 1 064 9 65 958 1145 Co 28 . 21 7 . 31 6 . 52 3 . 42 3 . 31 8 . 12 6 . 23 5 . 23 2 . 83 3 . 53 4 . 34 1 . 32 9 . 34 2 . 71 4 . 37 . 74 7 . 44 1 . 94 6 . 24 4 . 8 Ni 10 . 46 . 25 . 81 3 . 78 . 37 . 01 1 . 43 0 . 72 9 . 72 6 . 7 105 . 59 3 . 27 9 . 49 3 . 63 6 . 21 7 . 24 9 2 . 04 3 7 . 4 466 . 65 1 1 . 4 Cu n.d. 59 . 84 1 . 6 n .d. n .d. n.d. 134 . 09 1 . 61 0 2 . 91 0 2 . 54 8 . 89 4 . 64 0 . 89 1 . 74 8 . 31 8 . 73 7 . 03 3 . 13 8 . 92 9 . 8 Zn 55 . 96 8 . 26 5 . 66 0 . 86 3 . 56 7 . 57 9 . 0 117 . 18 9 . 08 7 . 16 9 . 06 1 . 36 5 . 26 1 . 24 7 . 23 9 . 76 0 . 04 3 . 15 7 . 64 3 . 0 Ga n.d. 18 . 61 8 . 8 n .d. n .d. n.d. 1 7 . 82 0 . 21 9 . 62 0 . 41 9 . 81 7 . 72 0 . 01 7 . 72 1 . 21 9 . 21 2 . 61 2 . 01 2 . 81 1 . 8 Rb 58 44 46 18 84 45 59 45 43 44 99 98 117 8 5 1 40 110 1 089 2 114 1 412 1 045 Sr 401 412 411 453 431 401 431 463 419 4 45 771 643 9 45 630 1 394 1382 7 04 670 733 661 Y1 3 . 52 0 . 91 8 . 31 1 . 81 9 . 01 4 . 41 7 . 82 3 . 82 2 . 82 3 . 32 1 . 92 2 . 71 9 . 62 0 . 71 5 . 77 . 61 4 . 71 2 . 91 4 . 81 3 . 1
Volcanic field: KLVG Tatun Volcanic Group (TTVG) Kuanyinshan (KYS) Tsaolingshan (TLS) Sample no.: CH-14 A-3 A -4 A-10 A-18 A-31 A-99 A-129 H-B-1 B -2 K-41 K-57 K-60 K-64 K-99 K-108 TLS-1 TLS-3 TLS-8 TLS-12 Zr 36 . 66 7 . 76 5 . 67 1 . 06 9 . 16 3 . 67 1 . 3 108 . 29 9 . 01 0 9 . 2 120 . 91 2 3 . 51 3 8 . 41 1 3 . 01 6 2 . 94 9 . 71 1 8 . 71 1 0 . 81 2 1 . 41 1 1 . 2 Nb 4 . 15 . 35 . 14 . 75 . 53 . 65 . 49 . 58 . 39 . 61 4 . 11 9 . 41 9 . 71 7 . 82 9 . 43 3 . 91 6 . 31 5 . 41 7 . 11 5 . 3 Cs 2 . 77 1 . 39 1 . 45 2 . 56 2 . 62 1 . 89 4 . 68 4 . 06 3 . 53 4 . 17 3 . 83 6 . 62 7 . 42 1 . 95 26 . 10 11 . 14 136 . 75 173 . 89 166 . 84 125 . 42 Ba 415 406 402 452 515 396 382 434 420 427 629 558 7 26 539 1 092 1 060 9 38 997 9 68 1009 La 10 . 20 16 . 49 15 . 31 7 . 37 15 . 28 12 . 78 13 . 32 19 . 13 16 . 78 18 . 57 28 . 32 25 . 59 35 . 12 22 . 46 57 . 66 50 . 37 24 . 36 26 . 16 24 . 70 25 . 94 Ce 21 . 03 2 . 63 0 . 51 9 . 83 1 . 92 3 . 32 7 . 94 1 . 63 7 . 24 2 . 05 4 . 04 6 . 86 2 . 94 3 . 09 0 . 86 8 . 74 8 . 75 2 . 04 9 . 05 2 . 2 Pr 2 . 48 4 . 05 3 . 64 2 . 39 4 . 02 3 . 35 3 . 41 5 . 36 4 . 75 5 . 30 6 . 41 5 . 67 7 . 02 5 . 17 9 . 37 7 . 31 5 . 90 6 . 25 5 . 93 6 . 31 Nd 9 . 85 16 . 42 14 . 88 10 . 35 16 . 66 13 . 81 14 . 63 23 . 01 20 . 68 22 . 76 24 . 18 22 . 24 25 . 02 20 . 32 29 . 47 21 . 83 23 . 70 25 . 63 23 . 72 25 . 98 Sm 2 . 13 3 . 28 2 . 96 2 . 37 3 . 61 2 . 76 3 . 10 4 . 96 4 . 45 4 . 93 4 . 36 4 . 43 4 . 26 4 . 14 4 . 01 2 . 83 4 . 45 4 . 88 4 . 47 4 . 93 Eu 0 . 635 0 . 910 0 . 860 0 . 640 0 . 920 0 . 818 0 . 960 1 . 480 1 . 330 1 . 480 1 . 306 1 . 365 1 . 261 1 . 260 1 . 117 0 . 875 1 . 117 1 . 144 1 . 087 1 . 218 Gd 2 . 14 3 . 35 3 . 03 2 . 30 3 . 33 2 . 47 3 . 21 4 . 87 4 . 52 4 . 95 3 . 75 4 . 07 3 . 55 3 . 87 2 . 70 1 . 78 3 . 53 3 . 60 3 . 50 3 . 72 Tb 0 . 336 0 . 530 0 . 470 0 . 394 0 . 517 0 . 380 0 . 490 0 . 720 0 . 690 0 . 740 0 . 590 0 . 627 0 . 539 0 . 593 0 . 433 0 . 279 0 . 465 0 . 510 0 . 466 0 . 519 Dy 2 . 05 3 . 06 2 . 69 2 . 59 3 . 14 2 . 32 2 . 84 3 . 88 3 . 77 4 . 01 3 . 46 3 . 71 3 . 11 3 . 48 2 . 38 1 . 41 2 . 47 2 . 62 2 . 47 2 . 72 Ho 0 . 437 0 . 670 0 . 600 0 . 578 0 . 655 0 . 503 0 . 600 0 . 810 0 . 790 0 . 830 0 . 708 0 . 745 0 . 621 0 . 705 0 . 485 0 . 278 0 . 490 0 . 532 0 . 480 0 . 548 Er 1 . 30 2 . 04 1 . 85 1 . 71 1 . 88 1 . 50 1 . 83 2 . 33 2 . 30 2 . 41 2 . 07 2 . 10 1 . 84 1 . 99 1 . 46 0 . 77 1 . 38 1 . 49 1 . 37 1 . 55 Tm 0 . 211 0 . 300 0 . 270 0 . 256 0 . 270 0 . 219 0 . 250 0 . 320 0 . 320 0 . 320 0 . 324 0 . 314 0 . 289 0 . 300 0 . 229 0 . 104 0 . 205 0 . 221 0 . 204 0 . 221 Yb 1 . 39 2 . 02 1 . 88 1 . 69 1 . 77 1 . 47 1 . 79 2 . 11 2 . 13 2 . 18 2 . 15 2 . 00 1 . 89 1 . 89 1 . 53 0 . 70 1 . 28 1 . 37 1 . 29 1 . 40 Lu 0 . 224 0 . 310 0 . 280 0 . 266 0 . 274 0 . 241 0 . 260 0 . 310 0 . 310 0 . 310 0 . 332 0 . 305 0 . 300 0 . 287 0 . 252 0 . 103 0 . 197 0 . 203 0 . 196 0 . 206 Hf 1 . 15 1 . 67 1 . 58 1 . 95 1 . 87 1 . 59 1 . 75 2 . 77 2 . 55 2 . 85 3 . 08 3 . 05 3 . 52 2 . 90 4 . 33 1 . 47 3 . 16 3 . 42 3 . 17 3 . 43 Ta 0 . 363 0 . 300 0 . 290 0 . 264 0 . 306 0 . 205 0 . 280 0 . 540 0 . 480 0 . 550 0 . 739 1 . 075 1 . 055 0 . 994 1 . 780 1 . 986 0 . 885 0 . 975 0 . 925 0 . 945 Pb 5 . 83 6 . 29 7 . 26 12 . 02 9 . 54 8 . 05 6 . 88 7 . 32 7 . 09 7 . 15 15 . 12 13 . 53 22 . 30 12 . 10 40 . 63 39 . 03 30 . 99 27 . 83 27 . 10 25 . 59 Th 3 . 33 5 . 60 5 . 30 2 . 29 4 . 86 3 . 21 6 . 96 5 . 92 5 . 33 5 . 45 10 . 48 8 . 17 14 . 08 7 . 91 22 . 42 23 . 91 19 . 17 22 . 85 19 . 56 22 . 88 U1 . 12 0 . 79 0 . 82 1 . 85 1 . 48 1 . 48 1 . 15 0 . 89 0 . 83 0 . 86 4 . 86 3 . 54 6 . 35 3 . 39 10 . 67 6 . 26 18 . 02 21 . 24 18 . 42 21 . 67 Volcanic field: T saolingshan (TLS) Sample no.: TLS-17 TLS-18 TLS-23 TLS-24 TLS-27 T-16 T-20 T-24 T-30 T-43 T-48 TLS-5 T LS-14 TLS-19 TLS-20 TLS-21 TLS-29 T-17 T-21 T-22 Major element (wt %) SiO 2 47 . 06 47 . 02 47 . 18 47 . 88 47 . 03 44 . 62 47 . 15 48 . 83 48 . 24 48 . 95 47 . 93 47 . 70 47 . 96 47 . 58 47 . 30 47 . 22 47 . 29 48 . 32 47 . 91 48 . 54 TiO 2 0 . 82 0 . 82 0 . 83 0 . 81 0 . 80 0 . 80 0 . 92 0 . 82 0 . 83 0 . 83 0 . 79 0 . 80 0 . 81 0 . 83 0 . 83 0 . 83 0 . 81 0 . 84 0 . 84 0 . 82 Al 2 O3 12 . 07 11 . 98 13 . 01 11 . 70 12 . 86 17 . 49 12 . 38 11 . 71 11 . 72 11 . 80 12 . 04 12 . 63 12 . 39 12 . 20 12 . 39 12 . 62 12 . 52 11 . 92 12 . 24 11 . 56 Fe 2 O3 * 7 . 34 7 . 38 7 . 40 7 . 33 7 . 35 7 . 48 8 . 53 7 . 71 7 . 63 7 . 58 7 . 50 7 . 29 7 . 35 7 . 38 7 . 39 7 . 42 7 . 58 7 . 69 7 . 87 7 . 77
Table
1:
continued
Volcanic field: Tsaolingshan (TLS) Sample no.: TLS-17 TLS-18 TLS-23 TLS-24 TLS-27 T-16 T-20 T-24 T-30 T-43 T-48 TLS-5 TLS-14 TLS-19 TLS-20 TLS-21 TLS-29 T-17 T-21 T-22 MnO 0 . 13 0 . 13 0 . 13 0 . 13 0 . 13 0 . 13 0 . 14 0 . 13 0 . 13 0 . 13 0 . 13 0 . 12 0 . 13 0 . 13 0 . 13 0 . 13 0 . 13 0 . 13 0 . 13 0 . 13 MgO 16 . 01 16 . 12 14 . 82 15 . 16 15 . 23 13 . 93 15 . 52 14 . 21 14 . 24 14 . 25 15 . 50 15 . 04 14 . 91 14 . 79 14 . 73 14 . 76 15 . 00 14 . 13 14 . 39 14 . 51 CaO 7 . 08 7 . 10 7 . 46 7 . 27 7 . 16 7 . 02 7 . 48 7 . 35 7 . 30 7 . 26 6 . 81 7 . 28 7 . 33 7 . 41 7 . 46 7 . 49 7 . 31 7 . 39 7 . 45 7 . 35 Na 2 O1 . 72 1 . 72 1 . 99 1 . 83 1 . 77 1 . 89 1 . 83 1 . 89 1 . 92 1 . 84 1 . 73 1 . 80 2 . 00 1 . 86 1 . 93 1 . 94 2 . 15 2 . 03 1 . 88 1 . 95 K2 O5 . 10 5 . 12 4 . 26 5 . 28 5 . 03 3 . 66 2 . 84 5 . 29 5 . 28 5 . 49 5 . 15 4 . 79 4 . 34 4 . 94 4 . 49 4 . 31 4 . 13 4 . 82 4 . 44 4 . 92 P2 O5 1 . 57 1 . 58 1 . 56 1 . 57 1 . 53 1 . 44 1 . 66 1 . 53 1 . 51 1 . 59 1 . 57 1 . 56 1 . 56 1 . 56 1 . 57 1 . 57 1 . 56 1 . 54 1 . 54 1 . 53 LOI n.d. n.d. n.d. n.d. 0 . 18 0 . 58 1 . 30 0 . 10 0 . 80 0 . 12 0 . 04 n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. Total 98 . 90 98 . 97 98 . 64 98 . 96 99 . 07 99 . 04 99 . 75 99 . 57 99 . 60 99 . 84 99 . 19 99 . 01 98 . 78 98 . 68 98 . 22 98 . 29 98 . 48 98 . 81 98 . 69 99 . 08 Mg no. 0 . 83 0 . 83 0 . 81 0 . 82 0 . 82 0 . 80 0 . 80 0 . 80 0 . 80 0 . 80 0 . 82 0 . 82 0 . 82 0 . 81 0 . 81 0 . 81 0 . 81 0 . 80 0 . 80 0 . 80 Trace element (ppm) Sc 25 . 42 4 . 03 0 . 52 8 . 32 7 . 72 5 . 92 9 . 02 9 . 32 8 . 22 8 . 02 7 . 02 2 . 32 2 . 92 4 . 02 2 . 52 3 . 02 3 . 32 5 . 02 5 . 52 4 . 9 V 141 192 209 153 189 160 176 143 155 152 148 n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. Cr 1169 1218 979 992 1054 1052 1182 1053 1056 1057 1148 1 201 1 129 1 083 1 080 1 088 1146 n.d. n.d. n.d. Co 44 . 54 9 . 54 8 . 74 4 . 74 7 . 14 5 . 14 9 . 64 4 . 54 4 . 24 3 . 44 7 . 11 2 6 . 2 141 . 71 3 2 . 01 3 4 . 21 3 3 . 71 4 8 . 3 n .d. n .d. n.d. Ni 511 . 7 538 . 5 487 . 3 463 . 64 8 3 . 8 463 . 2 520 . 54 5 6 . 9 449 . 84 3 7 . 3 532 . 54 0 5 . 0 411 . 04 0 8 . 04 0 9 . 04 1 6 . 04 2 6 . 0 n .d. n .d. n.d. Cu 33 . 93 9 . 14 5 . 53 1 . 83 4 . 43 2 . 93 8 . 52 7 . 63 4 . 83 2 . 43 2 . 5 n .d. n .d. n .d. n.d. n.d. n.d. n.d. n.d. n.d. Zn 45 . 35 7 . 96 0 . 44 7 . 75 8 . 24 7 . 05 2 . 54 8 . 15 2 . 84 8 . 75 2 . 3 n .d. n .d. n .d. n.d. n.d. n.d. n.d. n.d. n.d. Ga 11 . 91 2 . 71 4 . 01 2 . 01 2 . 81 4 . 81 3 . 91 2 . 81 2 . 71 2 . 81 2 . 7 n .d. n .d. n .d. n.d. n.d. n.d. n.d. n.d. n.d. Rb 1025 1084 2098 1046 1068 2546 190 1081 1063 1266 1089 n .d. n .d. n .d. n.d. n.d. n.d. n.d. n.d. n.d. Sr 664 720 822 658 703 671 771 648 657 663 662 667 677 697 7 08 707 6 73 n.d. n.d. n.d. Y1 3 . 11 4 . 71 6 . 11 3 . 21 4 . 61 3 . 71 5 . 61 4 . 41 4 . 31 4 . 01 3 . 9 1 3 1 71 4 1 41 61 5 n .d . n .d . n .d . Zr 110 . 1 116 . 0 127 . 4 108 . 51 1 7 . 0 111 . 1 124 . 81 1 1 . 7 114 . 81 1 6 . 7 114 . 2 1 19 119 121 1 21 121 1 18 n.d. n.d. n.d. Nb 15 . 21 6 . 71 7 . 91 5 . 01 6 . 21 5 . 11 7 . 11 4 . 61 5 . 41 5 . 71 5 . 5 1 2 1 21 3 1 31 31 3 n .d . n .d . n .d . Cs 122 . 41 122 . 05 214 . 44 114 . 86 123 . 82 304 . 55 23 . 58 120 . 32 112 . 95 124 . 46 118 . 46 130 . 79 251 . 73 135 . 08 164 . 77 186 . 57 183 . 87 455 3 86 397 Ba 1022 959 1028 885 922 850 979 851 864 925 920 963 1 064 1 004 1 029 1 042 1021 1014 1057 936 La 26 . 22 24 . 30 26 . 04 23 . 38 23 . 89 23 . 14 26 . 52 24 . 62 24 . 30 24 . 75 24 . 56 24 . 02 24 . 90 25 . 64 24 . 65 24 . 71 25 . 98 26 . 12 6 . 42 5 . 8 Ce 52 . 94 8 . 55 1 . 84 6 . 74 7 . 74 6 . 85 3 . 14 9 . 04 8 . 24 9 . 04 9 . 15 1 . 45 8 . 25 8 . 65 0 . 95 0 . 44 9 . 25 3 . 75 9 . 05 1 . 6 Pr 6 . 36 5 . 91 6 . 33 5 . 61 5 . 77 5 . 66 6 . 43 5 . 91 5 . 82 5 . 94 5 . 94 n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. Nd 26 . 31 23 . 91 25 . 40 22 . 92 23 . 19 23 . 21 26 . 26 24 . 10 23 . 83 24 . 48 24 . 31 22 . 16 24 . 31 23 . 66 23 . 16 22 . 20 22 . 95 24 . 12 5 . 42 5 . 7 Sm 5 . 00 4 . 52 4 . 79 4 . 37 4 . 36 4 . 40 4 . 98 4 . 61 4 . 57 4 . 59 4 . 62 5 . 90 6 . 13 6 . 08 5 . 68 5 . 60 5 . 77 6 . 15 . 96 . 0 Eu 1 . 212 1 . 113 1 . 183 1 . 065 1 . 055 1 . 134 1 . 251 1 . 090 1 . 149 1 . 128 1 . 105 1 . 046 1 . 149 1 . 129 1 . 117 1 . 121 1 . 157 1 . 31 . 21 . 2 Gd 3 . 74 3 . 57 3 . 76 3 . 37 3 . 53 3 . 37 3 . 86 3 . 41 3 . 35 3 . 39 3 . 32 n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. Tb 0 . 525 0 . 468 0 . 497 0 . 466 0 . 459 0 . 480 0 . 542 0 . 497 0 . 491 0 . 484 0 . 484 0 . 924 0 . 939 1 . 006 0 . 879 0 . 952 0 . 992 0 . 98 1 . 08 0 . 97 Dy 2 . 74 2 . 49 2 . 68 2 . 38 2 . 42 2 . 47 2 . 79 2 . 60 2 . 57 2 . 54 2 . 53 n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. Ho 0 . 552 0 . 492 0 . 524 0 . 482 0 . 476 0 . 499 0 . 566 0 . 527 0 . 522 0 . 518 0 . 509 n .d. n .d. n .d. n.d. n.d. n.d. n.d. n.d. n.d.
Volcanic field: Tsaolingshan (TLS) Sample no.: TLS-17 TLS-18 TLS-23 TLS-24 TLS-27 T-16 T-20 T-24 T-30 T-43 T-48 TLS-5 TLS-14 TLS-19 TLS-20 TLS-21 TLS-29 T-17 T-21 T-22 Er 1 . 55 1 . 40 1 . 49 1 . 37 1 . 35 1 . 42 1 . 62 1 . 47 1 . 45 1 . 43 1 . 43 n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. Tm 0 . 227 0 . 206 0 . 221 0 . 198 0 . 198 0 . 207 0 . 235 0 . 216 0 . 212 0 . 207 0 . 205 n .d. n .d. n .d. n .d. n .d. n .d. n .d. n .d. n .d. Yb 1 . 41 1 . 29 1 . 38 1 . 21 1 . 26 1 . 30 1 . 44 1 . 34 1 . 31 1 . 28 1 . 28 1 . 55 1 . 65 1 . 74 1 . 56 1 . 03 1 . 23 1 . 31 . 31 . 6 Lu 0 . 212 0 . 196 0 . 211 0 . 185 0 . 191 0 . 195 0 . 214 0 . 201 0 . 196 0 . 192 0 . 190 0 . 179 0 . 208 0 . 222 0 . 213 0 . 217 0 . 194 0 . 24 0 . 21 0 . 25 Hf 3 . 46 3 . 04 3 . 31 2 . 95 3 . 04 3 . 07 3 . 41 3 . 02 3 . 09 3 . 13 3 . 09 2 . 94 7 . 21 3 . 10 3 . 03 3 . 09 3 . 10 3 . 22 . 83 . 1 Ta 0 . 959 0 . 884 0 . 950 0 . 832 0 . 858 0 . 835 0 . 937 0 . 791 0 . 819 0 . 844 0 . 829 0 . 649 0 . 751 0 . 765 0 . 717 0 . 745 0 . 704 0 . 74 0 . 84 0 . 70 Pb 30 . 02 24 . 73 32 . 10 23 . 45 20 . 91 19 . 87 23 . 29 19 . 76 19 . 28 20 . 15 19 . 59 25 27 23 24 23 30 n.d. n.d. n.d. Th 23 . 33 17 . 68 20 . 31 19 . 76 18 . 75 19 . 32 21 . 67 19 . 76 19 . 28 20 . 15 19 . 59 19 . 12 19 . 99 20 . 53 18 . 22 18 . 70 20 . 54 19 . 92 0 . 61 9 . 6 U2 2 . 13 18 . 39 19 . 16 18 . 21 17 . 53 18 . 25 20 . 01 17 . 53 17 . 23 17 . 58 18 . 12 21 . 65 22 . 42 22 . 79 21 . 67 20 . 94 22 . 53 20 . 42 0 . 42 0 . 6 Volcanic field: Tsaolingshan (TLS) Sample no.: T -25 T-33 T-34 T-36 T-41 T-46 Major element (wt %) SiO 2 48 . 37 48 . 76 47 . 92 48 . 16 48 . 70 48 . 46 TiO 2 0 . 83 0 . 82 0 . 84 0 . 81 0 . 82 0 . 81 Al 2 O3 12 . 05 11 . 49 12 . 20 11 . 98 12 . 37 12 . 14 Fe 2 O3 * 7 . 63 7 . 57 7 . 70 7 . 46 7 . 55 7 . 52 MnO 0 . 13 0 . 12 0 . 13 0 . 12 0 . 13 0 . 13 MgO 14 . 22 14 . 19 14 . 45 14 . 01 14 . 40 14 . 36 CaO 7 . 25 7 . 21 7 . 22 7 . 14 7 . 23 7 . 23 Na 2 O1 . 91 1 . 91 1 . 93 1 . 91 1 . 80 1 . 77 K2 O5 . 25 5 . 37 4 . 45 5 . 53 5 . 08 4 . 85 P2 O5 1 . 52 1 . 60 1 . 57 1 . 57 1 . 58 1 . 58 LOI n.d. n.d. n.d. n.d. n.d. n.d. Total 99 . 16 99 . 04 98 . 41 98 . 69 99 . 66 98 . 85 Mg no. 0 . 80 0 . 80 0 . 80 0 . 80 0 . 81 0 . 81 Trace element (ppm) Sc 24 . 22 4 . 82 5 . 52 5 . 02 4 . 32 4 . 6 V n .d. n .d. n .d. n .d. n .d. n .d. Cr n.d. n.d. n.d. n.d. n.d. n.d. Co n.d. n.d. n.d. n.d. n.d. n.d. Ni n.d. n.d. n.d. n.d. n.d. n.d.
Table
1
:
continued
Volcanic field: Tsaolingshan (TLS) Sample no.: T -25 T-33 T-34 T-36 T-41 T-46 Cu n.d. n.d. n.d. n.d. n.d. n.d. Zn n.d. n.d. n.d. n.d. n.d. n.d. Ga n.d. n.d. n.d. n.d. n.d. n.d. Rb n.d. n.d. n.d. n.d. n.d. n.d. Sr n.d. n.d. n.d. n.d. n.d. n.d. Y n .d. n .d. n .d. n .d. n .d. n .d. Zr n.d. n.d. n.d. n.d. n.d. n.d. Nb n.d. n.d. n.d. n.d. n.d. n.d. Cs 288 282 254 317 283 344 Ba 1053 953 1045 963 927 1027 La 24 . 63 1 . 82 6 . 72 5 . 92 4 . 72 6 . 1 Ce 51 . 95 6 . 46 6 . 85 6 . 05 5 . 95 8 . 0 Pr n.d. n.d. n.d. n.d. n.d. n.d. Nd 25 . 72 8 . 12 7 . 22 7 . 02 7 . 22 4 . 6 Sm 6 . 16 . 26 . 66 . 46 . 26 . 4 Eu 1 . 31 . 21 . 31 . 21 . 21 . 1 Gd n.d. n.d. n.d. n.d. n.d. n.d. Tb 0 . 88 1 . 04 1 . 09 1 . 19 1 . 01 1 . 05 Dy n.d. n.d. n.d. n.d. n.d. n.d. Ho n.d. n.d. n.d. n.d. n.d. n.d. Er n.d. n.d. n.d. n.d. n.d. n.d. Tm n.d. n.d. n.d. n.d. n.d. n.d. Yb 1 . 51 . 81 . 61 . 71 . 61 . 6 Lu 0 . 21 0 . 26 0 . 24 0 . 24 0 . 22 0 . 20 Hf 3 . 33 . 03 . 23 . 22 . 93 . 3 Ta 0 . 72 0 . 74 0 . 77 0 . 81 0 . 76 0 . 83 Pb n.d. n.d. n.d. n.d. n.d. n.d. Th 19 . 62 0 . 22 1 . 22 0 . 41 9 . 72 0 . 9 U2 0 . 12 0 . 22 2 . 92 1 . 52 0 . 62 2 . 3 Fe 2 O3 * , total iron as Fe 2 O3 ; M g number ¼ atomic 100 (Mg/Mg þ Fe 2 þ ), assuming Fe 2 O3 /FeO ¼ 0 . 1; n.d., not determined. 1 Data from Shinjo (1998).
the various volcanic fields exhibit a trend of increasing K2O content and decreasing SiO2content from NE to SW (Fig. 3a). In a plot of K2O vs Na2O (Fig. 3b), most of the NTVZ volcanic rocks have relatively high K2O
contents, although only the TLS magmas have K2O contents higher than Na2O. The high K2O contents in some onshore volcanic fields with high SiO2and Na2O contents may result from fractional crystallization;
Table 2: Sr---Nd---Pb isotope compositions for the N T V Z volcanic rocks
Volcanic field Sample no. 87Sr/86Sr 143Nd/144Nd T
DM1 206Pb/204Pb 207Pb/204Pb 208Pb/204Pb SBS2 SBS-1 0.70406 SBS-2 0.70414 0.51289 18.351 15.574 38.524 SBS-7 0.70376 0.51284 18.283 15.547 38.389 KBS KBS-12 0.70384 0.51271 18.408 15.580 38.620 KBS-32 0.70398 0.51271 18.410 15.583 38.627 KO-4 0.70396 0.51272 18.407 15.587 38.633 KO-5 18.410 15.586 38.640 MHY MHH-01 0.70461 0.51298 MHY-2 0.70453 0.51301 18.588 15.599 38.729 MHY-3 0.70446 0.51290 MHY-4 0.51294 18.602 15.607 38.767 MHY-7 0.70438 0.51299 18.577 15.611 38.749 MHY-8 0.70440 0.51297 MHY-9 0.70447 0.51293 PCY Pen-20 0.70391 0.51289 PGU-04 0.70395 0.51295 18.446 15.574 38.535 PGU-05 0.70404 0.51297 18.443 15.576 38.531 KLVG TS-3 0.70482 0.51270 3.74 18.502 15.635 38.830 GML 0.70489 0.51272 2.66 CKS5-1 0.70474 0.51269 1.89 L-15 0.70496 0.51270 4.03 CH-7 0.70430 0.51282 T T VG A-3 0.70469 0.51273 2.63 A-10 0.70428 0.51278 A-18 0.70456 0.51273 A-31 0.70442 0.51268 A-129 0.70447 0.51280 18.517 15.627 38.763 H-B-1 0.70450 0.51276 18.525 15.627 38.763 KYS K-41 0.70416 0.51284 1.00 18.442 15.618 38.726 K-64 0.70407 0.51283 2.35 18.439 15.616 38.721 K-99 0.70427 0.51281 0.55 K-108 0.70417 0.51281 0.49 TLS TLS-8 0.70546 0.51268 1.97 18.450 15.628 38.775 TLS-18 0.70551 0.51263 2.21 TLS-23 0.70543 0.51266 2.06 TLS-27 0.51266 2.05 T-16 0.70543 0.51266 2.15 18.450 15.629 38.780 T-20 0.70542 0.51264 2.25 T-24 0.70540 0.51265 2.27 T-30 0.70543 0.51268 2.20 T-43 0.70546 0.51266 2.00 T-48 0.70551 0.51259 2.48 1
Nd modal age assuming derivation from a depleted mantle source with143Nd/144Nd¼ 0.513114 and147Sm/144Nd¼ 0.222
(Michard et al., 1985).
2
Data from Shinjo (1998).
Average analytical 2s errors:0.00004 for87
Sr/86Sr;0.00002 for143
Nd/144Nd;0.004 for206
Pb/204Pb;0.005 for207
Pb/
however, for some of the NTVZ mafic rocks fractional crystallization is not likely to be the reason for the high K2O contents (Fig. 3). As shown in Harker diagrams of CaO, Fe2O3(t), Al2O3, Cr, Sr and La vs MgO (Fig. 4), there is no significant trend of fractional crystallization for individual volcanic fields in the NTVZ, except for some onshore volcanic fields (TTVG and KYS).
Some NTVZ volcanic rocks have high Al2O3contents (17---20 wt %) and may be classified as high-Al basalts (e.g. Chen, 1990). According to the definition of high-Al basalts by Crawford et al. (1987) (SiO2554 wt %; Al2O3 4165 wt % and MgO 57 wt %), high-Al basalts occur in most areas of the NTVZ. All volcanic rocks from the SBS are high-Al basalts; however, none was found in the
MHY and TLS. The SBS have the lowest Mg number (05) in the NTVZ, whereas the MHY and TLS are relatively primitive magmas (Mg number¼ 06 and 08, respectively). The Mg number values for the MHY and TLS basalts are in equilibrium with the Fo contents of their olivine phencrysts (Fo ¼ 81 and 90, resepectively) based on the calculation for olivine---liquid equilibrium (Roeder & Emslie, 1970).
Trace-element compositions
Mafic rocks from the individual volcanic fields in the NTVZ have distinctive trace-element characteristics. The TLS basalts have the highest compatible
Na2O (wt.%) K-series High-K series Na-series K2 O (wt.%) K2O/N a2O= 2 K2O/Na2 O=0.5 Calc-alkaline series Shoshonitic series Low-K series High-K calc-alk aline SiO2 (wt.%) K2 O (wt.%)
(a)
(b)
NTVZ SBS KBS MHY PCY KLVG TTVG KYS N TAIWAN TLS 60 55 50 45 5 4 3 2 1 0 0 1 2 3 4 5 6 0 1 2 3 4 5 6Fig. 3. Variation of K2O vs SiO2(a) and Na2O (b) for volcanic rocks from the NTVZ. The series boundaries in (a) and (b) are from Gill (1981) and
Middlemost (1975), respectively. The grey arrow in (a) indicates the trend of spatial geochemical variation. The inset in (b) is a map showing the distribution of the main volcanic areas and the symbols used in the diagram. (For abbreviations see caption to Fig. 2.)
trace-element contents (Ni 500 ppm; Cr 1000 ppm). This characteristic, together with their major-element chemistry, is consistent with the TLS magmas being near-primary magmas. Incompatible trace-element characteristics are illustrated as chondrite-normalized rare earth element (REE) diagrams in Fig. 5 and as
primitive mantle-normalized element diagrams in Fig. 6. The REE patterns of the NTVZ volcanic rocks are light REE (LREE) enriched, but the extent of enrichment is variable between the volcanic fields. The SBS and MHY mafic rocks have the lowest abundances of LREE and show relatively flat REE patterns, whereas the TLS
20 15 10 5 0 MgO (wt.%) Al 2 O3 O (wt.%) high-Al basalts MgO (wt.%) 20 15 10 5 0 Fe 2 O3 (t) (wt.%) 20 15 10 5 0 MgO (wt.%) Cr (ppm ) 20 15 10 5 0 MgO (wt.%) Sr (ppm ) 20 15 10 5 0 0 10 20 30 40 50 60 MgO (wt.%) La (ppm ) 20 15 10 5 0 0 2 4 6 MgO (wt.%) CaO (wt.%) NTVZ SBS KBS MHY PCY KLVG TTVG KYS N TAIWAN TLS 0 2 4 6 8 10 12 8 10 12 14 10 12 14 16 18 20 22 0 1000 2000 1 10 100 1000 10000
Fig. 4. Variation diagrams of CaO, Fe2O3(t), Al2O3, Cr, Sr and La vs MgO, respectively, for volcanic rocks from the NTVZ. The inset shows a
La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu SBS-1 (B) SBS-2 (B) SBS-7 (B) La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu KBS-1 (B) KBS-3 (B) KO-4 (B) La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Pen-17 (B) Pen-20 (B) PGU-03 (BA) PGU-04 (BA) PGU-05 (BA) PGU-07 (BA) La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu MHY-2-1 (BA) MHY-2-2 (BA) MHH-01 (BA) MHY-1 (BA) MHY-7 (BA) La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu TS-3 (A) GML (A) CKS5-1 (A) L-2 (A) L-15 (A) L-25 (A) CH-7 (A) CH-14 (A) La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu A-3 (A) A-4 (A) A-10 (A) A-18 (BA) A-31 (A) A-99 (BA) A-129 (B) H-B-1 (B) B-2 (B) La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu K-41 (B) K-57 (B) K-60 (BA) K-64 (B) K-99 (A) K-108 (D) La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu TLS-8 (B) TLS-18 (B) TLS-23 (B) TLS-27 (B) T-16 (B) T-20 (B) T-24 (B) T-30 (B) T-43 (B) T-48 (B) Rock/C1 chondrit e
SBS
KBS
PCY
MHY
KLVG
TTVG
KYS
TLS
Offshore
Onshore
1 10 100 1 10 100 1000 1 10 100 1000 1 10 100 1 10 100 1 10 100 1 10 100 1 10 100Fig. 5. Chondrite-normalized REE variation diagrams for the NTVZ volcanic rocks. Normalization constants are from Sun & McDonough (1989). The letters in the legend of each diagram represent the lithology: B, basalt; BA, basaltic andesite; A, andesite; D, diorite.
Cs Ba U Nb La Pb Sr Nd Hf Eu Gd Dy Ho Tm Lu Rb Th K Ta Ce Pr P Zr Sm Ti Tb Y Er Yb Cs Ba U Nb La Pb Sr Nd Hf Eu Gd Dy Ho Tm Lu Rb Th K Ta Ce Pr P Zr Sm Ti Tb Y Er Yb Cs Ba U Nb La Pb Sr Nd Hf Eu Gd Dy Ho Tm Lu Rb Th K Ta Ce Pr P Zr Sm Ti Tb Y Er Yb Cs Ba U Nb La Pb Sr Nd Hf Eu Gd Dy Ho Tm Lu Rb Th K Ta Ce Pr P Zr Sm Ti Tb Y Er Yb Cs Ba U Nb La Pb Sr Nd Hf Eu Gd Dy Ho Tm Lu Rb Th K Ta Ce Pr P Zr Sm Ti Tb Y Er Yb Cs BaRb ThU NbK Ta Ce PrLa Pb SrPNd HfZr Sm TiEu Gd Dy Ho Tm LuTb Y Er Yb Cs Ba U Nb La Pb Sr Nd Hf Eu Gd Dy Ho Tm Lu Rb Th K Ta Ce Pr P Zr Sm Ti Tb Y Er Yb Cs Ba U Nb Nd Hf Eu Gd Dy Ho Tm Lu La Pb Sr Rb Th Ta Ce Pr Zr Sm Ti Tb Y Er Yb K 100 101 102 103 SBS-1 (B) SBS-2 (B) SBS-7 (B) 100 101 102 103 KBS-1 (B) KBS-3 (B) KO-4 (B) 100 101 102 103 Pen-17 (B) Pen-20 (B) PGU-03 (BA) PGU-04 (BA) PGU-05 (BA) PGU-07 (BA) 100 101 102 103 MHY-2-1 (BA) MHY-2-2 (BA) MHH-01 (BA) MHY-1 (BA) MHY-7 (BA) 100 101 102 103 104 105 TLS-8 (B) TLS-18 (B) TLS-23 (B) TLS-27 (B) T-16 (B) T-20 (B) T-24 (B) T-30 (B) T-43 (B) T-48 (B)
TLS
100 101 102 103 104 K-41 (B) K-57 (B) K-60 (BA) K-64 (B) K-99 (A) K-108 (D)KYS
100 101 102 103 TS-3 (A) GML (A) CKS5-1 (A) L-2 (A) L-15 (A) L-25 (A) CH-7 (A) CH-14 (A) 100 101 102 103 A-3 (A) A-4 (A) A-10 (A) A-18 (BA) A-31 (A) A-99 (BA) A-129 (B) H-B-1 (B) B-2 (B)Primitive mantle normalized
SBS
KBS
PCY
MHY
KLVG
TTVG
Offshore
Onshore
Fig. 6. Primitive mantle-normalized trace-element variation diagrams for the NTVZ volcanic rocks. Normalization constants are from Sun & McDonough (1989).
basalts are the most LREE enriched. None of the REE patterns has an obvious negative Eu anomaly, which may indicate that plagioclase was not a fractionating phase in the NTVZ volcanic rocks.
The primitive mantle-normalized trace-element pat-terns of the NTVZ volcanic rocks show significant enrich-ments in large ion lithophile eleenrich-ments (LILE) and LREE and a pronounced Pb spike (Figs 6 and 7a). Except for the MHY samples, which have relatively smooth trace-element patterns, all the NTVZ volcanic rocks have distinct high field strength element (HFSE; i.e. Nb, Ta and Ti) troughs in their patterns. The TLS magmas have the highest LILE contents, with Rb concentrations up to 2500 ppm, which is the highest reported value for terres-trial rocks (Chung et al., 2001b). High LILE and K contents suggest that phlogopite may be present in the
mantle source of the TLS magmas (Chung et al., 2001b). The most mafic NTVZ volcanic rocks also exhibit systematic enrichment in LILE and LREE from SBS in the NE to TLS in the SW (Fig. 7a), paralleling the spatial variation shown by major-element compositions.
Notably, the MHY magmas do not show HFSE depletion but they show positive Pb spikes in the trace-element plots (Fig. 7b). Overall the trace-trace-element patterns of the MHY magmas are similar to those of Miocene Taiwan intra-plate basalts (MTIB) in northwestern Tai-wan (Chung et al., 1994, 1995a) although with lower LILE and LREE abundances (Fig. 7b). Additionally, the MHY trace-element patterns are almost the same as those of high-Mg andesites from Iriomote-jima, southern Ryukyu (Shinjo, 1999), considered to be associated with extensional tectonic activity on the Asian Cs Rb Ba Th U K Nb Ta La Ce Pb Pr Sr Nd Zr Hf SmEu Ti Gd Tb Dy Y Ho Er TmYb Lu MHY OIB IR-HMA E-MORB NTVZ (except MHY) 101 1 102 103
Primitive mantle normalized
Miocene Taiwan intraplate tholeiites
(b)
Cs RbBa Th U K NbTa La CePb Pr Sr P Nd Zr Hf SmEu Ti Gd TbDy Y HoEr TmYb Lu SBS: 2.6 Ma KBS: 0.2 Ma PCY: 2.1~0.3 Ma TTVG: 2.8~0.2 Ma KYS: 1.1~0.2 Ma TLS: 0.2 Ma MHY: 2.6; 0.5 Ma NE SW
Primitive mantle normalized
(a) 1 10 100 1000 10000
Fig. 7. (a) Primitive mantle-normalized trace-element diagrams for representative volcanic rocks for each volcanic field from the NTVZ. It should be noted that only the mafic members are plotted and therefore KLVG is excluded. (b) Primitive mantle-normalized trace-element variation diagram for representative MHY high-Mg basaltic andesites in comparison with Miocene intraplate basalts from NW Taiwan (MTIB; Chung et al., 1994, 1995a), high-Mg andesites of Iriomote-jima, southern Ryukyus (IR-HMA; Shinjo, 1999), E-MORB, ocean-island basalt (OIB) and other NTVZ volcanic rocks. Normalization constants, E-MORB and OIB values are from Sun & McDonough (1989).
continental margin in the Miocene (Chung et al., 1994, 1995a).
Nd---Sr---Pb isotopic compositions
The TLS samples have the highest Sr isotope ratios (87Sr/86Sr 070540---070551) and lowest Nd isotope
ratios (143Nd/144Nd 051259---051268). The MHY
samples, however, have the most depleted Nd isotope ratios (143Nd/144Nd 051290---051301) similar to those of enriched mid-ocean ridge basalt (E-MORB; Sun et al., 1979) and the South China Sea (SCS) seamounts (Fig. 8; Tu et al., 1992), but more enriched than that of the Eastern Taiwan Ophiolite (ETO) repre-senting the composition of the local mantle source of depleted MORB ( Jahn, 1986; Chung & Sun, 1992). The isotopic composition of the SCS may represent the composition of the local mantle source of E-MORB (Tu et al., 1992). Additionally, the MHY Nd isotope ratios are more depleted than those of typical arc and back-arc magmas in the nearby Central Ryukyu Arc (CRA) and Middle Okinawa Trough (MOT; Fig. 8; Wang, 1998; Shinjo et al., 1999). The MHY and some PCY Sr isotope ratios are slightly elevated so that the data plot to the right of the mantle array in the Nd---Sr isotope diagram (Fig. 8). In terms of the Nd isotope composition, however, the other NTVZ volcanic rocks plot between the depleted
MHY and enriched TLS samples. In the Nd---Sr isotope diagram the overall data for the NTVZ show a distribu-tion similar to that of the MTIB magmas, which have been interpreted to have originated by interaction of partial melts of ascending asthenosphere with the over-lying sub-continental lithospheric mantle (SCLM) beneath the western Taiwan region (Chung et al., 1994, 1995a). The onshore NTVZ volcanic rocks have positive Nd model ages based on a depleted mantle reservoir (TDM 05---40 Ga; Table 2). The TLS magmas are unique in yielding positive ages that fall in a restricted range from 20 to 25 Ga. Other NTVZ volcanic rocks, which might have been the product of mixing of partial melts of different mantle source components, yield nega-tive Nd model ages (not shown in Table 2).
The NTVZ volcanic rocks have high207Pb/204Pb and 208Pb/204Pb at a given206Pb/204Pb ratio (Fig. 9), and all
lie above the Northern Hemisphere Reference Line (NHRL) of Hart (1984), consistent with the typical Pb isotopic characteristics of mantle-derived magmas in nearby regions (i.e. ETO, SCS, MOT and MTIB; see Chung et al., 2001a, and reference therein). The NTVZ data define a linear trend between the ETO and Ruykyu subducted sediment values (Sun, 1980). However, the NTVZ volcanic rocks show a restricted range in comparison with nearby magmatic provinces, and most of them plot within the SCS field (Fig. 9). Remarkably, unlike the
0.708 0.706 0.704 0.702 0.5124 0.5126 0.5128 0.5130 0.5132 87Sr/86Sr 10 20 30 40 50 60 15 80 143 Nd/ 144 Nd SCS MOT CRA MTIB NTVZ SBS KBS MHY PCY KLVG TTVG KYS N TAIWAN TLS Bulk Earth
Fig. 8. Variation of87Sr/86Sr vs143Nd/144Nd for the NTVZ volcanic rocks. MTIB from NW Taiwan (Chung et al., 1994, 1995a), South China
Seamounts (SCS; Tu et al., 1992), back-arc magmas from the middle Okinawa Trough (MOT; Wang, 1998; Shinjo et al., 1999) and basalts from the central Ryukyu Arc (CRA; Shinjo et al., 1999) are also shown as fields for comparison. The East Taiwan Ophiolite (ETO) field is from Jahn (1986) and Chung & Sun (1992). The composition of average terrigenous sediments from Taiwan is from Lan et al. (1990). The mixing curve represents variable degrees of mixing between melts derived from MHY and TLS mantle sources. The Sr isotope composition of E-MORB is used to represent the unmodified source of the MHY (the asthenospheric mantle source; see detailed discussion in text). Ticks with a number indicate the percentage involvement of the SCLM (the TLS source).
major- and trace-element compositions, the Sr---Nd---Pb isotopic compositions of the NTVZ volcanic rocks do not show any systematic NE to SW variation.
DISCUSSION
In the following sections we consider specific aspects of the geochemical characteristics of the NTVZ volcanic rocks including spatial and temporal variations, the man-tle source components involved in melt generation, and degrees of partial melting. To minimize the effects of fractional crystallization, the volcanic rocks from the KLVG [which are all intermediate to silicic in composi-tion (SiO2 55---58 wt %)] are excluded and only mafic rocks (SiO2554 wt %) are considered. Crustal contam-ination may be an important process in the petrogenesis of the volcanic rocks from the southwestern part of the NTVZ. However, as shown by a plot of87Sr/86Sr vs SiO
2 (Fig. 10a), it does not appear to have a major influence on the isotopic characteristics of the NTVZ volcanic rocks. In Fig. 10a the mixing line between the average composition of the Taiwan upper crust and the MOT basalt (assumed to have a similar mantle source to the NTVZ; see
subsequent discussion) defines a steep slope, distinct from the variation trends for the individual volcanic fields in the NTVZ.
Spatial and temporal geochemical variation
in magma compositions
The spatial geochemical variation from NE to SW in the NTVZ volcanic rocks, expressed as an increase in K2O content, reduction in SiO2content, and LILE and LREE enrichment (Figs 3 and 7a), suggests increasing involve-ment of an enriched mantle source component or decreasing degrees of partial melting in the petrogenesis of the most primitive mafic magmas. In terms of the Sr---Nd---Pb isotope compositions (Figs 8 and 9), however, they do not show any systematic spatial variation. For instance, the KYS magmas have the second highest contents of K2O, LILE and LREE among the NTVZ (lower only than the highest TLS magmas; Figs 5, 6 and 7a), whereas they have relatively higher Nd and lower Sr isotope ratios compared with the other NTVZ volcanic rocks (Fig. 8). Thus, the Nd---Sr isotope composi-tion of the NTVZ volcanic rocks does not support a
19.5 19.0 18.5 18.0 17.5 15.3 15.4 15.5 15.6 15.7 15.8 EM2 EM1 37.5 38.0 38.5 39.0 39.5 40.0 EM2 EM1 208 Pb / 204 Pb MOT MTIB NHRL ETO MOT NHRL ETO MTIB SCS Geochron 207 Pb/ 204 Pb 206Pb/204Pb Ryukyu subducted sediments Ryukyu subducted sediments SCS NTVZ SBS KBS MHY PCY KLVG TTVG KYS N TAIWAN TLS
Fig. 9. 208Pb/204Pb and207Pb/204Pb vs206Pb/204Pb diagrams for the NTVZ volcanic rocks. Data for the ETO and Ryukyu subducted sediments
are from Sun (1980). The enriched mantle components EM1 and EM2 are from Hart (1988). The NHRL is from Hart (1984). Other data sources are the same as in Fig. 8.
southwesterly increasing involvement of an enriched source component.
The La/Yb ratios in the NTVZ mafic rocks increase with La concentration (Fig. 10b) and also with NE to SW progression (Fig. 10c). This increase in the La/Yb ratios could not result from increased involvement of an enriched mantle source component because there is no supporting evidence from the Nd---Sr---Pb isotope composi-tions. The La/Yb variation trend plots within that defined by partial melting of a local enriched MORB mantle source estimated for the MOT in the garnet and spinel facies (Fig. 10b; Table 3) and is not controlled by amount of the residual garnet. Consequently, the degree of partial melting in the NTVZ mantle source may play the dominant role in this chemical variation.
The geochemical characteristics of the NTVZ volcanic rocks show not only a spatial variation but also a change
with eruption age. Older (28---26 Ma) volcanic rocks from the SBS and MHY are low-K (Fig. 3a), followed by the dominantly calc-alkaline series of the PCY and TTVG (21---02 Ma), then finally by the recent (02 Ma) high-K to shoshonitic volcanism of the KBS, KYS and TLS. The earliest SBS and MHY magmas have the lowest LILE and LREE abundances, whereas the youngest KYS and TLS magmas are extremely enriched in LILE and LREE. The PCY and TTVG magmas erupted at an intermediate time and show tran-sitional abundances of the trace elements (Fig. 7a). The
143Nd/144Nd ratios of the earliest SBS and MHY
mag-mas extend up to 051301; however, the youngest TLS magmas have the lowest143Nd/144Nd ratio of 051260.
Figure 10d shows that the highest Nd isotopic ratios occur in the earlier NTVZ magmas, and vice versa. These data indicate that in the mantle source region an
20 15 10 5 4 2 15 5 4 20 10 Primitive mantle 0 10 20 La (ppm) (b) La/Y b 30 20 10 0 Spinel facies Garnet faci es Estimated enriched MORB mantle 3 2 1 0 0.5125 0.5127 0.5129 0.5131 Age (Ma) 143 Nd/ 144 Nd (d) 70 60 50 40 (a) 87 Sr/ 86 Sr 0.703 0.704 0.705 0.706 0.707 MOT (47.9; 229; 0.70395)
Ave. continental crust (65.6; 185; 0.71300) [SiO2 (wt.%); Sr (ppm); 87Sr/86Sr] 5 10 30 [SiO2 (wt.%); Sr (ppm); 87Sr/86Sr] SiO2 (wt.%) Distance from TLS (km) La/Yb 1000 100 10 1 0 10 20 (c) NTVZ SBS KBS MHY PCY KLVG TTVG KYS N TAIWAN TLS
Fig. 10. (a)87Sr/86Sr vs SiO
2(wt %) for the NTVZ volcanic rocks. Compositions of average Taiwan continental crust and the MOT basalt are from
Lan et al. (1990) and Wang (1998), respectively. Numbers in the diagram indicate the percentage of crustal contamination. (b) La/Yb vs La for the NTVZ volcanic rocks. Continuous lines are model curves for partial melting of enriched MORB-source mantle, estimated from basalts in MOT (Wang, 1998), with spinel-facies and garnet-facies mineralogy. Ticks with a number represent the degree of partial melting. Values used in modelling are shown in Table 3. The assumed melting model is non-modal batch melting. It should be noted that variation in La/Yb for the NTVZ may result from change in the degree of partial melting. The composition of primitive mantle (Sun & McDonough, 1989) is shown for comparison. (c) La/Yb vs distance from the TLS of each of the NTVZ volcanic fields. Distances are calculated horizontally from the location of the TLS. Because of the logarithmic scale, the distance of the TLS is unity. (d) Eruption ages vs143Nd/144Nd for the NTVZ volcanic rocks.
