The change in magmatic conditions during magma course

The magmatic conditions estimated for the Neoproterozoic granites from the Guéra massif (Figure 6.7) show a systematic variation from high to low in temperature, pressure, and oxidation state (Figure 6.8).

The biotite crystallization temperatures of granites from Guéra massif and Lake Fitri region drop from ~652 to ~612^oC corresponding from the oldest to youngest rocks (Figure 6.8a), for each group, the low temperatures associated with the low Ti (Figure 6.10a) and silica (Figure 6.9) content. This variation is consistent with the transition in solidification conditions of magma from collision to extension regimes (Figure 6.12). Also, the low-temperature range (~611-652^oC) of these sample suites possibly indicates a late magmatic stage (Shand, 1944). Moreover, many experimental studies have proposed that granitic rocks will crystallize when the solidification temperature of granitic bulk compositions have cooled down to around 650-700^oC during metamorphism or hydrothermal alteration (Ackerson et al., 2018). Indeed, the yield of the average biotite temperature from 611 to 652^oC of this study lends support to this assertion.

102

Figure 6.7. The simplified location map showing the subdivision of biotites using the Fe-number, and the magmatic condition estimated for each intrusion. (a) modified from Pham (2018), (b, c) modified from Shellnutt et al. (2018). * denotes data from Shellnutt et al. (2018).

103

Figure 6.8. (a, b, c) the magmatic conditions of granitic rocks from the Guéra massif and Lake Fitri deduced from biotite composition.

(d, e) The plot of biotite emplacement pressure and oxidation state of studied rock with biotite crystallization temperature, and

(f) the plot of oxidation state and biotite emplacement pressure indicate a clear trend among Guéra and Lake Fitri granites, (g) the

amphibole pressure of Guéra granites generally drops during rock formation. * denotes data from Shellnutt et al. (2018).

104

Figure 6.9. The positive correlation between biotite temperature crystallization and silica content. * denotes data from Shellnutt et al. (2018).

Figure 6.10. The concentration of Ti reflects the variation of the crystallization temperature of biotite and oxygen fugacity of magma from Guéra massif and Lake Fitri region. * denotes data from

Shellnutt et al. (2018).

105

The oxygen fugacity of all investigated granites generally shows a trend toward slightly reducing condition from NNO to QFM buffer for collisional granites, QFM to WM buffer for Guéra collisional granites, and NNO to QFM for Lake Fitri post-collisional granites (Figure 6.6). In general, biotites have low O2 associated with low Ti content (Figure 6.9b). The concentration of ferrous iron usually varies among different sample suites that differ in redox condition, and the oxidation state of magma actively controls the extent of Fe²⁺-enrichment in the magma sequence during its evolution (e.g., Larsen, 1976). In this case, the biotite of 590 Ma-S, 570 Ma-E and 560 Ma-N plutons are calculated to be more enriched in Fe²⁺ which is produced from a magma under reducing conditions; whereas the poorer Fe²⁺ biotites of 595 Ma, 590 Ma-N, 570 Ma-W, 560 Ma-S plutons are formed from magma in oxidizing environment (Figure 6.11). On the other hand, the overlap of the concentration range of ferrous iron in Guéra granites indicates as evidence of an internal transition from more oxidizing to reducing condition in the individual intrusion.

Frost and Lindsley (1991) stated that the high O2 magmatic system usually produces Fe-Ti oxide minerals such as ilmenite, hematite, and magnetite especially, the appearance of hematite indicates the culmination in oxidation state reaching in felsic rocks. Nevertheless, this behavior does not clearly show in the studied intrusions. The results of EPMA analysis records no hematite and only extremely low content of ilmenite, magnetite that can be observed as the inclusions of opaque minerals under the microscope in biotite or amphibole. The concentration of SiO2 host rocks is very high ranging from 59.7 to 74.8 wt% for collisional granite, from 69.3 to 76.9 wt% for Guéra post-collisional granites (Pham, 2018) and from 73.7 to 76.9 wt%

106

for Lake Fitri post-collisional granites (Shellnutt et al., 2018) which may be the reason for the low abundance of Fe-Ti oxide minerals.

Figure 6.11. The variation of Fe²⁺ content records the transfer of the oxidation state in the course of magma during its evolution. (*) the data using from Shellnutt et al. (2018).

The change in estimated emplacement pressure of biotites from Guéra massif generally shows a decreasing trend from oldest to youngest rocks (Figure 6.8c, g), reflecting the decline of pressure from compression to extension. This feature is consistent with the scenario of the tectonomagmatic evolution in southern Chad (Figure 6.12) suggested by Shellnutt et al. (2017). The 560 Ma-S and 590 Ma-S plutons have the higher biotite pressure (2.76 ± 0.04, 2.49 ± 0.25 kbars, respectively) compared to the 560 Ma-N and 590 Ma-N (1.50 ± 0.06, 1.36 ± 0.04 kbars,

107

respectively) (Figure 6.8c). The barometric dichotomy could be due to a pressure gradient in 560 Ma and 590 Ma plutons. The amphibole and biotite pressures of 590 Ma intrusion (Figure 6.8c, g) show a contrast variation trend, in particular, the northern part of 590 Ma intrusion contains higher amphibole pressure (6.17 ± 0.6 kabrs) but lower biotite pressure (1.36 ± 0.04 kbars), in comparison with the southern part (PAm = 2.4 ± 0.7 kbars; PBt = 2.49 ± 0.25 kbars). It indicates a difference in the order of amphibole and biotite crystallization in the two parts of 590 Ma intrusion, i.e., the amphibole of 590 Ma-N likel crystallized earlier (at ~6.7 kbars), the subsequent amphibole and biotite of 590 Ma-S were crystallized at the same time (at ~2.4 kbars), and finally, the biotite of 590 Ma-N crystallized later (at ~1.36 kbars).

108

Figure 6.12. A possible tectomagmatic evolution suggesting repeated deformation/relaxation episodes in southern Chad (after Shellnutt et al. (2017). (a) Subduction-related magmatism and deformation

stages (D1 and D2). (b) Transtentional deformation D3 is followed by a first (c) crustal relaxation stage at ~ 570 Ma. (d) The final deformation stages D4 stage is followed by a second (e) (~560 Ma)

and (f) final crustal relaxation stage. SCLM: subcontinental lithospheric mantle. CAFB: Central African Fold Belt.

109 6.5. Biotite composition and parental magma

Biotite is predominantly ferromagnesian mineral in granites, and its composition reflects the primary nature of parental magma (Burkhard, 1993; Lalonde and Bernard, 1993; Shabani et al., 2003; Machev et al., 2004; Karimpour et al., 2011). The higher concentration of octahedral aluminum (Figure 6.13), total aluminum and iron in biotite (Figure 5.7f, Figure 5.9f) of granites from studied intrusions supposes that they are produced from Al-rich magma which contaminated by crustal materials or partial melting of Al-rich continental crust, consistent with whole-rock geochemical evidence. However, the parental magma of Lake Fitri granites has more crustal components than that in Guéra massif due to its relatively higher enrichment of total aluminum in biotite (2.90-3.59 apfu) among granites (Figure 5.5a, Figure 6.13c).

Moreover, the Nd isotopes (εNd(t)) are very distinct between post-collisional granite of Guéra massif and Lake Fitri region. The Lake Fitri granites have a relatively restricted range in values from +1.4 to +3.2, that are inidcaticative of a mantle-derived source produced by the melting of juvenile continental crust. Whereas, the Guéra massif granites are variable from -10.6 to +0.2, and can ranges from enriched to chondritic sources (Pham, 2018). Accordingly, it is likely that the Guéra Massif parental magmas were derived from different sources.

The concentration of Mg and octahedral Al vary in each age group (Figure 6.13) indicating the degree of Mg-enriched in biotite that caused by different magmatic phases or probably fractional crystallization took place during rock formation. The observation of high Mg and relatively low Al^vi content in biotite of Guéra granites (Figure 6.13a, b, c) reflect slightly fractionated magma (Hecht, 1994), that is

110

characteristic for I-type granites. Nevertheless, the biotite composition of Lake Fitri granites is low Mg and higher Al^vi content (Figure 6.13d) suggesting a forward magmatic fractionation (Hecht, 1994).

The chemical composition of biotite grains plays an essential role in the determination of the magmatic conditions of crystallization, and the Ti content is a criterion to demonstrate that biotite grains analyzed are of primary magmatic origin or not (Zhang et al., 2016). In other words, the Ti content of biotite is controlled by temperature, for example, the low-temperature hydrothermal alteration can result in the re-equilibration and neoformed biotite grains which have less Ti than those of primary magmatic biotites (Douce, 1993; Stussi and Cuney, 1996). In this study, all biotites plot in the primary magmatic and re-equilibrated biotite domain in the discrimination diagram defined by Nachit et al. (2005) (Figure 5.3, Figure 5.5c). This demonstrates that they were not affected by lateral thermal fluid activities. Moreover, they are free or poor in calcium content (Figure 5.7g, Figure 5.9g) suggesting that they are neither chloritized by meteoric fluid circulation nor related to post-magmatic deuteric alteration (Kumar and Pathak, 2010; Bora and Kumara, 2015).

111

Figure 6.13. Al^vi vs. Mg diagram for granites of Guéra massif and Lake Fitri region. * denotes data from Shellnutt et al. (2018).

112

6.6. Significance of biotite composition in the determination of tectonomagmatic setting

Biotite composition is considered to be a reliable indicator of the origin of the parental magma. It is also used as a powerful tool to determine the tectonic environment of host rocks (Abdel-Ranhman, 1994; Shabani et al., 2003; Machev et al., 2004; Bónová et al., 2009; Kumar et al., 2010; Zhang, 2016). This study employs two commonly tectonic discrimination diagrams based on the composition of biotite suggested by Abdel-Ranhman (1994) (Figure 6.14) and Shabani et al. (2003) (Figure 5.3a, Figure 5.5a) to better understand studied rocks.

For the collisional granites, the 595 Ma granite mostly shows as I-type granite (calc-alkaline metaluminous granites) (Figure 6.14a, Figure 5.3a), or strongly contamination and reduced I-type granite (SCR I-type granite) (Figure 5.3a).

Meanwhile, the 590 Ma granite belongs to A-type granite (Anorogenic alkaline suite) with slightly overlapping I-type granite (590 Ma-N) (Figure 6.14a, Figure 5.3a).

Indeed, the 595 Ma pluton is characteristic for volcanic arc granites and consistent with whole-rock geochemical signatures; but the 590 Ma plutons are different as they appear to be similar to an extensional setting rather than a collisional setting as proposed by Pham (2018). However, such evidence, together with the overlap and transition of biotite compositions and magmatic conditions point out that the tectonic evolution of Guéra massif at ~590 Ma was likely collisional. It is possible that the first generation of collisional granites were emplaced at 595 Ma (Figure 6.15a) and directly related to subduction of oceanic crust beneath the Saharan Metacraton (Figure 6.12a) which led to the formation of the 595 Ma pluton (Figure 6.15e). The subsequent 590

113

plutons are probably related to magmatism that occurred during continent-continent collision between Congo Craton and Saharan Metacraton.

For the post-collisional rocks, the granites plot as anorogenic alkaline suites (A-type granites) rather than peraluminous including S-(A-type suites (SCR I-(A-type granite, Figure 6.14b, c; Figure 5.5a). Whereas, the post-collisional granites from Lake Fitri region display the overlap between A- and P-field much more than that in Guéra Massif (Figure 6.14d) and mostly are SCR I-type granite (Figure 5.5). In general, they are representative for granites formed at extensional tectonic settings.

Furthermore, during the progress of the tectonic evolution of the Guéra massif, the first period of post-collisional magmatism occurred at 570 Ma (Figure 6.15c) when the crust had begun to relax (Figure 6.12c). The second period occurred at 560 Ma (Figure 6.15d) and correspond to the final stage of crustal relaxation of the Saharan Metacraton continent (Figure 6.12e). Their current exposure (Figure 6.15f) was likely caused by faulting either immediately after emplacement or possibly related to WCARS system (Genik, 1992).

114

Figure 6.14. Distribution of biotite composition on the FeO-MgO-Al2O3 discrimination tectonomagmatic diagram after Abdel-Ranhman (1994). FeO^T= [FeO+(0.89981*Fe2O3)], (*) the

data using from Shellnutt et al. (2018).

115

Figure 6.15. A conceptual scenario for the crustal evolution of the Guéra massif, South-Central Chad.

116

CHAPTER 7. CONCLUSION

This study reports the first estimates of the magmatic conditions of the granites from the Guéra massif and Lake Fitri region as well as the implications for the regional tectonic setting based on mafic mineral chemistry. The main conclusions are as follows:

1. The amphibole and biotite compositions show a trend of increasing total iron and decreasing magnesium content across time.

2. The biotite of collisional granites crystallized at a temperature of 639 ± 73 ^oC, at a pressure of 1.9 ± 0.1 kbar, under the more oxidizing condition with logO2= -18.3 ± 3.1 between NNO and QFM buffers.

3. The biotites of Guéra post-collisional granites crystallized at temperatures of 620 ± 44^oC to 616 ± 31^oC, at pressures from 1.8 ± 0.1 to 2.1 ± 0.1 kbars and transitioned from QFM to WM buffers with logO2= -19.5 ± 1.9 and -19.1 ± 1.6 for 570 Ma and 560 Ma, respectively.

4. The biotite of post-collisional granites from Lake Fitri region crystallized at 613 ± 45^oC, at pressure of 4.1 ± 0.1 kbars, at or near the NNO to QFM buffers with logO2 = -18.3 ± 3.1.

5. Both parental magmas of Guéra and Lake Fitri granites are contaminated by crustal components or partial melting of Al-rich continental crust. However, the Lake Fitri parental magmas are mantle-derived containing more crustal materials mixing with partial melting of juvenile continental crust; whereas, the Guéra parental magmas are crustal source.

117

6. The post-collisional granites from Lake Fitri region and Guéra massif have different redox conditions, emplacement depths, and compositions and sources of parental magma. Hence, the Lake Fitri granites are probably unrelated to the Guéra massif and were emplaced within a separate terrane.

118 References

Abdel-Rahman, A.M., 1994. Nature of Biotites from Alkaline, Calc-alkaline, and Peraluminous Magmas. Journal of Petrology, 35, 525-541.

Abdelsalam, M.G., Dawoud, A.S., 1991. The Kabus ophiolite melange, Sudan and its bearing on the western boundary of the Nubian Shield. Journal of the Geological Society, 148, 83-92.

Abdelsalam, M.G., Gao, S.S., Liégeois, J-P., 2011. Upper mantle structure of the Saharan Metacraton. Journal of African Earth Sciences, 60, 328-336.

Abdelsalam, M.G., Liégeois, J-P., Stern, R. J., 2002. The Saharan Metacraton. Journal of African Earth Sciences, 34, 119-136.

Abdelsalam, M.G., Stern, R.J., 1996. Mapping Precambrian structures in the Sahara Desert with SIR-C/X-SAR Radar: The Neoproterozoic Keraf Suture, NE Sudan. Journal of Geophysical Research, 101, 23063-23076.

Ackerson, M.R., Mysen, B.O., Tailby, N., Watson, E.B., 2018. Low-temperature crystallization of granites and the implications for crustal magmatism. Nature, 559, 7712.

Anderson, J.L., 1996. Status of thermo-barometry in granitic batholiths. Earth sciences, 87, 125-138.

Anderson, J.L., Smith, D. R., 1995. The effect of temperature and oxygen fugacity on Al-in-Hornblende barometry. American Mineralogist, 80, 549-559.

Arculus, R.J., 1985. Oxidation Status of the Mantle: Past and Present. In Annual Review of Earth and Planetary Sciences, 13, 75-95.

119

Ayati, F., Yavuz, F., Asadi, H.H., Richards, J.P., Jourdan, F., 2013. Petrology and geochemistry of calc-alkaline volcanic and subvolcanic rocks, Dalli porphyry copper-gold deposit, Markazi, Province, Iran. International Geology Review, 55, 158-184.

Ballard, J.R., Palin, J.M., Campbell, I.H., 2002. Relative oxidation states of magmas inferred from Ce(IV)/Ce(III) in zircon: application to porphyry copper deposits of northern Chile. Contributions to Mineralogy and Petrology, 144, 347-364.

Baranov, A.A., Bobrov, A.M., 2018. Crustal structure and properties of Archean cratons of Gondwanaland: Similarity and difference. Russian Geology and Geophysics, 59, 512-524.

Bardintzeff, J-M., Liégeois, J-P., Bonin, B., Bellon, H., Rasamimanana, G., 2010.

Madagascar volcanic provinces linked to the Gondwana break-up:

Geochemical and isotopic evidences for contrasting mantle sources. Gondwana Research, 18, 295-314.

Barley, M.E., Groves, D.I., 1992. Supercontinent cycles and the distribution of metal deposits through time. Geology, 20, 291-294.

Batchelor, R.A., Bowden, P., 1985. Petrogenetic Interpretation of Granitoid Rock Series Using Multicationic Parameters. Chemical Geology, 48, 43-55.

Benkhelil, J., Dainelli, P., Posnard, J.F., Popoff, M., Saugy, L., 1988. The Benue Trough: Wrench fault related basin, on the border of the Equatorial Atlantic, in Triasic-Jurassic Rifting-Continental Breakup and the Origin of the Atlantic Ocean and passive margins, W. Manspeizer (Editor). Developments in Geotectonics, Elsevier, Amsterdam, 22, 789-819.

120

Bermard, B., 1990. From orogenic to anorogenic settings: evolution of granitoid suites after a major orogenesis. Geological Journal, 25, 261-270.

Bessoles, B., Trompette, R., 1980. Géologie de L’Afrique: La Chaine Panafricaine, Zone Mobile d’Afrique Central (Partie sud) et Zone Mobile Soudanaise.

Mémoire du BRGM, Orléans, 92, 378.

Bickford, M.E., 1988. The formation of continental crust: Part 1. A review of some principles; Part 2. An application to the Proterozoic evolution of the southern North America. Geological Society of America Bulletin, 100, 1375-1391.

Black, R., 1992. Mission géologique au Tchad du 14 Janvier au 08 Féverier 1992.

Rapport PNUD/DRGM.

Black, R., Girod, M., 1970. Late Palaeozoic to Recent igneous activity in West Africa and its relationship to basement structure, in African Magmatism and Tectonics, Clifford, T.N. and Gass, I.C. (Editors). Oliver and Boyd, Edinburgh, 185-210.

Blundy, J.D., Holland, T.J.B., 1990. Calcic amphibole equilibria and a new amphibole-plagioclase geothermometer. Contributions to Mineralogy and Petrology, 104, 208-224.

Bónová, K., Broska, I., Petrík I., 2010. Biotite from Čierna hora Mountains granitoids (Western Carpathians, Slovakia) and estimation of water contents in granitoid melts. Geologica Carpathica, 61, 3-17.

Bora, S., Kumara, S., 2015. Geochemistry of biotites and host granitoid plutons from the Proterozoic Mahakoshal Belt, central India tectonic zone: implication for

121

nature and tectonic setting of magmatism. International Geology Review, 57, 1686-1706.

Botcharnikov, R. E., Koepke, J., Holtz, F., Mccammon, C., 2005. The effect of water activity on the oxidation and structural state of Fe in a ferro-basaltic melt.

Geochimica et Cosmochimica Acta, 69, 5071-5085.

Bowring, S.A., King, J.E., Housh, T.B., Isachsen, C.E., Podosek, F.A., 1989a, Neodymium and Lead isotope evidence for enriched Early Archean crustin North America. Nature, 340, 222-225.

Bradley, D.C., 2011. Secular trends in the geologic record and the supercontinent cycle. Earth-Science Reviews, 108, 16-33.

Buddington, A.F., Lindsley, D.H., 1964. Iron-Titanium Oxide Minerals and Synthetic Equivalents. Journal of Petrology, 5, 310-357.

Buiter, S.J.H., Torsvik, T.H., 2014. A review of Wilson cycle plate margins: a role for mantle plums in continental break-up along sutures? Gondwana Research, 26, 627-653.

Burkhard, D.J.M., 1991. Temperature and redox path of biotite-bearing intrusives: a method of estimation applied to S- and I-type granites from Australia. Earth and Planetary Science letters, 104, 89-98.

Burkhard, D.J.M., 1993. Biotite crystallization temperatures and redox states in granitic rocks as an indicator for tectonic setting. Geologie en Mijnbouw, 71, 337-349.

122

Burt, D.M., 1998. Vector treatment of the composition of some skarn minerals, in Mineralized Intrusion-Related Skarn Systems, Lentz, D.R., (Editor), Mineralogical Association of Canada, Short Course 26, 51-70.

Carmichael, I.S., Turner, F.J., Verhoogen, J., 1974. Igneous Petrology. New York:

McGraw-Hill. 250.

Carmichael, I.S.E., 1991. The redox state of basic and silicic magmas: a reflection of their source regions?, Contributions to Mineralogy and Petrology, 106, 129-141.

Castaing, C., Feybesse, J.-L., Thiéblement, D., Triboulet, C., Chèvremont, P., 1994.

Paleogeographical reconstructions of the Pan-African/Brasiliano orogen:

closure of an oceanic domain or intracontinental convergence between major blocks. Precambrian Research, 69, 327-344.

Castaing, R., 1951. Application of electron probes to local chemical and crystallographic analysis. Ph.D. Thesis, University of Paris. English translation by Duwez, P. and Wittry, D.B., California Institute of Technology, 1955.

Challener, S.C., Glazner, A.F., 2017. Igneous or metamorphic? Hornblende phenocrysts as greenschist facies reaction cells in the Half Dome Granodiorite, California. American Mineralogist, 102, 436-444.

Chiaradia, M., Ulianov, A., Kouzmanov, K., Beate, B., 2012. Why large porphyry Cu deposits like high Sr/Y magmas? Scientific Reports, 2: 685.

Christie-Blick, N., Biddle, K.T., 1985. Deformation and basin formation along strike-slip faults, in Strike-strike-slip Deformation, Basin Formation, and Sedimentation.

123

Biddle, K.T., and Christie-Blick, N., (Editors). SEPM, Special Publication, 37, l-34.

Clarke, D.B., 1992. Granitoid Rocks. Book, Chapman and Hall London.

Clifford, T.N., 1967. The Damaran episode in the Upper Proterozoic structural history of southern Africa. Geological Society of America, Special Paper 92.

Clifford, T.N., 1968. Radiometric dating and the pre-Silurian geology of Africa, in Radiometric dating for geologists, Hamilton, E.I., and Farquhar, R.M., (Editors). Interscience, N. Y., 299-419.

Condie, K.C., 2003. Supercontinents, superplumes and continental growth: The Neoproterozoic record, in Proterozoic East Gondwana: Supercontinent Assembley and Breakup, Yoshida, M., Windley, B.F., Dasguptas, S. (Editors).

Geological Society London Special Publications, 206, 1-21.

Condie, K.C., 2005. Earth as an Evolving Planetary System. Elsevier Academic Press, Amsterdam. 447 p.

Condie, K.C., Belousova, E., Griffin, W.L., Sircombe, K.N., 2009. Granitoid events in space and time: constraints from igneous and detrital zircon age spectra.

Gondwana Research, 15, 228-242.

Dai, L., Karato, S-I., 2014. Influence of oxygen fugacity on the electrical conductivity of olivine: Implications for the mechanism of conduction. Physics of The Earth and Planetary Interiors, 232, 57-60.

Daly, M.C., Chorowicz, J., Fairhead, J.D., 1989. Rift basin evolution in Africa: The influence of reactivated steep basement shear zones, in Inversion tectonics,

124

Cooper, M.A., and Williams, G.D., (Editors). Geological Social Special Publications, 44, 309-334.

David, J.R., Clive, R.J., 2004. Tectonic evolution of the Doba and Doseo basins, Chad: Controls on trap formation and depositional setting of the three fields area, Chad, in Sandstone Deposition in Lacustrine Environments: Implications for Exploration and Reservoir Development, AAPG Hedberg Research Conference, Abstract.

Dawaï, D., Bouchez, J.L., Paquette, J.L., Tchameni, R., 2013. The Pan-African quartz-syenite of Guider (north-Cameroon): magnetic fabric and U-Pb dating of a late-orogenic emplacement. Precambrian Research, 236, 132-144.

Deer, W.A., Howie, R.A., Zussman, J., 1992. An Introduction to the Rock-Forming Minerals. Book, 2^nd edition, Longman, London.

Dilles, J.H., Kent, A.J.R., Wooden, J.L., Tosdal, R.M., Koleszar, A., Lee, R.G., Farmer, L.P., 2015. Zircon compositional evidence for sulfur-degassing from ore-forming arc magmas. Economic Geology, 110, 241-251.

Dou, L., Wang, J., Wang, R., Wei, X., Shrivastava, C., 2018. Precambrian basement reservoirs: Case study from the northern Bongor Basin, the Republic of Chad.

AAPG Bulletin, 102, 1803-1824.

Dou, L., Xiao, K., Hu, Y., Song, H., Cheng, D., du, Y., 2011. Petroleum geology and a model of hydrocarbon accumulations in the Bongor Basin, the Republic of Chad. Acta Petrolei Sinica, 3, 379-386.

125

Douce, P., A.E., 1993. Titanium substitution in biotite: an empirical model with applications to thermometry, O2 and H2O barometries, and consequences for biotite stability. Chemical Geology, 108, 133-162.

Doumnang, J.C., Pouclet, A., Vidal, M., Vicat, J.P., 2004. Lithostratigraphy of the Pan-African grounds of the south of Chad (area of the lake of lere) and geodynamic significance of the magmatic formations. IGCP Second Annual Field Conference, Cameroon: Garoua, Abstract.

Eby, G.N., 1992. Chemical subdivision of the A-type granitoids: Petrogenetic and tectonic implications. Geology, 20, 641-644.

El-Makhrouf, A.A., 1988. Tectonic interpretation of Jebel Eghei area and its regional application to Tibesti orogenic belt, south-central Libya (S.P.L.A.J.). Journal of African Earth Sciences, 7, 945-967.

El-Makhrouf, A.A., 1988. Tectonic interpretation of Jebel Eghei area and its regional application to Tibesti orogenic belt, south-central Libya (S.P.L.A.J.). Journal of African Earth Sciences, 7, 945-967.

在文檔中 An assessment of the magmatic conditions of Late Neoproterozoic collisional and post-collisional granites from the Guéra Massif, South-Central Chad (頁 117-0)