HR: 0800h
AN: T31B-0468    [Abstracts]
TI: The Petrogenesis of Cretaceous A-type Granites, SE Tibet: Geochemical and Nd Isotopic Constraints
AU: * Lin, I
EM: r94224201@ntu.edu.tw
AF: Department of Geosciences, National Taiwan University, Taipei P.O. Box 13-318, Taipei, 10699, Taiwan
AU: Chung, S
EM: sunlin@ntu.edu.tw
AF: Department of Geosciences, National Taiwan University, Taipei P.O. Box 13-318, Taipei, 10699, Taiwan
AU: Chu, C
EM: julie0104@yam.com
AF: Department of Geosciences, National Taiwan University, Taipei P.O. Box 13-318, Taipei, 10699, Taiwan
AU: Sylvain, G
EM: Gallet@ntu.edu.tw
AF: Department of Geosciences, National Taiwan University, Taipei P.O. Box 13-318, Taipei, 10699, Taiwan
AU: Ji, J
EM: grsange@pku.edu.cn
AF: School of Earth and Space Sciences, Peking University, Beijing, 100871, China
AB: Northward subduction of the Neo-Tethyan oceanic lithosphere beneath South Asia gave rise to an Andean-type convergent margin marked with arc magmatism starting from the early Jurassic (≥190Ma) and lasting until the Eocene (~45Ma). The Cretaceous to Paleocene volcano-plutonic belt thus formed in Bomi to Chayu areas, SE Tibet, consists of three major batholiths, namely, Achakung, Temula, and Chayu, respectively. While all granitoids and volcanics from this region are characterized by depletions in HFSE, enrichment in LILE and LREE, thus showing incompatible trace element patterns similar to those of typical arc magmas from the active continental margins, in the Temula batholith A-type granites with diagnostic features including high alkalis, Fe₂O_3T/MgO, Ga/Al, Rb, and HREE, large Eu negative anomalies, and low Ba and Sr contents were identified. The A-type granites, emplaced at 122±2Ma, exhibit crustal type Nd isotopic signatures [ε Nd(T)~-12]. To account for the petrogenesis of the Cretaceous A-type granites and associated arc rocks in this part of the Neo-Tethyan subduction zone, we propose a two-stage magma differentiation model involving (1) deep differentiation and crustal contamination of mantle-derived mafic liquids that intrude/underplate in the lower part of the continental crust around the Moho and (2) additional differentiation and upper crustal contamination of such differentiated liquids as they rise and install in shallow-level magma chambers. The shallow intrusion, moreover, may have triggered low-pressure (P≤4kbar) partial melting of calc-alkaline basement rocks, e.g., those atop the magma chambers, and hence produced the Temula A-type granites.
DE: 1009 Geochemical modeling (3610, 8410)
DE: 1031 Subduction zone processes (3060, 3613, 8170, 8413)
DE: 3619 Magma genesis and partial melting (1037)
DE: 3640 Igneous petrology
DE: 8102 Continental contractional orogenic belts and inversion tectonics
SC: Tectonophysics [T]
MN: 2007 Fall Meeting