HR: 1340h
AN: V33C-1512    [Abstracts]
TI: Coeval Intrusion and Batholith-Wide Mingling in the Gobi-Tienshan Intrusive Complex, Southern Mongolia
AU: * Economos, R C
EM: economos@usc.edu
AF: University of Southern California, Department of Earth Sciences, 3651 Trousdale Parkway, ZHS 117, Los Angeles, CA 90089-0740, United States
AU: Said, L O
EM: lchagwaa@yahoo.com
AF: Mongolian University of Science and Technology, School of Geology and Petroleum Engineering, P.O. Box 46/520, Ulaanbaatar, 210646, Mongolia
AU: Paterson, S R
EM: paterson@usc.edu
AF: University of Southern California, Department of Earth Sciences, 3651 Trousdale Parkway, ZHS 117, Los Angeles, CA 90089-0740, United States
AU: Anderson, J L
EM: anderson@usc.edu
AF: University of Southern California, Department of Earth Sciences, 3651 Trousdale Parkway, ZHS 117, Los Angeles, CA 90089-0740, United States
AB: The Gobi-Tienshan Intrusive Complex (GTIC) in southern Mongolia is the southernmost magmatic belt of the Central Asian Orogenic Belt (Geomin, 2003). The GTIC was likely generated as an active continental margin by the closure of the final ocean basin between Mongolia and the Tarim block (Fillipova, 1990), evidenced by its calc- alkaline, magnetite series magmatism and medium to high-K compositions. The system was likely augmented by subsequent continental collision (Fillipova, 1990). Detailed mapping of the GTIC reveals a batholith and associated volcanics constructed by a wide spectrum of magma compositions, which include hbl>bt granodiorites and hbl cumulates, hbl-free granites, high-K red granites, syenogranites and syenites, and andesite to quartz diorite dikes. Field evidence for the coeval nature of granodiorites and granites includes cusbate/lobate margins between units and mutual diking. Dikes are commonly found disaggregating into microgranitoid enclaves and hybridizing with both hbl-rich granodiorites and hbl-free granites. Dikes are likely related to magma mingling seen throughout the GTIC in granodioritic units, including an enclave mega-plume, where enclave percentages increase sharply from 5 to 50% for 15 km2 in aerial extent. These features are commonly on a multi-km scale, thus are unlikely to be the effect of re-heating. Field relationships are reflected in chemical trends, including incongruent REE and trace element patterns for mutually intruded magmas. The transition from chemically distinct to highly hybridized enclaves is also observed both in the field and in REE and other trace element trends. Meanwhile, structural orientations in the GTIC are highly varied, with sheets dipping generally <45o cut by a huge diabase dike swarm that is sub-vertical. Sheets are approximately parallel to an enclave foliation striking 40 degrees and dipping shallowly, while mineral fabrics defined by hbl and bt have a similar strike, but consistently steep dips. The diverse magma types in the GTIC are traditionally interpreted to reflect different tectonic environments, therefore their coeval nature implies rapid changes in tectonic environment or a highly unusual tectonic setting. Thus, the GTIC presents a natural laboratory for such high-flux magmatic systems and will contribute to constraining the terminating continental collision of the Central Asian Orogenic Belt.
DE: 1036 Magma chamber processes (3618)
DE: 3640 Igneous petrology
DE: 3642 Intrusive structures and rocks
DE: 8035 Pluton emplacement
DE: 8178 Tectonics and magmatism
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting