HR: 1340h
AN: V23C-1561    [Abstracts]
TI: Monazite geochronology of the Bodonch metamorphic complex, southwestern Mongolia
AU: * Cina, S E
EM: saracina@ucla.edu
AF: Department of Earth and Space Sciences, University of California, Los Angeles, 595 Charles Young Drive East, Los Angeles, CA 90095, United States
AU: Yin, A
EM: yin@ess.ucla.edu
AF: Department of Earth and Space Sciences, University of California, Los Angeles, 595 Charles Young Drive East, Los Angeles, CA 90095, United States
AU: Dash, B
EM: ulziid@yahoo.com
AF: Department of Geology, Mongolian University of Science and Technology, P. O. Box-520, Ulaanbaatar, -46, Mongolia
AU: Manning, C
EM: manning@ess.ucla.edu
AF: Department of Earth and Space Sciences, University of California, Los Angeles, 595 Charles Young Drive East, Los Angeles, CA 90095, United States
AB: The Bodonch metamorphic complex in southwestern Mongolia is a steeply dipping assemblage of low to high grade metamorphic rocks exposed along a ~30 km stretch of the Bodonch River which has been variably regarded as either a microcontinental block, due to presence of gneissic foliation; a metamorphic core complex; or an accretionary complex in the Central Asian Orogenic System. Metamorphic grade generally increases from subgreenschist facies at the southern margin of the complex to amphibolite facies in the central section, and decreases again to subgreenschist facies further to the north. Foliation is approximately E-W striking and predominately dips northward, although isoclinal folding is pervasive at all scales. Lithologically, the complex consists primarily of metapelites, with minor interbedded metavolcanics and metacherts. Carbonates and quartzites are generally absent and are observed only in thin depositional lenses. The entire complex is intruded by granitic dikes ranging from ~1 m in thickness to several tens of meters which postdate the metamorphism. The most striking feature of the Bodonch metamorphic complex is the occurrence of garnet bearing schist in the central section which contains zones of almost pure garnet mineralization. Along its southern margin, the assemblage is thrust over a sequence of unmetamorphosed to low grade Devonian-Carboniferous volcanics and sediments which are classified as belonging to an oceanic island arc terrane. Based on the observed lithologies, lack of crystalline basement, and style of deformation we favor the accretionary complex model for the tectonic origin of the Bodonch metamorphic complex. We present new Th-Pb ages of monazite inclusions in garnets obtained using in situ ion-microprobe techniques, which are interpreted to correspond to the timing of accretion related metamorphism.
DE: 1115 Radioisotope geochronology
DE: 3613 Subduction zone processes (1031, 3060, 8170, 8413)
DE: 3660 Metamorphic petrology
DE: 3690 Field relationships (1090, 8486)
DE: 8170 Subduction zone processes (1031, 3060, 3613, 8413)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting