T274 Subduction Zone Systems: Geochemical, Petrochronological, and Geophysical Constraints on Lithospheric Structure, Composition, and Geodynamics (Posters)

Wednesday, 25 September 2019
9:00 AM - 6:30 PM
Hall AB, North Building

NEOPROTEROZOIC TECTONIC EVOLUTION OF THE OPHIOLITIC BAYANKHONGOR SUTURE ZONE, CENTRAL ASIAN OROGENIC BELT (CENTRAL MONGOLIA)

Paper number: T274-13
Program: Technical Sessions
Time: 9:00 AM – 6:30 PM

Authors

Abstract

The amalgamation of the Central Asian Orogenic Belt (CAOB) in central Mongolia is represented by tectono-magmatic processes that accompanied Neoproterozoic ocean-basin closure and collision between the Khangai (to the northeast) and Baidrag (to the southwest) terranes along the ophiolitic Bayankhongor suture zone. The suture comprises a northeast-vergent thrust stack of (meta)sedimentary-matrix mélange units—from southwest to northeast, the Burd Gol, Delb Khairkhan, Haluut Bulag, and Dzag mélanges—that collectively bound a central ophiolite unit. Middle Paleozoic volcano-sedimentary and late Paleozoic sedimentary strata unconformably overlie or are in fault contact with the suture. The NW–SE-trending Bayankhongor ophiolite is 150–270 km long and ≤7 km wide and discontinuously exposes a complete pseudostratigraphic section including altered ultramafic rocks, layered and isotropic gabbros, sheeted dikes, pillow basalts, and pelagic sedimentary rocks—which previous researchers interpreted to reflect oceanic lithosphere generated via mid-ocean-ridge spreading, supra-subduction-zone spreading, or plume magmatism. New geologic mapping and structural analysis broadly contextualize petrologic and tectonic processes during and after crystallization and suturing. Zircon U/Pb geochronology for a plagiogranite intrusion from the ophiolite constrains its crystallization age to ~650 Ma. Youngest detrital-zircon-crystallization-age populations from mélange units young from south to north, possibly reflecting progressive terrane accretion. Ongoing mineral chemistry, whole-rock chemistry, and igneous-zircon geochronology for the Bayankhongor ophiolite will elucidate the tectonic setting in which it formed, improving regional-tectonic models for the CAOB.

Geological Society of America Abstracts with Programs. Vol. 51, No. 5

doi: 10.1130/abs/2019AM-334401

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