T35 Advances and Applications of Thermochronology to Tectonic, Magmatic, Basin, and Geomorphic Problems (Posters)

Sunday, 22 September 2024
8:00 AM - 5:30 PM
Hall D

INVESTIGATING CARBONIFEROUS TO JURASSIC CYCLES OF MOUNTAIN BUILDING RECORDED BY DETRITAL ZIRCON U-Pb GEOCHRONOLOGY AND (U-Th)/He THERMOCHRONOLOGY IN THE MONGOLIAN ALTAY

Paper number: T35-8
Program: Technical Sessions
Time: 8:00 AM – 5:30 PM

Authors

Abstract

The Mongolian Altay, located in western Mongolia, are currently part of the largest intracontinental orogenic system on Earth. The last time the Altay were located near an active plate boundary was during the construction of the Mongol-Okhotsk orogenic belt. Sparse low-temperature thermochronological data from the Altay preserve fast rock cooling phases during the Mesozoic; however, the tectonic significance of these cooling ages has been understudied. Furthermore, the aridification and uplift of several ranges within Central Asia and the relatively large amounts of sedimentary burial in Altay basins have preserved those pre-Cenozoic cooling signals. This scenario makes the Mongolian Altay an excellent region to study ancient mountain-building processes and examine the role of inherited structures and/or topography in intracontinental orogens.

We performed detrital zircon double dating (U-Pb and (U-Th)/He, ZHe) on Cretaceous to Oligocene sandstones sampled within basins along the eastern margin of the Altay to reconstruct the orogenic evolution of source terranes and improve future provenance interpretations.

Our data contain four U-Pb-He age modes that we correlate with major cooling phases in the Mongolian Altay. The youngest cooling age corresponds to middle Jurassic (~150 Ma) ZHe ages with 160-165 Ma crystallization ages, which are interpreted as rapidly exhumed grains. A late Triassic (~220 Ma) cooling phase is recorded by grains with Permian, Devonian, and Cambrian crystallization ages. The most dominant cooling signal is early Permian (~280 Ma) in age and is characterized by rapidly exhumed grains with U-Pb ages at ~290 Ma, and non-rapidly exhumed grains with Devonian and Cambrian crystallization ages. The early Permian cooling phase is accompanied by volcanogenic grains that are recognized by their overlapping U-Pb and (U-Th)/He ages. Finally, the oldest cooling signal is recorded by Carboniferous (~320 Ma) ZHe ages with Devonian and Neoproterozoic-Cambrian U-Pb ages.

Our preliminary data suggest that the Permian and Carboniferous ZHe age modes coincide with plate reconstructions that place the Altay in the eastward closure of the Mongol-Okhotsk Ocean by that time. We also propose that the Mongolian Altay were proximal to active volcanism during the early Permian based on the presence of volcanogenic zircons.

Geological Society of America Abstracts with Programs. Vol. 56, No. 5

doi: 10.1130/abs/2024AM-402339

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