22 Evolution of Cordilleran-type orogenic systems (Posters)

This session seeks contributions that connect surface, crustal, and mantle processes associated with Cordilleran systems, specifically addressing geodynamics, kinematics, magmatism, uplift, erosion, basin subsidence, and sediment dispersal in ancient and modern settings.

Thursday, 23 April 2026
8:00 AM - 5:30 PM
LMH, 5th Floor Chapel

Zircon (U-Th)/He record of the growth and collapse of the Mongol-Okhotsk Belt in Central Asia

Paper number: 22-7
Program: Technical Sessions
Time: 8:00 AM – 8:00 AM

Authors

Abstract

Quantifying and disentangling exhumation related to the evolution of a collisional belt from that associated with its later extension is critical for reconstructing the magnitude and spatial extent of the collisional processes and for assessing the mechanisms driving its collapse. The closure of the Mongol-Okhotsk Ocean and the growth of the Mongol-Okhotsk Belt (MOB) marked the final assembly of the Central Asian Accretionary Belt, the largest accretionary orogen on Earth. Its Late Mesozoic extensional collapse is commonly interpreted as the result of gravitational instability of an overthickened crust. However, the preceding collisional orogeny is thought to have been short-lived (Late Jurassic to Early Cretaceous) and soft, as indicated by local limited Jurassic–Cretaceous exhumation. This study presents new zircon (U–Th)/He data collected along a ca. 300 km long horizontal transect across the northern side of the collisional belt (north of the suture zone). The transect intersects two orogen-scale domains: An outer domain, characterized by Precambrian to Triassic units and orogen-parallel strike-slip deformation, and an inner (core) domain composed of a Paleozoic accretionary complex and dominated by orogen-perpendicular dip-slip deformation. Cooling data in the outer domain record a collisional cooling signature, with Late Jurassic zircon (U–Th)/He ages that are interpreted to record and constrain the amount of exhumation along orogen-parallel shear zones during the collisional event along the northern side of the belt. New Early Cretaceous zircon (U–Th)/He data document enhanced cooling and exhumation since the Cretaceous within its core. In contrast, previous Cretaceous apatite fission track cooling ages in the outer domain suggest that during the extensional collapse, the outer part of the orogen experienced less cooling and less exhumation compared to its core. These results are consistent with a limited Cretaceous record and preserved Cretaceous-Paleocene peneplain surfaces north of the suture zone, and the development of a regional Cretaceous unconformity. Considering the northern and southern sides of the orogen, the preservation of several Cretaceous basins in the southern side (south of the suture zone) suggests asymmetric exhumation during orogenic collapse with enhanced exhumation in the northern side, particularly within its core, possibly driven by increased shortening and crustal thickening.

Geological Society of America Abstracts with Programs. Vol. 58, No. 3

doi: 10.1130/abs/2026CD-411062

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