Evolution of Tectonic Uplift, Hydrocarbon Migration, and Uranium Mineralization in the NW Junggar Basin: An Apatite Fission‐Track Thermochronology Study

Abstract

The Mesozoic–Cenozoic tectonic movement largely controls the northwest region of the Junggar Basin (NWJB), which is a significant area for the exploration of petroleum and sandstone‐type uranium deposits in China. This work collected six samples from this sedimentary basin and surrounding mountains to conduct apatite fission track (AFT) dating, and utilized the dating results for thermochronological modeling to reconstruct the uplift history of the NWJB and its response to hydrocarbon migration and uranium mineralization. The results indicate that a single continuous uplift event has occurred since the Early Cretaceous, showing spatiotemporal variation in the uplift and exhumation patterns throughout the NWJB. Uplift and exhumation initiated in the northwest and then proceeded to the southeast, suggesting that the fault system induced a post spread‐thrust nappe into the basin during the Late Yanshanian. Modeling results indicate that the NWJB mountains have undergone three distinct stages of rapid cooling: Early Cretaceous (ca. 140–115 Ma), Late Cretaceous (ca. 80–60 Ma), and Miocene–present (since ca. 20 Ma). These three stages regionally correspond to the Lhasa‐Eurasian collision during the Late Jurassic–Early Cretaceous (ca. 140–125 Ma), the Lhasa‐Gandise collision during the Late Cretaceous (ca. 80–70 Ma), and a remote response to the India‐Asian collision since ca. 55 Ma, respectively. These tectonic events also resulted in several regional unconformities between the J3/K1, K2/E, and E/N, and three large‐scale hydrocarbon injection events in the Piedmont Thrust Belt (PTB). Particularly, the hydrocarbon charge event during the Early Cretaceous resulted in the initial inundation and protection of paleo‐uranium ore bodies that were formed during the Middle–Late Jurassic. The uplift and denudation of the PTB was extremely slow from 40 Ma onward due to a slight influence from the Himalayan orogeny. However, the uplift of the PTB was faster after the Miocene, which led to re‐uplift and exposure at the surface during the Quaternary, resulting in its oxidation and the formation of small uranium ore bodies.

Late Paleozoic Exhumation of the West Junggar Mountains, NW China

“…Several published studies have previously applied AFT dating to intrusive igneous rocks in the West Junggar Mountains (Guo et al, ; Li et al, ; Qin et al, ). These studies produced mostly conflicting results.…”

Characteristics of Uranium Mineralization in Red Clastic Formations in the Southwestern Margin of the Ordos Basin

“…In summary, the key conditions (Zhang et al, 2018) and multiple stages of oxidation-reduction-reoxidation mineralization superposed on the slope belt. The aforementioned conditions, coupled together, similar to the uranium mineralization in the NW Jungar Basin (Qin et al, 2018), result in concentrations of uranium and the formation of uranium deposits in an area rich in organic matter.…”

Origin of Shallow Jurassic Heavy Oils in the Northwestern Margin of the Junggar Basin, NW China: Constraints from Molecular, Isotopic and Elemental Geochemistry

“…The northwestern margin of the Junggar Basin has experienced four tectonic evolutionary stages, namely the Hercynian, Indosinian, Yanshan and Himalayan, since the late Paleozoic (Zhao et al, 2019). It is a large-scale NE trending imbricated thrust nappe belt developed from late Carboniferous to the Triassic, gradually buried after the Middle Jurassic (Qin et al, 2018). The belt can be divided into a fault zone, slope zone and depression zone towards the centre of the basin (Fig.…”

“…The migratory pathway contained cross-cutting faults; the unconformities between Carboniferous and Permian (C/P), upper and lower Permian (P 2 /P 1 ), and Permian and Triassic (P/T); and various sand body layers (Wang et al, 2016;Lei et al, 2017). The study area underwent intense Yanshan episode II tectonic movement during the end of the Late Jurassic (Qin et al, 2018;Huang et al, 2018), resulting in the large-scale readjustment of deep primary oil reservoirs, especially relatively shallow buried reservoirs in the slope area (Sui, 2015;Song et al, 2019). The escaped mature oils then migrated and filled the shallow Jurassic traps of structure or lithology through penetrating faults, unconformity surfaces and sand body layers.…”