Apatite fission-track thermochronological constraints on the pattern of late Mesozoic–Cenozoic uplift and exhumation of the Qinling Orogen, central China

The Intra-Sudetic Basin, a Late-Paleozoic intramontane trough located on the NE flank of the Bohemian Massif, is comprised of numerous outcrops of continental (extension-related) Early-Permian volcanogenic rocks that are commonly altered to spilites. In this contribution, we provide insights into the formation of spilitized (albite- and chlorite-rich) trachyandesites from the Głuszyca quarry (Lower Silesia, Poland), based on mineralogical and micro-textural investigations supported by apatite fission-track dating (AFT). Our results indicate that the trachyandesites, emplaced as a shallow-level laccolith-type body, have been strongly affected by chloritization of both aegirine and augite, combined with an occasional celadonitization of volcanic glass. Furthermore, chlortitization of sodic pyroxenes must have released notable amounts of Na+, which could be involved during later pervasive albitzation of primary andesine-labradorite. According to various chemical and semi-empirical thermometers, the replacive chlorites formed in the range of 124–170 °C. Trachyandesites from Głuszyca contain abundant fluorapatites, marked by the occurrence of swallow-type terminations, which are indicative of rapid-cooling formation conditions. Central AFT ages of the samples vary between 161–182 Ma and correspond to the Middle-Jurassic period. Meanwhile, these ages are significantly younger than the emplacement of igneous rocks during the Middle-Rotliegendes period (~299–271 Ma). The discrepancy between the stratigraphic age of the rocks and the AFT results cannot be, however, explained by, for example, slow cooling rates of magmatic body, compositional variations of apatite, or burial under Late-Mesozoic sediments. Hence, it may be assumed that the obtained AFT ages (161–182 Ma) reflect the timing of spilitization and associated partial reheating of volcanic rocks from the Intra-Sudetic Basin above the apatite partial annealing zone (70–110 °C).

Download Full-text

New Detrital Apatite Fission Track Thermochronological Constraints on the Meso-Cenozoic Tectono-Thermal Evolution of the Micangshan-Dabashan Tectonic Belt, Central China

Frontiers in Earth Science ◽

10.3389/feart.2021.754137 ◽

2021 ◽

Vol 9 ◽

Author(s):

Tao Tian ◽

Peng Yang ◽

Jianming Yao ◽

Zhonghui Duan ◽

Zhanli Ren ◽

...

Keyword(s):

Fission Track ◽

Central China ◽

Accelerated Cooling ◽

Lateral Migration ◽

Apatite Fission Track ◽

Dabie Orogen ◽

Tectonic Zone ◽

Rapid Cooling ◽

Coupling Process ◽

Tectonic Belt

The Micangshan-Dabashan tectonic belt, located in the southern Qinling-Dabie Orogen near the northeastern Tibetan Plateau, is a crucial area for understanding the processes and mechanisms of orogenesis. Previous studies have been focused on the cooling process via thermochronology and the mechanism and process of basement uplift have been investigated. However, the coupling process of basement exhumation and sedimentary cap cooling is unclear. The tectono-thermal history constrained by the detrital apatite fission track (AFT) results could provide valuable information for understanding crustal evolution and the coupling process. In this study, we provided new detrital AFT thermochronology results from the Micangshan-Dabashan tectonic belt and obtained nine high-quality tectono-thermal models revealing the Meso-Cenozoic cooling histories. The AFT ages and lengths suggest that the cooling events in the Micangshan area were gradual from north (N) to south (S) and different uplift occurred on both sides of Micangshan massif. The cooling in Dabashan tectonic zone was gradual from northeast (NS) to southwest (SW). The thermal histories show that a relatively rapid cooling since ca. 160 Ma occurred in the Micangshan-Dabashan tectonic belt, which was a response to the event of Qinling orogenic belt entered the intracontinental orogenic deformation. This cooling event may relate to the northeastward dextral compression of the Yangtze Block. The sedimentary cap of Cambriano-Ordovician strata responded positively to this rapid cooling event and entered the PAZ since ca. 63 Ma. The deep buried samples may be limited affected by climate and water erosion and the accelerated cooling was not obvious in the Late Cenozoic. Collectively, the cooling processes of basement and sedimentary cap in Micangshan-Dabashan tectonic belt were inconsistent. The uplift of the sedimentary area is not completely consistent with that of the basement under thrust and nappe action. The rigid basement was not always continuous and rapidly uplifted or mainly showed as lateral migration in a certain stage because of the different intensities and modes of thrust and nappe action, and the plastic sedimentary strata rapidly uplifted due to intense folding deformation.

Download Full-text