Elucidating tectonic events and processes from variably tectonized conglomerate clast detrital geochronology: Examples from the Permian Hongliuhe Formation in the southern Central Asian orogenic Belt, NW China

Abstract

This article expands upon detrital zircon geochronology with a sampling and analysis strategy dating variably tectonized granitoid conglomerate clasts. Its purpose is to elucidate details of the provenance's tectonomagmatic history from deformation-relative age distributions. The method involves bulk samples of clasts, sorted based on the degree of internal ductile deformation. Isolating granitoid clasts, we divide them into three subsets: undeformed, slightly deformed, and deformed. Laser ablation, inductively coupled plasma mass spectrometry U-Pb geochronology is performed on zircon separates of each subset. Our case study, involving the Permian Hongliuhe Formation in the southern Central Asian Orogenic Belt, analyzes each of the three clast subsets, as well as sandstone detrital samples, at three stratigraphic levels and yields a profile of the unroofed provenance. Clast age distributions exhibit different, wider-age spectra than sandstone samples, an effect of proximity to the respective provenance. They indicate a minimal lag time, implying rapid exhumation rates, whereas sandstone data alone would indicate a 90 Myr lag time. Early Paleozoic arc-building episodes appear as Ordovician peaks in sandstone data and Silurian-Devonian peaks in clast data, indicating a younging of magmatism toward proximal provenance. A magmatic hiatus starts in the Devonian, correlating with the latest age of deformed clasts, interpreted as timing of collisional tectonics. The detailed age spectra provide regional tectonic context and interpretation of processes, as well as more robust provenance interpretation than could be determined from sandstone samples alone. The variably tectonized clast detrital geochronology method removes human sampling bias and the practical limits of studying regional granitoid distributions.

The Dashui Subduction Complex in the Eastern Tianshan‐Beishan Orogen (NW China): Long‐Lasting Subduction‐Accretion Terminated by Unique Mid‐Triassic Strike‐Slip Juxtaposition of Arcs in the Southern Altaids

“…The strata are characterized by many poorly sorted granitoid, gneissic, schistose, and limestone pebbles with boulder diameters in the conglomerate in the northern part. The ages of deformed and undeformed granitoid pebbles are given as Early Paleozoic and Late Paleozoic ages (Cleven et al., 2016). To the south, the lithologies change to pebbly sandstones with crude parallel or sub‐parallel bedding, lithic greywacke–arkoses, and mudstones.…”