Uplift and exhumation in the Tianshan,western China:New insights from detrital zircon morphology and thermochronology

The Tianshan in western China is rich in ore resources,but its tectonic uplift and exhumation history closely related to the resource exploration is still controversial.This study provides a new strategy to uncover the tectonic uplift processes in southern Tianshan by combining the morphological characteristics and thermochronological ages of detrital zircons in the Tarim Basin.The morphology of the Meso-Cenozoic detrital zircons in the Kuqa Foreland Basin,a secondary tectonic unit of the Tarim Basin,is dominated by three types of P,S,and G,and their average alkaline and temperature indexes are 668.0-677.2 and 347.6-413.5,respectively.Moreover,the U-Pb ages of these detrital zircons are primarily divided into two groups of 270-330 and 380-470 Ma.These features indicate that the Early Carboniferous-Early Permian and Middle Ordovician-Middle Devonian alkaline granites distributed in the South Tianshan and southern Central Tianshan were the main sources of the detrital zircons in the Kuqa Foreland Basin.The decomposition of the detrital zircon fission track ages further reveals that the provenances of the Kuqa Foreland Basin primarily consisted of the southern Central Tianshan,the eastern South Tianshan,and the central South Tianshan during Meso-Cenozoic.Among them,the eastern South Tianshan played a dominant role in the material supply.The synthesis of the decomposed zircon fission track(ZFT)ages and the lag-time evolution pattern indicated that the South Tianshan and the southern Central Tianshan mainly experienced five stages of tectonic uplifting that occurred in the Devonian,the Permian,the Middle Triassic-Middle Jurassic,the Cretaceous,and since the Miocene,respectively.They were related to the subduction of the South Tianshan Ocean northward to the bottom of the Central Tianshan,the compression and accretion after the closure of the South Tianshan Ocean,and a series of collisions between the Qiangtang-Lassa-India plates and the southern margin of the Eurasia plate in the Meso-Cenozoic,respectively.This study provides a new provenance analysis method,which was successfully applied in the Tianshan,and also develops a new way to study Central Asia’s tectonic evolution.

Detrital zircon U-Pb geochronology and geochemistry of the Riachuelos and Palma Sola beach sediments,Veracruz State,Gulf of Mexico:a new insight on palaeoenvironment

Zircons are abundant in the beach sediments.In this study,surface microtexture,mineralogy,bulk sediment geochemistry,trace element composition and U−Pb isotopic geochronology of detrital zircons collected from the Riachuelos and Palma Sola beach areas,southwestern Gulf of Mexico were performed to infer the sediment provenance and palaeoenvironment.The zircon microtexture was categorized as mechanically-and/or chemically-induced features.The weathering index values for the Riachuelos(~72−77)and Palma Sola(~71−74)beach sediments indicated moderate weathering of both of the two source areas.The major and trace element data of bulk sediments suggested passive margin settings for the two areas.The trace elemental ratios and chondrite-normalized rare earth element(REE)patterns of bulk sediments revealed that the sediments were likely sourced by felsic and intermediate igneous rocks.And the zircon Th/U ratios(mostly more than 0.2)and zircon REE patterns(with negative Eu and positive Ce anomalies)suggested a magmatic origin for both of the beach sediments from these two areas.Two distinct zircon age peaks respectively belonging to the Paleozoic and the Cenozoic were identified both in the Riachuelos and Palma Sola beach sediments.Zircon geochronology comparison research between the Riachuelos−Palma Sola beach sediments and potential source areas in SW Gulf of Mexico revealed that the source terrane supplied the Paleozoic zircons of this study was identified as the Mesa Central Province(MCP),and the Cenozoic zircons were transported from the nearby Eastern Alkaline Province(EAP).Moreover,although the Precambrian zircons were very few in the studied sediments,their geochronology and geochemistry results still could infer that they were contributed by the source terranes of Grenvillian igneous suites in the Oaxaca and the Chiapas Massif Complexes.