Provenance Variability of the Triassic Strata in the TurpanHami Basin: Detrital Zircon Record of Indosinian Tectonic Reactivation in the Eastern Tianshan

The Triassic strata in the Turpan-Hami Basin potentially chronicled the missing sedimentary record of Indosinian tectonic evolution in the Eastern Tianshan.In this study,we conducted detrital zircon U-Pb geochronological analyses on subsurface Triassic samples collected from the Turpan-Hami Basin to unravel sedimentary response of Indosinian tectonic reactivation and its geodynamics.The detrital zircon age spectra of the Triassic samples are quite different,reflecting significant provenance variability.The zircon grains in the Lower Triassic sample were mainly from the Central Tianshan,while the Jueluotag acted as a minor provenance.By contrast,the Late Paleozoic rocks in Jueluotag act as the main provenance for the Middle-Upper Triassic samples,while the Central Tianshan acted as a minor provenance.Furthermore,zircon grains in the Middle Triassic sample were mainly from the Permian rocks in Jueluotag,while Indosinian strike-slipdriven rapid exhumation brought deeper Carboniferous rocks of Jueluotag as an important age population for the Upper Triassic sample.The inter-sample variability of age spectra of the Triassic samples provides sedimentary evidence for Indosinian tectonic reactivation in the Eastern Tianshan and its periphery,which could be attributed to differential exhumation of different sources driven by coeval strike-slip tectonics along deep faults.The Indosinian tectonic behavior in the Eastern Tianshan,which is characterized by partial melting of the pre-thickened crust and strike-slip deformation,acted as a far-field respond to the coeval continental accretion occurring along the southern Eurasian margin.Additionally,our new detrital zircon data,together with previously published data in the Turpan-Hami Basin,demonstrate that there are significant changes in source-to-sink system from the Permian to the Triassic,suggesting that the Permian-Triassic unconformity in the Eastern Tianshan and its periphery was generated by Late Permian-Early Triassic tectonic contraction and inversion rather than an increasingly arid climate.

New insights from low-temperature thermochronology into the tectonic and geomorphologic evolution of the south-eastern Brazilian highlands and passive margin

The South Atlantic passive margin along the south-eastern Brazilian highlands exhibits a complex landscape,including a northern inselberg area and a southern elevated plateau,separated by the Doce River valley.This landscape is set on the Proterozoic to early Paleozoic rocks of the region that once was the hot core of the Aracuai orogen,in Ediacaran to Ordovician times.Due to the break-up of Gondwana and consequently the opening of the South Atlantic during the Early Cretaceous,those rocks of the Araquai orogen became the basement of a portion of the South Atlantic passive margin and related southeastern Brazilian highlands.Our goal is to provide a new set of constraints on the thermo-tectonic history of this portion of the south-eastern Brazilian margin and related surface processes,and to provide a hypothesis on the geodynamic context since break-up.To this end,we combine the apatite fission track(AFT)and apatite(U-Th)/He(AHe)methods as input for inverse thermal history modelling.All our AFT and AHe central ages are Late Cretaceous to early Paleogene.The AFT ages vary between 62 Ma and90 Ma,with mean track lengths between 12.2μm and 13.6μm.AHe ages are found to be equivalent to AFT ages within uncertainty,albeit with the former exhibiting a lesser degree of confidence.We relate this Late Cretaceous-Paleocene basement cooling to uplift with accelerated denudation at this time.Spatial variation of the denudation time can be linked to differential reactivation of the Precambrian structural network and differential erosion due to a complex interplay with the drainage system.We argue that posterior large-scale sedimentation in the offshore basins may be a result of flexural isostasy combined with an expansion of the drainage network.We put forward the combined compression of the Mid-Atlantic ridge and the Peruvian phase of the Andean orogeny,potentially augmented through the thermal weakening of the lower crust by the Trindade thermal anomaly,as a probable cause for the uplift.