Deciphering the origin of the Cenozoic intracontinental rifting and volcanism in eastern China using integrated evidence from the Jianghan Basin

Intracontinental rifting and low-volume volcanism are a globally common phenomenon, yet the underlying driving mechanisms and whether they can be explained through classic plate tectonic concepts, remain hotly debated. A prominent example is the Cenozoic rift and volcanic province in eastern China. Using an integration of geological, geophysical and geochemical data, we unravel the spatial and temporal variations of the rifting and volcanism in the Jianghan Basin. Both rifting and volcanism in the Jianghan Basin show two intense-to-weak cycles (65–50 Ma and 50–26 Ma, respectively) with significant enhancement in activity during the late rift phase. Moreover, rifting and depocentres progressively migrated eastward. The Jianghan basalts all share an asthenospheric origin while the source of the late phase basalts is slightly more enriched and heterogenous in Nd-Hf isotopes than that of the early phase basalts. The late phase basalts also display a smaller extent of partial melting even under a thinner lithosphere, likely indicating a significant decrease of volatile content in the mantle source. Based on regional tectonic correlations, the main stages of tectonic evolution of the Jianghan Basin and eastern China are not synchronous with changes in Pacific plate motion, while they are coincident with India-Asia collision processes. These observations lead us to propose that the asthenospheric flow driven by India-Asia collision rather than the rollback of the subducted Pacific slab has caused the widespread rifting and volcanism in eastern China. The variations of rifting and volcanism in the Jianghan Basin suggest a multiphase and eastward asthenospheric flow beneath eastern China driven by India-Asia collision, with an intense upwelling when passing through the North-South Gravity Lineament (NSGL). The much more intense rifting and volcanism during the late rift phase may indicate a much larger scale of volatile-poor asthenospheric flow than the early rift phase which could result in a more intense erosion of ancient enriched lithospheric mantle and the volatile content in the mantle source dropping sharply. This study provides an improved model based on our multidisciplinary observations for asthenospheric flow which may be an alternative driving mechanism for intracontinental rifting and low-volume volcanism in the regions where there are step changes in lithospheric thickness globally

Lithology and U–Pb Geochronology of Basement of Cenozoic Yitong Basin in Northeastern China: Implication for Basin Architecture and New Horizon of Deep Natural Gas Exploration

The lithology and formation age of basement rocks are significant for the understanding of the nature of basin architecture, evolution and the potential of hydrocarbons of a basin. In this study, the basement lithology of the Cenozoic Yitong Basin is investigated through the petrological analysis of cores, cuttings, and thin sections. The results suggest that the basement rocks of the Yitong Basin are mostly composed of unique igneous rocks that are different from nearby basins’ sedimentary and metamorphic basement. The igneous rocks are dominated by intrusive monzonite granite and alkali feldspar granite. Additionally, U⁻Pb zircon geochronology of basement samples by LA-ICP-MS and the geological interpretation of apparent resistivity data indicate that the igneous basement in major part of the basin was mainly formed by a lateral intrusion of granite into the Permian sedimentary stratum in the Yanshanian period from 177 to 170 Ma. The results also reveal the two-layer basin architecture with coal-bearing Carboniferous⁻Permian strata below the igneous basement covered with Tertiary sediments, thus providing a new geologic horizon for deep natural gas exploration in the older coal-bearing sedimentary rocks beneath the current igneous basement

3D structure and development of a metamorphic core complex in the northern South China Sea rifted margin

The 3D structure of continental metamorphic core complexes (MCCs) and their co-evolution along with the associated extensional detachments are still not well understood. In this study, analysis of a newly acquired high-resolution 3D seismic reflection volume reveals for the first time a well-imaged MCC in the proximal northern South China Sea (SCS) rifted margin, the Kaiping MCC (KP MCC). These data provide a 3D view of the KP MCC and the associated KP detachment fault. The KP MCC is characterized by ascend of ductile mid-crustal materials, and it is partially exhumated in the KP9 High. The KP detachment fault displays a domed low-angle geometry, and is characterized by pronounced NS-plunging corrugations, among which two mega-corrugations of tens of kilometers are revealed. Evidence show that the KP MCC developed according to the classical rolling-hinge model. A group of secondary normal faults and fractures, which are parallel to the axis of the KP MCC and offset the KP detachment surface at the crest of the MCC, developed in response to inelastic bending during progressive warping of the footwall. The migration of the domal seismic reflection layers provides a visual evidence for the kinematic process of the rolling-hinge activity, during which the brittle-ductile transition (BDT) and the rolling hinge gradually migrate as the detachment fault slips. The origin of the KP MCC in the northern SCS margin is suggested to have been favored by the existence of a pre-existing mid-crustal ductile layer and basement structures within the upper brittle crust

Structures, uplift, and magmatism of the Western Myanmar Arc: Constraints to mid-Cretaceous-Paleogene tectonic evolution of the western Myanmar continental margin

Knowledge of Trans-Himalayan tectono-magmatic evolution is critical to understanding the complex pre-collisional history of southern Eurasia active continental margin. It has been proposed that magmatic rocks of the Trans-Himalayan batholith, extending from southern Tibet to Southeast Asia, are now exposed as the Western Myanmar Arc and Central Granite Belt in Myanmar, yet origin, emplacement, and relationships of the two juxtaposed belts remain poorly constrained. In this study, 2D seismic and drilling data for the Western Myanmar Arc, zircon U-Pb age and Hf isotope and whole-rock geochemical data for magmatic rocks from the arc have been applied. Our seismic profiles, borehole stratigraphic sequences and zircon U-Pb data show that a typical arc-basin system was well developed along the western Myanmar continental margin. The magmatic arc has experienced at least three igneous events in the mid-Cretaceous (110-90 Ma), latest Cretaceous-Early Paleocene (69-64.5 Ma) and Eocene (53-38 Ma), as well as three associated uplift processes in the Late Cretaceous, Eocene and Late Oligocene. Whole-rock geochemical characteristics and zircons showing variable but predominately positive epsilon(Hf)(t) values, suggest a significant juvenile mantle source involving a proportion of ancient subducted sediments and juvenile crustal materials for these typical arc-related magmatic rocks. The identification of mid-Cretaceous to Paleogene magmatic rocks having positive epsilon(Hf)(t) values from the Western Myanmar Arc: 1) indicates that the magmatism can be correlated with the Gangdese arc within the Lhasa terrane of the southern Tibetan Plateau; 2) provides evidence for the proximal-derived model that Paleogene sediments in the Central Myanmar Basin were from the Western Myanmar Arc, but were not delivered by the paleo-Yarlung Tsangpo-lrrawaddy river system from the Gangdese arc; and 3) enables a model of eastward subduction of the Neo-Tethyan/Indian oceanic crust to reflect onset of the magmatism at the mid-Cretaceous and a long-existed back-arc extension in western Myanmar. (C) 2017 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved