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Marine shale reservoirs have experienced intense tectonic movements in southeastern Chongqing, resulting in widely developed folds, faults and bedding slip deformation. The gas content is of a wide range while the organic matter content and thickness are sufficient for shale gas accumulation. Here, we review previous work and present outcrop and core data from 11 shale wells around southeastern Chongqing to analyze and summarize tectonic types and their combinations, as well as their influence on shale gas preservation and enrichment. Fault and bedding slips are prevalent in shale reservoirs, and they apparently influence shale gas content. Bedding slip crush is usually formed at the bottom interval where the total organic content is high from intense horizontal compression. Bedding slip crushing and well-developed high-angle natural fractures form a net fracture system where shale gas is enriched in an anticline structure or lost to air in a syncline structure laterally. Strata dip is the key geological factor that controls bedding slip deformation in shale reservoirs in certain areas. According to the established bedding slip geological model, when bedding slip occurred, the critical strata dips of the lower Silurian Longmaxi Formation were 13.34°, respectively. Bedding slip crushed anticlines without faults and synclines without faults and bedding slip crushing are the two tectonic patterns that are favorable for shale gas preservation and enrichment, which should be the focus of further explorations of lower Paleozoic shale gas in southeastern Chongqing. [ABSTRACT FROM AUTHOR]

The Datong area is located in the western part of the Western Kunlun Orogen (WKO), occupying a key area of the Tethyan domain. Our new SHRIMP U–Pb zircon ages from the Datong area provide new information about the Palaeozoic evolution of the Western Kunlun Orogen. A 473.0 ± 2.8 Ma granite with 493.6 ± 4.8 Ma inherited zircons from the Kusilafu extrusive rocks is interpretation as an A‐type granite formed in a fore‐arc tectonic setting. The 485.5 ± 1.9 Ma granitoid of the Datongdong pluton combined with the 452.7 ± 7 Ma granitoid of the Datong pluton indicate that the Datong pluton is an intra‐oceanic arc complex formed by the southern subduction of the Proto‐Tethyan ocean crust. Zircons from gabbros of the Datong mafic–ultramafic complex have a 499.2 ± 2.1 Ma U–Pb crystallization age. Combined with its complicated whole‐rock geochemistry, we propose that there may have existed a Datong seamount in the early Palaeozoic. The detrital zircon results of Silurian–Devonian sandstones reveal that the Late Silurian sandstones have the characteristic zircons both from the Tarim Block and Datong Arc, suggesting that the Datong arc collided with the Tarim Block in the Late Silurian. The tectonic history of the WKO was characterized by a southern subduction of Proto‐Tethys terminated in the Late Silurian. [ABSTRACT FROM AUTHOR]

The high‐pressure Heilongjiang Complex belongs to a Jurassic accretionary complex in Yilan area, NE China. The complex is located in the junction of three orogenic systems in the NE Asia: the E‐W‐striking Central Asian Orogenic Belt (CAOB), the N‐S‐striking Paleo‐Pacific system, and the ENE‐WSW‐striking Mongol‐Okhotsk system. Thus, a detailed tectono‐metamorphic analysis coupled with accurate radiometric dating of the Heilongjiang Complex provided in this study represent important evidence for understanding the complex interactions between the three orogenic systems in the Late‐Palaeozoic to Mesozoic. New structural and microstructural data combined with the strain analysis highlight the presence of three distinct deformation events affecting the high‐pressure Heilongjiang Complex. The first deformation event D1 is related to development of blueschist facies prolate to plane strain fabrics that were subsequently reworked by the blueschist‐amphibolite facies event D2 that transposed all previous structures by the main west‐dipping schistosity. This planar fabric was folded by upright F3 folds and heterogeneously reworked by greenschist facies E‐W‐striking vertical cleavage during large scale N‐S shortening. Each deformation event was related to specific strain fabrics and metamorphic conditions highlighting dynamic evolution of the subduction complex during burial, exhumation, and final shortening. The first D1 event is related to westward directed prograde constrictional flow and progressive dismembering of competent mafic, ultramafic layers, and quartzites in highly stretched meta‐sedimentary matrix. This mélange was folded by recumbent detachment folds resulting in emplacement of the exhumed unit progressively reaching amphibolite facies conditions atop of W‐WSW‐dipping channel. This event is associated with dominant flattening implying increasing mechanical coupling between the colliding Songliao and Jiamusi blocks. Subsequently, the accreted subduction complex was reworked during N‐S‐directed horizontal shortening. This event was associated with an important post‐buckle flattening of fold limbs and rotation of competent blocks with inherited D1 and D2 strain ellipsoids along F3 fold axes. Our new 40Ar‐39Ar plateau ages on muscovite and phengite (173–177 Ma), together with previous radiometric data, are interpreted as reflecting exhumation of subduction channel during the blueschist‐amphibolite facies event while the N‐S shortening (D3) probably operated in Late Jurassic as indicated by some previously published cooling ages (~140–160 Ma). The westward‐oriented subduction and exhumation fabrics of the high‐pressure Heilongjiang accretionary complex followed by N‐S‐directed upright folding are interpreted to reflect transition from E‐W Pacific subduction regime to N‐S‐directed shortening related to the closure of the Mongol‐Okhotsk Ocean. [ABSTRACT FROM AUTHOR]

The Central Asian Orogenic Belt (CAOB) is regarded to have undergone multiple phases of intracontinental deformation during the Meso-Cenozoic. Located in a key position along the southern CAOB, the Alxa Tectonic Belt (ATB) connects the northernmost Tibetan Plateau with the Mongolian Plateau. In this paper we apply apatite U-Pb and fission track thermochronological studies on varieties of samples from the southwestern ATB, in order to constrain its thermal evolution. Precambrian bedrock samples yield late Ordovician-early Silurian (~ 430–450 Ma) and late Permian (~ 257 Ma) apatite U-Pb ages; the late Paleozoic magmatic-sedimentary samples yield relatively consistent early Permian ages from ~ 276 to 290 Ma. These data reveal that the ATB experienced multiple Paleozoic tectono-thermal events, as the samples passed through the apatite U-Pb closure temperature (~ 350–550 °C). We interpret these tectonic events to record the long-lived subduction-accretion processes of the Paleo-Asian Ocean during the formation of the southern CAOB, with possible thermal influence of the Permian Tarim mantle plume. Apatite fission track (AFT) data and thermal history modelling reveal discrete low-temperature thermal events for the ATB, inducing cooling/reheating through the AFT partial annealing zone (~ 120–60 °C). During the Permian, the samples underwent rapid cooling via exhumation or denudation from deep crustal levels to temperatures < 200 °C. Subsequent thermal events in the Triassic were thought to be associated with the final amalgamation of the CAOB or the closure of the Paleotethys. During the Jurassic-Cretaceous the study area experienced heating by burial, followed by renewed cooling, which may be related with the construction and subsequent collapse of the Mongol-Okhotsk Orogeny, or the Lhasa-Eurasia collision and subsequent slab break-off. These results indicate that the ATB may have been stable after late Cretaceous in contrast to the Qilian Shan and Tianshan. Finally, our results indicate differential exhumation scenario occurred across the southwestern ATB during the Cretaceous. [ABSTRACT FROM AUTHOR]