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There has been no consensus yet regarding the precise initial timing and duration of the late Mesozoic extensional tectonics in the South‐eastern China Block. This work focusses on the growth strata of the Early Cretaceous red beds in the South‐eastern China Block to determine the late Mesozoic tectonics and the precise timing of the initiation and duration of extensional tectonics in this area. Field observation of several terrigenous basins shows that the dip angles of the Cretaceous red beds have varied from moderate to gentle from basin edges to interiors (or centres). The visible and estimated thickness within a single bed increases slightly downwards from the upper to the lower part. These characteristics indicate that the sedimentary area of these beds has undergone an extensional process with expansion and deepening of the sedimentary basins. Rotation of the border surfaces (limbs) and downward warping of the hanging walls or retreat of the footwalls of listric normal faults causes three types of extensional growth (or syntectonic) strata in the deposits of different basins. Dating of the volcanic rocks related to the growth beds reveals that the sedimentary basins were enlarged and deepened when the Early Cretaceous strata were deposited in the South‐eastern China Block from ca 140 to 137 Ma. Regionally, under the influence of Palaeo‐Pacific plate rollback since ca 140 Ma, the South‐eastern China Block stress field has led to lithospheric uplift and pull‐apart structures near the surface, causing the half‐graben basins to receive sedimentation. Although the extensional event was interrupted by a short compressional event during 120 to 105 Ma, with the oceanward retreat of the trench, the area of extension gradually enlarged and rejuvenated south‐eastwards until the end of the Cretaceous. This Cretaceous extension event of the South‐eastern China Block must belong to a worldwide geological event with global significance. [ABSTRACT FROM AUTHOR]

The final closure time of the Paleozoic ocean in the Eastern Tianshan is debated, and the geotectonics are still poorly constrained; hence, research on late Paleozoic igneous rocks has important implications for the evolutionary processes involved in this area's tectonic history. However, limited attention has been given to the volcanic rocks in the late Paleozoic strata across the Eastern Tianshan because of their rarity and identification difficulty. This article focuses on the key site of an accretionary orogen in Central Asia, the Kalatage (Shaerhu)-Dananhu–Lop Nur area, to promote the study of tectonomagmatic evolution. The interbedded volcanic rock layers in late Paleozoic strata, including volcanic edifice deposits, are mainly rhyolitic volcanic, andesitic/dacitic, and basaltic rocks. These felsic, intermediate, and mafic rocks have zircon laser ablation ICP-MS U-Pb ages of 362.5–303 Ma. Geochemically, all samples have similar primitive mantle–normalized trace-element spider diagrams and chondrite-normalized rare earth element plots. The felsic and intermediate volcanic rocks are classified as I-type rocks and formed in a volcanic arc, and the mafic rocks belong to the tholeiite series and formed in island arc (earlier) and intraplate (later) settings. By the time the mafic rocks with intraplate basalt characteristics formed at 303 ± 13 Ma, the Paleo-Asian Ocean had completely closed, and the region had entered the intraplate evolution stage. On the basis of other findings regarding the ages of igneous rocks and synthetic analysis, the northward subduction of the Paleo-Asian oceanic slab can preferably explain the relationship between the distinctive tectonic environment and the age variation trend in the study area. The process generated subduction-, collision- and postcollision-related magmatism from the Devonian to the late Carboniferous, and after 310 Ma, the Kalatage-Dananhu–Lop Nur area synchronously underwent a tectonic transition from subduction and collision to an intracontinental environment. [ABSTRACT FROM AUTHOR]

The widespread Late Devonian-Middle Carboniferous volcanic rocks in the Chinese Western Tianshan provide important constraints on the subduction history of the South Tianshan oceanic lithosphere. Here, we investigate the basalt, basaltic andesite, andesite, trachyandesite, and rhyolite from the Dahalajunshan Formation from Western Tianshan. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U-Pb zircon geochronology constrains their age of formation to between 376 and 333 Ma (i.e., Late Devonian-Middle Carboniferous) with distinct variation in space (from west to east) and time (from early to late). Based on geochemical, zircon geochronological, and Sr-Nd isotopic data, we demonstrate that the Dahalajunshan volcanic was generated in a continental arc setting associated with the subduction of the south Tianshan Ocean during Late Devonian to Middle Carboniferous. The volcanic rocks belonging to Dahalajunshan Formation in the northwestern part of the Yili Block suggest that the northward subduction of the south Tianshan Ocean was initiated in the Early Devonian; those in the southern and eastern part of the Yili Block were probably produced by a northward subduction of South Tianshan Ocean during Late Devonian to Middle Carboniferous. [ABSTRACT FROM AUTHOR]

Large-scale volcanism in the late Mesozoic was a prominent geological event in southeast China. The late Mesozoic volcanic sequences, named the Moshishan Group, are exposed in Zhejiang Province and are predominantly felsic in composition with subordinate mafic magma and rare andesites. To understand the late Mesozoic tectonic evolution of southeast China, we present zircon U–Pb dating, major and trace element analyses, and Hf isotopic compositions from felsic volcanic rocks of the Moshishan Group. Zircon U–Pb dating shows that the Moshishan Group formed between 145 and 129 Ma. The εHf(t) of the analysed zircons ranges from −16.58 to +6.89, and theTDM2age ranges from 753 to 2238 Ma with a major peak at ca. 1870 Ma. Hf isotopic compositions of zircons in Early Cretaceous volcanic rocks are more radiogenic than that of the metamorphic basement rocks, indicating a juvenile component in these magmas. Major element concentrations show that the volcanic rocks mainly belong to the high-K calc-alkaline series. Both zircon saturation temperatures and the εHf(t) values of zircons gradually increased with the evolution of the magma. Trace element data indicates that neither magmatic differentiation of mantle-derived magma nor mixing of magmas from different sources were the predominant magmagenetic processes. Earlier studies suggest that contemporaneous underplating contributed to the heat source that induced crustal melting and to the material origin that inconsistently mixed with the local crustal melts. Magmatic underplating is likely to have occurred because of the southwestward subduction of the Pacific plate with episodic slab rollback. The data obtained in this study suggest that the crust–mantle interaction under the influence of slab rollback played a progressive role in the formation of Early Cretaceous felsic volcanic rocks in southeast China. [ABSTRACT FROM AUTHOR]

Abstract: New geochemical and isotopic data are reported from Cretaceous volcanic rocks of the Ganhang Tectonic Belt, southeast China. Two periods of basaltic eruptions (143±1.1–139±0.7Ma and 105–98Ma), each representing results of previous tectonic events, are recognized in the belt. Rock types associated with the eruptions are significantly different in mineral and chemical composition. For the 143±1.1–139±0.7Ma basalts, 87Sr/86Sr ratio (0.7041–0.7048) and Sm–Nd isotopic compositions (ɛNd =+3.78 to +4.38) suggest that the magma came from the depleted mantle and had not mixed with crustal material. During the second episode of magmatic and tectonic activities (105–98Ma), volcanism was accompanied by intense regional extension and the development of a series of “red basins”. The geochemical characteristics of these basalts exhibit both tholeiite and alkaline olivine-types, indicating inhomogeneous mixing of magma with crustal material. The tholeiites have a medium–high 87Sr/86Sr ratio (0.7054–0.7070) and a low ɛNd value (1.69–0.70), indicating that the magma of these basalts came from an unchanged mantle. The alkaline olivine basalts, on the other hand, have a relatively higher 87Sr/86Sr ratio (0.7076–0.7080) and a relatively lower value of ɛNd (−6.43 to −5.18), suggesting that these magmas came from mantle enriched by mixing with subducted crustal material. Based on comprehensive geological analyses, it is concluded that an extensional environment existed in the region from early in the Early Cretaceous, and the Ganhang Belt represents the main rift zone in southeast China during much of the Early Cretaceous. [Copyright &y& Elsevier]