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• Two phases of deformation occured in the south of the Shangdan suture zone across the Mianyuzui ductile strike-slip fault. • The metamorphic temperature of the early stage of shearing deformation is ∼ 600-700℃ and ∼ 300-500℃ for the late stage. • The subduction of the Shangdan Oceanic lithosphere was active till the Early Silurian, and subsequent collisions occurred during the Late Silurian. The Shangdan suture zone (SDSZ) subdivides the Qinling Orogenic Belt into North Qinling and South Qinling belts, marking the main tectonic boundary between the North China and South China Blocks. The Mianyuzi ductile strike-slip fault (MYZF) within the SDSZ separates the North China Block from the South China Block and contains valuable collisional information. This paper integrates the structural and geochronological data of the MYZF to investigate the Paleozoic tectonic evolution of the Qinling Orogenic Belt and the collision between the North China and South China Blocks. Two phases of deformation (D 1 -D 2a-b) are identified along the southern boundary of the SDSZ. The metamorphic temperature of mylonites is ∼ 600–700 ℃ for the early stage and ∼ 300–500 ℃ for the late stage of shearing deformation. U-Pb zircon analysis of the mylonites and diabase dike in the ductile shear reveals that zircons have major younger protolith populations at 480–460 Ma, 450–430 Ma, and 405–425 Ma, which suggests that rocks were probably derived from the North Qinling belt. The metamorphism and deformation cooling age from the MYZF have been constrained to be 339–328 Ma and 259 ± 1.6 Ma using U-Pb and 40Ar/39Ar dating. Combined with previously published data, we concluded that the subduction of the Shangdan Ocean was active until the Early Silurian and subsequent collisions occurred during the Late Silurian. Meanwhile, the shearing might have been related to the intraplate extension-exhumation during the Carboniferous-Late Permian in the Qinling Orogenic Belt. [ABSTRACT FROM AUTHOR]

[Display omitted] • Depleted continental mantles occur with different mineral chemistry and occurrence. • Mafic dikes were formed from melts via low-degree melting of asthenosphere mantles. • Orthopyroxenites were formed from reaction between SiO 2 -rich melts and peridotites. • Ophiolites were formed in a continental margin that was related to the Meso-Tethys. Whether the ophiolites in the southeast margin of the Gaoligong tectonic belt are related to subduction or rift is hotly debated. The aim of this paper is to present the geological and geochemical data of these ophiolitic blocks in order to understand the significance of these in the tectonic evolution of the Meso–Tethys. The peridotites in the ophiolites are dominantly harzburgites with high Mg# (88.7–92.2) and low Al 2 O 3 (<0.8 wt%) and CaO (<0.5 wt%) contents, and display U-shape chondrite-normalized rare-earth element patterns. However, they show two different groups of mineral chemistries and occurrences. Group I are with olivine Fo 90.6–92.3, orthopyroxene Mg# 91.0–92.6, clinopyroxene Mg# 91.1–93.3, and spinel Cr# 42.1–67.4 and Mg# 62.8–71.6. They exhumed adiabatically and were intruded by mafic dikes from the melts through low-degree melting of asthenospheric mantles and by orthopyroxenites in the Early Jurassic. Group II are with olivine Fo 89.8–95.3, orthopyroxene Mg# 91.3–94.6, and spinel Cr# 62.4–94.1 and Mg# 19.5–51.0. They underwent brittle deformation and medium- to low-temperature fluid replacement. The two group's peridotites have experienced the similar partial melting degrees and are the fragments of subcontinental lithospheric mantles. Extensive continental affinity tholeiites erupted in the Middle Jurassic, coeval with the primary spreading time of the Bangonghu–Nujiang Ocean in the central Tibet. The peridotites, mafic rocks, and marine-facies sediments represent the opening products of the Meso–Tethys in the Jurassic as ophiolites in a continental margin. [ABSTRACT FROM AUTHOR]

[Display omitted] • The depositional age of the Xiufeng Formation was estimated as 159 Ma. • The Mohe Formation has a bidirectional provenance from 150 Ma. • The tectonic setting transformed from compression to extension during 135–128 Ma. • A series of E-W and NE-SW-trending normal faults occurred since the Early Barremian. • The final closure of the Mongol-Okhotsk Ocean has been limited to 150–135 Ma. The Mohe basin is located to the south of the eastern Mongol–Okhotsk suture belt and contains critical stratigraphic records and thrust-nappe structures for understanding the closure of the eastern Mongol–Okhotsk Ocean. This paper discusses the formation ages, provenance, and tectonic setting of the Xiufeng and Mohe formations, and further reveals the timing of the final closure of the Mongol–Okhotsk Ocean and the tectonic evolution of the Mohe basin. The weighted mean 206Pb/238U ages for the youngest zircon of these samples indicate that the maximum depositional ages of the Xiufeng, Mohe and Tamulangou Formations were conservatively estimated at 159 Ma, 150 Ma and 128 Ma, respectively. From Late Triassic to Late Jurassic (150 Ma), the Mongol-Okhotsk Ocean was consumed by bidirectional subduction expressed by subduction under the Siberian Craton and the Erguna Block, respectively. The intense subduction led to the compression of the continental arc and the basement uplift of the Erguna Block, which provided abundant clastic sediments to the Xiufeng-Ershierzhan Formations. During the Late Jurassic-Valanginian (150–135 Ma), the Mongol-Okhotsk Ocean closed rapidly, which finally caused the collision between the Erguna Block and the Siberian Craton. Meanwhile, the southern margin of the Siberian Craton was uplifted and started furnishing sediments into the Mohe-Kaikukang Formations, which may have a bidirectional provenance. The subsequent crustal shortening associated with collision between the Erguna Block and the Siberian Craton led to nappe structures, syn‐collisional folds, and nearly N-S-trending reverse and oblique-slip faults occurred along the northwestern margin of the Mohe basin. Between 135 and 128 Ma, the Mohe basin entered the stage of tectonic setting transformation, which is the crucial period for the Mohe basin to transform from compression to extension. Since the Early Barremian (ca. 128 Ma), the compressional environment was transformed into a post-orogenic extensional tectonic environment, and a series of nearly E-W and NE-SW-trending normal faults occurred, which might have been controlled by the slab rollback of the Paleo-Pacific Plate and detachment of the Mongol-Okhotsk oceanic plate after the closure of the Mongol-Okhotsk Ocean. [ABSTRACT FROM AUTHOR]

Abstract: Despite more than 30 years’ studies in the Yarlung Zangbo Suture Zone (YZSZ), southern Tibet is still a region of discovery and the geological evolution of the Neo-Tethys here remains controversial. In this paper we present the new field observation, petrography, zircon U–Pb dating and geochemistry of the Zhongba mafic rocks in the western segment of the YZSZ. Zircon U–Pb analyses from a diabase using SIMS (Secondary Ion Mass Spectrometry) yielded a concordant age of 125.7±0.9Ma. All the Zhongba mafic rocks exhibit LREE enrichment (LaN/YbN =4.7–15.8) without Eu anomalies (δEu=0.97–1.01). Their Primitive-Mantle-normalized trace element patterns are similar to those of the average OIB and Hawaii alkaline basalts, as well as other OIB-type rocks already reported in the central-western YZSZ. These observations lead us to suggest the existence of a series of seamounts within the Neo-Tethys during the Early Cretaceous. These OIB-type rocks could be originated from (1) hotspot mantle; (2) near-ridge seamounts by melting-induced mixing of two distinct mantle sources; (3) late-stage magmatism fed by melts that originated from an asthenospheric window due to slab delamination. Combining literature data from the entire YZSZ, which include studies of the MORB- and IAB-type rocks and mantle peridotites, we prefer the third explanation that the OIB-type rocks represent a late-stage magmatic activity above an intra-oceanic supra-subduction zone within the Neo-Tethys. [Copyright &y& Elsevier]

Abstract: The Qilian Shan, located in the northern Tibetan Plateau of NW China, has an excellent record of early to middle Paleozoic subduction–accretion that resulted from convergence between the Alax and Qaidam blocks, but there is no consensus about its detailed tectonic history. This paper summarizes its tectonic divisions and discusses its tectonic evolution from the Cambrian to Devonian. The belt has the following tectonic divisions: In the far north the southern passive margin of the Alax block is juxtaposed against an early Cambrian to Ordovician, Marianan-type intra-oceanic arc (North Qilian). The North Qilian arc is separated from a Japanese-type arc (Central Qilian) to the south by a high-pressure metamorphic belt composed mostly of ophiolitic slices and oceanic crusts. The Central Qilian is bounded to the south by a wide mélange zone (South Qilian), consisting of ophiolitic slices and continental margin sequences. Farther to the south lies the Oulongbuluk microcontinent that is separated from the Qaidam block and farther south by an ultrahigh-pressure metamorphic belt. Tectonostratigraphic analysis, together with geochemical, geochronological, and geophysical data, indicates a complex evolution by subduction–accretion processes from the Cambrian to the Devonian before final amalgamation and docking to the northern Alax block. This model solves the long-lasting discussion on the polarity of subduction in Paleozoic time; this multiple subduction–accretion history sheds light on the continuity of Paleozoic sutures along the Qilian Shan and the nature of the Altyn Tagh fault, and thus contributes to an improved understanding of the tectonic architecture of Central Asia. [Copyright &y& Elsevier]

• Three magnetotelluric profiles were obtained at the western margin of Songliao Basin. • Two low-resistivity strips with opposite dips are developed in this region. • The Nenjiang-Balihan fault is arranged in en echelon pattern in the plane. • The formation of Nenjiang–Balihan fault was controlled by two main tectonic events. Located in the famous gravity gradient belt ranging from the Mt. Great Xing'an through Mts. Taihang and Wuling in East China, the Nenjiang-Balihan (NJBLH) fault is important for the understanding of the formation and evolution of Mesozoic and Cenozoic basins in NE China. The distribution and deep structure of the middle and northern segments of this fault are poorly known because of thick sedimentary cover. In this paper, an electrical structure across the western margin of the Songliao Basin and eastern margin of the Great Xing'an Range is revealed on the basis of three magnetotelluric (MT) sounding survey profiles. The results show the development of a low-resistivity layer (L2) and two low-resistivity strips with opposite dip (L1 and L3) in the lower portion of the small-scale basins or sags. The west-dipping low-resistivity strip L1 is considered to be the trace of a paleo-suture zone. The transverse low-resistivity layer L2 may reflect the Palaeozoic sedimentary strata in the basin, and the east-dipping low-resistivity strip L3 represents the NJBLH fault, the presence of which exhibits a gentle sloping tendency from the shallow to the deep portion of the fault cut through the Moho. The NJBLH fault is segmented on the plane, with an overall left-slip NE-trending en echelon arrangement. Presumably, the NJBLH fault began to form during the Jurassic under the influence of the closure of the Mongolia–Okhotsk Ocean in the northwest, and the fault subsequently experienced left-lateral strike-slip movements due to the NW-trending subduction of the Paleo-Pacific Izanagi Plate toward the Eurasian Plate. [ABSTRACT FROM AUTHOR]