LATE TRIASSIC OBLIQUE EXTRUSION OF UHP/HP COMPLEXES IN THE ATBASHI ACCRETIONARY COMPLEX OF SOUTH TIANSHAN, KYRGYZSTAN

The exhumation and tectonic emplacement of eclogites and blueschists take place in forearc accretionary complexes by either forearc- or backarc-directed extrusion, but few examples have been well analysed in detail. Here we present an example of oblique wedge extrusion of UHP/HP rocks in the Atbashi accretionary complex of the Kyrgyz South Tianshan.The exhumation and tectonic emplacement of eclogites and blueschists take place in forearc accretionary complexes by either forearc- or backarc-directed extrusion, but few examples have been well analysed in detail. Here we present an example of oblique wedge extrusion of UHP/HP rocks in the Atbashi accretionary complex of the Kyrgyz South Tianshan

ZIRCON U-PB AND HF ISOTOPIC STUDY OF THE KAWABULAKE OPHIOLITE EASTERN TIANSHAN: IMPLICATION FOR THE TECTONIC EVOLUTION OF CAOB

The Eastern Tianshan belt, located in the southern CAOB, played an important role in the crustal evolution, particularly because it links the Southern Tianshan suture to the west with the Inner Mongolia Solonker suture to the east. However, some critical issues, such as the exact position and formation age of the final suture zone of the Paleo-Asian ocean are still obscure or in controversy. Thus, here we have performed detailed studies of the Kwabulake ophiolit zone, a key part of the southern suture of the CAOB. New LA- ICPMS zircon U–Pb ages, Hf isotopic values, and whole-rock geochemical data have been presented to: (1) constrain the age of the Kawabulake ophiolite, (2) understand the petrogenesis of the granodiorites and their tectonic setting, and (3) reveal their implications for geodynamics of the Eastern Tianshan belt.The Eastern Tianshan belt, located in the southern CAOB, played an important role in the crustal evolution, particularly because it links the Southern Tianshan suture to the west with the Inner Mongolia Solonker suture to the east. However, some critical issues, such as the exact position and formation age of the final suture zone of the Paleo-Asian ocean are still obscure or in controversy. Thus, here we have performed detailed studies of the Kwabulake ophiolit zone, a key part of the southern suture of the CAOB. New LA- ICPMS zircon U–Pb ages, Hf isotopic values, and whole-rock geochemical data have been presented to: (1) constrain the age of the Kawabulake ophiolite, (2) understand the petrogenesis of the granodiorites and their tectonic setting, and (3) reveal their implications for geodynamics of the Eastern Tianshan belt

Regeneration Through in vivo Cell Fate Reprogramming for Neural Repair

The adult mammalian central nervous system (CNS) has very limited regenerative capacity upon neural injuries or under degenerative conditions. In recent years, however, significant progress has been made on in vivo cell fate reprogramming for neural regeneration. Resident glial cells can be reprogrammed into neuronal progenitors and mature neurons in the CNS of adult mammals. In this review article, we briefly summarize the current knowledge on innate adult neurogenesis under pathological conditions and then focus on induced neurogenesis through cell fate reprogramming. We discuss how the reprogramming process can be regulated and raise critical issues requiring careful considerations to move the field forward. With emerging evidence, we envision that fate reprogramming-based regenerative medicine will have a great potential for treating neurological conditions such as brain injury, spinal cord injury (SCI), Alzheimer's disease (AD), Parkinson's disease (PD), and retinopathy

P-wave velocity structure and implications for magmatism and metallogenesis in the southern Altaids: Constraint from wide-angle seismic data along the Altai-Eastern Tianshan traverse

Altaids in the Central Asian Orogenic Belt (CAOB) is one of the world’s largest orogenic belts containing mineral deposits. Together with the Junggar terrain they open an important window to study the Paleozoic tectonic evolution of the CAOB. In this paper, we analyze a 637-km-long wide-angle refraction/reflection seismic profile across the Altai-Eastern Tianshan orogenic belt in the southern Altaids, conducted in September 2018 using 10 large explosive charges fired in drilled holes. We use a traveltime inversion method to reconstruct the lithospheric P-wave velocity structure along the profile. The lithosphere is composed of a 43-55-km-thick crust, a ∼10-km-thick crust-mantle transition layer beneath the Altai Mountain, and a ∼25-km-thick layer of lithospheric mantle. The results clearly reveal: a prominent Moho uplift beneath the Yemaquan Island Arc, two major crustal-scale low-velocity anomalies (LVAs) beneath the Yemaquan Arc and Bogda Mountain, and three high-velocity anomalies (HVAs) near the surface around the Kalatongke, Yemaquan and Kalatage mining areas. We hypothesize that the subduction of the Paleo-Asian Ocean occurred with strong mantle upwelling. We suggest that continued compression of the Paleo-Asian Ocean causes the delamination of lithosphere, as well as asthenospheric material upwelling and magma underplating into the crust. Consistently, Paleozoic mafic-ultramafic rocks and mantle-derived minerals related to gold, copper and nickel deposits, are widely extended in the area. Our results show that the P-wave velocity-depth curves for deeper depths (>30 km) in the southern Altai and Junggar Basin are close to those of the continental arcs and global continent average. Despite powerful Paleozoic subduction activity, orogeny and volcanism strongly modified the lower crust in the region, part of ancient continental crust was still preserved below the southern Altai and Junggar Basin. In addition, the upper part (depth 5–30 km) of the velocity-depth curve for the Junggar Basin is close to that of the Costa Rica volcanic front and the British Columbia accreted terrain, suggesting that Paleozoic orogenic activity has intensively reconstructed the upper-middle crust beneath the Junggar Basin

Ordovician 40Ar/39Ar phengite ages from the blueschist-facies Ondor Sum subduction-accretion complex (Inner Mongolia) and implications for the early Paleozoic history of continental blocks in China and adjacent areas

We obtained 453.2 ± 1.8 Ma and 449.4 ± 1.8 Ma (2{sigma}) laser step-heating 40Ar/39Ar plateau ages for phengite from quartzite mylonites from the blueschist-facies Ondor Sum subduction-accretion complex in Inner Mongolia (northern China). These ages are within error of the inverse isochron ages calculated using the plateau steps and the weighted mean ages of total fusion of single grains. The compositional change from glaucophane in the cores to crossite in the rims of blue amphiboles, as revealed by electron microprobe analysis, points to decompression, probably caused by progressive exhumation of the subducted material. The Late Ordovician ages were not affected by excess argon incorporation because in all likelihood the oceanic sediments were wet on arrival at the trench and free of older detrital mica. The ca. 450 Ma ages are, hence, interpreted as the time of crystallization during mylonitization under high fluid activity at fairly low temperatures. This means that accretion of the quartzite mylonite unit occured about 200 Ma before final closure of the Paleo-Asian Ocean, amalgamation of the Siberian, Tarim and North China cratons, and formation of the end-Permian Solonker suture zone. We argue that the Early Paleozoic evolution of the Ondor Sum complex occurred along the northeastern Cimmerian margin of Gondwana, which was composed of micro-continents fringed by subduction-accretion complexes and island arcs. The later evolution took place during the building of the Eurasian continent following middle Devonian and younger rifting along the East Gondwanan margin and northward drift of the detached North China craton. An extensive review shows that this type of two-stage scenario probably also applies to the geodynamic evolution of other micro-continents like, South China, Tarim, a number of Kazakh terranes, Alashan, Qaidam and Kunlun, as well as South Kitakami and correlatives in Japan, and probably Indochina. Like the North China craton, these were bordered by Early Paleozoic subduction-accretion complexes, island arcs or contained calc-alkaline volcanic margins, like for example, the central Tienshan, North Qinling, North Qaidam-Altun, North Qilian and Kunlun belts in China, as well as the Oeyama and Miyamori ophiolites and Matsugadaira-Motai blueschist belt of Japan and the dismembered Sergeevka ophiolite of the southern part of the Russian Far East. This implies that a vast orogenic system, comprising an archipelago of micro-continents, seems to have existed along the Cimmerian margin of East Gondwana in Early Paleozoic time in which the ultrahigh-pressure metamorphism that characterizes the early evolution of many of the Asian micro-continents occurred

The p53 Pathway Controls SOX2-Mediated Reprogramming in the Adult Mouse Spinal Cord

Although the adult mammalian spinal cord lacks intrinsic neurogenic capacity, glial cells can be reprogrammed in vivo to generate neurons after spinal cord injury (SCI). How this reprogramming process is molecularly regulated, however, is not clear. Through a series of in vivo screens, we show here that the p53-dependent pathway constitutes a critical checkpoint for SOX2-mediated reprogramming of resident glial cells in the adult mouse spinal cord. While it has no effect on the reprogramming efficiency, the p53 pathway promotes cell-cycle exit of SOX2-induced adult neuroblasts (iANBs). As such, silencing of either p53 or p21 markedly boosts the overall production of iANBs. A neurotrophic milieu supported by BDNF and NOG can robustly enhance maturation of these iANBs into diverse but predominantly glutamatergic neurons. Together, these findings have uncovered critical molecular and cellular checkpoints that may be manipulated to boost neuron regeneration after SCI

Contrasting P-T-t-d paths of the polycyclic Palaeozoic tectono-metamorphic event in the Southern Chinese Altai: an example from Kalasu area

To understand the polycyclic Palaeozoic tectono-metamorphic evolution of the Southern Chinese Altai, petrological and structural studies together with thermodynamic modelling and dating were carried out in the Cambro-Ordovician metapelitic sequence of the Kalasu area. The sequence is divided into upper, middle and lower crustal orogenic levels according to their metamorphic grade and structural patterns. Metamorphism increases from low to high-grade towards the deeper crustal levels with garnet-biotite schists in the upper crustal level, sillimanite-garnet and staurolite-garnet-sillimanite schists and gneisses in the middle crustal level, and cordierite-sillimanite-K-feldspar migmatites in the lower crustal level. Structural succession involves a subhorizontal S1 foliation folded by NE-SW open to tight and upright F2 folds (with no metamorphism associated), reworking by an orthogonal D3 deformation, characterized by NW-SE open to close F3 folds with moderately plunging axes, steeply dipping S3 axial planes and S3 cleavage. Early Devonian calc-alkaline granitoids intruded the sequence parallel to S1 foliation, whereas Permian undeformed gabbroic bodies were emplaced in the lower crust and granites in the upper crust coevally with D3. The P-T-t-d paths indicate that the crystalline rocks underwent a clockwise evolution marked by Early Devonian burial associated with heating, followed by Permian decompression, in agreement with studies from other parts of the Chinese Altai. The burial is recorded in the middle and lower levels by the presence of g-st-ky-ru relics within the S1 fabric. This stage is related to crustal thickening, whereas heating is related to intrusions of Devonian granite sheets during an extensional setting. A subsequent decompression (around 3-5 kbar) is recorded in all crustal levels, associated with intrusions of gabbro and granite along the southern border of the Chinese Altai and coeval with the last Permian deformation. This last stage is related to the collision between the Junggar arc system and the Chinese Altai orogenic belt

Post-collisional magmatism associated with the final closure of the Rushan-Pshart Meso-Tethys Ocean in Pamir, Tajikistan: Inference from Cretaceous igneous rocks of the Pshart accretionary complex

The Pamir orogen was formed by the subducted accretion and amalgamation of Cimmerian terranes from the northern margin of Gondwana with the southern margin of Eurasia. The Mesozoic magmatic rocks are widespread in Pamir and record the tectonic evolution in different stages. The Rushan–Pshart suture zone represents an ancient ocean between Central and Southern Pamir. This paper reports the petrography, geochronology, and geochemistry of Cretaceous granites and diabase dikes that intrude into the Pshart complex. The granites were emplaced between 124 and 118 Ma, based on their zircon U-Pb ages. These granites are characterized by high-K calc-alkaline, low magnesian, and high SiO2, A/CNK, and K2O+Na2O values. They also display strong depletion of Ba, Sr, Eu, and Ti and comparatively weak negative Nb anomalies in spidergrams. Thus, we proposed in this study that these are highly fractionated, strongly peraluminous S-type granites. They were generated by the partial melting of the metasedimentary rocks in the plagioclase stability field and underwent subsequent fractional crystallization during their ascent. The diabase dikes contain low SiO2, and high MgO levels and negative Nb and Ta anomalies, which were interpreted to form in an extensional environment. Late Jurassic–Early Cretaceous closure of the Rushan–Pshart Ocean and subsequent foundering of its oceanic lithosphere caused local extension and upwelling of the asthenospheric mantle. The underplating of mafic magma provided a heat source to melt the metasedimentary-derived granitic that formed in the initial post-collisional environment. The subsequent local extension caused the emplacement of diabase dikes. Based on our new data and combined with data from previous studies, we concluded that the Rushan–Pshart suture zone is the remnant of the Meso-Tethys Ocean and may represent the western continuation of the Bangong–Nujiang suture of the Tibetan Plateau

Mesozoic-Cenozoic Topographic Evolution of the South Tianshan (NW China): Insights from Detrital Apatite Geo-Thermochronological and Geochemical Analyses

The present-day topography of Tianshan is the product of repeated phases of Meso-Cenozoic intracontinental deformation and reactivation, whereas the long-term Mesozoic topographic evolution and the timing of the onset of Cenozoic deformation remain debated. New insights into the Meso-Cenozoic geodynamic evolution and related basin-range interactions in the Tianshan were obtained based on new detrital single-grain apatite U-Pb, fission-track, and trace-element provenance data from Mesozoic sedimentary sequences on the northern margin of the Tarim Basin. Detrital apatite U-Pb age data from Early-Middle Triassic clastic rocks show two prominent age populations at 500–390 Ma and 330–260 Ma, with a paucity of ages between 390 and 330 Ma, suggesting that sediment source is predominantly from the northern Tarim and South Tianshan. From the Late Triassic to Early Jurassic, the first appearance of populations in the 390–330 Ma and 260–220 age ranges indicates that the Central Tianshan-Yili Block and Western Kunlun Orogen were source regions for the northern margin of Tarim Basin. In the Cretaceous strata, south-directed paleocurrents combined with the decrease in the 390–330 Ma age population from the Central Tianshan-Yili Block imply that South Tianshan was uplifted and again became the main source region to the Baicheng-Kuqa depression during the Cretaceous. Our new apatite fission-track data from the southern Chinese Tianshan suggest that rapid cooling commenced at c. 30 Ma along the southern margin, and the Early Mesozoic strata exposed on the southern flank of the Tianshan underwent c. 4–5 km of late Cenozoic exhumation during this period. This age is approximately synchronous with the onset of exhumation/deformation not only in the whole Tianshan but also in the interior of the Tibetan Plateau and its margins. It suggests that far-field, N-directed shortening resulting from the India-Asia collision was transmitted to the Tianshan at that time