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The Jiutai area is tectonically situated at the eastern segment of the Central Asian Orogenic Belt (CAOB) and is close to the North China Craton (NCC) to the south, serving as an ideal place to investigations of the closure of the Paleo‐Asian Ocean (PAO). Sandstone samples collected from the Yangjiagou Formation and the Lujiatun Formation in this area have been studied in detail in terms of petrology, geochronology and geochemistry. The maximum depositional time of the Yangjiagou and Lujiatun formations has been constrained to early Middle Triassic (ca. 245 Ma) and middle Late Triassic (ca. 219 Ma), respectively. The Yangjiagou Formation, with a major provenance of dissected island arcs, is dominantly composed of Phanerozoic sediments from Northeastern China (NE China) massifs. The Lujiatun Formation, with major sediments from active continental margins, has a relatively larger proportion of Precambrian sediments, in which the ∼1.85 Ga and ∼2.5 Ga sediments are typical of the crystalline basements of the NCC and NE China massifs, which were uplifted and eroded during the closure of the PAO. Besides, both formations show the enrichment in LREEs and the depletion in HREEs, the common Eu negative anomalies, and trace element contents similar to that of the upper continental crust. Based on the provenance analysis of these two formations, the final closure time of the PAO in this area is constrained as from the early Middle Triassic (ca. 245 Ma) to the middle Late Triassic (ca. 219 Ma). [ABSTRACT FROM AUTHOR]

The calcite mylonites in the Xar Moron‐Changchun shear zone show a significance dextral shearing characteristics. The asymmetric (σ‐structure) calcite/quartz grains or aggregates, asymmetry of calcite c‐axes fabric diagrams and the oblique foliation of recrystallized calcite grains correspond to a top‐to‐E shearing. Mineral deformation behaviors, twin morphology, C‐axis EBSD fabrics, and quartz grain size‐frequency diagrams demonstrate that the ductile shear zone was developed under conditions of greenschist facies, with the range of deformation temperatures from 200 to 300°C. These subgrains of host grains and surrounding recrystallized grains, strong undulose extinction, and slightly curved grain boundaries are probably results of intracrystalline deformation and dynamic recrystallization implying that the deformation took place within the dislocation‐creep regime at shallow crustal levels. The calculated paleo‐strain rates are between 10−7.87 s−1 and 10−11.49 s−1 with differential stresses of 32.63–63.94 MPa lying at the higher bound of typical strain rates in shear zones at crustal levels, and may indicate a relatively rapid deformation. The S‐L‐calcite tectonites have undergone a component of uplift which led to subhorizontal lifting in an already non‐coaxial compressional deformation regime with a bulk pure shear‐dominated general shear. This E‐W large‐scale dextral strike‐slip movement is a consequence of the eastward extrusion of the Xing'an‐Mongolian Orogenic Belt, and results from far‐field forces associated with Late Triassic convergence domains after the final closure of the Paleo‐Asian Ocean. [ABSTRACT FROM AUTHOR]

The geological corridor of Western Liaoning province is an area of length 100 km and width 20 km and located in the eastern segment of northern margin of North China Craton (NCC), with the wide distribution of Mesozoic granitic magmatism. It is the ideal area to study the granitic petrogenesis, the nature of magma source and the tectonic attribute. In this paper, we do the systematic researches about the petrology, geochronology, geochemistry and Zircon Hf isotopic of granitic rocks. Based on the mentioned above, we have built the geochronological framework and have discussed the petrogenesis, the nature of magma source and the tectonic setting of granitic rocks. And according to the information about the crust-mantle interaction recorded in granitic rocks and the regional data, we also discuss the relationship between Mesozoic granitic magma activities and lithosphere thinning, destruction of Craton mechanism in the eastern segment of northern margin of NCC. The Mesozoic granitic magma activities in The geological corridor of Western Liaoning province are divided into four stages (Fig. 1): Late Triassic (230 Ma∼ 228 Ma), early-middle Jurassic (194 Ma∼169 Ma), Late Jurassic (161 Ma∼155 Ma) and Early Cretaceous (139 Ma∼121 Ma). The late Triassic granitic rocks are composed of adamellite, monzogranite and diorite. The samples have high Sr, Cr, Ni content and low Yb, Y content, and the sample have high Mg# and high ratio of Sr/Y and La/Yb. The characteristics of inhomogenous negative value of εHf(t) (−6.40∼+0.19) in magmatic zircons and ancient crustal TDM2 values of 1.25 Ga∼1.67 Ga(Fig. 2), indicate that the Triassic granitic rocks were formed in a post-collisional extensional tectonic setting after subduction of Paleo-Asian Ocean and the subduction of Yangtze Craton, and they are the product of partial melting of ancient lower crust under the condition of the mantle-derived magma underplating, and geochemical features of the high Sr and low Y are inherited from the source of magma which is also enriched in Sr and depleted in Y. The geochemical features and assemblages of rocks formed during Jurassic-early Cretaceous are similar. The early-middle Jurassic granitic rocks are composed of syenogranite, monzogranite, quartz monzonite, granitic porphyry, granodiorite and quartz diorite. The late Jurassic granitic rocks are composed of monzogranite, granitic porphyry, and quartz diorite. The early Cretaceous granitic rocks are composed of monzogranite, quartz syenite, granitic porphyry, and quartz monzodiorite. The samples are characterized by the high SiO2 content and total alkalis and are belonged to the high-K calc-alkaline series. And the characteristics of quasi-aluminous to weakly peraluminous (A/CNK<1.1, A/NK>1.0) and the negative relationship between P2O5 and SiO2 are similar to the characteristics of I-type granite. The samples are enriched in LREE contents and K, Pb and depleted in Nb, Ta, Ti and P. The characteristics of assemblage and geochemical features indicate the Jurassic-Cretaceous granitic rocks formed in the setting of active continental margin related to the subduction. The magmatic zircons of early-middle Jurassic granitic rocks have negative εHf(t) (−16.60∼−4.15) and ancient crustal TDM2 values of 1.49 Ga∼2.28 Ga which indicates the primary magma is from the partial melting of ancient middle-lower crust(Fig. 2). These rocks formed in the setting of active continental margin of subduction of Paleo-Pacific plate. The magma source of granitic rocks is from partial melting of the ancient lower-middle curst caused by the underplating of mantle magma, which formed in the condition of fluid derived from the dehydration of subducted slab affected on the lithosphere mantle. The magmatic zircons of late Jurassic granitic rocks have negative εHf(t) (−26.24∼−18.56) and ancient crustal TDM2 values of (2.39 Ga∼2.87 Ga) which indicates the primary magma is from the partial melting of ancient upper-middle crust (Fig. 2). And these rocks may be formed in the setting of active continental margin of intense subduction of Paleo-Pacific plate. In the intense subduction, the mantle magma is formed in the interaction of fluid derived from the dehydration of subducted slab with the lithosphere mantle, then further underplated the ancient middle-upper crust and make the ancient middle-upper curst partial melting. In this setting, the late Jurassic rocks are distributed widely in eastern North China. The samples in early Cretaceous have a wide range of values of Hf isotope: −24.92∼−20.88 (139 Ma), −4.72∼ +6.22 (130 Ma), −17.30∼−11.56 (125 Ma∼121 Ma), and the characteristics of Hf isotope indicate the source of early Cretaceous magma (middle-upper crust, middle-lower crust or juvenile crust) is very complicated (Fig. 2). The early Cretaceous granitic rocks were formed in the lithosphere extensional environment when the Paleo-Pacific plate subducted/roll-backed quickly in the direction of NNW with high angle. The regional extension made the asthenosphere upwell and be unstable, and the magma of mantle was formed. Then wide mantle-crust interactions make the crust partial melt, as a result, the source of early Cretaceous igneous rocks which are distributed widely in eastern North China Craton. The participation of depleted mantle components in the process of Late Triassic rock formation in western Liaoning area indicate the time of the lithosphere thinning in the eastern segment of northern margin of NCC begin from the late Triassic (∼230 Ma). The double subduction of Paleo-Asian Ocean and Yangtze Craton in the early period is the reason of the lithosphere thinning. After the double subduction, the mantle-derived magma upwell and underplate the lithosphere mantle and lower crust in a post-collisional extensional tectonic setting. As a result, the lithosphere began to thin but the Craton destruction was not obviously in this period. The participation of depleted mantle components makes the continental crust slightly reforms and grows. The eastern segment of northern margin of NCC was in the setting of active continental margin in Jurassic, and the continuing dehydration and metasomatism of subduction slab changed the physical and chemical properties of the lithosphere mantle. The initial weak subduction in early-middle Jurassic makes the lithosphere become thin but no obvious destruction of Craton. And in this period, the continental crust reformed and grew slightly. As the subduction became stronger during late Jurassic, the thickness of lithosphere in eastern segment of northern margin of NCC become thinner and the destruction of Craton occurred locally and the continental crust reformed and grew to some extent. In early Cretaceous, the change of direction and angle of subduction of Paleo-Pacific led to the regional extension, which is the reason for massive mantle material upwelling and intense crust-mantle interaction. And the lithosphere thinning and destruction of Craton reached the peak. As a result, the effects of reconstruction and hyperplasia of continental crust are obviously. In our opinions, the underplating mechanism of mantle-derived magma occurred mainly in the initial stage (early Mesozoic) of lithosphere thinning, and the delamination of lithosphere mantle or lower crust coexisted while erosion action of mantle material occurred in the stage (late Mesozoic) of strong lithosphere thinning and destruction of Craton. [ABSTRACT FROM AUTHOR]

The Badu Complex is the oldest metamorphic rock in Cathaysia Block which experienced several episodes of metamorphism Especially indosinian metamorphic reworking in the southwestern Zhejiang Province, South China. The degree of indosinian metamorphism reaches granulite facies. However, there is still insufficient understanding of the characteristics of the Indosinian granulite metamorphism in the Cathaysia and many interpretations of its tectonic significance. Therefore, we present detailed petrology, mineral chemistry and LA‐ICP‐MS zircon U‐Pb age in this paper from pelitic granulites of the Badu Complex, which is composed of "sillimanite + garnet + cordierite + spinel + biotite + k‐feldspar" assemblage and garnet pyroxenite with garnet amphibolite which is consists of "garnet + clinopyroxene + orthopyroxene + amphibole + plagioclase". By comprehensive study we get following new findings: Pelitic granulites record four stages of metamorphic mineral assemblages, including prograde (M1), pressure peak (M2), Peak (M3) and post‐peak decompressional and then cooling (M4) stages. The prograde M1 assemblage consists of garnet1 (core) + staurolite + kyanite + biotite + quartz ± rutile ± chlorite; The pressure peak M2 assemblage consists of garnet1 (mantle) + sudoite + rutile + kyanite + corundum + biotite + quartz; The peak M3 have garnet2 (rim‐mantle) + biotite + sillimanite + quartz ± K‐feldspar ± plagioclase ± ilmenite assemblag; the M4 stage is consist of garnet + cordierite + biotite + sillimanite + quartz + ilmenite ± spine ± K‐feldspar. The garnet pyroxenite and garnet amphibolites have experienced three stages of metamorphic evolution. Peak high‐pressure granulite facies stage M2 consists of garnet + sahlite ± ilmenite ± quartz; Post‐peak near isothermal decompression medium granulite facies stage M3 is characterized by typical decompression reaction textures and assemblage of orthopyroxene + plagioclase (An=90–92); amphibolites facies retrograde metamorphic stage M4 is characterized by amphibole + plagioclase (An=33–35) + ilmenite ± sahlite ± quartz mineral assemblage. By means of phase equilibrium simulation and traditional thermobarometer, P‐T conditions of 785–820 °C and 8.9–9.9 kbar for M3 stage, 780–860 °C and 5.7–6.2 kbar for decompressional M4 stage, 705–720 °C and 4.5–4.7 kbar for cooling M4 stage in pelitic granulites were obtained. And also 11.6–12.5 kbar and 780–840 °C for M2 stage, 7.4–8.2 kbar and 800–880 °C for M3 stage, 6.6–7.5 kbar and 500–560 °C for M4 stage were obtained in garnet pyroxenite and garnet amphibolite. A clockwise P‐T path is confirmed in the two type rocks of the Badu Complex which reflected a near‐isothermal decompressional metamorphic process. The peak metamorphism can reach high‐pressure granulite facies. In addition, the mineral assemblage of garnet + rutile + kyanite + corundum in the peak metamorphic stage of pelitic granulite indicates that it may underwent ultra‐high‐pressure metamorphism, and the acidic plagioclase exsolution of clinopyroxene in garnet pyroxenite also suggests that it may be retrograded eclogites, which indicates that the deeper Cathaysian block may have eclogite metamorphism. Analyses of LA‐ICP‐MS zircon U‐Pb dating indicate that the metamorphic age of pelitic granulite is 233.5 Ma–subduction/collision followed by rapid exhumation and cooling events. The events may relate with the amalgamation of the Indochina Block‐South China Block North China Block in the paleo‐Tethyan domain. [ABSTRACT FROM AUTHOR]

Blueschists in the Yilan area, Heilongjiang Province, are known as important parts of the Heilongjiang Complex. However, their metamorphic evolution history is still unclear. Petrographical, and mineral chemical investigations on the blueschists from the Yilan area are carried out in this study. P‐T pseudosections are calculated in the system Na2O‐CaO‐K2O‐MnO‐FeO‐MgO‐Al2O3‐SiO2‐H2O‐TiO2‐O (Fe2O3) (NCKMnFMASHTO) with the PERPLE_X software for three blueschist samples. Peak metamorphic conditions are estimated to be 500‐525°C, 1.14‐1.2 GPa for garnet‐barroisite schist (g‐brs‐wnc‐act‐phn‐chl‐ep‐ab‐stlp); 480°C, 1.4 GPa for chlorite‐epidote glaucophane schist (gl‐brs‐wnc‐act‐chl‐ep‐stlp) and 450‐500°C, 0.95‐1.2 GPa for phengite‐glaucophane schist (gl‐wnc‐phn‐ab‐ep‐chl‐sph), which indicate that they all underwent peak metamorphism in the limit epidote‐blueschist facies conditions. Combined with the previously reported geochemical and geochronological data, the clockwise P‐T paths of the blueschists are constructed. The formation of blueschists in the study area marks the young oceanic crust subduction, and represents the final closure of the Paleo‐Asian Ocean and the beginning of the Paleo‐Pacific tectonic system. The P‐T pseudosection recorded the P‐T increasing process before the metamorphic peak and that the maximum temperature was coincident with the maximum pressure in the process, which indicates that the epidote‐blueschist facies conditions implemented in the process of subduction, rather than exhumation. The retrograde trajectory nearly coincidently retraced the prograde trajectory, which represents the similar geothermal gradient (11‐14°C/km) in the subduction and the relatively slow exhumation process. [ABSTRACT FROM AUTHOR]