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Large-scale Mesozoic volcanisms in the Great Xing’an Mountains (GXM), northeastern (NE) China, are being extensively interested recently. However, the petrogenesis and geodynamic implications of these volcanic rocks are still on controversy. In this study, geochronology and geochemistry of the intermediate and felsic volcanic rocks of Late Mesozoic from the southern GXM was investigated. Zircon U–Pb geochronology yields 206Pb/238U ages ranging from 154.3 ± 1.7 Ma to 127.0 ± 2.4 Ma for the eight selected volcanic rocks, where the major period of the Mesozoic volcanisms is constrained during the Early Cretaceous. The presented volcanic rocks are andesite–trachydacite–rhyolite and show calc-alkaline to shoshonitic features. They have elevated incompatible trace element concentrations and significantly negative Nb–Ta–Ti and positive Pb anomalies, which display characteristics of typical subduction-related magmas rather than within-plate magmatic signature. Sr–Nd isotopic data indicate that their magma sources were mixed with proportions of old crustal components. Geochemical features, therefore, indicate that the intermediate and felsic shoshonitic magma was plausibly derived from partial melting of the subduction-modified lithospheric mantle and thickened lower crust, respectively, induced by delamination and/or asthenosphere upwelling in extensional setting. Combined with the tectonic evolution of the Great Xing’an area, we propose a hypothesis that the large-scale Mesozoic volcanisms in NE China were controlled by the transition of regional stress from southward to westward, which are induced by the changes of tectonic regimes from the previous Mongol–Okhotsk subduction to the succeeding paleo-Pacific subduction during Late Mesozoic.

The small serrated flow, severe Portevin Le Chatelier (PLC) phenomenon and abnormal strain rate sensitivity (SRS) were observed from the tensile curves of extruded Mg–5Li–3Al–1.5Zn–2RE alloy. The serrated curves were investigated by optical microscopy, step-tensile test and transmission electron microscopy. The small serrated flow is due to the traditional dynamic strain ageing. The positive SRS is caused by dynamic strain ageing. The severe Portevin Le Chatelier phenomenon and the negative SRS are attributed to a larger number of twins. Transmission electron microscope diffraction pattern reveals the { 10 1 ¯ 2 } twin and { 10 1 ¯ 1 } twins.

The Mg-5Li-3Al-1.5Zn-2RE (LaPrCe) alloy was prepared by hot-chamber extrusion process after casting. The alloy consists of α-Mg solid solution and intermetallic phases (Al11RE3 phase and Al2RE phase). The microstructural analysis of the alloy reveals the correlation between microstructure and creep properties. The stress exponent of n varies from 4.25 to 6.23, and the activation energy varies from 104 to 134 kJ/mol. There is a transition between dislocations climb dominated creep mechanism and dislocation creep controlled by non-basal planes slip. Tensile creep tests were combined with detailed transmission electron microscopy in order to characterize the Al11RE3 phase, which had thermal stability at 448K during the creep test. The dislocations pinned and cross-slip dislocations were observed.

The tensile and fatigue properties of the Mg–5Li–3Al–1.5Zn-2RE (LAZ531-2RE) alloy were presented. The alloy was prepared by hot extrusion after vacuum casting. The Portevin–Le Chatelier (PLC) phenomenon was observed during tensile deformation. The PLC effect was attributed to the dynamic interaction between solute atoms (Li) and dislocation movement. The abnormal negative strain rate sensitivity (SRS) in high strain rate regime can be explained by the dynamic strain ageing (DSA) mechanism. The higher ductility may be associated with finer-grained microstructure and Li addition. Fatigue crack propagation was characterized by striation-like features. The smaller spacing of fatigue striations and larger fatigue crack propagation zone at the lower total strain amplitude gave rise to a longer fatigue life.

A fusuline fauna consisting of 9 species of 4 genera from the Xiala Formation of the Mujiucuo section, Xainza County, Tibet, China is described. The fusuline fauna is dominated byNankinellaandChusenellaand indicates a Midian (Late Guadalupian) age. The earliest record of fusuline fauna during the Midian in the Lhasa Block suggests that the block rifted later than the Qiangtang Block to the north and the Baoshan and Tengchong blocks to the east, all of which yield much earlier fusuline faunas of Yakhtashian (Artinskian) age, but had drifted away from Gondwana to a relatively warm temperate zone in the Late Guadalupian (Middle Permian).

The effects of semi-solid isothermal process parameters on the microstructure evolution of Mg-Gd rare earth alloy produced by strain-induced melt activation (SIMA) were investigated. The formation mechanism of the particles in the process of the isothermal treatment was also discussed. The results show that the microstructure of the as-cast alloy consists of α-Mg solid solution, Mg5RE and Mg24RE5 (Gd, Y, Nd) phase. After being extruded with an extrusion ratio of 14:1 at 380 °C, the microstructure of Mg-Gd alloy changes from developed dendrites to near-equiaxed grains. The liquid volume fraction of the semisolid slurry gradually increases with elevating isothermal temperature or prolonging isothermal time during the partial remelting. To obtain an ideal semisolid slurry, the optimal process parameters for the Mg-Gd alloy should be 630 ? for isothermal temperature and 30 min for the corresponding time, respectively, where the volume fraction of the liquid phase is 52%.

Using squeeze-infiltration technique, Mg-9Al-1Zn-0.8Ce composite reinforced by graphite particles and Al2O3 short fibers was fabricated. The reinforcing phases combined closely with the matrix and no agglomeration was observed. The microstructure, hardness and wear property of the composites with the graphite content of 5%, 10%, 15% and 20% were investigated, respectively. The results reveal that Ce tends to enrich around the boundaries of graphite particles and Al2O3 short fibers, and forms Al3Ce phase. When the graphite content increases to 20%, the grain size becomes small. Moreover, with increasing the graphite content, the microhardness of the composites decreases but the wear resistance increases. The graphite which works as lubricant during dry sliding process decreases the wear loss. At low load, the wear mechanism of the composite is mainly abrasive wear and oxidation wear; at high load, except that the composite with 20% graphite is still with abrasive wear and oxidation wear, the wear mechanism of other composites changes to delamination wear.

As-cast and extruded Mg-11Li-3Al-1Ca alloys were successfully prepared. The microstructure of specimens was analyzed with OM, SEM, EDS and XRD. It was found that as-cast specimens were composed of β phase (Lithium), small pieces of divorced eutectic α phase (Magnesium), MgLi 2 Al and Al 2 Ca compounds. During the extrusion process, the microstructure was refined and partial recrystallization was observed. Uniaxial tension tests were carried out under different strain rate. The ultimate intensities were obviously higher than common β phase Mg-Li alloys to compare with past studies. Deformation capacity of the extruded specimen at room temperature was estimated by strain-rate sensitivity exponent (m value), which was 0.071. Serrated flows were apparent through out the deformation history and the phenomenon was interpreted through the competition between dynamic strain aging (DSA) of solute atoms and shearing of precipitates by dislocations.

Members of the Lyttoniidae Waagen, 1883 (Lyttonioidea Waagen, 1883, Brachiopoda) are characterized by numerous peculiarities, including their disproportionately inequivalve, rudimentary articulatory apparatus and asymmetrically developed muscle scars. The ventral valve of lyttonioids usually possesses a posterior flap and complementary septal apparatus and the dorsal valve has corresponding lobes and slits to fit around the ventral septa (Noetling, 1905; Fredericks, 1926; Wanner, 1935; Williams, 1953; Grant, 1976; Williams et al., 2000). Externally, the Lyttoniidae have been previously described as being smooth or having some growth banding, lines, or disturbances only (Cooper and Grant, 1974; Williams et al., 2000). Spines were previously reported by Sarytcheva (1964), but subsequently not confirmed by Cooper and Grant (1974, p. 387) and Williams et al. (2000). Radial ornamentation has never been reported prior to this study. In 2002, two specimens with Linoproductus -like costellae and Oldhamina -like septal apparatus were found by one of the authors (CLR) from the Middle Permian Xiala Formation at the Xinji Section in the Xainza area (89–91°E, 30–31°N) in northern Tibet (Fig. 1.1, 1.2) during 1:250,000 mapping. We consider that the present specimens represent another distinct phylogenetic branch within the Lyttoniidae, although only two specimens were found. Further collecting is currently impossible because of the inaccessibility of the remote area in northern Tibet. In this paper we aim to propose a new subfamily of Lyttoniidae based on the specimens found from northern Tibet. Figure 1 —Map showing the fossil locality and the Permian columnar section in the Xainza area, northern Tibet (biostratigraphical and lithostratigraphical data after Cheng, personal commun) The Lhasa Block was attached to the northern peri-Gondwanan margin during the Late Paleozoic. Subsequently this block rifted northwards in late Early Permian or Middle Permian, and incorporated into the Cathaysian Province …