Late Carboniferous magmatism in the Chinese Altai provides an important view of geodynamic processes active during crustal growth in the Central Asian Orogenic Belt (CAOB). In this study, five representative peraluminous granite plutons from the Chinese Altai were selected for systematic geochronological, geochemical and Sr–Nd–Hf isotopic analyses (Table 1). These granites were emplaced between 449 and 327 Ma in an active subduction zone, and have moderate to high SiO2 (66.54–76.13 wt%), moderate Na2O+K2O (6.27–7.66 wt%), and high Al2O3 contents (12.43–16.18 wt%). All granite samples in this study showed significant decoupling of the Nd and Hf isotope systems. Results show negative εNd(t) values (−3.3 to −0.9), and predominantly positive εHf(t) values (+0.24 to +8.01, n=57) except for a few negative εHf(t) values (−7.44 to −0.03, n=9), high Mg# values (28.69–53.33), high Nd/Hf ratios (4.26–43.57), and enrichment of large-ion lithophile elements (LILEs; e.g. Pb, Th, and U), suggesting that the granites were derived from the partial melting of oceanic sediments and the associated mantle wedge, with fractionation of plagioclase, K-feldspar and biotite. In situ zircon Hf isotopic analyses yield negative εHf(t) values from −30.6 to −13.7 for the zircon xenocrysts. The U–Pb ages and Hf isotopic ratios of these zircon xenocrysts were probably inherited from oceanic sediments. Zircon saturation temperatures suggest that these peraluminous granites were emplaced at 537–765°C. We propose that: (1) the Nd isotopic system more faithfully reflects the source of peraluminous magmas in the Chinese Altai than the Hf isotopic system, and (2) the oceanic sediment recycling was an important process during continental growth in the CAOB.

Eastern Australia was affected by late Cenozoic intraplate deformation in response to far-field stress transmitted from the plate boundaries, but little is known about the intensity and pattern of this deformation. We used recently surveyed two-dimensional seismic reflection lines and aeromagnetic data, and data from the recently released Australian Stress Map, to investigate the structure of the Nagoorin Basin in eastern Queensland. The western margin of the Nagoorin beds was displaced by the Boynedale Fault, which is a NNW-striking SW-dipping oblique strike-slip reverse fault with a vertical throw of c. 900 m and c. 16 km sinistral displacement. A significant part of this large sinistral displacement is interpreted to have occurred prior to late Cenozoic time. Several low-angle (<30°) thin-skinned thrusts with a flat-ramp geometry also displaced the Nagoorin beds, which are interpreted to have developed along detachment surfaces in oil shales and claystone. The Boynedale Fault is a segment within longer NNW-striking faults that include the North Pine and West Ipswich fault systems in eastern Queensland. These NNW-striking faults are potentially active, and may accommodate neotectonic thrust movement in response to the present-day NE–SW orientation of SHmax. Results of this study, in conjunction with previous information on sedimentary basins in eastern Australia, indicate that Cenozoic contractional deformation is stronger at the continental margins, possibly due to the presence of pre-existing rift-related structures.

Magnetic, petrological and mineralogical data from 13 sites (99 independently oriented samples) of the Lower Triassic rocks located in the SW segment of the West Spitsbergen Fold and Thrust Belt (WSFTB) are presented in order to identify the ferrimagnetic carriers and establish the origin of the natural remanent magnetization (NRM). Volcanic lithoclasts and other detrital resistive grains in which the primary magnetization might endure are present in some samples. On the other hand, petrological studies indicate that sulphide remineralization could have had an important influence on the remagnetization of these rocks. The dominant ferrimagnetic carriers are titanomagnetite and magnetite. While the titanomagnetite may preserve the primary magnetization, the magnetite is a more likely potential carrier of secondary overprints. The complex NRM patterns found in most of the samples may be explained by the coexistence and partial overlapping of components representing different stages of magnetization. Components of both polarities were identified in the investigated material. The reversal test performed on the most stable components that demagnetized above 300°C proved to be negative at the 95% confidence level at any stage of unfolding. They are better grouped, however, after 100% tectonic corrections and the most stable components are clustered in high inclinations (c. 70–80°). This suggests that at least part of the measured palaeomagnetic vectors represent a secondary prefolding magnetic overprint that originated in post-Jurassic time before the WSFTB event. Vitrinite reflectance studies show these rocks have not been subjected to any strong heating (<200°C).

The Luziyuan Pb–Zn skarn deposit, located in the Baoshan–Narong–Dongzhi block metallogenic belt in SW China, is hosted by marble and slate in the upper Cambrian Shahechang Formation. Three skarn zones have been identified from the surface (1495 m above sea level (asl)) to a depth of 1220 m asl: zone 1 consists of chlorite–actinolite–calcite–quartz, zone 2 of rhodonite–actinolite–fluorite–quartz–calcite, and zone 3 contains garnet–rhodonite–actinolite–fluorite–quartz–calcite. The deposit formed in four distinct mineralization stages: an early anhydrous skarn (garnet, rhodonite and bustamite) stage (Stage 1), a hydrous skarn (actinolite and chlorite) stage (Stage 2), an early quartz (coarse barren quartz veins) stage (Stage 3) and a late sulphide-forming (fine sulphide-bearing quartz veins) stage (Stage 4). The Stage 1 skarn-forming fluid temperature was at least 500 °C according to the geothermometer with rhodonite/bustamite trace elements measured by laser ablation – inductively coupled plasma – mass spectrometry (LA-ICP-MS). A decrease in ore fluid temperatures with time is consistent with the decreases in the δ18Ofluid and δDfluid values from Stage 3 to 4. This trend suggests that the ore fluid was mainly derived from magmatic water and mixed with large amounts of meteoric water during mineralization. The δ34S values of Stage 4 chalcopyrite, sphalerite and galena are similar to those of an Ordovician gypsum layer, and together with the high-salinity fluids in Stage 4 indicate the dissolution of evaporites in the Luziyuan region. Overall, the results of this study suggest that the Luziyuan deposit is a distal Pb–Zn skarn deposit that formed in response to multi-stage alteration associated with a combination of magmatic water and meteoric water.

Data from offshore oil and gas explorations have revealed that mud diapirs occur widely not only at continental margins but also in foreland basins and may have played an important role in the entrapment of oil and gas. Although the structural features and formation mechanism of salt diapirs have been extensively investigated, mud diapirs are still not fully understood, largely due to the difficulty of identifying them from seismic data. In this paper, the structural features and main controlling factors of mud diapirs in the Andaman Sea Basin are investigated based on seismic profiles combined with drilling data and regional tectonic settings. The results show that there are five types of mud diapir in the Andaman Sea Basin: turtleback mud diapir, mud dome, piercing mud diapir, mud volcano and gas chimney-like mud diapir. Turtleback mud diapirs mainly occur in the southern segment of the accretionary wedge of the Andaman Sea Basin, which is far from the Bengal Fan and characterized by low deposition rate and strong compression tectonic setting. Piercing mud diapirs exist mainly in the central segment of the accretionary wedge, which is close to provenances of sediments and characterized by rapid sedimentation rates, large mudstone thickness and transpressional tectonic setting. Mud domes and mud volcanoes mainly occur in the northern segment of the accretionary wedge, which is characterized by rapid sedimentation rates, large mudstone thickness and sedimentary wedge growth tectonic setting. The gas chimney-like mud diapirs only occur in the northern segment of the back-arc depression close to the Sagaing strike-slip fault belt, which is characterized by high deposition rate, large mudstone thickness and high geothermal gradient. These features suggest that thick mudstone deposit, rapid sedimentation rates, large geothermal gradient, strong tectonic stress and gravitational spreading and sliding may have prompted the formation of mud diapirs in the Andaman Sea Basin.

Four complete platysiagid fish specimens are described from the Luoping Biota, Anisian (Middle Triassic), Yunnan Province, southwest China. They are small fishes with bones and scales covered with ganoine. All characters observed, such as nasals meeting in the midline, a keystone-like dermosphenotic, absence of post-rostral bone, two infraorbitals between dermosphenotic and jugal, large antorbital, and two postcleithra, suggest that the new materials belong to a single, new Platysiagum species, P. sinensis sp. nov. Three genera are ascribed to Platysiagidae: Platysiagum, Helmolepis and Caelatichthys. However, most specimens of the first two genera are imprints or fragmentary. The new, well-preserved specimens from the Luoping Biota provide more detailed anatomical information than before, and thus help amend the concept of the Platysiagidae. The Family Platysiagidae was previously classed in the Perleidiformes. Phylogenetic analysis indicates that the Platysiagidae is a member of basal Neopterygii, and its origin seems to predate that of Perleidiformes. Moreover, platysiagid fishes are known from the Middle Triassic of the western Tethys region. The newly found specimens of platysiagids from Luoping provide additional evidence that both eastern and western sides of the Tethys Ocean were biogeographically more connected than previously thought.

Jurassic sandstones in the Xiongcun porphyry copper–gold district, southern Lhasa subterrane, Tibet, China were analysed for petrography, major oxides and trace elements, as well as detrital zircon U–Pb and Hf isotopes, to infer their depositional age, provenance, intensity of source-rock palaeo-weathering and depositional tectonic setting. This new information provides important evidence to constrain the tectonic evolution of the southern Lhasa subterrane during the Late Triassic – Jurassic period. The sandstones are exposed in the lower and upper sections of the Xiongcun Formation. Their average modal abundance (Q21F11L68) classifies them as lithic arenite, which is also supported by geochemical studies. The high chemical index of alteration values (77.19–85.36, mean 79.96) and chemical index of weathering values (86.19–95.59, mean 89.98) of the sandstones imply moderate to intensive weathering of the source rock. Discrimination diagrams based on modal abundance, geochemistry and certain elemental ratios indicate that felsic and intermediate igneous rocks constitute the source rocks, probably with a magmatic arc provenance. The detrital zircon ages (161–243 Ma) and εHf(t) values (+10.5 to +16.2) further constrain the sandstone provenance as subduction-related Triassic–Jurassic felsic and intermediate igneous rocks from the southern Lhasa subterrane. A tectonic discrimination method based on geochemical data of the sandstones, as well as detrital zircon ages from sandstones, reveals that the sandstones were most likely deposited in an oceanic island-arc setting. These results support the hypothesis that the tectonic background of the southern Lhasa subterrane was an oceanic island-arc setting, rather than a continental island-arc setting, during the Late Triassic – Jurassic period.

In this paper, zircon U–Pb geochronology, major and trace elements, and Sr–Nd isotope geochemistry of the Baiyanghe dolerites in northern West Junggar of NW China are presented. The U–Pb dating of zircons from the dolerites yielded ages of 272.2±4 Ma and 276.7±6.2 Ma, which indicate the emplacement times. The dolerites are characterized by minor variations in SiO2 (46.89 to 49.07 wt%), high contents of Al2O3 (13.60 to 13.92 wt%) and total Fe2O3 (11.14 to 11.70 wt%), and low contents of MgO (2.67 to 3.64 wt%) and total alkalis (Na2O+K2O, 5.1 to 5.97 wt%, K2O/Na2O = 0.37–0.94), which indicate affinities to metaluminous tholeiite basalt. The REE pattern ((La/Sm)N = 2.25–2.34, (La/Yb)N = 7.42–8.36), V–Ti/1000 and 50*Zr–Ti/50–Sm discrimination diagrams show that these rocks are OIB-type. The high contents of Zr and Ti indicate a within-plate tectonic setting, and samples plot in the ‘plume source’ field shown on the Dy/Yb(N) versus Ce/Yb(N) diagram. The positive εNd(t) values (+7.09 to +7.48), high initial 87Sr/86Sr ratios (0.70442 to 0.70682) and depletions of Nb and Ta elements in the samples can be explained by the involvement of subducted sediments. In summary, it is possible that the Baiyanghe dolerites were derived from an OIB-like mantle source and associated with a mantle plume tectonic setting. Therefore, our samples provide the youngest evidence for the existence of a mantle plume, which may provide new insights into the Late Palaeozoic tectonic setting of West Junggar.

The abundance of specimens of Ichthyosaurus provides an opportunity to assess morphological variation without the limits of a small sample size. This research evaluates the variation and taxonomic utility of hindfin morphology. Two seemingly distinct morphotypes of the mesopodium occur in the genus. Morphotype 1 has three elements in the third row: metatarsal two, distal tarsal three and distal tarsal four. This is the common morphology in Ichthyosaurus breviceps, I. conybeari and I. somersetensis. Morphotype 2 has four elements in the third row, owing to a bifurcation. This morphotype occurs in at least some specimens of each species, but it has several variations distinguished by the extent of contact of elements in the third row with the astragalus. Two specimens display a different morphotype in each fin, suggesting that the difference reflects individual variation. In Ichthyosaurus, the hindfin is taxonomically useful at the genus level, but species cannot be identified unequivocally from a well-preserved hindfin, although certain morphologies are more common in certain species than others. The large sample size filled in morphological gaps between what initially appeared to be taxonomically distinct characters. The full picture of variation would have been obscured with a small sample size. Furthermore, we have found several unusual morphologies which, in isolation, could have been mistaken for new taxa. Thus, one must be cautious when describing new species or genera on the basis of limited material, such as isolated fins and fragmentary specimens.

Detailed structural, volcanic, and sedimentary investigations of the crustal response to the emplacement of the Middle–Late Permian Emeishan large igneous province show that a rifting system developed prior to the main stage of flood basalt eruptions, in the form of sedimentary breccias, clastic sedimentary deposits and mafic hydromagmatic units. Detrital zircon grains from sandstones yield ~750–800 Ma LA-ICP-MS 206Pb/238U age clusters, showing that material was sourced from the Yangtze crystalline basement. Gabbros and pegmatites intruded along the normal faults of the rift system yield zircon ages of 264–260 Ma, and thus constrain the timing of rifting. N–S-trending rift zones developed along the western flank of the Pan-Xi palaeo-uplift, with NE–SW- and NNE–SSW-trending rifts on the eastern side and along the western and eastern margins of the Yangtze Block. The rifting progressed in pulses, with an initial phase of normal faulting followed by rapid deposition of breccias. Later there was lower-energy deposition of sandstone, with accompanying rhyolitic eruptions. This was followed by low-energy sedimentation of mudstones and dolomites, with accompanying hydromagmatic deposits. Rift system formation was constrained by a combination of far- and near-field tectonic stresses due to plate motions and lithospheric interaction with initial Emeishan volcanism.