A Large-Scale Palaeozoic Dextral Ductile Strike-Slip Zone:the Aqqikkudug-Weiya Zone along the Northern Margin of the Central Tianshan Belt,Xinjiang,NW China

Abstract The nearly E-W-trending Aqqikkudug-Weiya zone, more than 1000 km long and about 30 km wide, is an important segment in the Central Asian tectonic framework. It is distributed along the northern margin of the Central Tianshan belt in Xinjiang, NW China and is composed of mylonitized Early Palaeozoic greywacke, volcanic rocks, ophiolitic blocks as a mélange complex, HP/LT-type bleuschist blocks and mylonitized Neoproterozoic schist, gneiss and orthogneiss. Nearly vertical mylonitic foliation and sub-horizontal stretching lineation define its strike-slip feature; various kinematic indicators, such as asymmetric folds, non-coaxial asymmetric macro- to micro-structures and C-axis fabrics of quartz grains of mylonites, suggest that it is a dextral strike-slip ductile shear zone oriented in a nearly E-W direction characterized by “flower” strusture with thrusting or extruding across the zone toward the two sides and upright folds with gently plunging hinges. The Aqqikkudug-Weiya zone experienced at least two stages of ductile shear tectonic evolution: Early Palaeozoic north vergent thrusting ductile shear and Late Carboniferous-Early Permian strike-slip deformation. The strike-slip ductile shear likely took place during Late Palaeozoic time, dated at 269±5 Ma by the40Ar/39Ar analysis on neo-muscovites. The strike-slip deformation was followed by the Hercynian violent S-type granitic magmatism. Geodynamical analysis suggests that the large-scale dextral strike-slip ductile shearing is likely the result of intracontinental adjustment deformation after the collision of the Siberian continental plate towards the northern margin of the Tarim continental plate during the Late Carboniferous. The Himalayan tectonism locally deformed the zone, marked by final uplift, brittle layer-slip and step-type thrust faults, transcurrent faults and E-W-elongated Mesozoic-Cenozoic basins.

On Palaeozoic Tectonics in the Alxa Region, Inner Mongolia, China

Abstract: Two ophiolitic mélange belts in the Late Carboniferous formations have been discovered recently in the Alxa region. One is in the Engger Us fault and possesses properties of oceanic crust. The other is in the Badain Jaran fault and shows properties of a back-arc basin. These two faults, together with the Yagan fault, constitute the important boundaries of tectonic units in the Alax region. The four tectonic units delimited by these faults are different in rock assemblages, metamorphism and geochemistry. They reflect the nature of tectonic environments in which they are found. The tectonic units may be traced and correlated to the eastern and western neighbouring areas. The formation and evolution process of the units and their interaction in the Alxa region may be described in terms of the evolution of the Palaeo-Mongolian Ocean and its continental margins.

Rare Earth Element Geochemistry of Late Palaeozoic Coals in North China

Abstract: Instrumental Neutron Activation Analysis (INAA) was done to determine the abundances of rare earth elements (REE) of 58 samples of Late Palaeozoic Carboniferous-Permian coals and related rocks in North China. Detailed study of REE geochemistry shows that the ?REE of most coals studied in this paper is in a normal range between 30×10?6 and 80×10?6 with a mean of 56×10?6. The REE in the Taiyuan Formation in the northern part of North China are much richer than those in the southern part. This is due to the shorter distance to the source area in the north. Moreover, the ?REE is in positive correlation to coal ash, especially closely related to the content of clay minerals <2 μm in size. This reveals that most REE were carried by terrigenous clastic materials, especially fine clay minerals. In the coals the light REE (LREE) are much richer than the heavy REE (HREE), and the LREE/HREE ratio in coals generally varies from 2 to 8. The LREE/HREE ratio of high-ash, low-sulphur coals is higher than that of low-ash, high-sulphur coals, and is even higher in the roof and floor rocks, reaching 12 with the highest (up to 21) in pyrite concretions, which shows that the HREE have a stronger affinity to organic matter in a reducing environment influenced by seawater. Furthermore, Eu is generally depleted in coals. The REE chondrite-normalized distribution patterns are very similar in coals of the whole of North China. From the REE geochemical characteristics it can be concluded that during the formation of Late Palaeozoic Carboniferous-Permian coals in North China, the supply of terrigeneous materials remained quite stable. The ?REE in low-ash, high-sulphur coals is relatively low and the REE are mainly carried by fine-grained minerals and organic matter and a certain percentage of REE are adsorbed by organic matter; while the ?REE in high-ash, low-sulphur coals is higher and the REE are mainly present in detritus. The ?REE of magmatism-influenced coals is the highest, which suggests that the introduction of magmatic substances may increase the ?REE, thus causing the REE distribution patterns to show an abnormal feature. Moreover, some harmful elements such as U, W and As usually increase when the coals are influenced by magmatism.

Carbon and Strontium Isotopes of Late Palaeozoic Marine Carbonates in the Upper Yangtze Platform,Southwest China

238 marine carbonate samples were collected from seven sedimentary sections ofthe entire late Palaeozoic (Permian, Carboniferous and Devonian) in the Upper Yangtze Plat-form, southwest China. Based on the absence of cathodoluminescence and very low Mn (gener-ally<50 ppm) contents of the samples, it is thought that they contain information on the orig-inal sea water geochemistry. The results of isotopic analyses of these samples are presented interms of δ^(13)C and ^(87)Sr/^(86)Sr ratios versus geological time. The strontium data, consistent withother similar data based on samples from North America, Europe, Africa and other areas inAsia, support the notion of a global consistency in strontium isotope composition of marinecarbonates. The strontium data exhibit three intervals of relatively low ^(87)Sr/^(86)Sr ratios in thelate Middle Devonian to early Late Devonian, Early Carboniferous and Early Permian, corre-sponding to global eustatic high sea level stands. The lowest ^(87)Sr/^(86)Sr ratio recorded in theLate Permian was probably caused by substantial basalt eruptions in the Upper Yangtze Plat-form at the time. Three corresponding periods of relatively high δ^(13)C values at roughly the samethe intervals were caused by a relatively high rate of accumulation of organic carbon duringsea level rises at these times. The deposition of coal was probably responsible for the increaseof sea water δ^(13)C at other times. The δ^(13)C values drop dramatically near theDevonian/Carboniferous, Carboniferous/Permian and Permian/Triassic boundaries, con-sistent with other similar data, which further support the notion that geological time boundariesare associated with mass extinction and subsequent rejuvenation.

A Carbon Isotopic Stratigraphic Pattern of the Late Palaeozoic Coals in the North China Platform and Its Palaeoclimatic Implications

This paper gives the stable carbon isotopic data in coals from the Late Namurian to Kazanian stages in the Serteng Mt., Xishan and Huainan coalfields of the North China Platform. Its stratigraphic pattern shows that several isotopic shifts are apparent, and the large δ13C negative shifts (approximately 2.5 to 3.0 %%) occurred during the Stephanian, Artinskian and Kazanian are observed in three Permo-Carboniferous coalfields. Those negative shifts are neither related to the coal rank and coal macerals, nor caused by the variety of peat-forming plants. The general decrease in the δ13C values of the Stephanian, Artinskian and Kazanian coals is consistent with an overall decrease in the δ13C values of ambient atmospheric CO2 and/or a relative increase in atmospheric Pco2 during the coal-forming periods. Therefore the authors postulate that the oxidation of peat, and the δ13C-depleted CO2 flux into the atmosphere during the above stages may have contributed to coeval palaeoclimatic warming by way of the greenhouse effect.

Discovery of Palaeozoic Karsts in the Qaidam Basin and Their Oil and Gas Prospects

Objective Complex geological factors have been constraining the oil and gas exploration in the Paleozoic strata of the Qaidam Basin,although there are high-quality hydrocarbon source rocks.One of the most important reasons may be reservoir densification due to the multiple stages of destructive cementation,which has hindered our understanding of the Paleozoic petroleum enrichment rules in the Qaidam basin.In recent years.

The Late Palaeozoic Rifting on Hainan Island, China

There occurred rifting on Hainan Island in the Late Palaeozoic. Bimodal volcanic rocks composed ofbasalt and rhyolite developed in the Carboniferous. Widespread in the Late Palaeozoic formations are severallayers of fluvial intermontane conglomerates whose distribution is controlled by rift faults. The Late Palaeozoicdeposits dominaled by clastic rocks are, for a major part, of marine facies and of continental facies in the lowerand upper parts. Lithological and lithochemical studies indicate that the detrital rocks were formed in atectonic setting of continental rifting. The evolution of the rifting terminated at the stage of transition form anintra continental rift to an intercontinental one and the rift basin was a bay opening westward to the sea.

Genesis of Coal Metamorphism of Late PalaeozoicCoals in the South of North China——A Further Approach to the Effects of ThermalGroundwater on Coal Metamorphism

The close relationship between the genesis of coal metamorphism and the evolution of the regional tectonic framework is expounded on the basis of an analysis of the geological factors causing the metamorphic zonation of the Late Palaeozoic coals in southern North China; in terms of the mechanism for the formation of palaeogeothermal anomalies, the effects of thermal groundwater on coal metamorphism is highlighted and a geological model for thermal groundwater metamorphism of coal established; with the concept of the palaeogeotherm-coal metamorphism system, the genesis of coal metamorphism is analysed according to the distribution pattern of three geological factors: heat source, heat-carrier and channel, and heat-collector.

Early Palaeozoic Granites in the Northern Tian Shan,Kyrgyzstan:Their Zircon Ages and Evolution Processes

The Tian Shan Orogenic Belt, which is a subsidiary of the Central Asian Orogenic Belt, is the largest accretion area of continental crust on the Earth during the Phanerozoic. It has experienced several accretionary processes during the Palaeozoic period and has attracted much concern among geologists. An Early Palaeozoic intrusive rock belt extends for 1000 km from east to west, occupying about 40% of the total area within the Kyrgyz Northern Tian Shan Orogenic Belt. Previous studies show that the petrology of these rocks is similar, consisting of granites and granodiorites.

Early Paleozoic basement diorite of arc-magmatism from Kutch basin, Western India

In this study,we report for thefirst time an Early Palaeozoic basement diorite from the drilled well Nirona-A in the Banni Half-Graben of the Kutch basin,western India.The 40Ar–39Ar dates provided a plateau age of 441.84±2.66 Ma and another pseudo plateau of 441.28±5.82 to 388.08±16.65 Ma for the basement diorite.These ages constrain the basement formation age to the Late Ordovician-Early Silurian period.The obtained basement ages are correlatable with the later part of Cambro-Ordovician alkaline magmatism that has been reported from the Huqf area in Central Oman,whereas their lithological and petrographic correlativity with base-ment diorites occurring in the Dinsi Body of Nagar Parkar igneous complex in Pakistan can also be envisaged.The geochemical studies characterized the diorite with enrich-ment of LILE(Rb,Ba,and K)and LREE(La,Ce,Nd),strong depletion of HFSE(Nb,Sr,P,and Ti),along with weakly negative Eu anomalies.The geochemical signatures indicate their petrogenetic affiliation with mantle-derived magmas,as well as their tectonic setting to be arc-related,having post-collisional continental-arc type affinity.The*440 Ma basement of Kutch,therefore,appears to rep-resent the later thermal event associated with the reworked Neoproterozoic subduction-related suite from Greater India’s northwest edge,which has implications for Gond-wana assembly in the northwest Indian subcontinent.

Palaeozoic stromatoporoid futures:A discussion of their taxonomy,mineralogy and applications in palaeoecology and palaeoenvironmental analysis

Palaeozoic stromatoporoids are calcified sponges common between Middle Ordovician and Late Devonian times in reefs and related facies.Taxonomic work is well known,but controversial because of conflict between classification schemes based on the calcareous skeleton versus spicules(which are almost completely lacking in Palaeozoic stromatoporoids);however,lower-level taxonomy(at genus-level) of the calcareous skeleton is considered reliable to be applied in palaeobiological study.Knowledge of stromatoporoid ecology is poorly developed,such that comprehensive information is available for only a few case studies,in some Silurian and Devonian examples.Thus an overall understanding of stromatoporoid responses to environmental conditions has not yet been achieved,although stromatoporoids were likely able to deal with fine grained sediment where they mostly occur.Many stromatoporoid genera have only certain growth forms,so future focus on the use of low-level taxonomy in ecological studies,by comprehensive sampling in high-resolution studies,may establish the relationships between stromatoporoids and their environments.Intergrown organisms and growth banding in stromatoporoids are aspects that have great potential in such work.Mineralogy of stromatoporoids remains poorly understood.Regardless of their apparent state of preservation(ranging from apparently well-preserved to complete loss of calcareous skeleton features) all stromatoporoids are in fact substantially recrystallized.They underwent a peculiar diagenesis,whereby the calcareous skeleton and gallery cements of all stromatoporoids are overprinted by irregular elongated calcite crystals arranged normal to the growth laminations,most clearly visible in cross-polarized light.Stromatoporoids cooccur with mollusc shells that are always either fully recrystallized or dissolved(present as internal and external moulds);this difference means that while molluscs are likely under-represented in the fossil record,stromatoproids are not,providing confidence for palaeoecological work on their assemblages.Stromatoporoids lack characters which would readily classify them as being originally aragonite or low-Mg calcite;they may have been high-Mg calcite but the evidence is circumstantial.Their peculiar diagenetic fabric also has implications for the debate about the relationship between stromatoporoids and the concept of aragonite/calcite seas,which requires more work.

RECENT ADVANCES IN GEOLOGICAL RESEARCH IN PARTS OF LESSER AND TETHYS HIMALAYA OF INDIA, SOUTH OF TIBETAN PLATEAU (KUMAON, GARHWAL AND ARUNACHAL PRADESH)

Recent advances in geological, palaeobiological and stable isotopic research in Kumaon\|Garhwal Lesser and Tethys Himalaya suggest that India was part of a major single super continent Rodinia during Neoproterozoic—Lower Palaeozoic times. The breakup of Rodinia and fragmentation of Gondwana land, existence of large Proto\|Tethys ocean, low latitude glaciation and global warming reflected by carbon isotopes and imprints of Pan African rifting events have been recently recorded in the Indian Himalaya, South of Tibetan Plateau (Tewari, 1998). A detailed correlation of these events in other parts of the NW and NE Himalaya and China further supports that these events are of global significance.The complete sequence of Lower Palaeozoic is missing in the Lesser Himalaya after regression of sea in the Lower Cambrian, however three major marine transgressions during Permian, Cretaceous and Eocene have been recorded over Terminal Proterozoic/Cambrian sequences. The discovery of microstromatolites and microbiota from the Menga (Buxa) dolomite of eastern Himalaya, Arunachal Pradesh (Tewari, 1999) also confirm Terminal Proterozoic age and sedimentation. The Permian marine transgression throughout the Himalaya suggest birth of Neotethys sea.Shallow marine reef builders, cyanobacteria\|bacteria and stromatolites of Early Carboniferous age were thriving in the Himalayan Tethys of India. 13 C records from Lesser and Tethys Himalaya reflect global isotopic variations in Neoproterozoic to Palaeozoic oceans of the world.

Volcanic Event Layers——A Marker Bed of Correlation of Coal Measures

Upper Carboniferous-Lower Permian volcanic event deposits from two cross sections in Nanpiao, Liaoning Province, and the Daqing Mountains, Inner Mongolia, were examined by systematic rock and mineral identification, differential thermal analysis, X-ray diffraction, scanning electron microscopy and trace element and rare earth element quantitative analysis. According to the results, twelve sequences of volcanic event deposits have been distinguished from bottom to top, including 34–39 volcanic event layers. As these layers each have their own distinctive petrological, mineralogical and geochemical characteristics and were derived from the same source, they provide new evidence for further ascertaining the distribution characteristics of volcanic event deposits on the northern margin of the North China plate and carrying out the stratigraphic correlation using volcanic event layers as marker beds.

Plate tectonic setting and genetic types of gas (oil)-bearing basins in China

The plate tectonic setting and genetic types of the gas (oil)-bearing basins in China are studied. Based on the history of break-up and amalgamation of Pangea, the three tectonic evolutionary megastages can be divided and the sedimentary basins in China are classified as Palaeozoic and Meso-Cenozoic basins. The Palaeozoic gas(oil)-bearing basins are mainly located in intracratonic basins, on which different types of Meso-Cenozoic basins are superimposed, and located in cratonic marginal basins and aulacogens destroyed with a slight degree, (n contrast, the Mesozoic and Cenozoic gas (oil)-bearing basins mainly formed in extensional foreland and intracontmental shortening flexural basins.