Characterization of Coal Porosity for Naturally Tectonically Stressed Coals in Huaibei Coal Field, China

The enrichment of coalbed methane (CBM) and the outburst of gas in a coal mine are closely related to the nanopore structure of coal. The evolutionary characteristics of 12 coal nanopore structures under different natural deformational mechanisms (brittle and ductile deformation) are studied using a scanning electron microscope (SEM) and low-temperature nitrogen adsorption. The results indicate that there are mainly submicropores (2~5 nm) and supermicropores (<2 nm) in ductile deformed coal and mesopores (10~100 nm) and micropores (5~10 nm) in brittle deformed coal. The cumulative pore volume (V) and surface area (S) in brittle deformed coal are smaller than those in ductile deformed coal which indicates more adsorption space for gas. The coal with the smaller pores exhibits a large surface area, and coal with the larger pores exhibits a large volume for a given pore volume. We also found that the relationship between S and V turns from a positive correlation to a negative correlation when S>4 m2/g, with pore sizes <5 nm in ductile deformed coal. The nanopore structure (<100 nm) and its distribution could be affected by macromolecular structure in two ways. Interconversion will occur among the different size nanopores especially in ductile deformed coal

Caractéristiques de l évolution de la partie orientale du bloc de Chine du Sud au Mésozoïque supérieur et implications géodynamiques (Etude pluridisciplinaire de la mise en place des massifs granitiques de Qingyang-Jiuhua, Hengshan et de la côte du Fujian et des structures tectoniques associées)

La vaste distribution géographique et la longue durée du magmatisme au Mésozoïque supérieur (Jurassique et Crétacé) en Chine du Sud présente le cas unique dans le monde. Ceci présente un laboratoire naturel très favorable a l étude des processus de magmatogénèse, et des modes de mise place des plutons granitiques. Il permet également d aborder l analyse des relations magmatisme-tectonique et les contextes géodynamiques de la mise en place de magma dans leur cadre lithosphérique. Depuis les années 50, et surtout les années 90, des scientifiques ont mis un effort important sur la cartographie géologique, mené des études pétrologiques et géochronologiques et ainsi obtenu une base solide pour la compréhension de l évolution tectonique du Bloc de Chine du Sud (SCB). Cependant, des questions fondamentales restent encore sans réponses ou vivement débattues. Dans le but de progresser sur ces sujets fondamentaux, nous avons mené des études pluridisciplinaires sur les massifs d âge Mésozoïque supérieur de Qingyang-Jiuhua (Province d Anhui), Hengshan (Province de Hunan) et certains plutons affleurant dans la zone côtière du Fujian. Le choix des massifs est fonde sur leur distance variable par rapport à la paléozone de subduction, les âges comparables de ces massifs et les déformations associées. Les méthodes d étude comprennent l observation de terrain, l analyse microscopique de lames minces, la datation par U-Pb de monazite, l ASM, le paléomagnétisme, la modélisation gravimétrique et la barométrie à partir de Al-total dans l amphibole magmatique. Bien que chaque massif présente des caractéristiques distinctes, ils partagent des points communs du point de vue de leur orientation préférentielle, de la déformation de leurs encaissants et de l influence de la tectonique régionale sur leur mise en place, D après nos nouveaux résultats et en intégrant les données précédentes, nous discutons dans cette thèse les contextes tectoniques de mise en place de ces massifs granitiques et l évolution géodynamique de SCB, et proposons un scénario géodynamique en 3 étapes. (1) Pendant la période 145-130 Ma, la subduction vers le NW de la plaque Paléo-Pacifique sous le continent asiatique fait rapprocher le micro-continent de l Ouest-Philippines avec le continent de Chine du Sud, produisant l important magmatisme d arc et formant un régime tectonique en extension en SCB ? Dans l arrière-arc; (2) Pendant la période 130-110 Ma, dûe à la collision entre le micro-continent de l Ouest Philippines et SCB, une structure compressive vers le NW a été développée dans la zone de Changle Nan ao, produisant des déformations ductiles. Cependant, l intérieur de la partie orientale du SCB était encore en régime tectonique extensif de direction NW-SE; (3) Pendant la période 105-90Ma, une nouvelle zone de subduction a été développée au SE du micro-continent de l Ouest Philippines, le panneau subductant atteint la zone de Changle-Nan ao, avec probablement des morceaux de panneau cassé, provocant l ascension de l asthénosphère, responsable de la mise en place d importants massifs granitiques et de filons. La tectonique de SCB pendant cette période est caractérisée par un système tectonique d extension générale. Ce dispositif a été significativement perturbe par l ouverture oligo-miocène de la mer de Chine du Sud et par la compression miocène de la marge à Taiwan. Ce modèle géodynamique reste à être amélioré par de futures investigations géologiques, géophysiques et géochimiques.The vast distribution and long duration of the Late Mesozoic magmatism in the eastern part of South China presents a unique case in the world. This offers a natural laboratory to study the process of magma genesis, the magma emplacement mode, the relationship between magmatism and tectonics, the geodynamic role on the magma emplacement and lithospheric evolution. Since 50 s, particularly 90 s of the last century, geoscientists have made important efforts in geological cartography and carried out numerous studies with remarkable scientific achievements, building a solid background to understand the tectonic evolution of the South China Block (SCB). However, certain fundamental questions mentioned above remain unsolved and/or are in hot debate. In order to make progress in these scientific issues, we have carried out in a multi-disciplinary study in the Late Mesozoic Qingyang-Jiuhua massif, Hengshan massif and Fujian coastal zone according to their distance with respect to the paleo subduction zone of the Paleo-Pacific plate, the ages of granitic massifs and related tectonics, including field observation on the structure geology, micro-observation on thin section, U-Pb dating on monazite, AMS, paleomagnetism, gravity modeling and P condition concern the granite emplacement. In the view of deformation in these granitic massifs and their country rocks, mode and influence of regional tectonics on the emplacement, though each studied zone reveals its distinguished characteristics, they show some intrinsic and common relationships between them. With our new results and integrating previous data, in this thesis, we discuss the tectonic context of emplacement of these Late Mesozoic magmatic massifs and the geodynamic evolution of the SCB., We propose a 3-step geodynamic model: (1) during 145-130 Ma period, the Paleo-Pacific plate subducted northwestwardly, the West Philippines micro-continent, approaching to SCB, important subduction-related arc volcanism was produced in the coastal areas of Southeast China coast (Zhejiang-Fujian-Guangdong), forming a back-arc extension tectonic system in SCB; (2) during 130-110 Ma period, due to the collision between the West Philippines microcontinent and SCB, the compressional tectonic structures were developed in the Changle-Na ao coastal zone, producing ductile deformation zones. However, the inland of the eastern part of SCB was under a NW-SE extensional tectonic regime; (3) during 105-90 Ma period, a new subduction zone was developed in the SE flank of the West Philippines micro-continent, the subducting slab reached the Changle-Nan ao tectonic belt, with the possible break-off of slab, the asthenospheric ascent was responsible for the important emplacement of plutonic massifs and dykes. The tectonics of the eastern part of SCB was characterized by a general extensional system in this period. This tectonic pattern has been significantly disturbed by the Oligocene-Eocene opening of the South China sea,and the Miocene shortening of the SCB margin in Taiwan. Of course, this model should be improved by more geological, geophysical and geochemical investigations.ORLEANS-SCD-Bib. electronique (452349901) / SudocSudocFranceF

Mineralogy, Geochemistry and Tectonic Setting of the Raobazhai Ultramafic Complex, North Dabie

The Raobazhai ultramafic complex is located in the north of the Dabie Mountains and is composed of spinel peridotites accompanied by a few lenticular mafic metamorphic rocks. The spinel peridotites are mostly harzburgite, along with minor dunite and lherzolite. This study reports the petrological, geochemical, and Re-Os isotopic data of spinel and chromite harzburgites from Raobazhai. The major and trace whole-rock geochemistry characteristics indicate that the rocks are remnants of partial melting to different degrees (6–17%). Both mineral and whole-rock geochemistry showed typical abyssal peridotite affinity. Due to the presence of water-bearing minerals, the Sr, Ba, and U were enriched, and the Nb, Zr, and Hf were depleted, which can be attributed to the strong metasomatism of the boninitic melting/fluid in the fore-arc domain. The flat distribution of platinum group elements (PGE) and the decoupling of Pt-Pd were also the result of the fore-arc melting/fluid interaction. The 187Os/188Os ratios (0.1149–0.1266) were generally lower than the recommended value of the primitive mantle and fell within the abyssal peridotite isotope range. This indicated that the Raobazhai harzburgites were likely mantle peridotites with oceanic characteristics that underwent a fore-arc boninitic melting/fluid transformation event

Mineralogy, Geochemistry and Tectonic Setting of the Raobazhai Ultramafic Complex, North Dabie

The Raobazhai ultramafic complex is located in the north of the Dabie Mountains and is composed of spinel peridotites accompanied by a few lenticular mafic metamorphic rocks. The spinel peridotites are mostly harzburgite, along with minor dunite and lherzolite. This study reports the petrological, geochemical, and Re-Os isotopic data of spinel and chromite harzburgites from Raobazhai. The major and trace whole-rock geochemistry characteristics indicate that the rocks are remnants of partial melting to different degrees (6&ndash;17%). Both mineral and whole-rock geochemistry showed typical abyssal peridotite affinity. Due to the presence of water-bearing minerals, the Sr, Ba, and U were enriched, and the Nb, Zr, and Hf were depleted, which can be attributed to the strong metasomatism of the boninitic melting/fluid in the fore-arc domain. The flat distribution of platinum group elements (PGE) and the decoupling of Pt-Pd were also the result of the fore-arc melting/fluid interaction. The 187Os/188Os ratios (0.1149&ndash;0.1266) were generally lower than the recommended value of the primitive mantle and fell within the abyssal peridotite isotope range. This indicated that the Raobazhai harzburgites were likely mantle peridotites with oceanic characteristics that underwent a fore-arc boninitic melting/fluid transformation event