The characteristic and evolution of coal-forming swamp in Hanshuiquan district,Santanghu Coalfield, Xinjiang,NW China,during the Middle Jurassic: evidence from coal petrography,coal facies and sporopollen

Santanghu Coalfield is the largest integrated coalfield exploration area in China. The major coal seams developing in Xishanyao Formation (Middle Jurassic) are the high-quality steam coals characterized by large thickness, favorable horizontal continuity and high coal quality. In this paper, twenty-two samples were collected from the three typical boreholes in Hanshuiquan disirict, representing the 11 coal seam sequences (7#,8#,9#,13#, 14#,15#,17#,18#,19#,20#,22#), respectively. The petrographic characteristics of the coal-bearing sequence in Xishanyao Formation were firstly summarized systematicly, and then the coal-forming swamp characteristics and succession mechanism of the coal seam in Xishanyao Formation were defined by analyzing the samples. The maceral composition, structure, geochemical and geophysical characteristics of coal are in eluded in original genetic criteria of coal-forming swamp an alysis. And the composition of coal petrography, maceral and microlithotype are the most frequently used parameters. Coal is composed of microscopic constituents and inorganic substances. The Xishanyao Formation maceral mainly consists of vitrinite (65.74%-97.01 %), inert i nite (1.93%-34%), and the exinite shows the mode of regular change. The coal-forming swamp in Xishanyao Formation possesses the characteristics of mainly marsh, wet forest swamp facies, and shallow water covered forest swamp facies, and a few of coal seams distribute in the deep water covered forest swamp facies. In addition, the sporopollens in Xishanyao Formation are mainly Pinaceae evergreen broad leaf and needle-leaved plants. Osmundaceae, Cyatheaceae and Lygodiaceae, indicating that the warm and humid tropic-subtropical climate conductive to the persistent growth of coal-forming plants in the Middle Jurassic. The coal-forming swamp shows the characteristics of vertically upward fluctuation through the periodic transition. It indicates a shallow-deep-shallow change process of the water covered depth in the swamp. This is the prin ci pal factor for the formation of the high-quality and continuous coal seam in Hanshuiquan district, Santanghu Coalfield.

Peraluminous granitoids within the Hangloa area,Adamawa-YadéDomain,Cameroon:Petrogenesis and tectonic implication

Hangloa granitoids form part of the wide range calc-alkaline Pan-African granitic suites within the Adamawa Yade Domain(AYD)in Cameroon.There are several reports on metaluminous granitoids within this domain.The peraluminous suite has been locally reported and their petrogenesis is not fully understood.Petrography and whole-rock geochemistry were used to study the petrogenesis/formation of granitic rocks within this area.The results show that the granitoids are composed of quartzo-feldspathic,made up of granites,monzonites and quartz monzonites which were intruded in the Paleoproterozoic orthogneissic basement.The major and trace element compositions show that they are high-K calc-alkaline to shoshonites,with S-type affinity.The molar ratio A/CNK is>1.1,while the ratio of CaO+Na_(2)O/Al_(2)O_(3) is generally<1 making them strongly peraluminous.The REE shows enrichment in the LREE over the HREE,with(La/Yb)N varying from 11.9 to 53.32,(Dy/Yb)N from 0.77 to 2.13 and moderately negative Eu anomaly((Eu/Eu^(*))N range from 0.42 to 0.93).Most granite samples show depletion in P,with CaO/Na_(2)O<0.3 and Rb/Sr≤1 indicative of clay-poor metapelitic source,while the others show clay-rich metagreywackes sources.The strong peraluminosity,S-type affinity,high Ba/Sr,Ba/Rb and low Rb/Sr indicate they are crustal-derived.The compositional variation might be induced by the partial melting of different source materials followed by fractional crystallization of the granitic magma.The source nature requires fragments of Paleoproterozoic metasedimentary and metaigneous rocks derived from the collision between the north-central Cameroon block and the Congo Craton during the Pan-African.

Petrogenesis of Peridotites from the Purang Ophiolite in Western Part of Yarlung-Zangbo Suture Zone, Southern Tibet

Peridotites are an important part of ophiolites： they not only record plate tectonic settings and events, but also offer help to interpret the composition of the mantle and the effect of the deep mantle. The Yarlung-Zangbo suture zone extends more than 2000 km along southern Tibet,