新疆中天山北缘望峰地区花岗岩的地球化学、锆石U-Pb年代学及Hf同位素组成研究

新疆中天山北缘望峰地区花岗岩的岩石学、地球化学及锆石U-Pb-Hf同位素研究表明:(1)望峰地区花岗岩岩石类型主要为二云母二长花岗岩和黑云母二长花岗岩,岩体高SiO2、Al2O3,中等富碱且相对富钾,A/CNK≥1.1,稀土含量中等(ΣREE=162.6×10-6～211.8×10-6),轻重稀土分馏明显且富集轻稀土,具中等Eu负异常(δEu=0.42～0.49),相对富集LILE和LREE,亏损Ba、Sr、P、Ti、Nb、Ta、HREE等,属高钾钙碱性过铝质S型花岗岩;(2)锆石LA-ICP-MSU-Pb定年获得岩浆结晶年龄为439.9±2.2Ma,成岩时代为早志留世;(3)锆石Hf同位素组成较均一,εHf(t)=-5.0～-1.3,平均-2.72,二阶段模式年龄tDM2变化范围在1294～1482Ma之间,岩浆主要来源于中元古代中期地壳结晶基底岩系的部分熔融,源岩为经历过风化旋回、成熟度较低的硬砂岩,形成于中天山北缘早古生代碰撞造山期同碰撞环境。

Geochemistry of the Palaeo–Mesoproterozoic Tadpatri shales,Cuddapah basin, India: implications on provenance,paleoweathering and paleoredox conditions

The Palaeo–Mesoproterozoic Tadapatri formation of the Cuddapah basin is comprised of clastic sedimentary rocks with minor carbonates and mafic–ultramafic sill bodies. Geochemistry of the shale is used to study the provenance, paleoweathering and paleoredox conditions of this Tadpatri formation in order to better understand the development of the Cuddapah basin during Palaeo–Mesoproterozoic time. The higher CIA(average 74.39), PIA(average 85.94) and CIW(average 87.59) values of the Tadpatri shales suggest intensely weathered sources.Higher Al2_ O_3/TiO_2(average 30.78) and LREE/HREE ratio(average 8.80) with negative europium anomaly indicate derivation of the clastic sediments from a felsic source rock. The geochemical parameters like U, U/Th, Cu/Zn,Ni/Co, V/Cr ratios reveal that the Tadpatri shales are mainly deposited in an oxic condition.

SEDIMENTARY ORGANIC MATTER'S CLASSIFICATION OF OIL-GAS SOURCE ROCKS IN CHINA

According to the study on the oil-gas source rocks in China for ten years,in connection with the microscopic, submicroscopic levels, the authors used the microscope photometry together with transmission electronic microscopy, scanning electronic microscopy and proposed a new classification for sedimentary organic matters.

Two types of the crust-mantle interaction in continental subduction zones

Plate subduction is an important mechanism for exchanging the mass and energy between the mantle and the crust,and the igneous rocks in subduction zones are the important carriers for studying the recycling of crustal materials and the crust-mantle interaction.This study presents a review of geochronology and geochemistry for postcollisional mafic igneous rocks from the Hong’an-Dabie-Sulu orogens and the southeastern edge of the North China Block.The available results indicate two types of the crust-mantle interaction in the continental subduction zone,which are represented by two types of mafic igneous rocks with distinct geochemical compositions.The first type of rocks exhibit arc-like trace element distribution patterns(i.e.enrichment of LILE,LREE and Pb,but depletion of HFSE)and enriched radiogenic Sr-Nd isotope compositions,whereas the second type of rocks show OIB-like trace element distribution patterns(i.e.enrichment of LILE and LREE,but no depletion of HFSE)and depleted radiogenic Sr-Nd isotope compositions.Both of them have variable zircon O isotope compositions,which are different from those of the normal mantle zircon,and contain residual crustal zircons.These geochemical features indicate that the two types of mafic igneous rocks were originated from the different natures of mantle sources.The mantle source for the second type of rocks would be generated by reaction of the overlying juvenile lithospheric mantle with felsic melts originated from previously subducted oceanic crust,whereas the mantle source for the first type of rocks would be generated by reaction of the overlying ancient lithospheric mantle of the North China Block with felsic melts from subsequently subducted continental crust of the South China Block.Therefore,there exist two types of the crust-mantle interaction in the continental subduction zone,and the postcollisional mafic igneous rocks provide petrological and geochemical records of the slab-mantle interactions in continental collision orogens.

Thermal evolution and applications of aromatic hydrocarbons in highly mature coal-bearing source rocks of the Upper Triassic Xujiahe Formation in the northern Sichuan Basin

Based on the GC-MS analytical data of aromatic fractions of over forty highly mature coal-bearing source rock samples collected from the Upper Triassic Xujiahe Formation in the northern Sichuan Basin, the thermal evolution of aromatic hydrocarbons during late-mature to over-mature stage （R0=1.13%-2.85%） was characterized, and aromatic indicators suitable for recognizing the organic source and sedimentary environment of high maturity source rocks were discussed. The results indicated that the concentrations of low carbon-cycle naphthalene as well phenanthrene series reduce gradually with increasing Ro at the highly mature levels. However, some high-cyclic components such as chrysene, benzofluoranthene, and benzo[e]pyrene are relatively enriched, in companying an enhancement of parent aromatic compounds. The variations are attributed to thermal cracking and polymerization reactions due to continuous dehydrogenation under enhanced burial temperature. As thermal maturity rises, MPI1 （Methylphenanthrene Index） values display a two-modal varying trend, namely, increasing when Ro is below 1.80% and decreasing above 1.8% Ro. The relationships between Ro and MPI1 are Ro=0.98MPI1＋0.37 for R0〈1.80% and R0=-0.90MPI1＋3.02 at R0〉1.8%, being different from the previous research. The amount of dibenzofurans declines sharply at Ro higher than 1.1%, leading to a significant change of relative composition among dibenzothiophenes, dibenzofurans and fluorenes （referred as three-fluorenes series composition）. Thus, this parameter appears to be unsuitable for identifying the sedimentary environment of the highly matured source rocks. 4-/1-MDBT （methyldibenzothiophene） ratio could be served as an effective indicator for organic facies, and can distinguish coals from mudstones at over-maturity in this case. The ratios of 2,6-/2,10-DMP （dimethylphenanthrene） and 1,7-/1,9-DMP and relative abundance of triaromatic steroids in these highly mature rocks could be considered as biological source parameters for relative input of terrigenous versus aquatic organic matter.

The distribution characteristic and its significance of compound specific isotopic composition of aromatic hydrocarbon from marine source rock and oil in the Tarim Basin, western China

Aromatic hydrocarbons are generally main distillation of crude oil and organic extract of source rocks. Bicyclic and tricyclic aromatic hydrocarbons can be purified by two-step method of chromatography on alumina. Carbon isotopic composition of in- dividual aromatic hydrocarbons is affected not only by thermal maturity, but also by organic matter input, depositional envi- ronment, and hydrocarbon generation process based on the GC-IRMS analysis of Upper Ordovician, Lower Ordovician, and Cambrian source rocks in different areas in the Tarim Basin, western China. The subgroups of aromatic hydrocarbons as well as individual aromatic compound, such as 1-MP, 9-MP, and 2,6-DMP from Cambrian-Lower Ordovician section show more depleted 13C distribution. The δ13C value difference between Cambrian-Lower Ordovician section and Upper Ordovician source rocks is up to 16.1%o for subgroups and 14%o for individual compounds. It can provide strong evidence for oil source correlation by combing the δ13C value and biomarker distribution of different oil and source rocks from different strata in the Tarim Basin. Most oils from Tazhong area have geochemical characteristics such as more negative δI3Cg_Mp value, poor gam macerane, and abundant homohopanes, which indicate that Upper Ordovician source rock is the main source rock. In contrast, oils from Tadong area and some oils from Tazhong area have geochemical characteristics such as high 613C9-MP, value, abun dant gammacerane, and poor homohopanes, which suggest that the major contributor is Cambrian-Lower Ordovician source rock.