Paleocene-Eocene potential source rocks in the Avengco Basin,Tibet: Organic geochemical characteristics and their implication for the paleoenvironment     

《Journal of Asian Earth Sciences》2014

The Avengco Basin is located in the western part of the Tibetan Plateau and is similar to the Nima Basin in the central part of the plateau and the Lunpola Basin in the eastern part in terms of sedimentary characteristics and tectonic settings, which are well known to provide a good source rock potential. However, the organic geochemical characteristics of the Paleocene-Eocene potential source rocks in the Avengco Basin have been under debate. Thirty-four marl and mudstone outcrop samples of the Niubao Formation in the Avengco Basin were collected and subjected to the following analyses: total organic carbon (TOC), Rock–Eval pyrolysis, stable carbon isotopes of kerogen, gas chromatography (GC) and gas chromatography–mass spectrometry (GC–MS). Here, we present the results indicating the organic matter of the upper Niubao Formation is mainly composed of Type II kerogen with a mixed source, which is dominated by algae. However, the lower Niubao Formation has the less oil-prone Type II–III kerogen, and the sources of the organic matter are mainly terrestrial plants with less plankton. In addition, the samples are thermally immature to marginally mature. The Niubao Formation was deposited in an anoxic–oxic environment which was brackish with an imperceptible stratified water column. The upper Niubao Formation has a medium to good hydrocarbon-generating potential. However, the lower Niubao Formation has a zero to poor hydrocarbon-generating potential.  相似文献   

Estimation of compressional seismic wave attenuation of carbonate rocks in Abu Dhabi,United Arab Emirates     

《Comptes Rendus Geoscience》2014,346(7-8):169-178

The subsurface geology of Abu Dhabi in the United Arab Emirates is primarily composed of carbonate rocks. Such media are known to be highly heterogeneous. Very few studies have attempted to estimate attenuation in carbonate rocks. In Abu Dhabi no attenuation profile has been published. This study provides the first seismic wave attenuation profiles in Abu Dhabi using dense array of VSP data. We estimated three attenuation profiles: the apparent, the scattering, and the intrinsic attenuations. The apparent attenuation profile was computed using amplitude decay and spectral-ratio methods. The scattering attenuation profile was estimated using a generalized reflection–transmission matrix forward model. It is usually estimated from the sonic log, but to be more consistent with the apparent attenuation, we succeeded in this paper to estimate it from the VSP data. We subtracted the scattering attenuation from the apparent attenuation to deduce the intrinsic attenuation. The results of the study indicate that the scattering attenuation is significant compared to the published studies that are mainly based on clastic rocks. The high scattering attenuation can reach up to 0.02. It can be explained by the strong heterogeneity of the carbonate rocks. This study demonstrates that the Simsima and Rus Formations have considerable scattering and intrinsic attenuations. These formations are considered aquifers in Abu Dhabi; we therefore interpreted this high intrinsic attenuation zones to be due to the heterogeneity and to the fluids contained in these formations. The Umm-Er-Radhuma Formation is a more homogenous formation with limited aquifer potential. Hence, scattering and intrinsic attenuations of the Umm-Er-Radhuma Formation are low.  相似文献   

Early Permian East-Ujimqin mafic–ultramafic and granitic rocks from the Xing’an–Mongolian Orogenic Belt,North China: Origin,chronology, and tectonic implications     

《Journal of Asian Earth Sciences》2014

The East-Ujimqin complex, located north of the Erenhot–Hegenshan fault, North China, is composed of mafic–ultramafic and granitic rocks including peridotite, gabbro, alkali granite, and syenite. We investigated the tectonic setting, age, and anorogenic characteristics of the Xing’an–Mongolian Orogenic Belt (XMOB) through field investigation and microscopic and geochemical analyses of samples from the East-Ujimqin complex and LA-MC-ICP-MS zircon U–Pb dating of gabbro and alkali granite. Petrographic and geochemical studies of the complex indicate that this multiphase plutonic suite developed through a combination of fractional crystallization, assimilation processes, and magma mixing. The mafic–ultramafic rocks are alkaline and have within-plate geochemical characteristics, indicating anorogenic magmatism in an extensional setting and derivation from a mantle source. The mafic–ultramafic magmas triggered partial melting of the crust and generated the granitic rocks. The granitic rocks are alkali and metaluminous and have high Fe/(Fe + Mg) characteristics, all of which are common features of within-plate plutons. Zircon U–Pb geochronological dating of two samples of gabbro and alkali granite yielded ages of 280.8 ± 1.5 and 276.4 ± 0.7 Ma, placing them within the Early Permian. The zircon Hf isotopic data give inhomogeneous ε_Hf(t) values of 8.2–14.7 for gabbroic zircons and extraordinary high ε_Hf(t) values (8.9–12.5) for the alkali granite in magmatic zircons. Thus, we consider the East-Ujimqin mafic–ultramafic and granitic rocks to have been formed in an extensional tectonic setting caused by asthenospheric upwelling and lithospheric thinning. The sources of mafic–ultramafic and granitic rocks could be depleted garnet lherzolite mantle and juvenile continental lower crust, respectively. All the above indicate that an anorogenic magma event may have occurred in part of the XMOB during 280–276 Ma.  相似文献   

金沙江缝合带西段蛇绿岩与弧火山岩成对性关系——来自地球化学和LA-ICP-MS锆石U-Pb年龄证据     

刘银  李荣社  计文化  潘术娟  陈奋宁  张海迪 《地质通报》2014,33(7):1076-1088

对金沙江缝合带西段青海治多地区的多彩蛇绿混杂岩和当江荣中酸性岛弧火山岩进行了研究,野外地质剖面显示,蛇绿岩主要由辉长岩、堆晶辉长岩和玄武岩组成,缺少地幔橄榄岩单元。通过对蛇绿岩内部细粒辉长岩、基性熔岩的地球化学测试及堆晶辉长岩的LA-ICP-MS锆石U-Pb测年发现,基性熔岩可分为2种类型,即洋岛玄武岩OIB型和MORB-IAT型。前者并非蛇绿岩组分,为构造就位时带入;后者为过渡类型,具有典型洋中脊—岛弧蛇绿岩地球化学特征。辉长岩具有明显的TNT槽等岛弧信号,与类型二均属于蛇绿岩成分。测得的堆晶辉长岩中锆石U-Pb年龄为252.50Ma±0.58Ma(MSWD=0.95),是蛇绿岩的形成年龄。研究认为,多彩蛇绿岩与当江荣火山岩具有成对性关系,结合造山带沟—弧—盆体系构造格局,认为前者形成于岛弧偏海沟的弧前构造背景,是晚二叠世金沙江洋持续俯冲的产物。  相似文献   

Grain-size distribution characteristics and sedimentary environment of Silurian- -Devonian sandstone in Keping area of Xinjiang Province     

YAN Kun  MA Wei  LIU Xiaodan  LI Na 《中国地质调查》2014,7(4):76-84

In order to systematically study the evolution characteristics of Silurian- -Devonian sedimentary environment in Keping area, the authors analyzed the sandstone in detail through sedimentary, stratigraphic and grain size analysis. Four sedimentary environments, including river-controlled delta, tidal-controlled delta, tidal flat and coast, were identified, with their own unique grain-size characteristics and probability cumulative curves. River-controlled delta is featured with typical two stages, hop-suspension transition and low-skew multistage. Fan delta is featured with the upper arch arc. Tidal-controlled delta is featured with typical three stages and multistage. Coastal area is feotured with high oblique two stages and high oblique multistage. The sedimentary environment gradually changed from wet river-controlled delta to dry coastal deposit from Silurian to Devonian, with the increasing maturity of sandstone. This indicates that Keping area was gradually away from provenance area and in the background of structural stability.  相似文献   

Pressure-temperature Evolution of the Metapelites in the Motuo Area,the Eastern Himalayan Syntaxis     

DONG Hanwen  XU Zhiqin  LI Yuan  LIU Zhao 《《地质学报》英文版》2014,88(2):544-557

The Motuo area is located in the east of the Eastern Himalayan Syntaxis. There outcrops a sequence of high-grade metamorphic rocks, such as metapelites. Petrology and mineralogy data suggest that these rocks have experienced three stages of metamorphism. The prograde metamorphic mineral assemblages(M1) are mineral inclusions(biotite + plagioclase + quartz ± sillimanite ± Fe-Ti oxides) preserved in garnet porphyroblasts, and the peak metamorphic assemblages(M2) are represented by garnet with the lowest XSps values and the lowest XFe# ratios and the matrix minerals(plagioclase + quartz ± Kfeldspar + biotite + muscovite + kyanite ± sillimanite), whereas the retrograde assemblages(M3) are composed of biotite + plagioclase + quartz symplectites rimming the garnet porphyroblasts. Thermobarometric computation shows that the metamorphic conditions are 562–714°C at 7.3–7.4 kbar for the M1 stage, 661–800°C at 9.4–11.6 kbar for the M2 stage, and 579–713°C at 5.5–6.6 kbar for the M3 stage. These rocks are deciphered to have undergone metamorphism characterized by clockwise P-T paths involving nearly isothermal decompression(ITD) segments, which is inferred to be related to the collision of the India and Eurasia plates.  相似文献   

内蒙古中部镁铁质-超镁铁质岩带铜镍硫化物矿床地质特征   总被引：1，自引：0，他引：1       下载免费PDF全文

党智财  李俊建  宋雪龙  赵泽霖  付超  唐文龙 《地质找矿论丛》2014,29(3):329-335

内蒙古中部出露1条近EW向的含铜镍镁铁质-超镁铁质岩带,宽约30km,长约400km。该岩带横跨2个构造单元:宝音图岩浆弧和狼山—白云鄂博台缘坳陷。文章按构造单元将其划分为2个成矿亚带:额布图—特颇格日图矿带和克布—小南山矿带。额布图—特颇格日图矿带构造单元为宝音图岩浆弧,主要形成以富镍为主、伴生Co元素的镍矿床(点),包括额布图、达布逊和特颇格日图;克布—小南山矿带构造单元为狼山—白云鄂博台缘坳陷,形成以富铜、镍为主,伴生Pt,Pd等铂族元素的铜-镍(PGE)矿床,包括克布、黄花滩和小南山。赋矿岩体呈似层状、透镜状、扁豆状及串珠状产出,矿石矿物以金属硫化物为主,含少量氧化物。区内不同构造单元内岩体形成2种不同类型矿床,其原因可能是古亚洲洋板块向华北板块北缘俯冲,岩石圈地幔发生部分熔融形成岩浆,在不同构造单元底侵上升,经过不同的介质及围岩,形成2种明显差异的成矿亚带。  相似文献   

通化县四方山铁矿地质特征     

刘先权  高明珠  韩雪  车海龙  路猛  张庆连 《吉林地质》2014,(3):50-55

四方山铁矿经历了三期变形。第一期,当太古宙表壳岩形成后,来自东西向挤压作用,地层和矿体(S0)形成近南北向紧密褶皱构造。第二期,来自北西—南东方向挤压作用,使已经变形地层和矿体(S1)又一次变形,形成走向北东—南西叠加褶皱构造,这一期为四方山铁矿主期构造。第三期,来自北—西向和南东向不对称推力作用,使已经历二次变形地层、矿层均形成了S形,使S2又一次变形。  相似文献   

豫西熊耳群火山岩中杏仁体研究及其意义     

唐洪敏  王娜  王永亮 《四川地质学报》2014,34(3):330-332

河南豫西中元古界熊耳群火山岩系广泛分布,且遭受多次构造活动、岩浆侵入及剥蚀的影响。区域火山活动贯穿整个中元古代熊耳期,时间自NE向SW由早到晚。通过对熊耳群火山岩的岩石学研究,确定了熊耳群的岩石系列及火山岩中的杏仁体,通过对其中杏仁体分布、形状及内部构造的研究,可为今后有找矿勘查打好基础。  相似文献   

羌塘地块南部晚白垩世火山岩离子探针测年及其对红层时代的约束   总被引：3，自引：0，他引：3  

吴珍汉  吴学文  赵珍  陆露  叶培盛  张耀玲 《地球学报》2014,35(5):567-572

羌塘地块南部广泛出露陆相红层,1:25万区域地质调查将大部分红层划归为中新统康托组,但缺乏可靠的年代学依据。野外观测发现火山岩与红层之间存在喷发不整合接触关系,室内从火山岩选出很多岩浆锆石;应用离子探针U-Pb同位素测年方法精确测定岩浆锆石年龄,能够为研究火山喷发期次和红层形成时代提供重要依据。对羌塘地块南部红层内部粗面安山岩夹层—比洛错火山岩和扎加藏布北侧红层上覆安山岩,挑选岩浆锆石进行高精度的离子探针U-Pb同位素测年,发现比洛错粗面安山岩锆石206Pb/238U同位素年龄为(83.3±1.3)Ma,扎加藏布北侧安山岩锆石206Pb/238U同位素年龄为(75.65±0.82)Ma。这些年龄良好地揭示了晚白垩世不同期次的火山喷发时代,同时为红层形成时代和红层盆地演化提供了重要的年代学约束。根据比洛错和扎加藏布北侧火山岩的锆石U-Pb同位素测年资料,将羌塘盆地南部红层时代归属上白垩统阿布山组,这对分析羌塘地块南部油气地质构造保存条件和构造地貌演化具有重要意义。  相似文献