Geochemistry of the Jurassic Mirdita Ophiolite (Albania) and the MORB to SSZ evolution of a marginal basin oceanic crust

The Middle Jurassic Mirdita Ophiolite in northern Albania is part of an ophiolite belt occurring between the Apulian and Pelagonian subcontinents in the Balkan Peninsula. The upper mantle and crustal units of the Mirdita Ophiolite show major changes in thickness, rock types, and chemical compositions from west to east as a result of its complex evolution in a suprasubduction zone (SSZ) environment. The  3–4-km-thick Western Mirdita Ophiolite (WMO) includes lherzolite–harzburgite, plagioclase–lherzolite, plagioclase–dunite in its upper mantle units and a plutonic complex composed of olivine gabbro, troctolite, ferrogabbro, and gabbro. These peridotites and gabbroic rocks are overlain directly by a  600-m-thick extrusive sequence containing basaltic pillow lavas and hyaloclastites. Sheeted dikes are rare in the WMO. The  12-km-thick Eastern Mirdita Ophiolite (EMO) includes tectonized harzburgite and dunite with extensive chromite deposits, as well as ultramafic cumulates including olivine clinopyroxenite, wehrlite, olivine websterite, and dunite forming a transitional Moho with the overlying lower crustal section. The plutonic rocks are made of pyroxenite, gabbronorite, gabbro, amphibole gabbro, diorite, quartz diorite, and plagiogranite. A well-developed sheeted dike complex has mutually intrusive relations with the underlying isotropic gabbros and plagiogranites and feeds into the overlying pillow lavas. Dike compositions change from older basalt to basaltic andesite, andesite, dacite, quartz diorite, to late-stage andesitic and boninitic dikes as constrained by crosscutting relations. The  1.1-km-thick extrusive sequence comprises basaltic and basaltic andesitic pillow lavas in the lower 700 m, and andesitic, dacitic and rhyodacitic massive sheet flows in the upper 400 m. Rare boninitic dikes and lavas occur as the youngest igneous products within the EMO. The basaltic and basaltic andesitic rocks of the WMO extrusive sequence display MORB affinities with Ti and Zr contents decreasing upsection (TiO₂ = 3.5–0.5%, Zr = 300–50 ppm), while _Nd(T) (+ 8 to + 6.5) varies little. These magmas were derived from partial melting of fertile MORB-type mantle. Fractional crystallization was important in the evolution of WMO magmas. The low Ti and HREE abundances and Cs and Ba enrichments in the uppermost basaltic andesites may indicate an increased subduction influence in the evolution of the late-stage WMO magmas. Basaltic andesites in the lower 700 m of the EMO volcanic sequence have lower TiO₂ ( 0.5%) and Zr ( 50 ppm) contents but _Nd(T) values (+ 7 to + 6.5) are similar to those of the WMO lavas. These rocks show variable enrichment in subduction-enriched incompatible elements (Cs, Ba, Th, U, LREE). The basaltic andesites through dacites and boninites within the upper 400 meters of EMO lavas show low TiO₂ ( 0.8–0.3%) and _Nd(T) (+ 6.5 to + 3.0). The mantle source of these rocks was variably enriched in Th by melts derived from subducted sediments as indicated by the large variations in Ba, K, and Pb contents. EMO boninitic dikes and lavas and some gabbroic intrusions with negative _{Nd (T)} values (− 1.4 and − 4.0, respectively) suggest that these magmas were produced from partial melting of previously depleted, ultra-refractory mantle. The MORB to SSZ transition (from west to east and stratigraphically upwards in the Mirdita Ophiolite and the progression of the _Nd(T) values from + 8.0 to − 4.0 towards the east resulted from an eastward shift in protoarc–forearc magmatism, keeping pace with slab rollback in this direction. The mantle flow above the retreating slab and in the arc-wedge corner played a major role in the evolution of the melting column, in which melt generation, aggregation/mixing and differentiation occurred at all levels of the sub-arc/forearc mantle. The SSZ Mirdita Ophiolite evolved during the intra-oceanic collapse and closure of the Pindos marginal basin, which had a protracted tectonic history involving seafloor spreading, protoarc rifting, and trench-continent collision.     

柴达木盆地北缘沉积凝灰质岩层段的地层时代

柴达木盆地北缘深部沉积凝灰质岩层段的地层归属存在2种观点,下侏罗统和石炭系。本文通过岩石薄片、微量元素、孢粉组合以及海相化石碎片等多种资料的综合分析,认为沉积凝灰质岩层段与其上的下侏罗统之间岩性、电性出现突变的主要原因是沉积时火山事件以及晚期方解石脉充填造成的,并不能代表下伏的老地层;沉积凝灰质岩层段的海相化石碎片为搬运再沉积的结果,没有地层指示意义;孢粉组合能反映沉积凝灰质岩层段沉积的地质年代,据此确认沉积凝灰质岩层段为下侏罗统湖西山组二段。     

拟刺葵(苦戈维尔叶)亚属Phoenicopsis(Culgoweria)在内蒙古鄂尔多斯盆地中侏罗统的发现

大量茨康类压型化石在鄂尔多斯盆地中侏罗世含煤地层延安组中被发现。本文根据叶外部形态和表皮构造特征,首次发现拟刺葵属的苦戈维尔叶亚属Phoenicopsis(Culgoweria),并建立了鄂尔多斯拟刺葵(苦戈维尔叶)(新种)Phoenicopsis(Culgowaria)ordosensis sp.nov。新种代表了该亚属在我国中侏罗世的第一个化石记录,为研究其地质、地理分布提供了新的证据,也为研究该类植物在欧亚大陆中侏罗世的多样性增添了新内容。     

澳大利亚波拿巴盆地侏罗系烃源岩热史及成熟史模拟

澳大利亚波拿巴盆地侏罗系海陆过渡相烃源岩热史及成熟史研究对波拿巴盆地浅水油气勘探具有指导意义.在恢复波拿巴盆地北部地史和热史的基础上,利用EASY％Ro模型计算了波拿巴盆地下—中侏罗统(Plover组泥岩)和中—上侏罗统(Elang组泥岩和Frigate组页岩)两套烃源岩的成熟史,并分别对比了下—中侏罗统和中—上侏罗统...     

Control of Facies and Potential on Jurassic Hydrocarbon Accumulation and Prediction of Favorable Targets in the Hinterland Region of the Junggar Basin

<正>Exploration practices show that the Jurassic System in the hinterland region of the Junggar Basin has a low degree of exploration but huge potential,however the oil/gas accumulation rule is very complicated,and it is difficult to predict hydrocarbon-bearing properties.The research indicates that the oil and gas is controlled by structure facies belt and sedimentary system distribution macroscopically,and hydrocarbon-bearing properties of sand bodies are controlled by lithofacies and petrophysical facies microscopically.Controlled by ancient and current tectonic frameworks,most of the discovered oil and gas are distributed in the delta front sedimentary system of a palaeo-tectonic belt and an ancient slope belt.Subaqueous branch channels and estuary dams mainly with medium and fine sandstone are the main reservoirs and oil production layers,and sand bodies of high porosity and high permeability have good hydrocarbon-bearing properties;the facies controlling effect shows a reservoir controlling geologic model of relatively high porosity and permeability.The hydrocarbon distribution is also controlled by relatively low potential energy at the high points of local structure macroscopically, while most of the successful wells are distributed at the high points of local structure,and the hydrocarbon-bearing property is good at the place of relatively low potential energy;the hydrocarbon distribution is in close connection with faults,and the reservoirs near the fault in the region of relatively low pressure have good oil and gas shows;the distribution of lithologic reservoirs at the depression slope is controlled by the distribution of sand bodies at positions of relatively high porosity and permeability.The formation of the reservoir of the Jurassic in the Junggar Basin shows characteristics of favorable facies and low-potential coupling control,and among the currently discovered reservoirs and industrial hydrocarbon production wells,more than 90%are developed within the scope of faciespotential index FPI0.5,while the FPI and oil saturation of the discovered reservoir and unascertained traps have relatively good linear correlation.By establishing the relation model between hydrocarbonbearing properties of traps and FPI,totally 43 favorable targets are predicted in four main target series of strata and mainly distributed in the Badaowan Formation and the Sangonghe Formation,and the most favorable targets include the north and east of the Shinan Sag,the middle and south of the Mobei Uplift,Cai-35 well area of the Cainan Oilfield,and North-74 well area of the Zhangbei fault-fold zone.     

国外海相油气田勘探实例之二西班牙卡萨布兰卡裂缝性喀斯特油田

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珠穆朗玛峰北坡下侏罗统层序地层及沉积相研究

珠穆朗玛峰北坡下侏罗统由乌垅组、康堆组和水佳组三个岩石地层单位组成。它们分别形成于碳酸盐缓坡、断陷盆地和碳酸盐台地三种不同的沉积环境，共包括６个沉积相。本区在早侏罗世经历了强烈的继陷下，属成熟裂谷盆地。     

内蒙古科右中旗扎木钦地区新民组地层的厘定及其地质意义

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