封闭系统中的白云石化作用及其石油地质学和矿床学意义——以四川盆地东北部三叠系飞仙关组碳酸盐岩为例

作为优质储层的四川盆地东北部三叠系飞仙关组的结晶白云岩是通过埋藏成岩过程的封闭条件下的白云石化作用形成的。岩石所具有的高孔隙度与封闭体系中的白云石化反应:2CaCO_3+Mg^(2+):CaMg(CO_3)_2+Ca^(2+)有关。埋藏成岩体系中的高锶流体是该封闭条件下白云石化作用的产物,深埋藏条件下的热化学硫酸盐还原作用是锶进一步富集的原因,因而三叠系的大型和超大型天青石矿床的成因与这些因素有关。结晶白云岩极低的锰含量、与同期海水类似的δ^(13)C值表明白云石化流体具有强烈的海源色彩,同时也说明白云石化过程没有与大气水交换;相对较低的δ^(18)O值表明白云石化发生在较晚的埋藏成岩阶段。大多数已有的白云石化机制都是基于近地表成岩条件建立的,系统具有良好的开放性,但开放体系中的白云石化(或白云石沉淀)作用对油气储集空间和与成岩过程元素迁移有关的沉积层控矿床的形成没有多少实际意义。在四川盆地东北部三叠系飞仙关组地层中,作为非储层的微晶或泥晶白云岩以及原始结构保存的粒屑白云岩的白云石化作用主要是在有大气水介入的开放体系中发生的。

华南地区栖霞组菊花状天青石的交代及其地质意义

本文在收集大量菊花石标本的基础上 ,通过岩石薄片镜下鉴定及X射线衍射分析 ,识别了华南地区栖霞组菊花石假象内矿物的成因类型 ,建立了矿物交代序列 ,并通过对菊花石假象内各种矿物成分的电子探针分析和对交代方解石、脉方解石及其围岩的氧、碳同位素分析 ,探讨了菊花石交代过程中的成岩环境变化 。

贵州台江早寒武世台江生物群

台江八郎下、中寒武统界线之下的灰绿色粉砂质泥岩中存在一个布尔吉斯页岩型生物群 ,即台江生物群。现已发现的台江生物群含 8个门类 4 0多个属的生物化石。其中三叶虫特多 ,其次为刺胞动物、“蠕虫动物”、海绵动物等。非三叶虫节肢动物、软躯体化石很少。这一生物群形成于浅海内陆棚环境。

碳酸岩是大陆岩石圈构造背景和地幔交代作用的指示岩石

根据已知碳酸岩的地质产状、岩石学特征、Nd—Sr—Pb同位素及痕量元素地球化学特征，结合高温高压实验岩石学资料，论述了其地幔源区的物质成分、交代过程、软流圈地幔部分熔融机制和碳酸岩岩浆的演化模型碳酸岩既可以产生于裂谷环境，由起源于软流圈地幔的霞石质超基性-基性岩浆经液态不混溶作用而形成，与硅酸不饱和过碱性杂岩构成环状碳酸岩-碱性杂岩；也能够产生于碰撞造山过程中派生的引张岩石圈断裂带，直接导源于岩石圈地幔的低程度部分熔融作用，形成单一的透镜状。

塔里木盆地下寒武统底部高熟海相烃源岩中有机质的赋存状态

近年来的研究证明 ,中新生代未熟 -低熟海相富有机质泥质烃源岩中有机质是通过溶解在水中的分子规模的碳有机质以化学吸附的形式被吸附到矿物表面上和蒙脱石结构层内 .然而 ,对于高熟海相泥质烃源岩中有机质的赋存状态却少有报道 .通过对塔里木盆地下寒统底部高熟海相泥质烃源岩的有机碳含量、矿物表面积、扫描电镜和透射电镜的综合分析 ,得到了其有机质以细小的颗粒状保存于沉积物颗粒之间的结论 .同时 ,通过高熟海相烃源岩与现代未熟海相烃源岩有机质赋存状态的对比 ,提出了值得进一步研究的有关科学问题 .

月球的起源与地球内部结构极早期演化

基于地球内部结构模型 (EISEM) ,建立了一个模型 (IAMTM)来模拟地球早期绝热压缩过程中的地球内部角速度的转移。计算的时间范围是从地球吸积完成开始 5Ma。改变不同的参数 ,模型得出结论 ,当t=1 85Ma时 ,由于地心引力不稳定性 ,地球外层的熔融层从地球赤道甩出。抛射过程持续了 0 0 5～ 0 15Ma ,抛射出的物质质量为 1 2～ 2 5M0 (M0 是现在的月球质量 ) ,这些物质碎片相互碰撞聚集逐渐在Roche极限附近形成月球。随着物质分异和地核的逐渐增大 ,地球的半径在抛射后减小到最小值 (R =5 0 75 16km)。随着潮汐摩擦力和地球体积的增大 ,地球自转角速度变慢。 2Ma后地球和月球之间的距离增大到

贵州中寒武世凯里生物群中的蠕形动物化石

描述了凯里生物群中的蠕形动物Ottoia ,Maotianshania ,Palaeoscolex ,Circocosmia?及Selkirkia。这些软躯体的蠕虫化石在凯里生物群中都是首次发现。其中Ottoia也发现于布尔吉斯页岩生物群 ,Maotianshania ,Circocosmia ?则见于澄江生物群 ,而Palaeoscolex则从澄江生物群至布尔吉斯页岩生物群中都有保存 ,这是凯里生物群处于承前启后位置的又一证据。蠕动动物的发现 ,增加了凯里生物群软躯体化石内容 ,反映了凯里生物群是典型的布尔吉斯页岩生物群。

中国坡缕石晶体化学研究

本研究通过对坡缕石化学成分分析数据的系统数理统计分析及结合透射电镜研究提出了Al2O3、Fe2O3、Mgo同SiO2一样为坡缕石的自身氧化物组分，而CaO、K2O、Na2O、TiO2等为主要以吸附态存在的非自身氧化物成分。相应的坡缕石晶体化学式为（Mg、Al、Fe、）5SiO20。（OH）2：·4（H2O）·nH2O（□—空位）。Ala3+、Fe3+、Mg2+异价类质同象置换的线性方程为Mg2+=4．978－1．519（Al3+＋Fe3+）。穆斯堡尔谱、红外光谱及（020）面网晶格条纹象的分裂研究表明了阳离子占位形式：MIM2M3M3M1，其中边缘M1=（Fex3＋）（Mg），中间M3=（A13+＋Fe3＋），M2=Al3+（缺Fe3+）或M2=（Fe3+＋Al3+）或等于（Fe3+）和（□）。坡缕石的Mg2+－Al3+－Fe3+组分三角形图解揭示了：富Fe外生沉积成因为主的土状坡缕石和贫Fe富Al的热液交代蚀变充填作用为主的纤维状坡缕石的成分成因分类。

超高压变质岩中柯石英—石英相变动力学研究的评述

含柯石英超高压变质岩的发现是陆壳岩石向地慢深部俯冲的岩石学证据，也揭示了深部变质沉积物折返地表的可能性。超高压变质岩的形成和折返机制是当前地球科学中最有挑战性的前沿课题之一，具有深刻的大陆动力学意义。文中讨论和总结了世界上8个典型超高压变质岩地区的柯石英和柯石英假像特征，以及近10年来关于柯石英的显微结构、相变动力学和流变学研究成果。

Geology and D-O-C Isotope Systematics of the Tieluping Silver Deposit,Henan, China: Implications for Ore Genesis

The Tieluping silver deposit, which is sited along NE-trending faults within the high-grade metamorphic basement of the Xiong'er terrane, is part of an important Mesozoic orogenic-type Ag-Pb and Au belt recently discovered. Ore formation includes three stages: Early (E), Middle (M) and Late (L), which include quartz-pyrite (E), polymetallic sulfides (M) and carbonates (L), respectively. The E-stage fluids are characterized by δD=-90‰, and δ 18 O=9‰ at 373°C, and are deeply sourced; the L-stage fluids, with δD=-70‰, and δ 18 O=-2‰, are shallow-sourced meteoric water; whereas the M-stage fluids, with δD=-109‰, and δ 18 O=2‰, are a mix of deep-sourced and shallow-sourced fluids. Comparisons of the D-O-C isotopic systematics of the E- stage ore-forming fluids with the fluids derived from Mesozoic granites, Archean-Paleoproterozoic metamorphic basement and Paleo-Mesoproterozoic Xiong'er Group, show that these units cannot generate fluids with the measured isotopic composition (highδ 18 O and δ 13 C ratios and lowδD ratios) characteristic of the ore-forming fluids. This suggests that the E-stage ore-forming fluids originated from metamorphic devolatilization of a carbonate-shale-chert lithological association, locally rich in organic matter, which could correspond to the Meso-Neoproterozoic Guandaokou and Luanchuan Groups, rather than to geologic units in the Xiong'er terrane, the lower crust and the mantle. This supports the view that the rocks of the Guandaokou and Luanchuan Groups south of the Machaoying fault might be the favorable sources. A tectonic model that combines collisional orogeny, metallogeny and hydrothermal fluid flow is proposed to explain the formation of the Tieluping silver deposit. During the Mesozoic collision between the South and North China paleocontinents, a crustal slab containing a lithological association consisting of carbonate-shale-chert, locally rich in organic matter (carbonaceous shale) was thrust northwards beneath the Xiong'er terrane along the Machaoying fault. Metamorphic devolatilization of this underthrust slab provided the ore-forming fluids to develop the Au-Ag-(Pb-Zn) ore belt, which includes the Tieluping silver deposit.

Determination of the Neoproterozoic Shicaogou Syn-collisional Granite in the Eastern Qinling Mountains and Its Geological Implications

The Shicaogou granite has been identified as a magnesian (Fe-number=0.71-0.76), calcic to calc-alkalic (MALI=3.84-5.76) and peraluminous (ASI=1.06-1.13) granite of the syn-collisional S-type, with high SiO2(>71%), A12O3 (>13%) and Na2O+K2O (6.28%-7.33%, equal for NaO2 and K2O). Trace element and REE analyses show that the granite is rich in LILE such as of Rb, Sr, Ba and Th, and poor in HFSE like Yb, Y, Zr and Hf. Its Rb/Sr ratio is greater than 1; the contents of Nb and Ta, and the ratio of Nb/Ta as well as the REE geochemical features (e.g. REE abundance, visible fractionation of LREE and HREE and medium to pronounced negative Eu anomalies) are all similar to those of crust-origin, continent-continent syn-collisional granite. Moreover, the granite exhibits almost the same pattern as that of the typical continent-continent syn-collisional granite on the spider diagram and all samples fall within the syn-collisional granite field.The cathodoluminescence (CL) investigations have revealed that the zircon from the Shicaogou granite represents a typical magmatic product characterized by its colorless, transparent and euhedral crystals, and distinct zoning of oscillatory bands. Residual cores of irregular zircon can be found in a few enhedral grains. Trace element studies of the zircon grains, with high contents of P, Y, Hf, Th, U and REE and high ratios of Th/U, obviously positive Ce anomalies and HREE enrichment compared to LREE, also result in the same conclusion.The LA-ICP-MS U-Pb isotopic data from 24 spots of 21 zircon grains demonstrate that 20 spots in the oscillatory zone yield an average weighted 206Pb/238U age of 925±11 Ma, indicating that the Shicaogou granite was formed in the Neoproterozoic. Combined with other Neoproterozoic syn-collisional granites found in the study area, the present geochronological determination can further reveal that collision-amalgamation events could have occurred among some continental blocks in the Qinling orogenic belt during the Neoproterozoic. This in turn provides an accurate chronological constraint on the Neoproterozoic break-up and convergence in the belt.

Age, Mechanism and Direction of East Qinling-Dabieshan Lithosphere Delamination Petrological Evidence and Stipulation

Through studies of P\|T\|t paths and decompressive retrograde metamorphic textures of metamorphic rocks in the East Qinling\|Dabieshan region, the authors determined the Mesozoic crust rapid uplifting age, and then inferred that in the East Qinling\|Dabieshan region lithosphere delamination occurred from T\-3 to J\-1. The Yanshanian granites produced by delamination are developed well in the East Qinling\|Dabieshan region. But due to the Gondwana plate effect, magmatism in the region caused by delamination lagged until J\-3 when the northern Tibet terrane and the Eurasian plate completely amalgamated. Additionally, due to western Pacific plate subducting underneath the Eurasian plate, in the East Qinling\|Dabieshan region the stress state was transformed from compression to extension. So in the region from J\-3 to K\-2 magmatism was most intensive, and liberalization was also relatively strong. Geophysical data reflect that in the East Qinling\|Dabieshan region the asthenosphere rose to the shallow level, the Moho is flat with no mountain root, and the crustal thickness is less than 40 km on average. These features agree with those of collisional orogenes in which delamination has occurred. Through contrasting differences in surface and interior depth between east and west Qinling we believe that delamination proceeded from east to west.

Geochemical Characteristics and LA-ICP-MS Zircon U-Pb Dating of Amphibolites in the Songshugou Ophiolite in the Eastern Qinling

Geochemical studies on the arnphibolites in the Songshugou ophiolite from Shangnan County, Shaanxi Province demonstrate that the protolith of the amphibolites is tholeiitic. The arnphibolites can be classified into two groups according to their REE patterns and trace element features. Rocks of the first group are depleted in LREE while rocks of the second group are slightly depleted in LREE or flat from LREE to HREE without significant Eu anomaly. The first group of rocks have (La/Yb)N=0.33-0.55, (La/Sm)N= 0.45-0.65, and their La/Nb, Ce/Zr, Zr/Nb, Zr/Y and Ti/Y ratios are averaged at 1.20, 0.12, 31.02, 2.92 and 198, respectively, close to those of typical N-MORB. The second group of rocks have (La/Yb)N=0.63-0.95, (La/ Sm)N = 0.69--0.90, and their average La/Nb, Ce/Zr, Zr/Nb, Zr/Y and Ti/Y ratios are 0.82, 0.83, 1.15, 0.16, 19.00, 2.58 and 225, respectively, which lie between those of typical N-MORB and E-MORB but closer to the former. The two groups of rocks both exhibit flat patterns from Th to Yb in the highly incompatible elements spider diagram, but the first group of rocks have lower element abundances than the modern N-MORB, indicating a derivation of their mantle source from more depleted mantle source than the present N-MORB. The abundances of Th, Ta, Nb, La and Ce in the second group of rocks are slightly higher than those of the present N-MORB, and other elements, such as Hf, Zr, Sm, Ti, Y and Yb, are close to those of the N-MORB, indicating that the original magma was derived from depleted mantle but mixed with the enriched mantle. These characteristics, combined with the regional geology and previous studies, provide further evidence that the mafic-ultramafic rocks have the features of a typical ophiolite.Zircon grains from the amphibolite are generally rounded, and in most of them a distinguishable core-mantle texture is preserved as shown in the cathodoluminescence (CL) images. The core or core-mantle parts of the zircon grains are also rounded, same as those in basalts from other regions of the world. The LA-ICP-MS trace element and U-Pb isotopic analyses show that the zircon grains from the amphibolites are similar to the typical magmatic zircon in terms of their very low U and Th contents (62.36-0.10 μg/g and 78.47-0.003 μg/g, respectively). Seven pits from the core and core-mantle parts of the zircon grains yielded an average weighted 206Pb/ 238U age of 973±35 (2σ) Ma with the Th/U ratios range from 0.01 to 8.38 and mostly greater than 0.23. This age is consistent within the error range with the whole-rock Sm-Nd isochron age of 1030±46 Ma for the same kind of rocks reported by Dong et al. (1997a). In a combined analysis with the zircon positions on the CL images and the corresponding Th/U ratios, the age of 973±35 Ma is probably the formation age of tholeiite, the protolith of the Songshugou amphibolite. The geochronological determination gives further evidence that the Songshugou ophiolite was formed during the Neoproterozoic. In addition, there is one pit from the rim of a zircon grain giving a 206Pb/ 238U age of 5721199 (1σ) Ma with a Th/U ratio of 0.08. It may represent the age of the accretionary zircon in the amphibolite-facies metamorphism.

U-Pb Zircon Geochronology and Geochemistry of Granitoids in the Douling Group in the Eastern Qinling

LA-ICPMS U-Pb zircon dating of the Sanpinggou, Gangou and Fengzishan granitoids in the Douling Group of the Eastern Qinling yields ages of 760-685 Ma, which represents a strong tectono-magmatic event in the southern Qinling during the late Neoproterozoic. Geochemical data show that these intrusions have wide compositions ranging from minor gabbros through diorites to granodiorites. They are relatively enriched in LILE, poor in HFSE and strongly depleted in Nb and Ta, displaying affinities of Ⅰ-type granites formed in an active continental margin with oceanic subduction. In contrast to granitoids, gabbros and enclaves in the granitoids have higher REE abundances, relatively flat REE patterns, lower LILE, slightly higher HFSE and more depletion in Nb and Ta. All these suggest that the gabbros were formed by partial melting of the upper mantle above the subduction zone and the granitoids by the partial melting of the lower crust. Combined with regional geological data, the subduction-related granitoids in the Douling Group, together with the Tuwushan A-type granite with an age of 725 Ma and contemporaneous basic dikes in the Wudang Block, provide evidence for local subduction of oceanic basins between different blocks during the rifting in the Southern Qinling in the Neoproterozoic. Thus, the coexistences of various magmatic rocks formed in different tectonic environments indicate a complicated tectonic evolution and variety of tectonic frameworks in the Qinling area in the Neoproterozoic.

The GSSP of the Second （Upper） Stage of the Lower Ordovician Series： Diabasbrottet at Hunneberg, Province of Vaeistergoetland, Southwestern Sweden

Diabasbrottet, selected by the International Subcommisson on Ordovician Stratigraphy and in 2002 ratified by the International Commission on Stratigraphy as the GSSP of the Second (Upper) Stage of the Lower Ordovician, is located on the Hunneberg Mountain in southwestern Sweden. The stratigraphic succession represents an outer shelf environment near the Baltic Shield margin. The shale-dominated, biostratigraphically complete, richly fossiliferous boundary interval is completely exposed in a disused quarry. The GSSP is in the lower TФyen Shale 2.1 m above the top of the Cambrian and is marked by the first appearance of the graptolite Tetragraptus approximatus Nicholson. The boundary interval contains a diverse graptolite fauna and biostratigraphically diagnostic conodonts and trilobites that make it possible to define the boundary in terms of zone schemes based on these groups. In this respect, the Diabasbrottet and nearby sections are unique in the world among described localities having this boundary interval. Based on the appearance of T. approximatus, the base of the Second Stage can be identified in many graptolitiferous successions round the world but this level is currently more difficult to recognize precisely in some carbonate sequences outside Baltoscandia. We propose the Second Stage be called the Floan Stage. It is named for the Village of Flo, which is situated about 5 km southeast of the GSSP.

Conodont Biostratigraphy of the Middle Cambrian through Lowermost Ordovician in Hunan, South China

Since 1985, samples with a total weight of more than 14,000 kg, mainly from three key sections in western and northwestern Hunan, South China, have been processed for conodonts. In strata older than the late Late Cambrian paraconodonts have proved useful for stratigraphic subdivision and correlation. Thirteen conodont zones are proposed in the Middle Cambrian through lowermost Ordovician. The correlation between these zones and those of North China, western U. S.A., western Newfoundland, Canada, and Iran is discussed. In ascending order, these 13 zones are as follows: The Gapparodus bisulcatus-Westergaardodina brevidens Zone, Shandongodus priscus-Hunanognathus tricuspidatus Zone, Westergaardodina quadrata Zone, Westergaardodina matsushitai-W. grandidens Zone, Westergaardodina lui-W. am Zone, Westergaardodina cf. calix-Prooneotodus rotundatus Zone, Proconodontus tenuiserratus Zone, Proconodontus Zone, Eoconodontus Zone, Cordylodus proavus Zone, Cordylodus intermedius Zone, Cordylodus lindstromi Zone, and Cordylodus angulatus Zone (lower part). The Westergaardodina lui-W. ani and Westergaardodina cf. calix-Prooneotodus rotundatus Zones replace the Westergaardodina proligula and Westergaardodina cf. behrae-Prooneotodus rotundatus Zones, respectively, in the lowermost Upper Cambrian. Two new species (Westergaardodina Iui and Westergaardodina ani) and one conditionally identified species (Westergaardodina cf. calix) are described.

Underplating of Mesozoic Mantle-derived Magmas in Tongling, Anhui Province: Evidence from Megacrysts and Xenoliths

Lithological observations and mineralogical analyses on pyroxene and hornblende megacrysts and pyroxene and hornblende cumulates in xenoliths in the Mesozoic plutons of the Tongling region, Anhui Province, provide evidence for the magmatic underplating of mantle-derived alkali-olivine basalt at circa 140 Ma. The pyroxene and hornblende megacrysts and cumulates were formed through the AFC process at depths ranging from 27 to 35 km.

Enantiornithine Bird with Diapsidian Skull and Its Dental Development in the Early Cretaceous in Liaoning, China

A Iarge number of enantiornithine birds are discovered from the Early Cretaceous Jiufutang Formation in western Liaoning, China. They are all small-sized birds with a few small teeth. The enantiornithine bird from the Jiufutang Formation in the Shangheshou area, Chaoyang, Liaoning Province reported in this paper is the largest individual known in all enantiornithine birds of the Early Cretaceous. However, its teeth possess a feature of pseudoheterodont. Some different development stages of the new teeth substitute the earlier stages and the stages of development are preserved in this specimen. This development pattern is similar to that of Archaeopteryx and alligator but not dinosaur. A well-developed postorbital was also preserved in the skull, which was a diapsidian skull like that of Confuciusornis. Additionally, the distinctive preservation of its prefrontal distinguishes it from other enantiornithine birds of the Early Cretaceous.

Pressure Solution of Sulphides in Some Massive Sulphide Zinc-lead Deposits of Western Canada:Its Significance in Mobilization of Ore-forming Materials

Pressure solution is a common phenomenon in massive sulphide zinc-lead deposits of western Canada and may have been an important factor leading to the mobilizahon of ore-forming materials during diagenesis, deformation and metamorphism of sedimentary ores. The control of ductile shear zones over gold mineralization could be explained in view of pressure solution of gold-bearing miner-als under shearing stress and the resultant mobilization of this metal.