青藏高原西部甜水海地区白垩纪花岗岩类的岩石学地球化学特征及其地质意义

甜水海地区广泛分布白垩纪的中酸性侵入岩,可分为早白垩世（123Ma）、晚白垩世早期（100~93Ma）和晚白垩世晚期（79~74Ma）3期。早期侵入体零星,为正长花岗岩、二云母花岗岩及含石榴子石花岗岩,属高钾钙碱性系列,A/CNK大于1.1,K2O含量大于Na2O,负Eu异常明显,刚玉分子数大于1.1,属于典型的强过铝质S型花岗岩。晚白垩世早期花岗岩分布广泛,以英云闪长岩和花岗闪长岩为主,主要属中—高钾钙碱性系列,个别属于钾玄岩系列,A/CNK主体小于1.15,负Eu异常中等,刚玉分子数多小于1.1,主体属I型花岗岩。晚白垩世晚期花岗岩同样分布广泛,为花岗闪长岩、二长花岗岩组合,主要属于高钾钙碱性系列,个别为中钾钙碱性系列,A/CNK主体大于1.05,负Eu异常较明显,刚玉分子数多大于1.1,主体属于典型的S型花岗岩。综合分析认为,甜水海地区白垩纪中酸性侵入岩与班公湖-怒江残余洋盆消减、闭合有关,可能记录了羌塘-冈底斯带之间的同碰撞（早期）、碰撞后（晚白垩世）等构造岩浆演化过程。     

Arc volcanism initiated on the eastern margin of Eurasia during the Early Cretaceous: Geochemistry of the Takanokura volcanic rocks in the Abukuma Mountains,Northeast Japan

The Early Cretaceous Takanokura Formation in the eastern part of the Abukuma Mountains consists of a lower felsic ignimbrite and upper intermediate lavas and volcaniclastic rocks, representing the initial arc-type in northeast Japan. In this study, I analyzed the major and trace element contents and Sr-Nd-Pb isotopic ratios of these eruptive products; then, I discussed their magma genesis based on their geochemical properties. Although igneous rocks of the same period in other localities of northeast Japan are characterized by the occurrence of adakites, these volcanism are composed of non-adakitic high- to medium-K andesite to rhyolite that are rich in large-ion lithophile elements and poor in high-field-strength elements and have low Sr/Y values and flat heavy rare earth element patterns. Furthermore, these rocks have high radiogenic Pb isotopic ratios. The rhyolite and dacite have been thought to derive from crustal melting, whereas the andesite formed by the mixing of crustal felsic melts and mafic magmas generated by melting of the lithospheric mantle. Although previous studies attributed the formation of the Early Cretaceous adakites to the hot subduction of a mid-ocean ridge, recent global plate motion reconstructions reject this model. To generate magma from a cold slab and lithospheric mantle that does not spontaneously melt, the mantle wedge under northeast Japan must have experienced heating. During this period, the volcanic province along the eastern margin of Eurasia expanded rapidly toward the trench, forming grabens. Therefore, I concluded that the advance of the hot asthenosphere into the forearc region that led to this expansion, which caused the retreat of the subduction boundary of the paleo-Pacific plate to retreat and ultimately converted northeast Japan from an accretionary complex into a volcanically active region.     

Contribution à l'étude d'une partie du bassin d'Essaouira (Maroc) par sismique réflexionContribution to part of the Essaouira Basin (Morocco) by seismic reflection

A large number of seismic reflection lines and boreholes have been carried out in the Essaouira Basin by the oil industry. The present study concentrates on the reinterpretation of these data in the restricted area of Khemis Meskala, in order to better characterise the structure of the Cretaceous aquiferous system. The reflector corresponding to the bottom of the Vraconian formation has been identified on the different seismic sections. This horizon, which marks the base of the aquiferous system, was first digitised on time migration sections and then converted to depth sections using a suitable linear velocity law. The isobath map of the bottom of the Vraconian resulting from this study images the 3D geometrical structure of this horizon and shows that it is slightly folded in domes and basins. This document will be useful for rationalising the future hydrogeological researches that will be undertaken in the Khemis Meskala area. To cite this article: M. Jaffal et al., C. R. Geoscience 334 (2002) 229–234.     

白垩纪：中国及邻区板块构造演化的一个重要变换期

中国及邻区是一系列不同起源的微大陆（克拉通）和地块经多期增生和碰撞而形成的复合大陆,海西-印支旋回和新特提斯旋回在其形成中起了决定性的作用。侏罗纪末白垩纪初部分新特提斯洋（有人称中特提斯）闭合,亚洲大陆的雏形出现,白垩纪末新特提斯洋全面消减,亚洲大陆形成,因而白垩纪是中国及邻区板块构造演化的一个重要变换期。笔者从地球动力学系统的变换、构造格局的变换、北东向新生构造的出现和造山作用类型的多样化等方面论述了这一变换。这一变换集中表现在中国及邻区的构造演化由原来的南、北分异在白垩纪转变为东、西两部发生分异,西部以构造的继承性为特色,东部则新生构造起了主要作用。反映在地形一地貌上,早白垩世该区东高西低,白垩纪末开始出现今日的西高东低面貌。盆地发育和“盆”“山”系统也在白垩纪开始发生重要变换,说明东亚大陆边缘因向太平洋的蠕散而不断解体,大陆内部构造则日趋复杂。中国及邻区的这一实例再次说明必须坚持活动论构造观,以动态演化的思路来重塑区域大地构造演化。     

南襄盆地襄樊-枣阳凹陷油气勘探前景探讨

襄樊-枣阳凹陷位于南襄盆地的南部,与北部＂小而肥＂的南阳、泌阳凹陷相比,该区油气勘探一直未获得突破。通过对凹陷内核桃园组烃源岩特征的研究及油气资源评价表明,核桃园组烃源岩未成熟,生烃量和聚集烃量均较少,且已施钻的以核桃园组为主要目的层的钻井均未获得油气成果。因此,襄樊-枣阳凹陷核桃园组不能作为油气勘探的主要目的层。凹陷东部的部分盐井提供了区内白垩系烃源岩具有生油气潜力的信息,而且土壤地球化学勘探也指示了该区白垩系具有一定的勘探前景;襄参1井揭示区内震旦—寒武系碳酸盐岩有机质丰度高,其生油气潜力值得进一步探索,土壤地球化学勘探也显示,存在与震旦—寒武系有关的热演化气;土壤地球化学勘探显示区内存在幔源成因天然气。综合分析认为,中生界白垩系、幔源天然气及震旦—寒武系碳酸盐岩是襄樊-枣阳凹陷油气勘探值得探索的新层位和新领域。     

Osteoderms of Montealtosuchus arrudacamposi (Crocodyliformes,Peirosauridae) from the Turonian-Santonian (Upper Cretaceous) of Bauru Basin,Brazil

The skin of Crocodyliformes is characterized by osteoderms of various sizes and shapes. It plays roles in defence, thermoregulation, sexual attraction, calcium reserves, and locomotion. This study presents the morphometric characteristics of osteoderms preserved in the nuchal, dorsal, ventral and appendicular shield of Montealtosuchus arrudacamposi, a Peirosauridae crocodyliform from the Turonian-Santonian (Upper Cretaceous) of Adamantina Formation, Bauru Basin, Brazil. The results of the analysis show that its dermal shield had protective and thermoregulatory functions and a well-defined mechanical function allowing terrestrial locomotion and enabling good agility and capacity for movement.     

六盘山群沉积物磁化率记录的早白垩世气候变化

白垩纪气候环境研究对认识现今全球环境格局的形成具有重要意义,现有的白垩纪环境变化记录均来自海洋沉积物,本文通过对我国中部六盘山地区六盘山群地层沉积与岩石磁化率测量分析,获得了128.15～115.82Ma期间陆相沉积物记录的气候变化信息。结果显示磁化率值总体较低,以125Ma为界大致可以分为前低后高两个阶段;结合岩石磁学测量及沉积相、岩石中铁含量与磁化率变化关系分析,认为岩石磁化率主要与源区磁性矿物的种类及含量有关,据此揭示六盘山地区在该时间段气候总体为干热环境,并可分为128.15～125Ma间气候相对湿热和125～115.82Ma间气候相对温湿两个阶段。磁化率记录的这种气候转变与海洋沉积物记录的全球海平面温度变化趋势一致,但相对海平面温度由升高到降低的转折时间提前约1.7Ma。     

边界元法在地下水补给量计算中的应用

本文是边界元法在地下水补给量计算中应用的一次尝试,它成功地把边界元法应用到考虑有垂向补给或排泄的实际水文地质问题中。文中详细地推导了考虑有垂向补给或排泄均质各向同性承压含水层非稳定流边界元法的计算公式,结合长春市八里堡群井开采试验的水位观测资料计算了河流边界的补给量;分析了目前边界元法在水文地质计算中出现的时间积分和面积积分问题,在这两个问题的解决上做了些改进;结合简单水文地质模型给出了边界元法的精确度。     

陕西华清池温泉热储温度的估算

本文以华清池泉水化学成分为例,采用水—岩化学平衡计算的方法,进行了热储温度估算。根据9种矿物平衡温度的统计结果,得出华清池温泉深部热储温度为53.44±6.11℃。这和温泉附近几个热水孔的温度测定结果是基本一致的。     

辽宁西部中白垩世火山旋回的划分与对比

辽宁西部地区中生代白垩纪存在两期火山旋回,时代分别属早白垩世早期和中白垩世早期。早白垩世火山旋同即义县组,中白垩世火山旋回本文称为大兴庄火山岩,该期火山岩火山活动微弱,火山岩分柑局限,主要出露于阜新—义县盆地的东侧上齐台一带,以宁静的侵出和次火山岩侵入为主,是早白垩世阜新组沉积之后,中白垩世孙家湾组沉积之前的一次火山活动,它与孙家湾组共同组成一个火山喷发—沉积旋回。