黄河三角洲地区末次盛冰期以来浅地层划分与海平面变化的响应     

成海燕  姜胜辉  李安龙  龚建明 《海洋地质前沿》2010,26(1)

通过对黄河三角洲几个钻孔的分析.将其自上而下划分成3个海相层和3个陆相层,并且划分为1个4级层序(准层序)和4个5级层序。每个层序代表了一次海平面的升降旋回。4级层序的海退沉积与末次冰期的后期对应,海平面下降最大时期是末次冰期最盛期(LGM)的反映。  相似文献   

The timing of eclogite facies metamorphism and migmatization in the Orlica–Śnieżnik complex, Bohemian Massif: constraints from a multimethod geochronological study     

M. BRÖCKER  R. KLEMD  M. COSCA  W. BROCK  A. N. LARIONOV  N. RODIONOV 《Journal of Metamorphic Geology》2009,27(5):385-403

The Orlica–?nie?nik complex (OSC) is a key geological element of the eastern Variscides and mainly consists of amphibolite facies orthogneisses and metasedimentary rocks. Sporadic occurrences of eclogites and granulites record high‐pressure (HP) to ultrahigh‐pressure (UHP) metamorphic conditions. A multimethod geochronological approach (⁴⁰Ar–³⁹Ar, Rb–Sr, Sm–Nd, U–Pb) has been used to gain further insights into the polymetamorphic evolution of eclogites and associated country rocks. Special attention was given to the unresolved significance of a 370‐ to 360 Ma age group that was repeatedly described in previous studies. Efforts to verify the accuracy of c. 370 Ma K–Ar phengite and biotite dates reported for an eclogite and associated country‐rock gneiss from the location Nowa Wie? suggest that these dates are meaningless, due to contamination with extraneous Ar. Extraneous Ar is also considered to be responsible for a significantly older ⁴⁰Ar–³⁹Ar phengite date of c. 455 Ma for an eclogite from the location Wojtowka. Attempts to further substantiate the importance of 370–360 Ma zircon dates as an indicator for a melt‐forming high‐temperature (HT) episode did not provide evidence in support of anatectic processes at this time. Instead, SHRIMP U–Pb zircon dating of leucosomes and leucocratic veins within both orthogneisses and (U)HP granulites revealed two age populations (490–450 and 345–330 Ma respectively) that correspond to protolith ages of the magmatic precursors and late Variscan anatexis. The results of this study further underline the importance of Late Carboniferous metamorphic processes for the evolution of the OSC that comprise the waning stages of HP metamorphism and lower pressure HT overprinting with partial melting. Eclogites and their country rocks provided no chronometric evidence for an UHP and ultrahigh‐temperature episode at 387–360 Ma, as recently suggested for granulites from the OSC, based on Lu–Hf garnet ages ( Anczkiewicz et al., 2007 ).  相似文献   

Polymetamorphism in the mainland Lewisian complex,NW Scotland – phase equilibria and geochronological constraints from the Cnoc an t’Sidhean suite     

T. E. JOHNSON  R. W. WHITE  T. ZACK 《Journal of Metamorphic Geology》2012,30(8):865-885

The metamorphic evolution of rocks cropping out near Stoer, within the Assynt terrane of the central region of the mainland Lewisian complex of NW Scotland, is investigated using phase equilibria modelling in the NCKFMASHTO and MnNCKFMASHTO model systems. The focus is on the Cnoc an t’Sidhean suite, garnet‐bearing biotite‐rich rocks (brown gneiss) with rare layers of white mica gneiss, which have been interpreted as sedimentary in origin. The results show that these rocks are polymetamorphic and experienced granulite facies peak metamorphism (Badcallian) followed by retrograde fluid‐driven metamorphism (Inverian) under amphibolite facies conditions. The brown gneisses are inferred to have contained an essentially anhydrous granulite facies peak metamorphic assemblage of garnet, quartz, plagioclase and ilmenite (±rutile, K‐feldspar and pyroxene) with biotite, hornblende, muscovite, chlorite and/or epidote as hydrous retrograde minerals. P–T constraints imposed by phase equilibria modelling imply conditions of 13–16 kbar at >900 °C for the Badcallian granulite facies metamorphic peak, consistent with the field evidence for partial melting in most lithologies. The white mica gneiss comprises a muscovite‐dominated matrix containing porphyroblasts of staurolite, corundum, kyanite and rare garnet. Previous studies have suggested that staurolite, corundum, kyanite and muscovite all grew at the granulite facies peak, with partial melting and melt loss producing a highly aluminous residue. However, at the inferred peak P–T conditions, staurolite and muscovite are not predicted to be stable, suggesting they are retrograde phases that grew during amphibolite facies retrograde metamorphism. The large proportion of mica suggests extensive H₂O‐rich fluid‐influx, consistent with the retrograde growth of hornblende, biotite, epidote and chlorite in the brown gneisses. P–T conditions of 5.0–6.5 kbar at 520–550 °C are derived for the Inverian event. In situ dating of zircon from samples of the white mica gneiss yield apparent ages that are difficult to interpret. However, the data are permissive of granulite facies (Badcallian) metamorphism having occurred at c. 2.7–2.8 Ga with subsequent fluid driven (Inverian) retrogression at c. 2.5–2.6 Ga, consistent with previous interpretations.  相似文献   

FEM simulation of formation of metamorphic core complex with ANSYS software     

Guoqing YIN  Wei JIN  Xianli YANG 《世界地质(英文版)》2007,10(1)

This study utilizes ANSYS to establish FEM's model of metamorphic core complex,and used thermal-structure analysis to simulate metamorphic core complex's temperature field and stress field.The metamorphic core complex formation mechanism is discussed.The simulation results show that the temperature field change appearing as the earth surface's temperature is the lowest,and the temperature of metamorphic core complex's nucleus is the highest.The temperature field is higher along with depth increase,and the stress field change appearing as the biggest stress occurs in the nucleus.The next stress field occurs at the top of the cover.  相似文献   

河北平山小觉地区阜平岩群中三种岩类深熔现象的岩相学特征   总被引：7，自引：1，他引：7       下载免费PDF全文

程裕淇  万渝生  高吉凤  马瑞 《地质论评》2001,47(1):1-8

深熔作用(Anatexis)引起了地壳内部固体物质的重溶与熔融和进一步的初始花岗质岩浆的形成。本文主要从岩相学角度对河北平山阜平岩群3种主要变质岩类中一部分岩石在薄片中所显示的初期深熔特征进行了报道,提出识别深熔作用发生发展初期的一些岩相学标志,为相应的理论探讨提供岩相学方面的依据。区域变质岩石初始深熔的共同特征之一是不同矿物粒度都较相应的同类变质岩石为粗。由于经历粒间流体作用的重溶、溶蚀乃至再度晶出的过程,长英质岩石中长石、石英等矿物改变为具有弯曲、波纹状外形的缝合线结构,而“铰链状结构”的形成则是两微斜长石颗粒之间出现钠交代的结果。深熔作用过程中微斜长石显示出不均匀的光性特征,形成具交代成因的条纹长石细脉和条痕;斜长石出现不规则长方形和补丁状的微斜长石反条纹长石,显示“糟化”或绢云母化,或存在不同程度的“暗化”区域,也可转变成为纤维状至细柱状夕线石,沿斜长石中的一些细小裂纹和遭受应变的解理还出现几乎不透明的物质,它们可能原由深熔作用所形成,可称之为“网格状结构”;黑云母可部分地发生分解,在适当的温压条件下则完全分解,形成原可能为熔体的物质,也可转变成为纤维状至细柱状夕线石;角闪石存在一定程度的“暗化”,并形成与斜长石中所见类似的“网  相似文献   

新疆哈密拗陷北部早侏罗世地层及其孢粉组合     

尹凤娟  张子福 《地质通报》2001,20(4):377-383

哈密拗陷北部下侏罗统按其岩性、化石组合和地震波组等特征自下而上分为八道湾组和三工河组.根据两组所产的孢粉化石,建立了两个孢粉组合Osmundacidites Apiculatisporis Cycadopites组合和Cyathidites Pinuspollenites Cycadopites组合.根据孢粉组合特征及其对比,探讨了八道湾组和三工河组的地质时代.  相似文献   

钻进时同步显示钻孔地层柱状图技术探讨   总被引：3，自引：0，他引：3  

周劲辉  李晖等 《地质与勘探》2001,37(4):85-87

探讨了钻进时同步显示钻孔地层柱状图技术研究的意义，提出了用人工神经网络理论来解决地层识别的方法，开发了一套识别软件并用实际钻探资料进行了验证。  相似文献   

湖北大冶铁山矿床钠化蚀变与成矿关系的探讨   总被引：6，自引：0，他引：6  

杨峰华 《地质与勘探》2001,37(6):20-24

对于大冶铁矿内接触带钠化蚀变的岩石特征、钠质来源、动力机制、形成机理等作了比较系统的阐述。并着重指出了钠化蚀变是铁矿化的重要指示标志之一。  相似文献   

PAA无固相冲洗液在水敏岩层钻进中的应用   总被引：2，自引：1，他引：2       下载免费PDF全文

裴向军 《地质找矿论丛》2001,16(2):140-142

分析了PAA无固相冲洗液对坍塌层胶结护壁的作用机理，介绍了该冲洗液在吉林镍业公司富家矿千米钻使用过程中，酸性和含水合铁离子水质对PAA冲洗配制及使用的影响及应对措施，同时，介绍了PAA无固相冲洗液强防塌性能的发挥及使用。  相似文献   

沉积微相测井资料神经网络判别方法研究   总被引：3，自引：1，他引：3  

唐为清  郭荣坤  王忠东  王红  罗安银  毋学平 《沉积学报》2001,19(4):581-585

不同的沉积微相可以由不同的相标志组合识别,相标志与沉积微相之间的关系可以采用神经网络通过许多基本处理单元间并行的相互作用建立。沉积微相相标志既可以由地质资料的观察、岩芯分析直接获得,也可以由测井资料间接地求得  相似文献