豫西鱼池岭斑岩型钼矿床地质特征及其辉钼矿铼-锇同位素年龄

河南省嵩县鱼池岭钼矿是近几年在东秦岭钼矿带中新发现的超大型斑岩钼矿床.该钼矿床产于合峪复式花岗岩体及隐爆角砾岩中.含矿岩体以富二氧化硅、铝质、贫钙、富碱、高F以及K2O含量大于Na2O含量为特征.矿区内辉钼矿化主要类型为浸染状、细脉状、网脉状,薄膜状和薄饼状.成矿围岩蚀变类型有钾长石化、硅化、绢云母化、黄铁矿化、黄铁绢英岩化、绿帘石化、绿泥石化和高岭石化等,具典型的斑岩型钼矿床的矿化和围岩蚀变特征.笔者选取了6件不同矿化类型的辉钼矿样品进行Re-Os同位素定年,获得模式年龄(130.3±2.0)～(131.7±1.9)Ma,等时线年龄(131.2±1.4)Ma.表明该矿床形成于早白垩世,与赋矿的合峪花岗岩体的侵位年龄相一致,应为同一构造-岩浆-流体活动的产物.辉钼矿中Re的含量为12.48×10<'-6>～53.39×10<'-6>,表明成矿物质具有壳幔混源性质.鱼池岭钼矿与东沟、汤家坪等斑岩钼矿形成于同一时期,应为东秦岭-大别地区晚中生代区域岩石圈大规模伸展的响应.     

滇西施甸地区晚泛非运动的地层学和岩石学响应

保山地块的寒武系露头少,研究范围有限。长期以来,地学界对寒武系与奥陶系之间的接触关系存在较大争议,有人认为是整合接触,有人认为是假整合接触,囿于过去的工作精度,目前尚无定论。近年来,在保山施甸地区开展1∶5万区调工作时发现,区内普遍缺失早奥陶世沉积,仅在施甸半坡一带有中奥陶统,在大寨一带,中上奥陶统蒲缥组直接平行不整合在上寒武统保山组之上,结合晚寒武世—早奥陶世业已存在的岩浆活动,认为这是晚泛非运动的远程响应。     

南海中建南盆地构造样式分析

中建南盆地是发育于南海西部陆缘我国传统疆界线附近的新生代沉积盆地,大部分区域位于我国传统疆界线内。在对盆地近万千米多道地震资料综合分析解释的基础上,对盆地的主要构造样式以及它们与油气的关系进行了分析,结果表明,盆地分布面积广,沉积厚度大,油气前景良好。盆地是属于早期断陷、后期经走滑改造而成的复合型盆地,其构造演化经历了3个阶段,不同的阶段发育不同的构造样式:早期为断陷阶段,伸展型构造样式发育;中期为断坳—压扭或走滑反转阶段,产生走滑或压扭性构造样式;晚期为区域沉降阶段,以垂向沉积为主,无明显的构造样式发育。     

内蒙古锡林浩特东部地区早白垩世花岗岩地球化学、锆石U Pb年龄及地质意义

通过对锡林浩特东部地区早白垩世花岗岩体进行SHRIMP锆石U Pb测年、地球化学测试,讨论其形成构造环境。花岗岩测年结果为：正长花岗岩(DS214)(1391±17) Ma,花岗岩(DS220)(1347±17) Ma,表明研究区花岗岩形成于早白垩世早期。花岗岩地球化学具有高硅、富碱、相对低铝的特征,A/CNK平均值106,为弱过铝质花岗岩。微量元素相对富集大离子亲石元素(Th、U、K),明显亏损Nb、Ba、Sr、P、Ti等高场强元素;稀土总量高,为12290×10-6～36877×10-6,LREE/HREE值为571～1436,呈右倾模式,负Eu异常显著(010～050),表现为A型花岗岩特征。K2O-Na2O构造环境判别图表明样品为A型花岗岩,Y/Nb Ce/Nb图解显示花岗岩为A2型。主量元素、微量元素特征指示花岗岩形成于造山后岩石圈伸展作用阶段,在壳源岩浆演化过程中存在幔源物质混染作用。花岗岩成因可能是晚古生代末—中生代初期间古亚洲洋闭合引起的一系列板块碰撞作用(包括蒙古—鄂霍次克洋闭合),使造山后期地壳逐渐增厚并发生重力垮塌,导致构造环境由挤压转变为伸展,同时受古太平洋板块西向俯冲的影响。     

Centrifuge model tests on sand specimen under extensional load

The appearance of shear banding in granular materials has been investigated intensively during the last decades and is still of ongoing importance in terms of understanding the stress–strain behaviour of the material, the localization phenomena and the interaction between soil and structure. Only less attention has been paid to the occurrence of systems of shear bands although such systems can be identified in geotechnical structures as well as in geological formations. In this paper we present results of experiments on sand specimens under extensional load in natural gravity as well as in increased gravity in the centrifuge where the influence of the stress level on the geometry of a shear band pattern, specified by the spacing of the shear bands and the angle between failure surfaces and minor stress direction, has been investigated. X‐ray technique has been used to visualize the failure zones inside the specimen, an optical measurement system called Digital Image Correlation has been applied to identify and observe the appearing deformation mechanism on the sides of the specimens in natural gravity as well as during the flight in the centrifuge. It can be shown that the geometry of the shear band pattern is sparsely influenced by the change of the stress level. Copyright © 2004 John Wiley & Sons, Ltd.     

华北地台北缘玉皇顶山隆—滑构造

玉皇顶山隆—滑构造是在前造山期伸展构造作用体制下形成的 ,其结构由内核、外壳及接合面组成。具有独特的组合样式及构造特征。在内蒙古地轴东段元古代造山带构造变形演化序列中应占有重要的地位。     

据牙形石论鄂西茅口组顶部古岩溶不整合面形成时代

鄂西二叠纪茅口组顶部古岩溶不整合面粘土层中产丰富的牙形石，计有3属3种2未定种，标本色泽和被磨损特征等显示它们均为再沉积产物，通过对上述牙形石属种的演化特征、地质时限及产出层位的研究，认为该古岩溶不整合的形成时代为二叠纪Wordian晚期-Capitanian早期（M.aserrata带上部-M.postserrata带）。     

The Alpine geodynamic evolution of Penninic nappes in the eastern Central Alps

The eastern Central Alps consist of several Pennine nappes with different tectonometamorphic histories. The tectonically uppermost units (oceanic Avers Bündnerschiefer, continental Suretta and Tambo nappes, oceanic Vals Bündnerschiefer) show Cretaceous/early Tertiary W-directed thrusting with associated blueschist facies metamorphism related to subduction of the Pennine units beneath the Austroalpine continental crust. This event caused eclogite facies metamorphism in the underlying continental Adula nappe. The gross effect was crustal thickening. The tectonically lower, continental Simano nappe is devoid of any imprint from this event. In the course of continent-continent collision, high- T metamorphism and N-directed movements occurred. Both affected the whole nappe pile more or less continuously from amphibolite to greenschist facies conditions. Crustal thinning commenced during the regional temperature peak. A final phase is related to differential uplift under retrograde P–T conditions. Further thinning of the crust was accommodated by E- to NE-directed extensional deformation.     

“磨拉石建造”和“不整合”在地层对比中的意义——以扬子地块及其北缘晚前寒武纪地层为例

扬子地块及其北缘晚前寒武纪地层划分对比争议较大,主要是对“地层不整合”和“磨拉石建造”存在认识上的分歧,笔者据现代构造理论,对地壳变形和沉积建造的控制作用认为,地层不整合可以发育在被动大陆边缘形成初始阶段的裂谷期和裂谷期后,又可产生于造山作用过程;磨拉石建造应按构造动力学背景划分为拉张型、挤压型和剪切型三类;它们分别代表了威尔逊旋回不同阶段的产物。     

Petrology and geochemistry of potassic rocks in the Gölcük area (Isparta, SW Turkey): genesis of enriched alkaline magmas

The Lower Pliocene volcanic rocks occurring in the Gölcük area of SW Turkey exhibit alkaline major element trends with a general potassic character. The development of volcanism can be divided into 2 major stages such as trachytic ancient lavas/domes and tephriphonolitic, trachyandesitic to trachytic Gölcük eruptions (ignimbrites, lava/dome extrusions, phreatomagmatic deposits, and finally, young domes). Volcanic rocks consist primarily of plagioclase, clinopyroxene (which ranges in composition from diopside to augite and are commonly zoned), biotite, and phlogopite. Amphibole phenocrysts are restricted to the pyroclastic deposits. Pseudoleucites are also seen only in the lava/dome extrusions. Oxides and apatites are common accessory phenocryst phases. As would be expected from their potassic–alkaline nature, the volcanic rocks of the Gölcük area contain high amounts of LILE (Ba, Sr, Rb and K), LREE, and Zr. Concentrations of compatible elements such as Cr, Ni and V are very low, possibly indicating fractionation of olivine and clinopyroxene. Correlation of SiO₂, Rb/Sr and MgO with ⁸⁷Sr/⁸⁶Sr (0.703506–0.704142) exhibit an increasing trend in the direction of crustal contamination. However, the isotopic compositions of Sr are not as high to indicate a high level of crustal contamination. Geochemical data are consistent with the derivation of Gölcük volcanic rocks from a metasomatized and/or enriched lithospheric mantle source during crustal extension in the area. This metasomatism was probably occurred by fluids released from the northward subduction between African and Eurasian plates during Tertiary, as the Gölcük volcanic rocks display features of island-arc magmas with having high Ba/Nb (>28) ratios, and Nb and Ti depletions. Lower Pliocene volcanism in the Gölcük was response to extensional tectonics.