北祁连山东段嘹高山构造拼贴体的发现及其意义

瞭高山构造拼贴体的发现对于确定祁连造山带东段中祁连地块北部边界有重大意义，该拼贴体由奥陶系火山岩、大理岩和中晚元古代皋兰岩群绢云石英片岩、变杂砂岩、千枚岩等不同时代地层块体拼贴而成，形成于新元古代末一早古生代，整体成层无序，韧性剪切变形强烈，其变形序列特征反映早期正向逆冲，晚期压剪平移一正向伸展的造山拼贴过程。     

北祁连山东段瞭高山构造拼贴体的发现及其意义

瞭高山构造拼贴体的发现对于确定祁连造山带东段中祁连地块北部边界有重大意义.该拼贴体由奥陶系火山岩、大理岩和中晚元古代皋兰岩群绢云石英片岩、变杂砂岩、千枚岩等不同时代地层块体拼贴而成,形成于新元古代末-早古生代.整体成层无序,韧性剪切变形强烈.其变形序列特征反映早期正向逆冲,晚期压剪平移-正向伸展的造山拼贴过程.     

祁连地块东段北缘中元古代陆缘弧火山岩地球化学特征

分布于祁连造山带中祁连地块东端北缘的中元古代皋兰岩群火山岩为一套以基性-中基性-中酸性火山岩组合的浅变质岩,通过岩石组合、岩石化学、稀土及微量元素地球化学的综合分析研究,认为该套火山岩产于陆缘弧及弧后活动盆地的构造环境.     

北祁连东段西、南华山中酸性侵入岩地球化学特征

北祁连东段西、南华山中酸性侵入岩以花岗岩和花岗闪长岩为主,SiO2质量分数在66.23%~77.13%之间,具有钙碱系列的岩石组合特征和地球化学特征.微量元素Pb、Sr和La明显富集,Cs、Nb、Ti等元素呈现不同程度亏损,显示混合源岩浆的特征.∑REE的质量分数为(100.80~121.03)×10-6,低于世界酸性岩平均值.稀土配分模式呈右倾型,δEu=0.31~0.33,有负Eu异常,与北秦岭加里东期岛弧型花岗岩地球化学特征相似.中酸性岩体总体表现为壳幔混合型岩浆结晶分异的产物,反映北祁连地区中奥陶世末处于具沟-弧-盆体系的俯冲背景.     

赣北元古代地体拚贴带中高压变质矿物的发现及其构造意义

本文介绍了在赣北怀玉山地区首次发现的兰闪石等高压矿物详细特征,讨论了其产出环境和构造背景,论证了中晚元古代二个地体碰撞拼贴带和高压变质作用的存在,初步恢复了古板块构造的演化历史。     

北祁连西段卡瓦蛇绿岩的发现及其构造意义

正北祁连造山带呈NW-SE向展布于阿拉善地块与祁连一柴达木地块之间,与秦岭、昆仑一起构成了中国大陆内部巨型中央造山带.近半个世纪以来,作为大陆板块构造研究摇篮的北祁连造山带备受国内外学者的关注,国内最早报道的蛇绿岩就发现于此.以往发现的北祁连蛇绿岩主要分     

北祁连冷龙岭中东段-毛毛山地区金矿化地质特征

本文系统阐述了北祁连西段冷龙岭中东段-毛毛山地区的地质构造、金岩石地球化学特点,异常分布及特征,研究了引起双龙沟异常的青分岭石英脉型岩金矿的控矿条件,结合祁连西段成矿规律,总结出了本区金的成矿地质条件。     

中元古代食肉动物化石的发现及其意义

在中国辽宁省朝阳市凤凰山中元古代海相地层中首次发现了食肉的低等无脊椎动物石质宏观实体化石.通过观察化石中动物的形态和显微结构,发现这些动物具有捕食习性并具备口、消化道、消化腔等消化系统器官,以此确定了化石中动物的食肉属性,同时探讨了化石的形成机理.该种化石的发现可以充分证明中元古代低等动物已经进化到一定的水平,对华北中新元古代"动物化石"的重新认识和研究多细胞动物起源的历史具有重要意义;对人们认识中元古代动物的化石形态和解释达尔文因没有发现寒武纪以前的化石而困惑提供了充分的化石证据.     

北祁连石灰沟奥陶纪玄武岩流体组成及其地质意义

北祁连石灰沟地区中奥陶世发育了一套海相细碧岩--碱性火山岩组合,为岛弧火山作用产物.应用分步加热法测试了该区碱性玄武岩中橄榄石斑晶和基质的流体组成.玄武岩橄榄石斑晶和基质中流体组份都具有分阶段释放的特征,可分为低温(200～400?C)、中温(400～900?C)和高温(900～1 200?C)3个温度段,流体化学组成以H2O,CO2,CO+N2为主,次要组份是H2,SO2,CH4,O2,H2S等.石灰沟碱性玄武岩发育于相对氧化的流体环境,揭示其源区具有高的氧逸度,代表古岛弧形成的流体环境.     

SHRIMP U-Pb zircon age of the Jinchuan ultramafic intrusion and its geological significance

The Jinchuan ultramafic intrusion is located in the Longshoushan Uplift on the southwestern margin of the Alxa Block, to the north of the Northern Qilian Orogenic Belt (Fig.1). It is broadly dyke-like, and was intruded into a Paleoproterozoic sequence of migmatites, gneisses and marbles (Baijiazhuizi Formation). The intrusion is northwest-elongated, -6500 m long and 20-527 m wide, and     

Single-zircon dating of Precambrian strata in the west sector of the northern Qilian Mountains and its geological significance

Single_zircon evaporation method was employed in the present study to determine the age of the iron_bearing rock series in Precambrian strata in the western sector of the northern Qilian Mountains. Three zircon ages from the diabase of the Aoyougou ophiolite previously put into Upper Lithologic Formation of the Zhulongguan Group are (1 840±2), (1 783±2) and (1 784±2) Ma respectively, whereas the zircon ages from the welded breccias in the Zhulongguan Group are (733±7), (738±4) and (604±6) Ma respectively. These results show that they should belong to the bottom of the middle Proterozoic and the upper part of upper Proterozoic respectively.     

贺兰山地区三叠纪沉积特征及其地质意义

通过系统分析贺兰山地区三叠系的沉积特征,结合研究区盆地构造属性以及物源研究的最新成果,以探究贺兰山地区三叠世盆地演化的具体过程。研究后认为,研究区纸坊组相较于石千峰组物源供给充足、降水充沛,普遍发育辫状河沉积,荒草滩一带存在辫状河三角洲沉积,延长组一段至三段总体发育冲积扇和辫状河沉积,至延长组四段、五段,则以辫状河三角洲和湖相沉积为主。根据三叠系沉积相空间展布特征可知,研究区纸坊组、延长组一段至三段沉积相自西北向东南连续相变,此时与鄂尔多斯盆地完全连通;延长组四段、五段沉积相空间展布格局发生明显变化,且与鄂尔多斯盆地在东南大水沟一带连通,总体呈半连通态势。充足的物源供给、充沛的降雨以及盆地早期快速沉降是上三叠统延长组形成巨厚沉积的必要条件。从中三叠统纸坊组红层的逐渐减少到上三叠统充沛的降雨反映了整个贺兰山地区乃至华北板块西部古气候条件的快速变化,反映了古亚洲洋闭合对区域古地理、古气候的显著影响。     

南秦岭迷坝岩体的地球化学特征及其地质意义

目的 揭示南秦岭勉略带北部迷坝岩体的地球化学特征及其地质意义。方法 利用元素地球化学资料，结合岩体地质和岩相学特征进行研究。结果 岩体相对富集大离子亲石元素和轻稀土元素，亏损高场强元素，K2O Na2O和Sr含量及Zr／Y值较高；岩体具后碰撞高钾钙碱性花岗岩的特征；岩体是由二元岩浆尚未彻底混合而形成的。结论 指示晚三叠世秦岭造山带华北与扬子板块碰撞造山作用已进入到后碰撞演化阶段。     

The Dongcaohe ophiolite from the North Qilian Mountains： A fossil oceanic crust of the Paleo-Qilian ocean

The Dongcaohe ophiolite, located at the south of the North Qilian subduction complexes, is a tectonic block with an exposed area of about 3 km×6 km. It consists of an intrusive section overlain by an ex- trusive section. The lower part of the intrusive section consists of cyclic layers of cumulate dunites, troctolites, anorthosites, anorthositic gabbros, and gabbros with small discordant dunite and troctolite bodies. This layered sequence grades upward to isotropic gabbros and gabbronorites, which are overlain by the extrusive sequence of diabasic sheeted dikes and basaltic lavas. The overall mineral crystallization sequence was olivine±Cr-spinel, plagioclase, clinopyroxene, orthopyroxene, and Fe-Ti oxides. The Cr-spinel (Mg#: 42-66, Cr#: 41-57) in these layered cumulates and present-day abyssal peridotites have similar compositions. Also, the compositional variations of the plagioclase and cli- nopyroxene in the intrusive section reflect crystallization from melts compositionally similar to the present-day ocean basalts. Moreover, the rare earth element (REE) and multi-element distribution pat- terns of the intrusive and extrusive lithologies in the Dongcaohe ophiolite are consistent with crystal- lization of mid-ocean ridge basalts. The zircon grains separated from the gabbronorite have an SHRIMP average 206Pb/238U weighted age of 497 ± 7 Ma, which is considered as the tectonic emplacement age of the Dongcaohe ophiolite. The field occurrence, mineral and whole-rock compositions indicate that the Dongcaohe ophiolite represents a well-persevered oceanic crustal fragment composed of a complete oceanic crustal section of layered cumulates at bottom upgrading through isotropic cumulates to sheeted dikes and lava flows.     

北祁连山东段苏家山高Mg埃达克岩地球动力学意义

苏家山花岗闪长岩位于北祁连山东段,老虎山弧后盆地残留体北侧,侵入于原奥陶系阴沟群及前寒武纪变质岩系中,在空间分布上与米家山、扁强沟、清凹山、黄家凹山、银硐梁以及东侧南华山花岗岩共同构成长约220 km的花岗岩带,沿NW-NWW向展布.地球化学研究结果表明:苏家山花岗闪长岩富Na贫K,属钙碱性系列;高Sr低Y,Yb,高Mg#,Ni,Cr,可划归高Mg,Sr低Y型花岗闪长岩;微量元素蛛网图显示,岩石富集大离子亲石元素,亏损高场强元素及HREE,(w(La)/w(Yb))n>22,δEu轻微负异常;K-Ar同位素年龄为425 Ma.结果指示:苏家山花岗闪长岩具有高镁埃达克岩的特点,是在早古生代晚期北祁连东段造山作用过程中,滞留在地幔楔中的老虎山弧后盆地俯冲板片发生部分熔融,熔体与地幔橄榄岩发生明显的交代作用而形成.与此同时,阿拉善古陆南缘也卷入了造山作用,埃达克岩浆作用使陆壳在垂向上得以生长.     

Discovery of Paleoproterozoic rapakivi granite on the northern margin of the Yangtze block and its geological significance

The Huashanguan rapakivi pluton in Zhongxiang,Hubei Province,China,is the first discovered Proterozoic rapakivi pluton in the Yangtze block.Based on field and petrographical observations,a typical rapakivi texture was found in the northern portion of the Huashanguan granitic pluton.Almost all the K-feldspar phenocrysts were round to oval in shape and most had plagioclase coatings known as rapakivi phenocrysts.Alkali feldspars and quartz had two or more generations.Petrochemically,the Huashanguan rapakivi granites were characterized as having high values of Si,K,Fe,Th,U,La,Ga,Ce,Sm and LREE,low values of Ca,Mg,Sr,Nb,Y and HREE,and a negative Eu anomaly.These geochemical characteristics of the Huashanguan granites were concordant with typical rapakivi granites,and had an affinity to A-type granites.LA-ICP-MS U-Pb zircon dating also was conducted.The dating yielded a 207Pb/206Pb weighted mean age of 1851±18 Ma (MSWD =1.2),which represents the age of the pluton emplacement.The age of 803±170 Ma at the lower intercept in the concordia diagram corresponds to the age of a later deformation event which affected the pluton,and suggests that the Huashanguan pluton was influenced by Neoproterozoic thermo-tectonic events after its formation.The discovery of Paleoproterozoic Huashanguan rapakivi granites indicates continental rifting or a post-orogenic extensional event that took place in the Paleoproterozoic in the Yangtze block.These events may be related to the breakup of the Paleoproterozoic Columbia supercontinent.