辽西地区燕山板内造山带早中生代构造变形的年代学限定   总被引：4，自引：0，他引：4  

胡健民刘晓文  杨之青 《岩石学报》2007,23(3):605-616

在辽西进行的构造研究确认了这里曾经在早中生代期间发生过几次重要的构造变形事件,地质上,这几次构造变形的时代被限定在中三叠世老虎沟组沉积之后到晚侏罗世髫髻山/蓝旗组火山岩喷发之前。期间,第一期逆冲推覆构造被水泉沟组不整合覆盖,第二期逆冲推覆构造被髫髻山组/蓝旗组不整合覆盖。本文通过对水泉沟组火山岩、邓杖子组火山岩砾石、髫髻山组底部火山岩以及侵位到逆冲构造岩片中的安山玢岩脉体进行锆石SHRIMP法U-Pb定年,比较准确地限定了燕山板内造山带早中生代几次构造变形的时代。这对于研究燕山板内造山带早期变形特征和变形历史、研究整个燕山造山带的变形过程都具有重要的意义。  相似文献   

西准噶尔白碱滩二辉橄榄岩中两种辉石的出溶结构及其地质意义   总被引：3，自引：11，他引：3  

朱永峰  徐新 《岩石学报》2007,23(5):1075-1086

克拉玛依白碱滩尖晶石二辉橄榄岩主要由橄榄石、单斜辉石、斜方辉石和尖晶石组成,橄榄石和斜方辉石均发生程度不等的蛇纹石化。单斜辉石一般很新鲜。单斜辉石和斜方辉石均发育出溶结构,出溶条纹或者平直或者发生舒缓的弯曲变形(即便是在发生弯曲的情况下也是完全平行的)。透辉石-普通辉石出溶体一般呈针状(直径一般为1μm,长度>150μm),顽火辉石出溶条纹直径一般为1～3μm(长度>300μm)。斜方辉石主晶属于顽火辉石-易变辉石,单斜辉石主晶为透辉石(成分很均一)。地质温度压力估算表明,白碱滩二辉橄榄岩中辉石出溶结构发生的温度为700℃～1000℃、压力为2.0～2.7GPa,它们代表辉石出溶结构形成的最低PT条件。白碱滩二辉橄榄岩至少经历了三个演化阶段:原始辉石与尖晶石和橄榄石平衡共生(阶段Ⅰ,>94km);随着地幔上隆,原始辉石结构不稳定,分解并形成出溶结构(阶段Ⅱ,700℃～1000℃),斜方辉石开始分解的深度为94km,单斜辉石开始分解的深度为78km;之后,蛇绿岩经历的侵位事件导致辉石发生塑性变形(阶段Ⅲ)。蛇绿岩侵位之前,地幔岩曾发生了>50km的隆升,而且,在隆升过程中地幔岩没有发生明显部分熔融(地幔岩因此没有经历明显的岩浆抽提过程)。  相似文献   

克拉玛依侏罗纪橄榄玄武岩中菱铁矿的成因   总被引：2，自引：5，他引：2  

薛云兴  朱永峰 《岩石学报》2007,23(5):1108-1122

克拉玛依市西盆山交界处发育体罗纪杏仁玄武岩-橄榄玄武岩-含菱铁矿橄榄玄武岩组合,主要由橄榄石、单斜辉石、斜长石(中长石—拉长石为主)、钛铁矿、玄武玻璃及少量磷灰石组成,含菱铁矿橄榄玄武岩中存在原生菱铁矿(≈10%)和少量碱性长石。橄榄石及单斜辉石的Mg~#为≈70,单斜辉石属于富Ti普通辉石。含菱铁矿橄榄玄武岩中的菱铁矿常常包裹浑圆状斜长石,且与斜长石呈锯齿状接触。本文提供的岩相学观察表明,菱铁矿与玄武玻璃、斜长石、单斜辉石和钛铁矿呈明显的共生关系。在有些情况下观察到玄武玻璃与菱铁矿充填在斜长石格架的现象。含菱铁矿橄榄玄武岩玻璃中FeO含量最高至29.2%,CaO含量<1.5%,即熔体具有富Fe贫Ca的特点。早结晶的碳酸盐矿物是以菱铁矿为主的菱铁矿-白云石固溶体(另含少量菱锰矿)。斜长石大量结晶促使熔体不断亏损CaO,并导致较晚结晶的碳酸盐矿物向菱铁矿端元演化。菱铁矿发育有明显的成分梯变带(FeO和CaO含量表现出突变)。玄武玻璃的Mg~#普遍较低且变化范围大,橄榄玄武岩中玻璃的Mg~#值最高为64,含菱铁矿橄榄玄武岩中玻璃的Mg~#值最低至≈23。依据地质温压计,克拉玛依侏罗纪玄武岩浆的形成温度为1300℃～1340℃,压力为3.0～4.0GPa。基于本文的研究,我们认为克拉玛依侏罗纪含菱铁矿橄榄玄武岩岩浆由含CO_2,橄榄岩在软流圈中经极低程度部分熔融形成,该岩浆在快速上升过程中通过结晶分异作用形成了菱铁矿。  相似文献   

青海西秦岭地区晚中生代基性火山岩地球化学特征及构造意义   总被引：4，自引：0，他引：4  

范立勇  王岳军  李晓勇 《矿物岩石》2007,27(3):63-72

对青海省同仁县多禾茂地区火山岩进行系统的元素同位素地球化学研究表明:该地区白垩纪地层中发育的中基性火山岩,属于碱性火山岩系,岩石类型主要为玄武岩,该套玄武岩具有低且变化较小的Si O2质量分数(44.98%~48.20%),低MgO的质量分数高,变化较大(8.15%~10.98%),具有较高的Cr(208×10-6~418×10-6)和Ni(166×10-6~231×10-6)质量分数。所有样品都表现出轻稀土富集的右倾平滑分布模式,轻重稀土分异中等,(La/Yb)CN=10.09~27.2,重稀土弱分异,(Gd/Yb)CN=2.92~4.67,Eu异常不明显,Eu*/Eu=0.99~1.04。Ba,Nb-Ta和Th-U不亏损,Rb,K相对亏损,Sr正异常。该区火山岩具有亏损的Sr-Nd同位素组成,Sr-Nd同位素组成变化范围不大[87Sr/86Sr(t)=0.7033~0.7039,εNd(t)=6.13~8.03,t=110 Ma],与Hawaii-OIB的Sr-Nd同位素组成相似。其所有地球化学特征表明该火山岩具有类似OIB的特征,可能是含石榴子石橄榄岩低度部分熔融的产物。结合对西秦岭地质构造背景和演化历史的分析,暗示该地区晚中生代岩浆源区来源于软流圈,其起源可能与岩石圈拆沉作用,软流圈地幔上涌和岩石圈伸展减薄有关,可为秦岭大别造山带中生代岩石圈演化提供了有利的直接证据。  相似文献   

Mesozoic extension in the Basque–Cantabrian basin (N Spain): Contributions from AMS and brittle mesostructures     

Ruth Soto  Antonio M. Casas-Sainz  Juan J. Villalaín  Beln Oliva-Urcia 《Tectonophysics》2007,445(3-4):373-394

In this work we analyse and check the results of anisotropy of magnetic susceptibility (AMS) by means of a comparison with palaeostress orientations obtained from the analysis of brittle mesostructures in the Cabuérniga Cretaceous basin, located in the western end of the Basque–Cantabrian basin, North Spain. The AMS data refer to 23 sites including Triassic red beds, Jurassic and Lower Cretaceous limestones, sandstones and shales. These deposits are weakly deformed, and represent the syn-rift sequence linked to basins formed during the Mesozoic and later inverted during the Pyrenean compression. The observed magnetic fabrics are typical of early stages of deformation, and show oblate, triaxial and prolate magnetic ellipsoids. The magnetic fabric seems to be related to a tectonic overprint of an original, compaction, sedimentary fabric. Most sites display a NE–SW magnetic lineation that is interpreted to represent the stretching direction of the Early Cretaceous extensional stage of the basin, without recording of the Tertiary compressional events, except for sites with compression-related cleavage.Brittle mesostructures include normal faults, calcite and quartz tension gashes and joints, related to the extensional stage. The results obtained from joints and tension gashes show a dominant N–S to NE–SW, and secondary NW–SE, extension direction. Paleostresses obtained from fault analysis (Right Dihedra and stress inversion methods) indicate NW–SE to E–W, and N–S extension direction. The results obtained from brittle mesostructures show a complex pattern resulting from the superposition of several tectonic processes during the Mesozoic, linked to the tectonic activity related to the opening of the Bay of Biscay during the Early Cretaceous. This work shows the potential in using AMS analysis in inverted basins to unravel its previous extensional history when the magnetic fabric is not expected to be modified by subsequent deformational events. Brittle mesostructure analysis seems to be more sensitive to far-field stress conditions and record longer time spans, whereas AMS records deformation on the near distance, during shorter intervals of time.  相似文献   

支持向量机与卡尔曼滤波集合的西太平洋副热带高压数值预报误差修正   总被引：1，自引：0，他引：1  

刘科峰　张韧徐海斌  闵锦忠朱伟军 《气象学报》2007,65(3):450-457

基于T106数值预报产品资料,提出了支持向量机和卡尔曼滤波相结合的方法来进行夏季西太平洋副热带高压数值预报的误差修正与预报优化。首先采用支持向量机方法建立了西太平洋副热带高压面积指数的误差修正模型。基于支持向量机预报优化模型尽管有比较好的拟合精度和预报效果,但与实际副热带高压指数尚有一定的差异。究其原因,除预报对象(副热带高压)本身比较复杂、模型优化因子不够充分以及数值预报误差自身的随机性以外,优化模型的输入、输出基本上是一个静态映射结构,因此前一时刻的预测误差难以得到有效的反馈、调整和修正。为考虑前一时刻预报误差的反馈信息,动态跟踪副高的变化趋势,随后引入卡尔曼滤波方法建立支持向量机-卡尔曼滤波模型,对支持向量机模型的输出结果作进一步的调整和优化。试验结果表明,该方法模型的预报优化效果优于T106数值预报产品以及单纯的神经网络修正模型和卡尔曼滤波修正模型的优化效果,能够较为客观、有效地修正西太平洋副热带高压指数的数值预报误差,改进和优化西太平洋副热带高压的数值预报效果。该方法为副热带高压等复杂天气系统和要素场预报提供了一种新的思路,表现出较好的应用前景。  相似文献   

豫西小秦岭地区太华杂岩中花岗质片麻岩的元素地球化学及其构造意义   总被引：4，自引：0，他引：4       下载免费PDF全文

周汉文  钟国楼  钟增球  徐启东 《地球科学》1998,23(6)

豫西小秦岭地区太华杂岩中花岗质片麻岩为古老侵入岩,主要由黑云斜长片麻岩、黑云钾长片麻岩和黑云二长片麻岩等类型岩石组成,具有ＴＴＧ岩系的组成特征,元素地球化学特征反映其形成于类似现代板块碰撞带的构造环境．  相似文献   

浙西上奥陶统于潜组Spirodesmos遗迹化石组合的环境意义   总被引：4，自引：1，他引：3       下载免费PDF全文

晋慧娟 《地质科学》1998,33(3):282-289

在概述了浙江西部上奥陶统于潜组的沉积学特征,并进而描述了发现的14个遗迹化石属基础上,从4个方面对Spirodesmos为代表的遗迹组合进行了环境分析:(1)14个遗迹属中仅3个属为穿相型分子,其余占遗迹总属2/3以上的遗迹化石均为典型的深水型分子,它们都是Nereites遗迹相的主要成员,因此该遗迹组合可归属于深海Nereites遗迹相中;(2)大部分遗迹化石呈复杂规则弯曲的形态,这种形态的遗迹化石是深海环境的遗迹化石标志;(3)14个遗迹属均为觅食迹和牧食迹,它们的行为习性,尤其是牧食迹主要分布于深海环境;(4)多数遗迹属的水深分布均在200m以下。由此可认为Spirodesmos遗迹组合是半深海-深海环境的产物。  相似文献   

Characteristics of the Variation of Cross Fault Short-Baseline and Short-Range Leveling in Western Yunnan Earthquake Test Site Before Lijiang M_S7.0 Earthquake     

Li Zhonghua  Su Youjing  and Liu ZhuyinSeismological Bureau of Yunnan Province  Kunming  China 《中国地震研究》1998,(4)

Results of analysis of variation of cross fault short-baseline and short-range leveling in Western Yunnan Earthquake Test Site (WYETS), results show that among five observation stations of cross fault short-baseline and short-range leveling in WYETS before the Lijiang MS7.0 Earthquake occurred in February 1996 only Yongsheng observation station (epicentral distance 82 km) located at Chenghai fault shows great variation about one year before the earthquake. And the nearest observation station, Lijiang (epicentral distance 42 km); presents great coseismic variation, but does not show obvious anomalous variation before the earthquake. There are no significant variations related to the earthquake at the other three observation stations. Two methods are used in analysis of the observed data and some valuable results have been obtained.  相似文献   

Prograde high- to ultrahigh-pressure metamorphism and exhumation of oceanic sediments at Lago di Cignana, Zermatt-Saas Zone, western Alps   总被引：10，自引：0，他引：10  

T. Reinecke 《Lithos》1998,42(3-4):147-189

Pelagic metasediments and MORB-type metabasalts of the former Tethyan oceanic crust at Cignana, Valtournanche, Italy, experienced UHP metamorphism and subsequent exhumation during the Early to Late Tertiary. Maximum PT conditions attained during UHP metamorphism were 600–630 °C, 2.7–2.9 GPa, which resulted in the formation of coesite-glaucophane-eclogites in the basaltic layer and of garnet-dolomite-aragonite-lawsonite-coesite-phengite-bearing calc-schists and garnet-phengite-coesite-schists with variable amounts of epidote, talc, dolomite, Na-pyroxene and Na-amphibole in the overlying metasediments. During subduction the rocks followed a prograde HP/UHP path which in correspondance with the Jurassic age of the Tethyan crust reflects the thermal influence of relatively old and cold lithosphere and of low to moderate shear heating. Inflections on the prograde metamorphic path may correspond to thermal effects that arise from a decrease in shear heating due to brittle-plastic transition in the quartz-aragonite-dominated rocks, induced convection in the asthenospheric mantle wedge and/or heat consumption by endothermic reactions over a restricted PT segment during subduction. After detachment from the downgoing slab some 50–70 Ma before present, the Cignana crustal slice was first exhumed to ca. 60 km and concomitantly cooled to ca. 550 °C, tracing back the UHP/HP prograde path displaced by 50–80 °C to higher temperatures. Exhumation at this stage is likely to have occurred in the Benioff zone, while the subduction of cool lithosphere was going on. Subsequently, the rocks were near-isothermally exhumed to ca. 30 km, followed by concomitant decompression and cooling to surface conditions (at < 500 °C, < 1 GPa). During this last stage the UHPM slice arrived at its present tectonic position with respect to the overlying greenschist-facies Combin zone. In contrast to the well-preserved HP/UHPM record of the coesite-glaucophane eclogites, the HP/UHP assemblages of the metasediments have been largely obliterated during exhumation. Relics from which the metamorphic evolution of the rocks during prograde HP metamorphism and the UHP stage can be retrieved are restricted to rigid low-diffusion minerals like garnet, dolomite, tourmaline and apatite.  相似文献