Thrust tectonics and paleogene syntectonic sedimentation in the Empordà area,southeastern Pyrenees     

Jordi Pujadas  Josep Maria Casas  Josep Anton Muñoz  Francese Sabat 《Geodinamica Acta》2013,26(3):195-206

Abstract

The structure of the southern Pyrenees, east of the Albanyà fault (Empordà area), consists of several Alpine thrust sheets. From bottom upwards three main structural units can be distinguished : the Roc de Frausa, the Biure-Bac Grillera and the Figueres units. The former involves basement and Paleogene cover rocks. This unit is deformed by E-W trending kilometric-scale folds, its north dipping floor thrust represents the sole thrust in this area. The middle unit is formed by an incomplete Mesozoic succession overlain by Garumnian and Eocene sediments. Mesozoic rocks internal structure consists of an imbricate stack. The floor thrust dips to the south and climbs up section southwards. The upper unit exibits the most complete Mesozoic sequence. Its floor thrust is subhorizontal. The lower and middle units thrust in a piggy-back sequence. The upper unit was emplaced out of sequence.

Lower Eocene sedimentation in the Biure-Bac Grillera unit was controlled by emergent imbricate thrusts and synchronic extensional faults. One of these faults (La Salut fault) represents the boundary between a platform domain in the footwall and a subsident trough in the hangingwall. Southward thrust propagation produces the inversion of these faults and the development of cleavage-related folds in their hangingwalls (buttressing effect). This inversion is also recorded by syntectonic deposits, which have been grouped in four depositional sequences. The lower sequences represent the filling on the hangingwall trough and the upper sequences the spreading of clastics to the south once the extensional movement ends.  相似文献   

粤西印支期那蓬岩体的岩石学、地球化学特征及其成因     

李坤  孙万财  邓飞 《地质力学学报》2017,23(3):411-421

那蓬岩体为混合岩化-花岗岩化作用的产物,主体岩性为中细粒(斑状)黑云母二长混合花岗岩、弱片麻状细粒黑云母二长混合花岗岩,富含堇青石、矽线石、红柱石等富铝矿物,靠近岩体边部为混合片麻岩、花岗片麻岩,逐渐过渡至围岩。对中细粒黑云母二长混合花岗岩进行LA-ICPMS锆石U-Pb同位素测年,锆石以变质锆石为主、岩浆锆石为辅,获得多期锆石UPb年龄,将最新的变质年龄252±1.9Ma作为成岩年龄,将那蓬岩体的成岩时代定为早三叠世。那蓬岩体形成于碰撞造山构造环境。  相似文献   

河北阜平平阳片麻状奥长花岗岩的地质和岩相学特征   总被引：1，自引：1，他引：1       下载免费PDF全文

张西平  万渝生杨崇辉 《中国地质》2003,30(1):61-72

平阳片麻状奥长花岗岩位于河北阜平县平阳镇一带，围岩为包括混合岩和片麻岩在内的变质表壳岩，层位上相当于阜平群的下部，产阳地区空间上存在高级变质作用、混合岩化作用和深熔作用的“三位一体”，因而由变质岩到花岗岩显示了系统的岩石学、岩相学以及产出关系上的渐变过渡特点，花岗岩中的变质表壳岩以及部分包体不仅在岩性上可和外围的同类岩石对比，而且也显示了明显的深熔作用改造的痕迹，有较为充分的语气表明平阳片麻状花岗岩总体上是原地深熔的奥长花岗岩，局部发生了一定尺度的位移。平阳地区变质表壳岩的深熔作用经历了以流体活动占主导地位、以矿物的溶解和重结晶为主要特点的早期阶段，演变为以部分矿物的熔融占主导地位的高级阶段，平阳片麻状奥长花岗岩的形成代表了阜平岩群变质表壳岩深熔作用的高级演化阶段，对于客观认识阜平岩群的组成和地质演化具有重大意义。  相似文献   

Tectonomagmatism in continental arcs: evidence from the Sark arc complex     

Wes Gibbons  Teresa Moreno 《Tectonophysics》2002,352(1-2)

The island of Sark (Channel Islands, UK) exposes syntectonic plutons and country rock gneisses within a Precambrian (Cadomian) continental arc. This Sark arc complex records sequential pulses of magmatism over a period of 7 Ma (ca. 616–609 Ma). The earliest intrusion (ca. 616 Ma) was a composite sill that shows an ultramafic base overlain by a magma-mingled net vein complex subsequently deformed at near-solidus temperatures into the amphibolitic and tonalitic Tintageu banded gneisses. The deformation was synchronous with D₂ deformation of the paragneissic envelope, with both intrusion and country rock showing flat, top-to-the-south LS fabrics. Later plutonism injected three homogeneous quartz diorite–granodiorite sheets: the Creux–Moulin pluton (150–250 m; ca. 614 Ma), the Little Sark pluton (>700 m; 611 Ma), and the Northern pluton (>500 m; 609 Ma). Similar but thinner sheets in the south (Derrible–Hogsback–Dixcart) and west (Port es Saies–Brecqhou) are interpreted as offshoots from the Creux–Moulin pluton and Little Sark pluton, respectively. All these plutons show the same LS fabric seen in the older gneisses, with rare magmatic fabrics and common solid state fabrics recording syntectonic crystallisation and cooling. The cooling rate increased rapidly with decreasing crystallisation age: >9 Ma for the oldest intrusion to cool to lower amphibolite conditions, 7–8 Ma for the Creux Moulin pluton, 5–6 Ma for the Little Sark pluton, and <3 Ma for the Northern pluton. This cooling pattern is interpreted as recording extensional exhumation during D₂. The initiation of the D₂ event is suggested to have been a response to the intrusion of the Tintageu magma which promoted a rapid increase in strain rate (>10⁻¹⁴ s⁻¹) that focussed extensional deformation into the Sark area. The increased rates of extension allowed ingress of the subsequent quartz diorite–granodiorite sheets, although strain rate slowly declined as the whole complex cooled during exhumation. The regional architecture of syntectonic Cadomian arc complexes includes flat-lying “Sark-type” and steep “Guernsey-type” domains produced synchronously in shear zone networks induced by oblique subduction: a pattern seen in other continental arcs such as that running from Alaska to California.  相似文献   

康滇地轴大田地区铀成矿与重大地质事件     

尹明辉 《地质与勘探》2021,57(1):14-29

康滇地轴混合岩型铀成矿与混合岩化、构造以及脉岩的关系一直以来存在较大的争议,而大田地区分布的混合岩、长英质脉岩(构造蚀变带内)以及辉绿岩/花岗质脉岩,尤其是富含石墨矿物的石英片岩的年代学特征成为解决这一问题的理想研究对象。在结合研究团队前期年代学研究工作的基础上,本文对大田地区辉绿岩/花岗质脉岩、富石墨石英片岩进行了系统的年代学研究,并获得以下认识:(1)大田地区混合岩化作用发生于840～860 Ma,其原岩形成时代为中元古代;(2)晶质铀矿形成年龄约为775 Ma,与混合岩化作用并无直接的关系,其形成年代与辉绿岩/花岗质脉岩、构造蚀变带内脉岩形成年代较为接近,表明可能为一期产物;(3)锆石中U含量结果分析表明U元素在混合岩化过程中发生了明显的富集现象,表明混合岩是最可能的铀源之一;(4)粗粒晶质铀矿的形成与Rodinia大陆的裂解具有一定的耦合关系,期间断裂活动和脉岩活动提供了成矿热源、流体以及储矿空间。  相似文献   

The role of syntectonic sedimentation in the evolution of doubly vergent thrust wedges and foreland folds     

Leo Duerto  Ken McClay 《Marine and Petroleum Geology》2009

This paper shows the evolution of time-constrained two-dimensional scaled analogue models of doubly vergent thrust systems in the presence of syntectonic sedimentation. Two sets of experiments were considered: (1) the addition of a syntectonic layer composed of a polymer and overlying sand in the prowedge; and (2) the addition to the previous condition of a progradational sedimentary load. Results from the first set of experiments indicate that the foreland fold-and-thrust belt has a strong relationship with the competence of the syntectonic layers. When the competence is low, the deformation produces tight asymmetric detachment-folds. As the competence increases, the fold-and-thrust belt shows break-trough folds with longer and better defined foreland-vergence. Results from the second set of experiments indicate that structural vergence is determined by the sense of progradation of the syntectonic layers, and in the case of strong aggradation at the prowedge, extension and reactive diapirism form contemporaneously with the contraction. Three end-members are proposed for mountain front thrust systems formed in the presence of syntectonic polymer and sand sedimentation: (1) outcropping fold-and-thrust belt sequence, in the case of no syntectonic sedimentation; (2) long displacement blind-thrust sheets, in the case of under-filled basins and (3) short displacement blind-thrust sheets, in the case of over-filled basins. All results indicate that ductile units at the base of syntectonic layers increase the displacement of the underlying frontal thrusts at the prowedge, and reduce the critical taper. Results also indicate that at very high sedimentary rates and hyper-critical taper conditions the prowedge collapses. Conclusions drawn from this research may be applied as an analogue to foreland evolution and to evaluate hydrocarbon generation, migration, and entrapment in thrust belts in areas where seismic imaging is generally poor.  相似文献   

青城子铅锌矿床成因分析   总被引：7，自引：0，他引：7  

董存杰 《地质与勘探》2010,46(1):59-69

青城子铅锌矿床是我国北方的大型铅锌矿床,矿区赋矿层位下部产出层状矿体,上部产出脉状及不规则状矿体。经过对矿区矿石及岩石的铅、硫同位素研究表明,层状及脉状矿体成矿物质来源相同,主要来自地层。根据矿区内含硫矿物的组合特征、成矿流体的pH值及含硫矿物δ34S分布特征可以推断矿床成因不属于海相沉积成因。矿石中石英流体包裹体特征表明矿床形成后未遭受区域变质作用,成矿流体的温度180～280℃,流体成分Na+K+,Ca2+Mg2+,K+/Na+为0.66,Ca2+/Mg2+为6.67,(CH4+H2+N2)/CO2值为0.012～0.048,为Na+?Ca2+?Cl-弱还原型溶液,pH值为6.31。流体特征与矿区内的花岗岩相差较大,与变质热液有所差异,经流体的氢氧同位素测定,成矿热液具地热水氢氧同位素特征相似。综合研究表明,矿床的成因与区域变质期后局部地区的的混合岩化作用关系密切,由混合岩化作用分异的气水热液与地下水、层间水等混合后沿早期形成的层间滑脱部位和断裂充填成矿,形成了青城子矿田‘下层上脉’的空间组合。  相似文献   

辽宁省宽甸县东挂牌岭硼矿深部找矿前景探析     

贾玉国  李然菊 《化工矿产地质》2010,32(3):149-153

位于辽宁省宽甸县大西岔乡的东挂牌岭硼矿,处于杨木杆复式向斜构造南翼,含硼层位赋存于里尔峪组中下部,呈层状、似层状展布。地表赋矿层在走向和倾向上都具有膨缩现象。通过与邻近庙沟矿区的矿体特征、构造等成矿条件综合对比,二者均发育有大范围含矿层,且含矿层规模较大,同时严格受蛇纹石化镁橄岩层控制,为层控矿床;地表蚀变均较强烈,蛇纹石化较普遍。普遍存在较大规模的北北东向逆断层,赋矿层受此构造影响,普遍向深部侧伏等方面非常相似。通过地表及浅部钻孔(350m以上)控制,认为矿体具有一定的厚度和品位,在走向、倾向上延伸均较好,在倾向上有增厚的趋势。故推测东挂牌岭西区深部资源前景巨大,有望通过进一步工作,取得找矿突破。  相似文献   

Geology, geochemistry, and U–Pb geochronology of the Archean (2.74 Ga) Serra do Rabo granite stocks, Carajás Metallogenetic Province, northern Brazil     

Alex Souza Sardinha  Carlos Eduardo de Mesquita Barros  Robert Krymsky   《Journal of South American Earth Sciences》2006,20(4):327-339

The Carajás region, located in the southeastern part of the Amazon Craton, has been considered one of the most important mineral provinces in the world. The Serra do Rabo Granite (SRG) crops out near the eastern termination of the Carajás fault as two granite stocks, elongated approximately in an E–W direction, concordant with the regional structures. Leucomicrocline granite, hornblende–microcline granite, biotite–hornblende–microcline granite, hornblende syenogranite, and subordinate aplite are identified. The granites are grayish pink and coarse to medium grained and have mainly hypidiomorphic granular texture. Granophyric textures are common. The accessory minerals are ilmenite, apatite, zircon, allanite, and rare pyroxene.The SRG rocks are either massive or foliated, with a slightly anastomosed continuous S₁ foliation (E–W/subvertical) outlined by the preferred orientation of quartz, feldspars, and mafic minerals. Locally, decimeter- to meter-wide mylonite/ultramylonite bands (S_1m) occur along the E–W foliation. The S₁ foliation was developed under higher temperatures than those of the S_1m mylonite foliation. The SRG structural evolution was controlled by progressive deformation under decreasing temperature, indicative of syntectonic emplacement. The SRG also has relatively high SiO₂, K₂O, and Na₂O contents; high FeO*/(FeO*+MgO) ratios; high Zr, Ba, Nb, and Ga; and very high rare-earth element contents. The chemical signature is moderately alkaline and metaluminous, comparable to that of the A-type, A2, and ALK-3 granites. The origin of the SRG magmas may be related to the partial melting of crustal sources, such as previously metamorphosed calc-alkaline granites.The SRG crosscuts supracrustal rocks, promoting low-pressure/high-temperature metamorphism. The interaction between regional compressive stresses and the ballooning effect of the granite stocks promoted slight aureole flattening and rheological changes in the supracrustal rocks. The U–Pb zircon age of 2743±1.6 Ma is interpreted as the age of zircon crystallization, granite stock emplacement, and regional horizontal shortening. Other 2.7 Ga syntectonic alkaline granites (e.g. Estrela, Plaquê, Planalto) have been reported in the region.  相似文献   

中国东南地洼区的变质作用类型及其与壳体演化的关系   总被引：1，自引：2，他引：1  

潘传楚 《大地构造与成矿学》1994,18(4):321-330

本文论述了东南地洼区的五种变质作用类型：接触变质作用、动力变质作用、区域变质作用、混合岩化作用和成矿变质作用；探讨了它们与华南亚壳体的演化－运动史的关系；总结了华南亚壳体自身演化－运动及其与相邻壳体相互影响而产生的变质作用的特征。  相似文献