武当地块西部席状基性侵入岩群地球化学特征：南秦岭古生代底侵作用的依据

武当地块西部顺层侵位了大量的基性岩席。本文对其进行的岩石学、地球化学和Sr、Nd同位素等特征研究表明，该基性岩席群的岩浆属于大陆拉斑玄武岩系列，来源于混合异常大陆岩石圈地幔型源区，为武当地块裂解和中古生代时南秦岭地区曾发生大规模的地幔岩浆底侵及壳幔相互作用重要标志之一。此外，该基性岩席群的岩石地球化学特征与勉略地区玄武岩及变辉绿岩总体的特点具有较大的一致性，结合该基性侵入岩席群的形成时代(401—407Ma)、武当地块伸展构造(425—260Ma)与勉略带火山岩(230Ma)同位素年代学的差异，武当地块西部基性岩席群很可能是由于勉略洋拉开前地幔柱活动使大陆岩石圈拉伸减薄发生拆离、深部岩浆上涌的结果。因此，它们应该是勉略洋打开的早期阶段在武当地块区的响应。     

南秦岭构造带中-晚古生代伸展构造作用

华北板块与扬子板块于加里东晚期沿商丹带发生碰撞的同时,在扬子板块北缘,即现今南秦岭构造带,开始发育一条近东西向延伸的拉伸带,其中包括武当地块伸展滑脱构造、武当地块古生代大规模基性岩浆活动及其西侧紫阳-岚皋古生代碱性岩浆活动带、镇安-旬阳浅层塌陷盆地以及佛坪隆起等.该伸展构造带主体在时间上发生在秦岭两期碰撞事件之间,空间上位于南北两个缝合带之间,因此,是秦岭造山带演化过程中的一个非常重要的阶段.该伸展构造的开始很可能与南、北秦岭碰撞后的造山带重力塌陷有关,随着该伸展带南侧晚古生代勉略洋的形成,南秦岭逐渐演化为华北板块南侧的被动大陆边缘,从而使南秦岭的地壳伸展一直延续到早一中三叠世.武当地块伸展滑脱系统中顺层侵位的基性岩席群的年代学与岩石地球化学的研究表明,这些基性岩与勉略蛇绿岩组合中的变辉绿岩及变基性火山岩具有很大的相似性,因此勉略洋很可能也是南秦岭这次拉伸作用的结果.     

南秦岭构造带中——晚古生代伸展构造作用

华北板块与扬子板块于加里东晚期沿商丹带发生碰撞的同时，在扬子板块北缘，即现今南秦岭构造带，开始发育一条近东西向延伸的拉伸带，其中包括武当地块伸展滑脱构造、武当地块古生代大规模基性岩浆活动及其西侧紫阳－岚皋古生代碱性岩浆活动带、镇安－旬阳浅层塌陷盆地以及佛坪隆起等。该伸展构造带主体在时间上发生在秦岭两期碰撞事件之间，空间上位于南北两个缝合带之间，因此，是秦岭造山带演化过程中的一个非常重要的阶段。该伸展构造的开始很可能与南、北秦岭碰撞后的造山带重力塌陷有关，随着该伸展带南侧晚古生代勉略洋的形成，南秦岭逐渐演化为华北板块南侧的被动大陆边缘，从而使南秦岭的地壳伸展一直延续到早－中三叠世。武当地块伸展滑脱系统中顺层侵位的基性岩席群的年代学与岩石地球化学的研究表明，这些基性岩与勉略蛇绿岩组合中的变辉绿岩及变基性火山岩具有很大的相似性，因此勉略洋很可能也是南秦岭这次拉伸作用的结果。     

秦岭造山带武当地区古生代伸展构造

武当地块位于勉(县)略(阳)地区东侧,南部逆冲于扬子板块北缘之上,中-晚古生代期间曾经历过一期伸展构造作用。伸展构造系统以现今中元古代武当山群与新元古代耀岭河组之间的界面为主滑脱面,盖层系统由南往北滑脱拆离。沿主滑脱面上、下侵位了大量的基性岩席,其单颗粒锆石U-Pb年龄为401±14Ma和407±12Ma。滑脱系统上部次级滑脱面上新生白云母的⁴⁰Ar-³⁹Ar年龄为282±8.5Ma和261±0.25Ma,表明伸展作用可能一直持续到二叠纪。考虑到邻区同时代的碱性岩浆作用,作者认为伸展构造是伴随着古生代大规模的上地幔基性岩浆的底侵作用发生的,很可能代表了勉略洋打开的早期阶段。这对认识秦岭造山带的构造演化具有重要的意义。     

武当地块基性岩席群及其地质意义

侵位于武当地块内部的大量的板状为基性侵入体近年来一直被认为是800Ma左右发生的扬子古大陆裂解的重要依据。然而作者在武当地块北缘与西南部所做的1：5万地质填图以及相应的构造学和同位素年代学研究表明，它们与武当地块顺层伸展滑脱构造主滑脱面之顺层韧性一韧性变形带有密切的空间关系，是被褶皱了的岩席群。最新获得的岩体单颗粒锆石U－Pb年龄为401－407Ma，结合已有的地球化学研究成果，并考虑到邻区同时代碱性岩浆的侵位，作者认为，这套基性岩群代表了泥盆纪时南秦岭地区曾发生过大规模的上地幔岩浆的底侵作用，并因此导致南秦岭上部地壳的伸展减薄。     

武当地块基性侵入岩群的地质特征与构造意义

南秦岭构造带武当地块中发育密集侵位的基性侵入岩群，由于武当地区构造变形复杂，这些基性侵入岩体的侵位特征一直没有明确的研究结果。而查明它们的侵位特征，对认识其侵位机制、判断岩浆侵位的大地构造背景以及开展进一步的岩石地球化学和岩浆动力学的研究都具有重要意义。本文通过在武当地块不同构造部位所做的一些详细的1：5万地质填图以及相应的构造学研究表明，这些侵入岩体是顺层侵位到武当山岩群和耀岭河组中的，少数直接侵位到震旦系陡山沱组和邓影组中，侵入体密集发育的部位受武当地块古生代顺层伸展拆离构造的主拆离面控制。作者同时获得了402Ma的单颗粒锆石U—Pb年龄，表明这些基性侵入岩群形成于中古生代。因此无论这些基性侵入岩群的地质特征，还是其同位素年代学测试结果，都表明与前人所说的元古代超大陆的裂解很可能没有直接的成因联系。考虑到这个时期南秦岭构造带中发生的紫阳-岚皋碱性岩浆活动、镇安-旬阳浅层塌陷盆地、武当地块伸展滑脱构造及随枣地区基性侵入岩群的侵位等地质构造事件，作者认为武当地块基性侵入岩群很可能是古生代时期南秦岭岩石圈拉伸所导致的深部基性岩浆上侵的结果。     

南秦岭构造带内早古生代碱基性岩浆活动：古特提斯洋裂解的证据

位于南秦岭构造带南缘的勉略(勉县—略阳)洋是东古特提斯洋的北侧分支洋盆,在勉县—略阳地区发育有典型的蛇绿岩组合。然而,由于中三叠世晚期开始的碰撞造山作用以及之后陆内变形作用的改造,对于勉略洋盆在构造带东段的裂解和演化过程并不清晰。本文对发育于东南秦岭构造带内的基性岩墙群进行了岩石学、岩石地球化学、同位素年代学等方面的研究。结果表明,基性岩脉以辉长岩、辉绿岩等基性岩为主,其SiO 2含量为41.89%~49.75%,属基性—超基性岩类,并具有富钠、高钛的碱性岩特征。岩石的稀土、微量元素和Sr—Nd同位素特征与板内洋岛玄武岩(OIB)特征一致,岩浆源于具有地壳混染的板内洋岛玄武岩型地幔源区。该类基性岩脉顺层侵入到早古生代早期地层中,通过基性岩脉中的锆石SHRIMP测年获得岩脉顺层侵位的时代为晚志留世早期(约422 Ma)。这种岩浆作用很可能与古特提斯洋初始裂解有关,并导致南秦岭构造带内地壳伸展、基性岩浆侵位,该过程与南秦岭构造带北缘的商丹(商南—丹凤)原特提斯洋的消减和陆内俯冲可能相关。     

广西龙胜地鞠非构造侵位的蛇绿岩

广西龙胜地区的蛇绿岩并非是构造侵位于元古界丹洲群中的异地洋壳碎片，而是早期岩浆侵位的基性超基性岩席在原地遭受变形分解作用的透镜体型产物。龙胜蛇绿岩是一种非构造侵位的另一种类型的蛇绿岩。     

十亩地角闪辉长岩体特征及地质意义

十亩地角闪辉长岩体是新发现的晚古生代基性岩体,总体以线状沿秧田坝一十亩地构造直立带分布,岩石地球化学特征显示为洋中脊拉斑玄武岩性质。其岩石学、岩石地一民略阳县北三岔子勉略带蛇绿岩套中基性岩体的相似性及围岩变形变质等特征,反映秧田坝一十亩地构造直立带可能为勉略构造带一分支构造的东延。     

赣北程浪断裂带的形成:程浪超基性岩墙群和星子花岗岩的地球化学证据

对侵位于彭庐地块东南边缘与程浪断裂带毗邻的前寒武纪花岗岩和出露于程浪深断裂带内的超基性岩墙群的微量元素地球化学特征进行了研究,结果表明前者属板内与岛弧环境的过渡类型,后者代表典型的火山岛弧环境。结合前人在区域构造和地质年代学的研究成果,认为晋宁运动时期,扬子板块东南缘散布着多个小型块体,在华夏板块向扬子板块方向的俯冲过程中,障公山地块先与彭庐地块沿程浪断裂带发生拼合,同时形成程浪超基性岩墙群;与此同时,彭庐地块内则表现为大规模的岩浆侵入作用。在各小型块体陆续发生碰撞后,扬子板块与华夏板块在晋宁运动晚期最终碰撞拼合,火山岛弧环境转换为造山带构造,因此,彭庐地块、障公山地块等火山岛弧均成为华南造山带的组成部分。     

Geochemistry of Basic Dykes in Wudang Block and Its Tectonic Significance

Geochemical characteristics of the Neoproterozoic basic dykes widely exposed in the Wudang block of South Qinling show that the dykes possess the characteristics of continental tholeiitic basalts and were formed in a setting of continental rifting.Therefore,there was an ancient continental block in the areas of southern Qinling and Yangtze block during the Jinning period,and an important firting event of this ancient block occurred in the Early Neoproterozoic.     

秦岭造山带结构与演化若干问题的再认识

本文详细论述了北秦岭与商丹带、南秦岭、勉略带和太白－佛坪－汉南带的组成、结构特征;重新划分和阐述了秦岭造山带的构造单位及其发展演化。提出秦岭是由五类岩石地层地质体按非线性、混沌动力学的关系组合在一起并拼贴、镶嵌、叠置、堆垛而成的综合构造体,是南北与东西共存的构造格局。其经历了太古宙－古元古代陆核或古陆块增生或拼贴的发展阶段,中－新元古代板块构造体制发展阶段,震旦纪－三叠纪板内海相沉积盆地与造山带转换的发展阶段．印支期以来陆相沉积盆地和造山带转换的抽拉－逆冲岩片构造(或抽拉构造)体制的发展阶段。     

南秦岭中,新元古代地层划分对比新认识

在运用板块动力学模式研究晚前寒武纪地层划分对比问题的基础上,根据南秦岭构造带区域地质的实际情况,提出在中、新元古代南秦岭曾经历了晋宁期造山作用和澄江期裂解作用两次重大构造事件,它们控制了区内不同岩石建造的形成和时,空分布,据此对区域内中,新元古代地层的划分对比提出了新的认识。     

东秦岭造山带两类元古宙地壳基底及其地壳增生

通过研究南秦岭地区陡岭群、武当群和北秦岭地区秦岭群的变质基性岩等的铅同位素和微量元素组成，揭示出东秦岭造山带分布有两种性质及不同归属的元古宙地壳，指出中、古元古代时可能一个统一的地壳基底；南秦岭的中、古元古代地壳是在扬子陆地基底上通过岛弧的侧向加积形成和，北秦岭元古宙地壳则可能垂向增生于一个富入射性成因铅同位素组成的、具古洋壳幔性质的微地块之上，研究还表明陡岭群不是北秦岭地区的秦岭群，而应属于南秦     

秦岭构造带与转换断层

本文探讨转换断层在秦岭构造带演变中的作用。祁连洋扩张导致秦岭带的右行转换拉张作用,形成加里东期秦岭海。秦岭海消亡时,沿商丹断裂向北斜向俯冲。晚志留世,南、北大陆开始对接后,沿商丹断裂的斜向俯冲逐渐转变为左行走滑。左行走滑作用造成了海西早期平移造山作用和转换拉张作用相伴的构造格局。     

Fault zone evolution and its controls on ore-grade distribution at the Jian Cha Ling gold deposit, western Qinling region, central China

The Jian Cha Ling gold deposit is sited in folded and faulted Palaeoproterozoic rocks of the uplifted Mian-Lue-Yang block, adjacent to the Mianlue suture zone within the West Qinling mineral province, along the northern margin of the South China craton. Early Mesozoic gold mineralization at Jian Cha Ling, which has a pre-mined resource of about 536,000 oz Au, is controlled by the so-called F ₁ ⁴⁵ fault. The fault is a generally steeply N-dipping, WNW-trending deformation zone that is the result of dislocation along bedding planes, early foliation and axial planar surfaces of regional folds. The fault zone marks the contact between serpentinized, lower greenschist-facies dunites, harzburgites and minor gabbroic units in the footwall, and a metasedimentary sequence in the hanging wall that is dominated by metadolomite, metalimestone and phyllitic schists. Brittle–ductile deformation, partitioning of strain along pre-existing zones of weakness, and the formation of intrashear zone lozenges contributed to the development of a complex fault zone geometry. Variations in both dip and strike of discrete dislocation surfaces related to oblique, sinistral–reverse movement along the F ₁ ⁴⁵ fault zone focussed auriferous hydrothermal fluids along three dominant structural orientations. Gold was preferentially deposited along shallowly NNE-dipping and shallowly to moderately NNW-dipping fault segments, and is also associated with shallowly WSW-dipping, dolomite-dominated vein sets. Disseminated, economic gold grades (>4 g/t Au) are restricted to the footwall ultramafic rocks to within about 5 to 10 m of the contact with the hanging wall. Gold is related to laminated, realgar- and orpiment- bearing sheeted veins and hydrothermal breccias, as well as slickolites and fault gouge. Gold-bearing vein sets are located within the relatively undeformed, ultramafic intrashear zone lozenges. Gold-related alteration is dominated by extremely fine-grained, arsenic-bearing sulphide minerals and dolomite, with additional white mica and clay minerals. The structural setting of the deposit, combined with published data on the geological evolution of the West Qinling mineral province, suggest that the Jian Cha Ling gold deposit developed in an uplifted basement block during the final phases of northward subduction and suturing of the South China craton with the South Qinling orogen along the Mianlue Suture Zone, during the changeover from a compressional to transpressional tectonic regime in Late Triassic to Middle Jurassic times.     

鄂尔多斯盆地延长组长7段凝灰岩锆石U-Pb年龄、Hf同位素组成特征及其地质意义

鄂尔多斯盆地延长组长7优质烃源层中广泛分布了薄层和纹层状凝灰岩,凝灰岩中锆石U-Pb同位素年代学研究表明,长7段凝灰岩结晶年龄为234Ma左右。对比勉略缝合带、南秦岭的花岗岩的年龄,三叠系延长组凝灰岩应该形成于俯冲阶段。锆石的Hf同位素分析表明延长组长7段凝灰岩主要来自地壳岩石部分熔融,并且有一定的地幔物质加入。Hf同位素二阶段模式年龄大部分集中在1.1~1.3Ga,其中以1.2Ga为主峰,表明延长组凝灰岩主要来自元古代增生的地壳物质,在物质组成和时代上可能类似于南秦岭基底中的耀岭河群基性火山岩和郧西群酸性的混合。     

Collision leading to multiple-stage large-scale extrusion in the Qinling orogen: Insights from the Mianlue suture

The geologic framework of the Phanerozoic Qinling–Dabie orogen was built up through two major suturing events of three blocks. From north to south these include the North China craton (including the north Qinling block), the Qinling–Dabie microblock, and the South China craton (including the Bikou block), separated by the Shangdan and Mianlue sutures. The Mianlue suture zone contains evidence for Mesozoic extrusion tectonics in the form of major strike–slip border faults surrounding basement blocks, a Late Paleozoic ophiolite and a ca. 240–200 Ma thrust belt that reformed by 200–150 Ma thrusts during A-type (intracontinental) subduction. The regional map pattern shows that the blocks are surrounded by complexly deformed Devonian to Early Triassic metasandstones and metapelites, forming a regional-scale block-in-matrix mélange fabric. Five distinct tectonic units have been recognized in the belt: (1) basement blocks including two types of Precambrian basement, crystalline and transitional; (2) continental margin slices including Early Paleozoic strata, and Late Paleozoic fluviodeltaic sedimentary rocks, proximal and distal fan clastics, reflecting the development of a north-facing rift margin on the edge of the South China plate; (3) out of sequence oceanic crustal slices including strongly deformed postrift, deep-water sedimentary rocks, sheeted dikes, basalts, and mafic–ultramafic cumulates of a Late Paleozoic ophiolite suite, developing independent of the rift margin in a separate basin; (4) out-of-sequence island-arc slices; (5) accretionary wedge slices. All the tectonic units were deformed during three geometrically distinct deformation episodes (D₁, D₂ and D₃ during 240–200 Ma). Units 2–4 involved southward thrusting and vertical then southward extrusion of about 20 km of horizontal displacement above the autochthonous basement during the D₁ episode. Thrust slices 20 km south of the Mianlue suture are related to this vertical extrusion due to the same rock assemblages, ages and kinematics. The D₂ and D₃ episodes folded all the units in a thick-skinned style about east–west (D₂) and west–northwest (D₃) axes in the Mianlue suture zone. An early foreland propagating sequence of accretion of Late Paleozoic rocks deposited above the Yangtze craton is not involved in D₁ deformation but is temporally equivalent to the D₂ and D₃ deformation in the Mianlue suture. Two stages of strike–slip faulting mainly occurred at the end of D₂ and D₃, respectively. During D₂ deformation, the Bikou block was obliquely indented to the ESE into the Mianlue suture, rather than being thrust over the Mianlue suture from the north as a part of the Qinling–Dabie microblock. During D₃ deformation, however, the Bikou block was bounded by the south boundary fault of the Mianlue suture, and the Yangpingguan fault on the south. These faults are coeval strike–slip faults, but of opposite senses, and accommodated minor southwestward extrusion of the Bikou block into Songpan–Ganze orogen. The other basement blocks north of the Mianlue suture were extruded eastward by about 20 km of lateral displacement, based on the offset of the Wudang dome, during the D₃ episode due to the northeastward indentation of the Hannan complex of the South China craton. Post-D₃ emplacement of granite, cutting across the strike–slip faults such as the Mianlue suture, provides a minimum age of 200 Ma for D₃ deformation. Therefore, based on insights from the evolution of the Mianlue suture, the D₂ and D₃ episodes in the Mianlue suture and its neighbors are not responsible for and associated with the two-stage extrusion of the Dabie UHP-HP terranes from the Foping dome to the present erosional surface (more than 350 km).