Geology of the Talaud Islands, molucca sea collision zone, northeast Indonesia

The Talaud Islands lie at the northern margin of the collision zone between the Sangihe and Halmahera island arc systems. Rock units on Talaud are Neogene marine strata, basalt and andesite, tectonic mélange, and ophiolite. The units are exposed in N–S trending belts that are commonly separated by faults. The marine strata consist of tuffaceous siltstone, sandstone, shale and marl. They are strongly deformed by west-verging folds with wavelengths of 20–500 m. Volcanic rocks of island arc affinity are exposed on the east coast of Karakelang Island and appear to be interbedded with the lowermost marine strata. Tectonic mélanges contain blocks of serpentinite, gabbro, basalt, red middle Eocene chert and limestone, and greywacke turbidites. The blocks range in length from a few millimetres to hundreds of metres, and are enclosed in a scaly clay matrix. Several mappable slabs of ophiolite are separated by Tertiary strata or mélange. The dismembered ophiolites consist of serpentized peridotite, gabbro, spilites and cherts. Locally, the mélanges and ophiolites are thrust over the younger sedimentary rocks along east-dipping faults. The dominant eastward dips of mélange foliation, the westward vergence of structures in the Neogene strata, the Eocene ages of the cherts, and the Miocene age of the strata overlying the ophiolite slabs suggest that the ophiolites are pieces of Eocene or older oceanic crust (derived from a mid-ocean ridge or back-arc basin) and upper mantle that were emplaced as thrust slices into the lower slope of a west-facing arc during the Miocene and have been uplifted during arc—arc collision.     

哀牢山缝合带中两类火山岩地球化学特征及其构造意义

在哀牢山构造带的哀牢山断裂与花山－雅邑断裂之间出路大量不同构造环境的岩浆岩。除双沟蛇绿岩外,尚发现有景东火山岩和墨江火山岩。地球化学研究表明,景东火山岩具有类似于富集型洋中脊玄武岩（Ｐ－ＭＯＲＢ）地球化学特征,形成于以双沟蛇绿岩为代表的哀牢山洋盆先期的陆内裂谷构造环境;墨江火山岩具有岛弧火山岩地球化学特征,形成于哀牢山洋盆向西俯冲消减作用下的岛弧构造环境。景东裂谷型火山岩和墨江岛弧火山岩分别代表了     

北补连蛇绿岩的特征,形成环境及其构造意义

文中总结了北祁连蛇绿岩的特征，指出北祁连蛇绿岩大多具有ＭＯＲＢ的性质，有玻安岩产生，形成在弧后和岛弧环境，北祁连蛇绿岩大多侵位在岛弧增生楔或活动陆缘地体之上，蛇绿岩属于科迪勒拉型，早古生代的北祁连造山带属于科迪勒拉型造山带，部分蛇绿岩之上整合产出一套沉积一火山岩系，称为蛇绿岩的上覆岩系，指出蛇绿岩及其上覆岩系的枕状熔岩分别来自不同的源区，具有不同的构造意义，还讨论了北祁连早古生代板块构造格局，认为     

北祁连蛇绿岩的特征、形成环境及其构造意义

文中总结了北祁连蛇绿岩的特征，指出北祁连蛇绿岩大多具有ＭＯＲＢ的性质，有玻安岩产出，形成在弧后和岛弧环境。北祁连蛇绿岩大多侵位在岛弧增生楔或活动陆缘地体之上，蛇绿岩属于科迪勒拉型，早古生代的北祁连造山带属于科迪勒拉型造山带。部分蛇绿岩之上整合产出一套沉积－火山岩系，称为蛇绿岩的上覆岩系。指出蛇绿岩及其上覆岩系的枕状熔岩分别来自不同的源区，具有不同的构造意义。还讨论了北祁连早古生代板块构造格局，认为北祁连洋盆属于古亚洲洋的一部分，可能曾经是一个较大规模的洋盆。献中通常把它当成增生或俯冲杂岩带的一部分来看待〔１３，１６－１７〕；大岔大坂蛇绿岩带，其向两侧的延伸情况不清楚；九个泉（或塔墩沟）蛇绿岩带，向东可连到景泰县老虎山蛇绿岩，有人认为，向西可与榆树沟蛇绿岩相连〔２０〕。早先认为，北祁连存在新元古代、中寒武和早－中奥陶世三个时代的蛇绿岩〔２，１１〕，经过多年研究，目前大多数同意蛇绿岩主要是晚寒武－奥陶纪的〔１３，１６〕。图１北祁连早古生代蛇绿岩分布图１．前寒武纪基底；２．俯冲杂岩带；３．蛇绿岩。图中数字：１．九个泉；２．大岔大坂；３．边马沟；４．玉石沟；５．小八宝；６．百经寺；７．老虎山；８．榆树沟山２北祁连几     

祁连山地区镁铁——超镁铁岩的多样性

祁连山地区出露有不同类型的镁铁－超镁铁岩，包括蛇绿岩，阿拉斯加型岩体，橄榄岩－闪长岩型岩体以有产于北祁连西部的一种特殊的镁铁－超镁铁岩组合。不同的镁铁－超镁铁岩形成于一同的构造环境，蛇绿岩代表洋壳的残片，阿拉斯加型岩体产生岛弧或活动陆缘环境，橄榄岩一闪长岩体则是板块碰撞之后形成的，根据蛇绿岩与大致同时代的阿拉斯加型岩体产出的位置，推测在北祁连早古生代时存在向南的消减事件。     

The origin and emplacement of the Lajishankou ophiolite complex in the South Qilian belt: evidences from geological mapping

Many ophiolite complexes like those of Oman and New Caledonia represent fragments of ancient oceanic crust and upper mantle generated at supra‐subduction zone environments and have been obducted onto the adjacent rifted continental margin together with the accretionary complexes and intra‐oceanic arcs. The Lajishan ophiolite complexes in the Qilian orogenic belt along the NE edge of the Tibet‐Qinghai Plateau are one of several ophiolites situated to the south of the Central Qilian block. Our geological mapping and petrological investigations suggest that the Lajishankou ophiolite complex consists of serpentinite, wehrlite, pyroxenite, gabbro, dolerite, and pillow and massive basalts that occur in a series of elongate fault‐bounded slices. An accretionary complex composed mainly of basalt, radiolarian chert, sandstone, mudstone, and mélange lies structurally beneath the ophiolite complex. The Lajishankou ophiolite complex and accretionary complex were emplaced onto the Qingshipo Formation of the Central Qilian block which shows features typical of turbidites deposited in a deep‐water environment of passive continental margin. Our geochemical and geochronological studies indicate that the mafic rocks in the Lajishankou ophiolite complex can be categorized into three distinct groups: massive island arc tholeiites, 509 Ma back‐arc dolerite dykes, and 491 Ma pillow basaltic and dolerite slices that are of seamount origin in a back‐arc basin. The ophiolite and accretionary complex constitute a Cambrian‐early Ordovician trench‐arc system within the South Qilian belt during the early Paleozoic southward subduction of the South Qilian Ocean prior to Early Ordovician obduction of this system onto the Central Qilian block.     

蛇绿岩研究之检讨与反思:以“双沟蛇绿岩”为例

"双沟蛇绿岩"是笔者最早研究的蛇绿岩之一,位于云南哀牢山带。双沟出露的岩石有二辉橄榄岩、辉长岩、辉绿岩、斜长花岗岩、玄武岩、硅质岩等。辉长岩亏损LREE,锆石U-Pb年龄为362～328Ma。玄武岩具N-MORB和E-MORB的特征,锆石U-Pb年龄为249Ma。研究认为,"双沟蛇绿岩"可能产于陆间小洋盆或裂谷或裂陷槽背景。但是,双沟没有可信的深海沉积和混杂堆积的记录,虽然岩石组合类似蛇绿岩,地球化学也具有MORB的特征,暗示双沟可能不是一个典型的蛇绿岩。如果双沟不是蛇绿岩,则晚古生代的哀牢山带就不存在一个有一定规模的洋盆,也不可能存在大陆碰撞的记录。双沟不是蛇绿岩是什么?可能是造山橄榄岩(Orogenic peridotite)。造山橄榄岩与蛇绿岩的岩石组合类似,蛇绿岩的橄榄岩产于洋壳之下;造山橄榄岩产于陆壳之下。检讨双沟蛇绿岩的研究,反思蛇绿岩的概念。笔者认为,斯泰因曼的"三位一体"概念是合适的,1972年彭罗斯会议的决议是正确的,1996年怀柔会议构造学家对蛇绿岩概念的理解是对的。考虑到混杂堆积对于蛇绿岩的重要性,建议将混杂堆积也作为与蛇绿岩相伴的一个重要指标加进来。如果这个想法合适,则一个完整的蛇绿岩组合将由三个要素组成:1)岩浆岩(包括地幔岩、堆晶岩、侵入岩和火山岩,代表大洋岩石圈的物质组成); 2)深海沉积(代表洋盆顶部的物质组成); 3)混杂堆积(代表洋盆消失、陆块碰撞的构造产物)。蛇绿岩不同于其他岩浆岩,其研究需要特殊的方法和思路,明白这一点,蛇绿岩研究才能走上正轨。双沟蛇绿岩研究遇到危机,中国其他一些蛇绿岩也可能需要重新审视。因此,检讨双沟蛇绿岩,对反思蛇绿岩的研究具有一定的意义。     

Recognition of Ophiolite Belt and Granulite in Northern Area of Mian－Lue， Southern Qinling， China and Their Implication

ＲｅｃｏｇｎｉｔｉｏｎｏｆＯｐｈｉｏｌｉｔｅＢｅｌｔａｎｄＧｒａｎｕｌｉｔｅｉｎＮｏｒｔｈｅｒｎＡｒｅａｏｆＭｉａｎ－Ｌｕｅ，ＳｏｕｔｈｅｒｎＱｉｎｌｉｎｇ，ＣｈｉｎａａｎｄＴｈｅｉｒＩｍｐｌｉｃａｔｉｏｎ￥ＸｕＪｉｆｅｎｇ（Ｄｅｐａｒｔｍｅｎｔｏｆ...     

甘新交界红柳河地区早志留世蛇绿混杂岩的厘定及大地构造意义

地质、岩石化学、地球化学、同位素年代学综合研究证明,红柳河地区蛇绿混杂岩同橄榄岩、辉长岩、玄武岩和弧后火山－沉积岩系组成,玄武质岩石地球化学特征不同于典型大洋中脊,岛弧及板内玄武岩,并暗示其形成于大陆边缘向洋中脊过渡的构造环境,铀－铅同位素测年结果证明其侵位于早志留世,混杂时代早于晚泥盆地,上述成果表明中天山结晶基底与塔里木大陆之间在早志留世曾闰开形成红柳河小洋盆,于晚泥盆世之前发生碰撞混杂形成次级缝合带。     

甘孜—理塘蛇绿混杂岩带中段理塘地区混杂岩物质组成及其洋盆演化史

理塘混杂岩位于甘孜-理塘蛇绿混杂岩带中段新龙县-理塘县一带,其内部保存有完整的混杂岩系,包括蛇绿岩残片、洋岛残块、洋内弧残块、复理石建造、裂谷残片、高压变质岩等,是恢复和反演甘孜-理塘洋盆演化的理想地区。在总结前人研究的基础上,结合笔者近年来的研究成果,详细阐述了理塘混杂岩的物质组成、构造环境及形成时代,进一步约束了甘孜-理塘洋盆的时空、性质以及演化历程。LA-ICP-MS锆石U-Pb测年结果表明,甘孜-理塘混杂岩带内蛇绿岩年龄为（346±17）Ma、（286.2±5.1）Ma、（219.5±2.2）Ma、（216.1±2.3）Ma,洋岛年龄为（271±10）Ma、（245.1±1.5）Ma、（211.8±1.8）Ma,在侏罗纪瑞环山组粉砂岩夹层中测得碎屑锆石最新年龄为（196±3）Ma,结合大量的古生物化石鉴定结果,分析认为理塘混杂岩最早的年龄记录可追溯至中泥盆世,最晚可延至早白垩世,是甘孜-理塘洋盆中泥盆世-早白垩世连续演化的记录。综合以上研究成果,笔者还大致建立了甘孜-理塘洋盆晚古生代-中生代的演化过程模式。     

南天山区域大地构造与演化

塔里木和中天山之间的南天山造山带,经历了复杂的构造演化与地壳增生过程。综合分析南天山造山带的构造、地层、古生物、岩石、地球化学和同位素年代学等方面的资料,特别是放射虫、蛇绿岩、蓝片岩等方面的最新研究成果,讨论了南天山的区域构造格局和演化过程。南天山主体为一上百公里宽的增生-碰撞混杂带-南天山(蛇绿)混杂带;其北侧为中天山岛弧,是仰冲壳楔;南侧为塔里木陆块,是俯冲壳楔。古南天山洋为一广阔的大洋,南天山碰撞造山作用起始于二叠纪末-三叠纪初,新近纪-第四纪进入陆内造山作用阶段。     

蛇绿岩生成构造环境的Ba-Th-Nb-La判别图

Pearce的Ti-Zr-Y图不能很好区分洋脊和岛弧玄武岩,Ti对岩浆分离结晶作用很敏感,因此用这个图判别蛇绿岩生成构造环境效果不好,本文利用分配系数相近的Ba,Th,Nb,La四个非常不相容元素的(Ba/Nb)-Ba,(Nb/Th)-Nb,(La/Nb)-La和(Ba/Nb)-(Th/Nb)图解很好区分了洋脊、岛弧、洋岛玄武岩。弧后盆玄武岩同时具有洋脊和岛弧玄武岩的特征。这些元素在海水蚀变中较稳定,它们的比值在分离结晶过程中保持不变,因此这些图解有利于判别蛇绿岩(包括熔岩和均质辉长岩)生成的构造环境。     

Relicts of an intra-oceanic arc in the Sapi-Shergol mélange zone (Ladakh, NW Himalaya, India): implications for the closure of the Neo-Tethys Ocean

In the Ladakh–Zanskar area, relicts of both ophiolites and paleo-accretionary prism have been preserved in the Sapi-Shergol mélange zone. The paleo-accretionary prism, related to the northward subduction of the northern Neo-Tethys beneath the Ladakh Asian margin, mainly consists of tectonic intercalations of sedimentary and blueschist facies rocks. Whole rock chemical composition data provide new constraints on the origin of both the ophiolitic and the blueschist facies rocks. The ophiolitic rocks are interpreted as relicts of the south Ladakh intra-oceanic arc that were incorporated in the accretionary prism during imbrication of the arc. The blueschist facies rocks were previously interpreted as oceanic island basalts (OIB), but our new data suggest that the protolith of some of the blueschists is a calc-alkaline igneous rock that formed in an arc environment. These blueschists most likely originated from the south Ladakh intra-oceanic arc. This arc was accreted to the southern margin of Asia during the Late Cretaceous and the buried portion was metamorphosed under blueschist facies conditions. Following oceanic subduction, the external part of the arc was obducted to form the south Ladakh ophiolites or was incorporated into the Sapi-Shergol mélange zone. The incorporation of the south Ladakh arc into the accretionary prism implies that the complete closure of the Neo-Tethys likely occurred by Eocene time.     

西昆仑麻扎构造混杂岩带中－下侏罗统叶尔羌群源区构造背景分析

本文在收集和总结前人研究成果的基础上,通过对西昆仑麻扎地区中-下侏罗统叶尔羌群碎屑组分和砂岩地球化学特征分析,讨论了叶尔羌群沉积源区大地构造背景.在莎里塔什组沉积时期,物源区的构造背景主要为大陆岛弧、大洋岛弧的性质;杨叶组沉积时期,源区的大地构造背景为大陆岛弧,兼有活动大陆边缘性质;塔尔尕组沉积时期,源区构造背景复杂:既显示活动大陆边缘和岛弧(大洋岛弧、大陆岛弧)的性质,同时还显示出被动陆缘环境,其可能与晚三叠世造山开始时克拉通地块边缘的卷入有关.     

Past and present geotectonic position of Sulawesi, Indonesia

Sulawesi with its peculiar K-shaped pattern is situated in an area where the Eurasian, Indian—Australian and Pacific plates interact and collide.Complex geological processess in this area resulted in the transformation of a normal island-arc structure into an inverted one, deformation of an already tectonized belt, sweeping of fragments against unrelated terrain, thrusting of oceanic and mantle material over the island arc, closing of deep-sea basins behind the arc, trapping of old oceanic crust caused by the rolling up of an island arc, formation of a marginal basin by the spreading of the sea floor behind the arc, development of small subduction zones with reverse polarities etc.Small deep-sea basins surrounding Sulawesi such as the Gulf of Bone and the Gulf of Gorontalo originally formed the arc—trench gap of the Sulawesi island arc.The Banda Sea is considered as an oceanic crust trapped by the bending of the east—west trending Banda arc due to the northward drift of Australia combined with the westward movement of the Pacific plate. Similarly the Sulawesi Sea consists of an old Pacific crust trapped by the westward bending of the Sulawesi island arc, caused by the spearheading westward thrust along the Sorong transform-fault system, in which later a minor spreading center became active in its central part. The Molucca Sea comprises tectonic mélange in which presumably a small spreading center developed between the two colliding arcs of northern Sulawesi and western Halmahera. While the Benioff zones dip under the northern Sulawesi and Halmahera arcs in normal fashion, the mélange thrusts over them. The Strait of Makassar is a marginal basin which was brought into existence by the spreading of the sea floor between Kalimantan and Sulawesi.The evolution of Sulawesi started in Miocene time or even earlier when 800 km east of Kalimantan a north—south trending east-facing island arc came into existence, originating from a spreading center located in the Pacific Ocean. Volcanism and plutonism accompanied this subduction process.Collision between Sulawesi and the Australian—New Guinea plate which occurred in early Pliocene time severely transformed Sulawesi into an island with its convex side turned towards the continent, at the same time causing obduction of ophiolite in the eastern arc of this island.The movement of the Pacific plate continued and gradually pushed Sulawesi towards the Asian continent, resulting in the closing of the sea between Kalimantan and Sulawesi islands separated by small straits and deep seas resembling the complicated pattern of the Philippine Archipelago, in which the original double island-arc structure can no longer be recognized.     

新疆中天山南缘库米什地区蛇绿岩的锆石U-Pb同位素定年:早古生代洋盆的证据

新疆中天山南缘库米什地区的榆树沟和铜花山蛇绿混杂岩包括地幔橄榄岩,辉石岩、辉长岩、斜长岩等堆晶岩,辉绿岩墙和基性熔岩,以及上部的硅质岩等。岩石地球化学研究表明,蛇绿岩的岩石类型来自MORB型和SSZ型两种构造背景。蛇绿岩及有关岩石的锆石U-Pb同位素年代学的研究表明,与中天山南缘洋盆扩张和闭合有关的事件至少可以分为4期: (1)奥陶纪-志留纪的洋盆形成事件,证据来自蛇绿岩斜长花岗岩和斜长岩,两者的年龄分别为435.1±2.8Ma、439.3±1.8Ma;(2)志留纪的岛弧岩浆作用,获得岛弧火山岩英安岩年龄422.1±2.6Ma 和花岗闪长岩年龄423.1±1.8Ma;(3)泥盆纪的剪切变形和糜棱岩化变质作用,由于板块斜向俯冲和碰撞作用,产生大规模的走滑作用和与之伴生的由剪切作用形成的糜棱岩,糜棱岩的形成年龄为402.8±1Ma,为早泥盆世;(4)俯冲碰撞后的造山带伸展阶段的岩浆作用,在俯冲碰撞作用之后发生与垂直主受力面张裂作用伴生岩浆作用,获得石英正长斑岩294.8±1.2Ma年龄,即晚石炭世。 此外,认为榆树沟蛇绿岩北部出露的麻粒岩是一个很特殊的构造岩块,岩石的锆石中普遍存在500~1800Ma的老核,表明其原岩很复杂,不属于蛇绿岩的组合 。     

蛇绿岩与大陆缝合线

从六十年代以来,被誉为“地球科学革命”的板块构造学说,引起广泛的地质工作者的重视。因为它能圆满地解释地球的主要面貌之间的动力学关系。板块构造的概念是近二十年来从各海洋区搜集的大量地球物理资料而发展起来的,因而在阐明洋壳(约200兆年)的构造比陆壳获得较大的成功。由于板块构造提供了一个全球动力学体系的框架,使人们对中生代以来的大陆演化的许多作用有所了解。对板块学说有兴趣的地质工作者,想根据均变论的原则,去解释古大陆的形成、演化的历史。     

Cretaceous and Tertiary terrane accretion in the Cordillera Occidental of the Andes of Ecuador

New field, geochronological, geochemical and biostratigraphical data indicate that the central and northern parts of the Cordillera Occidental of the Andes of Ecuador comprise two terranes. The older (Pallatanga) terrane consists of an early to late (?) Cretaceous oceanic plateau suite, late Cretaceous marine turbidites derived from an unknown basaltic to andesitic volcanic source, and a tectonic mélange of probable late Cretaceous age. The younger (Macuchi) terrane consists of a volcanosedimentary island arc sequence, derived from a basaltic to andesitic source. A previously unidentified, regionally important dextral shear zone named the Chimbo-Toachi shear zone separates the two terranes. Regional evidence suggests that the Pallatanga terrane was accreted to the continental margin (the already accreted Cordillera Real) in Campanian times, producing a tectonic mélange in the suture zone. The Macuchi terrane was accreted to the Pallatanga terrane along the Chimbo-Toachi shear zone during the late Eocene, probably in a dextral shear regime. The correlation of Cretaceous rocks and accretionary events in the Cordillera Occidental of Ecuador and Colombia remains problematical, but the late Eocene event is recognised along the northern Andean margin.     

内蒙古海勒斯台俯冲增生混杂岩地质特征及发现的意义

采用"造山带混杂岩区"新理论,首次在贺根山-黑河缝合带中段发现海勒斯台俯冲增生混杂岩,建立由"基质"+"岩块"组成的俯冲增生杂岩体系,其构造样式为整体左行逆冲剪切.基质主要有糜棱岩、千糜岩、超糜棱岩及少量的沉凝灰岩、粉砂岩、细砂岩,构造环境为弧前盆地,时代主要为中寒武世;岩块有洋岛海山岩块、弧后洋盆洋壳残片、火山弧岩块、裂离陆块,岩块的年龄区间主要在中寒武世-中奥陶世,裂离陆块时代为新太古代.结合俯冲增生杂岩基质年龄、岩块的年龄、侵入混杂岩的TTG年龄（449 Ma）和变形程度、接触关系等,将海勒斯台俯冲增生杂岩的形成时代厘定为中晚奥陶世.认为研究区俯冲作用在早寒武世就已经开始,在大陆边缘形成火山岛弧;奥陶纪初期弧后发育弧后盆地,至中奥陶世弧后盆地出现洋壳;此时中寒武世的基质经俯冲下切后在中奥陶世时期折返上升;晚奥陶世时期由于区域的持续汇聚挤压,该弧后洋盆很快夭折;弧陆开始碰撞,导致双向俯冲.在弧陆碰撞过程中,晚期形成的弧后盆地洋壳等新岩块混入早期形成的基质中.海勒斯台俯冲增生混杂岩带的发现填补了贺根山-黑河缝合岩带中段的空白,对区域构造格架厘定具有非常重要的意义,为研究古亚洲构造域演化提供了新的证据.      

MULTI-ARC BASIN SYSTEM OF THE KUNLUN OROGENICBELT AND PAN-CATHYSIAN CONTINENTAL ACCRETION

After Rodinia supercontinent was disintegrated in Late Proterozoic, an ocean, namely, Tethys Ocean, occurred between Gondwana continental group and Pan-Cathaysian continental group from Late Proterozoic to Mesozoic. From Early Paleozoic to Mesozoic, Tethys Ocean was subducted toward Pan-Cathaysian block group, which results in backarc expansion, arc-land collision and forearc accretion. When the backarc basin expands and reaches the small oceanic basin, ophiolite melange will be generated. As accretion had already occurred in the south of the continental margin in the earlier stage, the succeeding backarc expansion and the frontal arc position were migrated toward south correspondingly. Therefore, multiple ophiolite belts and magmatic rock belts occurred, and show a trend of decreasing age from north toward south. As the continental margin was split and migrated toward south and reached a high latitude position, i.e., with the shortening and subduction of oceanic crust, the sedimentary bodies at high latitude was accreted continuously toward low latitude area together with the formation of oceanic island, mixing of cold-type and warm-type organism was generated. Moreover, blocks split and separated from Pan-Cathaysian or Gondwana continental group cannot traverse the oceanic median ridge and joins with another continental block. As a result, the Kunlun belt on the SW margin of the Pan-Cathaysian land was resulted from the multi-arc orogenesis such as the backarc seabed expansion, arc-arc collision, arc-land collision oceanic bed, and the continuous southward accretion process.