北秦岭武关地区丹凤群斜长角闪岩地球化学特征、锆石SHRIMP测年及其构造意义

本文运用岩石学、地球化学和同位素年代学对分布于丹凤县武关地区的丹凤群斜长角闪岩进行了相对系统研究,岩石学和地球化学特征表明该套岩石为岛弧钙碱性玄武岩,不具备蛇绿岩单元组成特性.锆石SHRIMP测年结果表明,该套岩石中包含有古元古代～晚泥盆世(2489～360Ma)多个时期的锆石;锆石CL图像以及锆石形状研究以及区域同位素年代学、古生物化石资料共同显示,丹凤群中可能包含有泥盆纪岩石组合.分析前人对丹凤群的区域研究资料,我们认为丹凤群并非一套具有单一地层时代以及相同构造环境的岩石地层单位,而是一套由不同时代不同构造环境的岩石组合构成的俯冲-增生杂岩.区域上,丹凤群与其南侧的武关岩群、罗汉寺岩群以及部分刘岭群共同构成华北板块南缘俯冲-增生体系,其中分布有大量与俯冲作用相关的泥盆纪钙碱性侵入体,这些事实进一步证明华北板块南缘洋盆消亡时间上限至少可以持续到晚泥盆世末期.     

秦岭岩群中两类斜长角闪岩的性质和时代及其地质意义

在北秦岭造山带核部秦岭岩群内发育两类不同产状的斜长角闪岩.一类与秦岭岩群中的大理岩紧密共生,呈规模较大的似层状或较小块体产于大理岩内,另一类则呈密集岩墙群型式侵入于秦岭岩群南段二云母石英片岩中.不同的产出状态表明两类斜长角闪岩的成因和时代存在显著差异,也具有不同的地质构造意义.地球化学上,两类不同产状的斜长角闪岩的原岩皆为玄武岩质的.侵入秦岭岩群二云母石英片岩中的斜长角闪岩墙群形成于板内拉张环境,SHRIMP锆石U-Pb测年揭示该类斜长角闪岩形成于晚奥陶世(449±11Ma),Sr-Nd同位素特征显示其岩浆源区为亏损地幔源区,40Ar/39Ar热年代学研究显示该类斜长角闪岩的角闪岩相变质作用发生于石炭纪末期(301.3±6.4Ma).地球化学和Sr-Nd同位素特征显示与秦岭岩群大理岩共生的似层状或块状斜长角闪岩的形成环境与侵入云母石英片岩中的斜长角闪岩墙群的存在显著差异,其形成于洋岛(OIB)或海山环境.40Ar/39Ar热年代学研究显示该类斜长角闪岩于晚二叠世(258.1±5.7Ma)发生了角闪岩相变质作用.不同性质、形成和变质时代、相似的变质作用等特点表明,秦岭岩群中的两类角闪岩分属不同性质的构造块体,秦岭岩群高级变地质地体可能是一个构造拼合地体.斜长角闪岩岩墙为晚奥陶世(449±11Ma)侵入秦岭岩群云英片岩中的基性岩墙群,是北秦岭晚加里东期后造山期热收缩而致的地壳伸展或岩圈拆离减薄的产物.与秦岭岩群大理岩共生的斜长角闪岩则可能是洋隆体的基性喷出岩+碳酸盐岩帽组合,是中二叠世(312～260Ma)期间构造移置而来的外来块体.     

滇西北羊拉乡贝吾玄武岩形成的大地构造环境探讨

贝吾玄武岩为滇西北金沙江蛇绿混杂岩带中的一个岩块。通过详细的野外调查和岩石地球化学研究认为,贝吾玄武岩为低钾拉斑玄武岩,分异程度较低,大离子亲石元素相对于高场强元素富集,稀土总量低,轻稀土略富集,整体特征介于正常洋脊玄武岩与岛弧玄武岩之间,为似洋中脊玄武岩。其类似于岛弧玄武岩的富集特征表明了成岩过程中俯冲作用的存在,综合岩性组合、构造特征和地质背景分析,认为其属前弧玄武岩,形成于初始俯冲的洋内弧环境。     

内蒙古合教BIF型铁矿的形成时代、地球化学特征及地质意义

内蒙古合教铁矿位于华北克拉通西部陆块北缘阴山地块,是固阳绿岩带内的一例具有中型规模的BIF型铁矿床.本文对矿区斜长角闪岩、铁矿石开展了年代学和岩石地球化学研究.对斜长角闪岩夹层进行LA-ICP-MS锆石U-Pb定年,锆石普遍发育振荡环带,Th/U比值均大于0.1（0.27~1.00）,得到上交点年龄为2 549±29 Ma（MSWD=0.51）,可大致代表合教BIF铁矿的形成时代,该时期是华北克拉通早寒武纪构造-变质-热事件和BIF（banded iron formation）形成最为强烈的时期（2.52~2.60 Ga）.斜长角闪岩原岩可能为玄武岩,表明合教铁矿为与火山活动关系密切的Algoma型BIF.斜长角闪岩稀土元素球粒陨石标准化配分曲线近于平坦,与E-MORB和弧后盆地玄武岩（BABB）曲线相似,原始地幔标准化蛛网图与BABB曲线相似,均存在Rb、Ba、Sr、K等大离子亲石元素的富集和Nb、Ta、U、Th等高场强元素的亏损,显示了岛弧岩浆岩的特征,结合前人提出的岛弧叠加地幔柱构造模式,认为合教斜长角闪岩原岩形成于弧后盆地构造环境,并有地幔柱的叠加作用,代表了合教BIF沉积时的构造环境.铁矿石LREE亏损,HREE富集[（La/Yb）_PAAS=0.29~0.50],具有轻微的La正异常（La/La*=1.00~1.13）,不明显的Ce负异常（Ce/Ce*=0.90~0.95）,明显的Eu正异常（Eu/Eu*=1.54~2.27）和较明显的Y正异常（Y/Y*=1.07~1.42）.铁矿石的稀土配分曲线与固阳绿岩带科马提岩和海底热液海水混合物均极为相似,表明合教BIF的形成与海底热液活动有关,认为合教BIF型铁矿的Fe主要由海底高温热液淋滤科马提岩提供.      

内蒙古锡林浩特岩群岩相学、地球化学特征及构造环境分析

锡林浩特岩群是内蒙古中东部锡林郭勒微地块内原锡林郭勒杂岩的重要组成部分,由一套片麻岩夹层状斜长角闪岩、磁铁石英岩和变粒岩等变质岩组成,形成于中元古代［1］。岩群中片麻岩样品显示轻稀土元素富集的中等分异特征((La/Yb)N=4.71~7.97),斜长角闪岩具有平坦型((La/Yb)N=0.74~0.95)和轻稀土元素微弱富集型((La/Yb)N=1.06~3.63)两种稀土元素配分模式。在微量元素N MORB标准化图解中,斜长角闪岩显示出洋中脊玄武岩和岛弧玄武岩的过渡类型特征。同时结合岩相学和岩石地球化学图解分析,推断片麻岩原岩为富含泥质的亚杂砂岩,而斜长角闪岩原岩为一套具有拉斑质到钙碱性过渡型特征的玄武岩;变质沉积岩形成于活动大陆边缘大陆岛弧环境;变质基性火山岩形成于岛弧弧后盆地。二者指示锡林浩特岩群形成于活动大陆边缘体系。     

哀牢山-大象山变质杂岩带中斜长角闪岩的地球化学、同位素年代学及其地质意义

哀牢山-大象山变质杂岩带位于青藏高原东南缘,是西南三江地区重要的北西向造山带。杂岩带主要由各种类型的副片麻岩、片岩、石英岩、大理岩和斜长角闪岩构成,岩石发生强烈的糜棱岩化。本文在哀牢山变质杂岩带东南段元江和金平地区以及大象变质杂岩带北段老街和Pho Rang地区发现了中二叠-早三叠世的斜长角闪岩。岩石地球化学和锆石U-Pb年龄研究表明,这些斜长角闪岩可分为4组：第1组为元江斜长角闪岩,具有类似于E-MORB的稀土和微量元素配分曲线特征,锆石U-Pb定年显示其原岩形成年龄为272.5±1.7Ma;第2组为勐桥-马鞍底斜长角闪岩,相比于元江斜长角闪岩（第1组）具有更高的轻/重稀土分馏程度,其稀土和微量元素配分曲线类似于E-MORB,微量元素比值（Nb/Yb、Th/Yb等）显示具有沿MORB-OIB序列演化的趋势,勐桥和马鞍底斜长角闪岩中的Ti含量和Ti/Y比值等特征分别类似于峨眉山低Ti玄武岩和高Ti玄武岩。锆石U-Pb定年结果表明,勐桥-马鞍底斜长角闪岩形成于265.2±1.0Ma~266.2±1.0Ma和250.4±1.5Ma~248.7±1.6Ma,其中晚期岩石中含有261.2±1.5Ma~257.9±1.6Ma的继承锆石,该年龄与峨眉山玄武岩（约260Ma）近于同期。上述证据表明勐桥-马鞍底斜长角闪岩岩浆演化过程中可能混染了部分具有OIB属性的峨眉山地幔柱物质成分;第3组为大象山老街-Pho Rang斜长角闪岩,具有类似于OIB的稀土和微量元素配分曲线特征,微量元素含量和比值（TiO₂=3.28%~4.31%,Nb/La=0.84~1.01,Ti/Y>500等）特征显示与峨眉山高Ti玄武岩相似的地球化学属性,表明峨眉山玄武岩在哀牢山-大象山变质杂岩带内广泛分布,该岩石成分可能为勐桥-马鞍底斜长角闪岩（第2组）的端元组分之一;第4组为大象山Pho Rang斜长角闪岩,该组岩石具有与元江斜长角闪岩（第1组）相似的E-MORB属性特征。进一步的研究表明,哀牢山-大象山变质杂岩带中具有类似于E-MORB属性的斜长角闪岩均表现出不同程度的Nb、Ta元素亏损和Rb、Ba等大离子元素富集,微量元素比值（Nb/Yb（0.72~5.29）,Th/Yb（0.11~0.87）,La/Nb（0.91~8.83））等特征类似于岛弧玄武岩,这些特征指示其原岩岩浆可能是俯冲环境下地幔楔岩石部分熔融的产物。结合哀牢山-大象山变质杂岩带、哀牢山-马江缝合带以及扬子地块之间的时-空关系,本文推测哀牢山-大象山变质杂岩带内的E-MORB类型岩浆岩形成于东古特提斯支洋（即哀牢山-马江洋）向东的俯冲过程,其俯冲持续时间为中二叠-早三叠世（272~248Ma）。     

Tectonic setting and geochemical characterisation of Neoproterozoic volcanics and granitoids from the Adobha Belt, northern Eritrea

The Adobha Belt consists largely of metamorphosed volcanic and sedimentary sequences and syntectonic granitoids. Identification of the ancient tectonic setting of the belt has been attempted using trace element (including rare earth element) geochemical data on igneous suites. The Himbol volcanics of the Nakfa Terrane represent a calc-alkaline island-arc setting, while the Uogame basalts and associated gabbros characterise a tholeiitic, transitional MORB setting. The chemistry and petrographic features of the basalts and gabbros clearly suggest that they are parts of a dismembered ophiolite. Other authors' work shows that further to the west, the Hager Terrane belongs to a calc-alkaline island-arc setting. The Uogame ophiolitic suite thus portrays a MORB crust sandwiched between two island-arc terranes. Based on the fact that the MORB-type crust occurs within a high strain zone that extends for several hundreds of kilometres along strike, it is concluded here that it represents a terrane-bounding Neoproterozoic ophiolite belt. It is further suggested that this belt might outline a suture that signifies the collision between the island-arcs.     

The late Neoproterozoic Enganepe ophiolite, Polar Urals, Russia: An extension of the Cadomian arc?

The Enganepe ophiolite, Polar Urals was formed at 670 Ma and records a diverse geochemical association of tholeiite, arc-tholeiite, adakite, and OIB-like lithologies. This constrains the tectonic setting of the protolith of the ophiolite to an oceanic island-arc, with ridge-trench interaction most readily explaining the diverse compositions. The initiation of intra-ocean subduction and the development of the Enganepe island arc off the eastern margin of Baltica probably pre-dated the formation of the Enganepe ophiolite, i.e. prior to 670 Ma. The timing of island-arc magmatism is similar in age to that recorded off Avalon in the Cadomian arc. We propose that the active margin of Baltica in the Vendian is an extension of the Cadomian arc. This requires the northeast margin of Baltica (present-day coordinates) to have been in a southerly position in the Vendian, in agreement with proposed tectonic reconstructions. Consequently, the post-Rodinia continental amalgamation, Pannotia, had active ocean-continent convergence along its entire southerly (west Avalonia and Amazonian cratons) margin at the time of its break-up.     

西藏羌塘中部亚丹高压变质岩年代学、地球化学特征及其构造意义

羌南和羌北地块沿龙木错-双湖缝合带碰撞对接,标志着古特提斯洋的最终闭合,然而古特提斯洋的构造演化,尤其它的打开时限一直争议不断。本文对龙木错-双湖缝合带以南荣玛地区的变质杂岩进行了岩相学、年代学和地球化学特征研究,进而约束古特提斯洋的开、合时限及其关闭后的构造演化特征。通过LA-ICP-MS锆石U-Pb定年,本文首次报道了1件新元古代斜长角闪岩,其加权平均年龄为717±7Ma(n=61,MSWD=1. 9),表明原岩形成于新元古代中期,反映羌南地区存在前寒武基底;另获得1件中侏罗世斜长角闪岩的锆石加权平均年龄为163±2Ma(n=26,MSWD=1. 9),表明其原岩形成于中侏罗世;获得2件石榴石多硅白云母石英片岩锆石边部谐和年龄范围分别为267～1349Ma和214～2050Ma;另对片岩中2组多硅白云母样品进行~(40)Ar/~(39)Ar定年,分别获得224. 2±1. 5Ma和223. 9±1. 5Ma的一致坪年龄,暗示区域变质作用可能从～224Ma持续到214Ma之后,且～214Ma的岩浆事件可能形成于碰撞过程中。新元古代和中侏罗世斜长角闪岩的岩石地球化学特征显示,前者原岩具E-MORB特征,后者原岩趋向于OIB特征。基于区域岩石组合与地球化学特征,推断二者均形成于伸展环境,前者可能形成于陆内伸展背景,响应Rodinia超大陆的裂解,后者可能形成于大陆裂谷环境,响应羌南、羌北地块碰撞结束后的裂解。综合前人与本文研究成果,认为新元古代中期(～717Ma),某未知陆块可能就已逐渐开始从羌南-印度大陆裂解,导致"古特提斯洋"在ca. 717～517Ma之间的某个时间点就已打开;古特提斯洋可能在～224Ma才完成闭合,羌南、羌北陆陆碰撞挤压持续到214Ma之后;中侏罗世区域为裂谷伸展环境,并发育OIB特征的碱性玄武岩和双峰式火成岩。     

The origin of the Pailin Crystalline Complex in western Cambodia,and back-arc basin development in the Paleo-Tethys Ocean

The Pailin Crystalline Complex, which consists of amphibolites, metagabbros, and felsic igneous rocks, is located in western Cambodia. We used the geochemistry of the amphibolites and the zircon UPb ages of felsic igneous rocks to constrain the origin of the Pailin Crystalline Complex and to gain insights into the tectonic framework of Southeast Asia. Geochemical analyses indicate that the amphibolites are normal (N-type) mid-ocean ridge basalts, similar to the Sa Kaeo Back-arc Basin basalts of southeastern Thailand. The zircon UPb ages are 283 ± 2 Ma (anorthosite dike), 280 ± 2 Ma (aplite dike), and 275 ± 2 Ma (plagiogranite). The geochemistry and detrital zircon UPb ages of sandstones adjacent to the Pailin Crystalline Complex suggest that they are sediments that filled the Sa Kaeo Back-arc Basin during the Triassic. We infer that the Pailin Crystalline Complex is part of a dismembered ophiolite related to the back-arc basin, and that the igneous rocks formed during the Early Permian. Most of the metamorphism occurred during continental collision in Southeast Asia. However, the amphibolites of the Pailin Crystalline Complex also experienced ocean-floor metamorphism at a back-arc spreading center, in a tectonic setting similar to that of the mafic metamorphic rocks of the Nan Back-arc Basin, northern Thailand. We conclude that the Pailin Crystalline Complex is the southernmost extension of a back-arc basin related to subduction of Paleo-Tethys oceanic crust and the Sukhothai Arc.     

西藏拉萨地体南缘汤白地区始新世辉绿岩脉——新特提斯洋壳断离的证据

拉萨地体南缘汤白地区广泛分布新生代的辉绿岩脉。为探讨该辉绿岩脉形成时代、岩石成因和地质意义,对其开展了详细的岩相学、地球化学、锆石U-Pb年代学及Hf同位素研究。LA-ICP-MS锆石U-Pb定年结果显示辉绿岩脉的结晶年龄为(54±1)Ma,表明其形成于早始新世。微量元素地球化学特征显示富集大离子亲石元素(LILEs:如Rb、Sr和Ba),亏损高场强元素(HFSEs:如Nb、Ta和Ti)。与典型的弧岩浆岩、区域上叶巴组和桑日岩群中的玄武岩相比具有较高的Nb、TiO_2和Zr含量,在微量元素构造环境判别图解中显示出板内玄武岩地球化学属性。微量元素地球化学特征结合锆石Hf同位素表明岩浆源区除被俯冲板片释放的流体交代的岩石圈富集地幔外,还有软流圈亏损地幔物质加入。汤白辉绿岩脉侵入年龄与区域上林子宗群火山活动峰期接近(52 Ma)。同时结合岩石成因及构造背景,作者认为汤白辉绿岩脉是54～52 Ma新特提斯洋壳断离诱发岩浆作用的产物。根据最新大陆碰撞及板片断离的三维数值模型,暗示了印度板块与欧亚大陆碰撞的起始时间为65 Ma或者更早。     

羌塘盆地东部那益雄组玄武岩地球化学特征及构造意义

羌塘盆地东部那益雄组玄武岩作为裂谷演化最后阶段的喷发产物,其成岩年龄和地球化学特征为裂谷的关闭时间和二叠纪构造演化提供了重要约束.在剖面地质调查基础上,对那益雄组玄武岩进行了LA-ICP-MS锆石U-Pb测年及全岩分析测试,结果显示:那益雄组玄武岩锆石U-Pb年龄为257.2±2.9 Ma,形成于晚二叠世;该玄武岩属于大陆拉斑玄武岩系列,轻微富集Ta元素而轻微亏损Nb元素,是软流圈地幔物质上涌与岩石圈地幔相互作用的产物,形成于裂谷关闭碰撞后的伸展背景.羌塘地块东部二叠纪玄武岩的地球化学数据显示,早二叠世-晚二叠世玄武岩具有由OIB型玄武岩向火山弧型玄武岩过渡的演化趋势,表明羌塘地块东部板内裂谷在早二叠世打开,中二叠世进入裂谷演化阶段,于晚二叠世关闭.      

Caribbean island-arc rifting and back-arc basin development in the Late Cretaceous: Geochemical, isotopic and geochronological evidence from Central Hispaniola

We present new regional petrologic, geochemical, Sr–Nd isotopic, and U–Pb geochronological data on the Turonian–Campanian mafic igneous rocks of Central Hispaniola that provide important clues on the development of the Caribbean island-arc. Central Hispaniola is made up of three main tectonic blocks—Jicomé, Jarabacoa and Bonao—that include four broad geochemical groups of Late Cretaceous mafic igneous rocks: group I, tholeiitic to calc-alkaline basalts and andesites; group II, low-Ti high-Mg andesites and basalts; group III, tholeiitic basalts and gabbros/dolerites; and group IV, tholeiitic to transitional and alkalic basalts. These igneous rocks show significant differences in time and space, from arc-like to non-arc-like characteristics, suggesting that they were derived from different mantle sources. We interpret these groups as the record of Caribbean arc-rifting and back-arc basin development in the Late Cretaceous. The> 90 Ma group I volcanic rocks and associated cumulate complexes preserved in the Jicomé and Jarabacoa blocks represent the Albian to Cenomanian Caribbean island-arc material. The arc rift stage magmatism in these blocks took place during the deposition of the Restauración Formation from the Turonian–Coniacian transition (~ 90 Ma) to Santonian/Lower Campanian, particularly in its lower part with extrusion at 90–88 Ma of group II low-Ti, high-Mg andesites/basalts. During this time or slightly afterwards adakitic rhyolites erupted in the Jarabacoa block. Group III tholeiitic lavas represent the initiation of Coniacian–Lower Campanian back-arc spreading. In the Bonao block, this stage is represented by back-arc basin-like basalts, gabbros and dolerite/diorite dykes intruded into the Loma Caribe peridotite, as well as the Peralvillo Sur Formation basalts, capped by tuffs, shales and Campanian cherts. This dismembered ophiolitic stratigraphy indicates that the Bonao block is a fragment of an ensimatic back-arc basin. In the Jicomé and Jarabacoa blocks, the mainly Campanian group IV basalts of the Peña Blanca, Siete Cabezas and Pelona–Pico Duarte Formation, represent the subsequent stage of back-arc spreading and off-axis non-arc-like magmatism, caused by migration of the arc toward the northeast. These basalts have geochemical affinities with the mantle domain influenced by the Caribbean plume, suggesting that mantle was flowing toward the NE, beneath the extended Caribbean island-arc, in response to rollback of the subducting proto-Caribbean slab.     

豫西小秦岭地区太华杂岩中斜长角闪岩地球化学及其大地构造意义

小秦岭地区太华杂岩的斜长角闪岩以多种产状出露于表壳岩系和花岗质片麻岩中，经历了角闪岩相区域变质作用，形成黑云斜长角闪岩、透辉斜长角闪岩、斜长角闪岩和黑云石榴斜长角闪岩等岩石类型。     

金沙江缝合带弯岛湖蛇绿混杂岩带的岩石地球化学特征及其构造背景

弯岛湖蛇绿混杂岩带是金沙江缝合带西段的重要组成部分。蛇绿岩混杂于上三叠统变质碎屑岩夹变质火山岩中,成份主要为镁铁质-超镁铁质杂岩,岩石类型有变质橄榄岩、变质堆晶质辉长岩及其伴生的岛弧型花岗岩系。岩石化学及地球化学特征表明:蛇绿岩主要为低Ti(岛弧-弧后)型、富集型洋中脊(E-MORB)拉斑玄武岩;与之共(伴)生的基性喷出岩、辉绿岩脉属板内洋岛型裂谷型碱性玄武岩及其过渡类型系列。在变质辉长岩获得全岩Sm-Nd等时线年龄值为232±11Ma,代表了镁铁质-超镁铁质杂岩的形成年龄,可能为洋壳初始俯冲变质的时间。在蛇绿岩上覆的硅质岩中发现有中三叠世拉丁晚期至晚三叠世卡宁早期的放射虫化石,表明弯岛湖镁铁质-超镁铁质杂岩可能形成于中三叠世多岛洋盆或弧后盆地构造环境。     

Kalikorva structure and its position in the system of the northern Karelian greenstone belts: Geochemical and geochronological data

New geochemical data on volcanic rocks and the first U-Pb zircon ages for the Kalikorva structure made it possible to determine the time and conditions of their formation and constrain geodynamic models. The lower sequences of the Kalikorva structure is dominated by metatholeiites with high MgO, Cr, and Ni contents, high Mg#, and REE distribution patterns close to the mantle level. They contain rare komatiite interlayers and lenses of pyroxenites and peridotites and can be considered as products of the deep melting of mantle material. At the same time, the tholeiitic metabasalts bear island-arc signatures and are intercalated with metagraywackes and metadacites (adakites). This rock association could be formed under spreading conditions at the beginning of an island-arc regime. The upper sequence is dominated by metagraywackes and contains diverse rocks with both MORB (tholeiitic and komatiitic basalts) and island-arc (calc-alkaline andesite and dacites, subalkaline basalts, and picritic basalts) affinity, which is typical of back-arc basins. The U-Pb dating of zircons from the metadacites and detrital zircons from the metagraywackes of the Kalikorva structure yielded similar ages of 2785 ± 13 and 2766 ± 21 Ma, respectively. They coincide with the age of the late volcanic complex of the Hisovaara Group of the Hisovaara structure (2780 Ma). Both complexes include island-arc associations with subduction signatures and contain adakites, Nb-Ti basalts, and basaltic andesites. The metagraywackes and metadacites of the Chupa sequence of the Belomorian mobile belt are older than the similar rocks of the Kalikorva complex and have an age of 2870 ± 30 Ma. Ages of 2735 ± 20 Ma and 2720 ± 4 Ma were previously obtained for the metaandesites of the Kichany volcanogenic complex, which could be an even younger volcanic arc.     

中国东南部晚中生代-新生代玄武岩与壳幔作用

中国东南部的火山活动在早中生代时期仅有很小规模,晚中生代最早的、较大规模的岩浆活动始于中侏罗世早期,至早白垩世是火山岩浆活动的鼎盛期,在近100个Ma的时间内形成了大面积分布的晚中生代火山-侵入岩,而在新生代则以面积较小的玄武岩浆喷出活动为主,局限分布于沿海一带。以晚中生代湘南、赣南和闽西南的近EW向火山岩带和浙、闽沿海地区的近NNE向火山岩带,以及新生代近NNE向火山岩带为研究对象,对这些火山岩的地球化学特征对比研究,结合时空分布,讨论了它们的起源及其与壳幔相互作用的关系,以及它们形成的构造环境,其结果显示,EW向晚中生代火山岩带（180～170Ma）的西段玄武岩独立产出,且明显属碱性系列;而中段和东段玄武岩和流纹岩伴生,其中的玄武岩均为亚碱性系列的拉斑玄武岩。它们形成于板内拉张构造环境,是中国东南部特提斯构造域向太平洋构造域转换、晚中生代大规模岩浆作用的序幕。研究表明,该火山岩带自西向东表现出不同程度的壳幔相互作用,玄武岩在成岩过程中有少量陆壳组分加入。NNE向晚中生代火山岩带（130～90Ma）主要为流纹质岩石,安山岩和玄武岩很少。即使是双峰式火山岩也以酸性岩为主,玄武岩仅占全部火山岩体积的30％以下。其中的玄武岩主要属钙碱性系列,少数属拉斑系列。它们形成于火山弧构造环境,是中国东南部受太平洋构造域影响发生大规模火山岩浆作用的主旋律。其中玄武岩岩浆成分受到了较高程度的陆壳物质混染,同时代的中性火山岩是由底侵的玄武岩岩浆和陆壳物质来源的酸性岩浆发生岩浆混合作用而形成的,反映了强烈的壳幔相互作用。NNE向新生代火山岩带,分布在浙闽沿海,以碱性系列玄武岩为主,均含幔源包体,并受NNE向大陆边缘断裂构造的控制。它们形成于板内裂谷环境,是中国东南沿海由晚中生代火山弧构造环境转换为新生代板内裂谷环境的标志,起源于软流圈地幔,并有EMII岩石圈地幔的混合组分,但基本没有受到陆壳物质的混染。     

Geology, Geochronology, and Geodynamics of the Khan Bogd alkali granite pluton in southern Mongolia

The Khan Bogd alkali granite pluton, one of the world’s largest, is situated in the southern Gobi Desert, being localized in the core of the Late Paleozoic Syncline, where island-arc calc-alkaline differentiated volcanics (of variable alkalinity) give way to the rift-related bimodal basalt-comendite-alkali granite association. The tectonic setting of the Khan Bogd pluton is controlled by intersection of the near-latitudinal Gobi-Tien Shan Rift Zone with an oblique transverse fault, which, as the rift zone, controls bimodal magmatism. The pluton consists of the eastern and the western ring bodies and comes into sharp intrusive contact with rocks of the island-arc complex and tectonic contact with rocks of the bimodal complex. The inner ring structure is particularly typical of the western body and accentuated by ring dikes and roof pendants of the country island-arc complex. According to preliminary gravity measurements, the pluton is a flattened intrusive body (laccolith) with its base subsiding in stepwise manner northwestward. Reliable geochronologic data have been obtained for both plutonic and country rocks: the U-Pb zircon age of alkali granite belonging to the main intrusive phase is 290 ± 1 Ma, the ⁴⁰Ar/³⁹Ar ages of amphibole and polylithionite are 283 ± 4 and 285 ± 7 Ma, and the Rb-Sr isochron yields 287 ± 3 Ma; i.e., all these estimates are close to 290 Ma. Furthermore, the U-Pb zircon age of red normal biotite granite (290 ± 1 Ma) and the Rb-Sr age of the bimodal complex in the southern framework of the pluton are the same. The older igneous rocks of the island-arc complex in the framework and roof pendants of the pluton are dated at 330 Ma. The geodynamic model of the Khan Bogd pluton formation suggests collision of the Hercynian continent with a hot spot in the paleoocean; two variants of this model are proposed. According to the first variant, the mantle plume, after collision with the margin of the North Asian paleocontinent, reworked the subducted lithosphere and formed a structure similar to an asthenospheric window, which served as a source of rift-related magmatism and the Khan Bogd pluton proper. In compliance with the second variant, the emergence of hot mantle plume resulted in flattening of the subducted plate; cessation of the island-arc magmatism; and probably in origin of a local convective system in the asthenosphere of the mantle wedge, which gave rise to the formation of a magma source. The huge body of the Khan Bogd alkali granite pluton and related volcanic rocks, as well as its ring structure, resulted from the caldera mechanism of the emplacement and evolution of magmatic melts.     

腾冲新生代火山作用构造—岩浆类型的探讨——一种滞后型的弧火山

腾冲火山群是我国著名的新生代火山群之一。它共分4个喷发期,根据K—Ar同位素地质年龄测定,第一期为2.93Ma,第二期为0.81Ma,第三期为0.31Ma,第四期为0.13Ma。该火山群为典型的钙碱性系列玄武岩—安山岩—英安岩弧火山岩组合。它喷发于晚上新世—晚更新世,但这一时期腾冲地区已为大陆板内环境,它可能与K₂末怒江洋壳俯冲作用有关。因此,腾冲弧火山岩的形成至少在俯冲作用停止以后60Ma,属于一种新的火山作用类型——碰撞后弧火山或滞后型弧火山。     

秦岭岩群中斜长角闪岩的年代学、地球化学特征及其地质意义

本文对秦岭岩群中的三个斜长角闪岩（变质沉积岩）样品进行了岩石学、锆石U-Pb年代学和岩石地球化学研究,限定了秦岭岩群的形成时代,讨论了秦岭岩群的构造背景及归属问题。锆石定年结果显示了971 Ma、1222 Ma和840 Ma三个最大沉积年龄。秦岭岩群是一个杂岩体,秦岭岩群中至少存在中元古代（较老组成部分）和新元古代早期（较新组成部分）的岩性单元。秦岭岩群变质沉积岩的锆石年龄峰主要集中在中元古代-新元古代早期,具有与扬子块体和华北块体明显不同的锆石年代学特征,秦岭岩群在中元古代-新元古代早期为独立发展的微陆块。结合秦岭岩群的年代学特征及前人的研究结果,秦岭岩群中的变质沉积岩应沉积于弧相关的构造环境。