Neoproterozoic and early paleozoic geological complexes of Eastern Antarctica: Composition and origin

Geological and geochemical data on Neoproterozoic and Early Paleozoic metamorphic and igneous complexes of East Antarctica are considered. Sedimentation and formation of mafic dikes in the Neoproterozoic point to dominant extension through most of the Antarctic Shield, although no indications of advanced rifting and opening of deep basins have been established so far. As well, no distinct evidence for large-scale Early Paleozoic convergence accompanied by closure of oceanic basins, which would be reflected in particular geological complexes of East Antarctica, has been recorded. The Early Paleozoic development peak is related to thermal and intrusive consequences of tectonic activation that determined structural reworking and repeated metamorphism of host Grenvillian complexes. The main phase of the Early Paleozoic tectogenesis may be interpreted as an intraplate response to the oblique collision of large continental blocks that occurred beyond present-day Antarctica and was accompanied by underplating of mantle material at the base of the crust.     

Paleozoic collisional and intraplate granitoids of the Baikal area: comparative geochemistry and petrogenesis

Early Paleozoic granitoids of autochthonous and allochthonous facies in the Baikal area (Ol’khon Island, Khamar-Daban Ridge) are in close spatial association with gneisses, migmatites, and plagiogranites and are usually confined to granite–gneiss domes. They are virtually not subjected to magmatic differentiation. Formation of granitoids of the Solzan massif and Sharanur complex lasted 26–28 Myr, which might be considered an indicator of collisional granitoid magmatism. Collisional granitoids of different provinces have a series of indicative features: They are peraluminous and highly potassic and are enriched in crustal elements (Rb, Pb, and Th) but sometimes have low contents of volatiles. In contrast to collisional magmatism, petrogenesis of intraplate granitoids does not depend on the composition and age of the enclosing rocks. The geochemical evolution of intraplate granitoid magmatism in the Baikal area is expressed as an increase in contents of F, Li, Rb, Cs, Sn, Be, Ta, Zr, and Pb and a decrease in contents of Ba, Sr, Zn, Th, and U during the differentiation of multiphase intrusions. The geochemical diversity of these granitoids formed both from crustal and from mantle sources and as a result of the mantle–crust interaction, might be due to the effect of plume on the geologic evolution of intraplate magmatism. The wide range of compositions and geochemical types of igneous rocks (from alkali and subalkalic to rare-metal granitoids) within the Late Paleozoic Baikal magmatism area suggests its high ore potential.     

论东天山觉罗塔格造山带的大地构造属性

觉罗塔格造山带位于吐哈盆地和中天山地块之间，长期以来，关于该造山带的大地构造属性争论较多，有晚古生代岛弧带、弧后盆地、裂陷槽、古生代陆缘增生带、石炭纪火山岩型被动陆缘等不同认识。基于晚古生代早期觉罗塔格地区处于板内拉张的动力学背景，而非挤压碰撞环境，结合对带内早石炭世雅满苏组火山—沉积建造较为系统的岩石学、岩石化学及岩石地球化学研究，认为觉罗塔格造山带应为一拉张型构造—岩浆岩带。     

北大巴山早古生代辉绿岩地球化学特征及其地质意义

对南秦岭北大巴山地区广泛分布的一套基性岩墙群中的辉绿岩进行采样,并进行了锆石U-Pb年代学、全岩地球化学分析。结果显示,岩石形成年龄为435~433 Ma,为早志留世晚期岩浆活动产物。这些辉绿岩具低硅、高碱、高钛的碱性岩特征。岩石微量及稀土元素具板内玄武岩特征,轻稀土元素相对富集,轻重稀土元素分异明显,富集不相容元素Ba、Nb、Ta,而K、Y、Yb相对亏损;K及Rb的负异常表明岩石源区残留角闪石或金云母,部分熔融模拟结果显示岩石起源于尖晶石角闪石岩高程度部分熔融。综合地球化学特征及前人研究结果,认为北大巴山地区在早古生代处于大规模伸展裂陷背景下,岩石圈的拉张诱发了低熔点的交代岩石圈地幔熔融,进而形成了这条碱性岩浆带。     

The Early Paleozoic basite magmatism of Western Transbaikalia: Composition,isotope age (U-Pb,SHRIMP RG), magma sources,and geodynamics

Remnants of the Early Paleozoic gabbro and gabbromonzonite with an age of 514.6 ± 7.2 Ma (U-Pb, Zrn, SHRIMP-RG, Turka Massif) were identified among basites spatially associated with Late Paleozoic granitoids of Western Transbaikalia. Obtained geochronological data are close to those of felsic subvolcanic rocks of the Early Cambrian volcanotectonic structures of the Uda-Vitim paleoisland arc and gabbro of the Dzhida island arc in Central and Southwestern Transbaikalia. As compared to the Late Paleozoic analogues, the Early Paleozoic gabbromonzonite is characterized by the moderately low potassic alkalinity, fractionated REE pattern, and LILE enrichment relative to HFSE. The Early Paleozoic gabbro and gabbromonzonite are depleted in Nb, Ta, Zr, and Hf and enriched in Pb and Sr, which is typical of suprasubduction magmatic rocks. Geochemical data indicate a contribution of crustal (subducted) material in a magma source. A combination of geological, geochemical, and isotope-geochronological data indicates that the Early Paleozoic gabbromonzonite was formed in the Uda-Vitim paleoisland arc system in a suprasubduction setting. The geochemical similarity of the Early Paleozoic rocks and Late Paleozoic basites, which are associated with the Late Paleozoic granitic rocks of the Angara-Vitim batholith and were formed 200 Ma later, is attributed to inheritance of mantle source.     

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。     

Main stages and geodynamic regimes of the Earth’s crust formation in East Antarctica in the Proterozoic and Early Paleozoic

Geological, geochemical, and isotopic data (U-Pb for zircon and Sm-Nd for whole-rock samples) are summarized for Proterozoic and Early Paleozoic geological complexes known from various regions of East Antarctica. The main events of tectonothermal and magmatic activity are outlined and correlated in space and time. The Paleoproterozoic is characterized as a period of rifting in Archean blocks, their partial mobilization, and formation of a new crustal material over a vast area occupied by present-day East Antarctica. In most areas, this material was repeatedly reworked at the subsequent stages of evolution (1800–1700, 1100–1000, 550–500 Ma). Complexes of Mesoproterozoic juvenile rocks (1500, 1400–1200, 1150–1100 Ma) arising in convergent suprasubduction geodynamic settings are established in some areas (basalt-andesite and tonalite-granodiorite associations with characteristic geochemical signatures). The evolution of the Proterozoic regions in East Antarctica may be interpreted as a Wilson cycle with the destruction of the Archean megacontinent 2250 Ma ago and the ultimate closure of the secondary oceanic basins by 1000 Ma ago. The Mesoproterozoic regions make up a marginal volcanic-plutonic belt that combines three provinces of different ages corresponding to consecutive accretion of terranes 1500–1150, 1400–950, and 1150–1050 Ma ago. The Neoproterozoic and Early Paleozoic tectonomagmatic activity developed nonuniformly. In some regions, it is expressed in ductile deformation, granulite-facies metamorphism, and postcollision magmatism; in other regions, a weak thermal effect and anorogenic magmatism are noted. The evolution of metamorphic complexes in the regime of isothermal decompression and the intraplate character of granitoids testify to the collision nature of the Early Paleozoic tectonomagmatic activity.     

First data on age of metarhyolites from the Turan Group of the Bureya Terrane, eastern part of the Central Asian Foldbelt

The U-Pb geochronological studies showed that metarhyolites from the Turan Group of the Bureya (Turan) Terrane to the east of the Central Asian Foldbelt are Middle Cambrian (504 ± 8 Ma), not Neoproterozoic in age, as was suggested before. Metarhyolites are younger than the Early Cambrian terrigenous-carbonate sediments from this terrane characterized by the Atdabanian archaeochyatid. Considering that volcanic rocks have features of intraplate origin, it may be assumed that their formation corresponds to the breakup of the Early Paleozoic passive continental margin.     

从板缘碰撞到陆内造山:华南东南缘早古生代造山作用演化

华南的广西运动被认为是发生在早古生代的陆内造山作用,然而触发陆内变形的地球动力学机制仍然不清.广西运动形成了泥盆系与下伏岩石之间广泛的不整合面以及分布在局部地区的下古生界内部的多个不整合面.广西运动期间的构造热事件和古生物响应时间在460~380 Ma,时间上对应于奥陶系和泥盆系之间的多个不整合,而分布在华南南缘的寒武系和奥陶系之间的不整合面（郁南运动）仅与少量的530~480 Ma之间的变质事件相当,但是却同步于广泛分布在东冈瓦纳北缘的造山事件.华南南部寒武系-奥陶系不整合面上下的碎屑锆石年代学研究表明,早古生代华南与印度北缘相连,而三亚地块在寒武纪是澳大利亚西缘的一部分,直到奥陶纪才与华南拼合,同步于冈瓦纳最终的聚合.郁南运动之后,华夏板块处于冈瓦纳内部,来自冈瓦纳东缘造山作用的应力向大陆内部传播,在具有弱流变学性质的南华盆地聚集,导致盆地构造反转,触发了广西运动.早古生代的华南经历了从板缘碰撞（郁南运动）到陆内造山（广西运动）的演化过程.      

Early paleozoic gabbro-amphibolites in the structure of the Bureya Terrane (eastern part of the Central Asian Fold Belt): First geochronological data and tectonic position

Resulting from U-Pb geochronological study, it has been found that the gabbro-amphibolites composing the Bureya (Turan) Terrane in the eastern part of the Central Asian Fold Belt are Early Paleozoic (Early Ordovician; 455 ± 1.5 Ma) in age rather than Late Proterozoic as was believed earlier. The gabbro-amphibolites and associated metabasalts are close to tholeiites of the intraoceanic island arcs in terms of the geochemical properties. It is suggested that the tectonic block composed of these rocks was initially a seafloor fragment that divided the Bureya and Argun terranes in the Early Paleozoic and was later tectonically incorporated into the modern structure of the Bureya Terrane as a result of Late Paleozoic and Mesozoic events.     

桂东南糯垌—安平地区(变质)中—基性火成岩的年代学、地球化学特征及其构造意义

文章对桂东南糯垌—安平地区出露的阳起石化斜长角闪岩(变质基性岩)和中—基性火山角砾岩进行了锆石U-Pb年代学和全岩地球化学分析研究,结果表明,糯垌地区岩体的形成时代晚于123 Ma,安平地区火山角砾岩记录了两期重要的岩浆活动,一组为燕山期(或之后),年龄上限为～138 Ma,一组为早古生代加里东期(452～450 Ma...     

秦祁结合部位王家岔石英闪长岩体锆石LA-ICPMS定年及地质意义

出露于秦岭、祁连造山带结合部位的王家岔石英闪长岩体,侵入于变质基底陇山岩群之中。岩石学、岩石化学、地球化学特征显示石英闪长岩侵入体具有俯冲花岗岩特征。利用LA-ICPMS（激光剥蚀等离子体质谱）测年技术,对石英闪长岩进行单颗粒锆石微区U-Pb同位素测定,获得加权平均年龄为（454.7±1.7） Ma,代表了岩石的形成年龄。这一新的成果资料,对研究秦祁结合部位早古生代构造演化、造山过程及秦、祁造山带的关系具有重要意义。     

新疆西准噶尔业姆奇花岗岩体形成时代及其构造意义

对新疆西准噶尔南部地区与早古生代蛇绿岩紧密伴生的业姆奇花岗岩体岩石学、岩石地球化学、同位素年代学进行研究,认为业姆奇花岗岩为低钾(拉斑)系列,岩石地球化学特征具板内靠近岛弧区域特征。通过对二长花岗岩LA-ICP-MS锆石U-Pb测年,获得比较准确的年龄数据539.7±2.6Ma,表明其形成时代为早寒武世,该侵入岩作为西准噶尔地区最老的岩浆活动产物,代表了在诺丁尼亚统一大陆形成之后早期裂解阶段古洋盆初期的地质记录。     

青藏高原羌塘中部蓝片岩的地球化学特征及其构造意义

青藏高原羌塘中部的冈玛日－桃形错地区蓝片岩被认为是板块构造边界的产物，通过对其主量元素、微量元素和稀土元素的地球化学特征的综合研究，其原岩属于洋岛型碱性玄武岩。再结合该地区的地质研究，表明在该地区存在一个古提斯洋，可以作为晚古生代冈瓦纳与劳亚大陆的分界线。     

Pacific superplume-related oceanic basalts hosted by accretionary complexes of Central Asia,Russian Far East and Japan

Plume-related oceanic magmatism form oceanic islands, seamounts and plateaus (hereafter “seamounts” or “paleoseamounts”), which are important features in geological history. The accretion of oceanic seamounts to active continental margins significantly contributed to the formation of the continental crust. This paper reviews occurrences of Late Neoproterozoic–Mesozoic seamounts of the Paleo-Asian and Paleo-Pacific oceans, which are hosted by accretionary complexes (ACs) of Russian Altai, East Kazakhstan, Mongolia, Russian Far East and Japan. The paleoseamounts commonly consist of Ti–LREE–Nb-enriched plume-related basalts (OIB-type or intraplate basalts) capped with massive limestone and associated with other units of oceanic plate stratigraphy (OPS): oceanic floor basalts (MORB), pelagic chert, epiclastic slope facies, etc. The paper presents available geochemical data on the plume-related basalts including the first geochemical data on the Middle Paleozoic OIB-type basalts of the Paleo-Asian Ocean hosted by the Ulaanbaatar AC of Mongolia. An emphasis is made for the structural setting of OPS units, specific geochemical features of intraplate basalts, problems of their identification, and distinguishing from magmatic units of a different origin such as MORB, island-arc and back-arc basalts. Finally, we propose a continuous, though periodical, evolution of the Pacific superplume-related magmatism, which can be more reliably proved by studying Middle Paleozoic OPS units hosted by ACs of Mongolia and Tien Shan, and discuss prospects of future studies.     

吉林延边地区棉田岩体锆石U-Pb年代学、地球化学及Hf同位素

对延边地区棉田花岗闪长岩岩体进行了锆石U-Pb年代学、岩石地球化学以及Hf同位素的研究, 以便对其岩石成因和古太平洋板块俯冲作用的开始时间给予制约.棉田岩体主要由花岗闪长岩和次要的花岗岩组成, 花岗闪长岩中锆石LA-ICP-MS U-Pb定年结果表明, 该岩体形成于早侏罗世(177±2 Ma, MSWD=1.13).在地球化学研究方面, 它们属于高钾钙碱性-钙碱性系列, A/CNK值介于0.88~1.12之间, 属准铝质, 为I型花岗岩, 并且明显富集大离子亲石元素(如K、Ba、Rb)、轻稀土元素(LREE)以及Th、U, 相对亏损高场强元素(如Ta、Nb、Ti、P).岩石的ε_Hf(t)值和二阶段模式年龄(T_DM2)分别介于±8.72~±12.28和437~663 Ma之间.结果表明, 岩体的原始岩浆源于新增生陆壳的部分熔融.综合区域同时代火成岩的研究成果, 认为棉田花岗闪长岩岩体形成于古太平洋板块向欧亚大陆俯冲下的火山弧环境.      

大兴安岭牙克石地区新元古代与晚古生代两类岩石组合的构造属性及其地质意义

在内蒙牙克石地区发育两种不同构造属性的岩石组合:一类为乌奴耳-头道桥蛇绿混杂岩,另一类为晚古生代弧属性侵入岩。乌奴耳-头道桥蛇绿混杂岩由辉长岩、辉长辉绿岩、辉绿玢岩(岩墙?)、变玄武岩和放射虫硅质岩组成;地球化学特征显示基性岩类属于拉斑玄武岩系列,具有相似的稀土和原始地幔标准化配分模式,与N-MORB的特征类似,不具有Nb-Ta负异常,Nb/Nb~*值平均1;构造环境判别图显示该蛇绿混杂岩可能形成于扩张脊。晚古生代弧属性侵入岩出露于白井山、乌尔其汗,由中基性单元(辉长岩、辉长闪长岩和石英闪长岩)和酸性单元(花岗闪长岩和二长花岗岩)组成;地球化学特征显示中基性单元和酸性单元属于钙碱性岩系列,富集LREEs和LILEs,具有Nb-Ta负异常,高Sr、Sr/Y值,低HREEs和Y,Eu异常不明显;酸性单元显示埃达克质岩的地球化学特征。乌奴耳-头道桥蛇绿混杂岩可能形成于新元古代,与头道桥蓝片岩、吉峰蛇绿混杂岩、新林蛇绿岩构成一条重要的缝合带,暗示本区古洋盆的存在。晚古生代弧属性侵入岩中,辉长岩的结晶年龄为326±1.9Ma,花岗闪长岩的结晶年龄为323.7±1.9Ma;微量元素的组成特征显示,中基性单元和酸性单元的形成与早石炭世洋壳板片的俯冲作用有关,暗示兴安地块和松嫩地块之间洋盆的萎缩。     

Age and geological position of the Okunyovo rare-metal ore magmatic complex (Western Sayan Mountains)

Geological, geochemical, and geochronological studies of rocks have been performed at the Okunyovo rare-metal ore magmatic complex (Western Sayan Mountains) composed of alkali granites and related F–Be mineralization. The geological data obtained and the features of the geochemical similarity of granite and ore mineralization identified are indicative of their genetic relation. Riebeckite from two granite samples has been subjected to ⁴⁰Ar/³⁹Ar analyses. The estimated age values of 481.5 ± 2.7 Ma and 486.5 ± 5.8 Ma are consistent within the limits of error and determine the age of Okunyovo alkali granite within 481–486 Ma ago. These data have made it possible to relate the studied rock and ore formation to the development of the Early Paleozoic ASFR controlled by the mantle plume. Along with the Okunyovo rare-metal granite massif, within the Sayan Region of the magmatic province, there are a number of Early Paleozoic alkali massifs related to the Aryskan, Raduga, and Kazyr rare-metal deposits. They are located in the conjugation area of the Western and Eastern Sayan ridges, in the Early Paleozoic Eastern Sayan rare-metal magmatism zone specialized in Be, W, Mo, Zr, Nb, and REEs.     

西准噶尔萨吾尔地区科克托别基性岩体岩石成因:地球化学和锆石U-Pb年代学证据

萨吾尔地区位于西准噶尔东北缘,广泛发育晚古生代中酸性侵入岩和火山岩以及少量基性侵入岩,这些岩浆岩的年代学研究对于限制西准噶尔地区石炭纪构造环境具有重要的意义。本文通过研究萨吾尔地区科克托别岩体的岩相学特征、锆石SHRIMP U-Pb年龄以及地球化学特征,探讨该岩体构造背景以及成因机制,为进一步论证西准噶尔地区石炭纪构造环境提供佐证。科克托别岩体包括中粗粒辉长岩、细粒辉长岩和闪长岩,在野外露头显示细粒辉长岩以脉状侵入中粗粒辉长岩中,细粒辉长岩中包裹有中粗粒辉长岩包体,中粗粒辉长岩与闪长岩之间呈渐变过渡接触关系,说明科克托别岩体是不同期次岩浆侵位形成的杂岩体,早期岩浆侵入形成中粗粒辉长岩和闪长岩,晚期岩浆上侵就位于中粗粒辉长岩构造裂隙中形成细粒辉长岩。科克托别岩体中细粒辉长岩锆石SHRIMP U-Pb年龄为323.2±6.2Ma,表明岩体形成于早石炭世晚期。该岩体成岩年龄晚于该地区蛇绿岩套岩石年龄,也晚于岛弧火山岩年龄以及含斑岩矿床侵入岩年龄,与该地区I型花岗岩年龄相似,而明显早于碰撞后A型花岗岩和双峰式火山岩的形成年龄,说明科克托别岩体可能形成于同碰撞构造环境中。不同岩相的岩石主量元素之间的相关关系以及微量元素配分型式相似性说明它们为同源岩浆结晶分异的产物。岩相学和地球化学特征表明岩体初始岩浆可能为软流圈地幔与上覆交代地幔相互作用形成,板片断离可能为软流圈地幔的上涌起到重要作用。     

Interaction of crustal and mantle materials,sources of trace elements during the formation and evolution of Early Paleozoic Li-rich granite-pegmatite systems in southeastern Tuva

We present new data on the age, composition, and environments of formation of granites of the Kystarys complex and the associated Li-rich rare-element pegmatites of the South Sangilen pegmatite belt including the large Tastyg lithium deposit. It has been established that they formed during the Early Paleozoic collisional orogeny in the Tuva-Mongolian massif at the Cambrian-Ordovician boundary. The granites of the Kystarys complex are moderately alkaline high-K rocks and are enriched in Zr, Nb, Y, and REE; therefore, they are classified as postcollisional, transitional to within-plate (A-type). The spodumene pegmatites of the South Sangilen pegmatite belt are similar to the above granites in age and isotopic and geochemical parameters, which suggests a paragenetic relationship between these rocks. Pegmatites form several pegmatite fields within the belt, which differ in trace-element signatures. In addition to predominant Li, Cs, and Ta, specific to all spodumene pegmatites (LCT family), pegmatites of two fields have high contents of Nb, Y, REE, and Zr, which are indicator elements of NYF family pegmatites. It has been established that the formation of spodumene pegmatites with combined LCT-NYF geochemical signatures was preceded by the intrusion of dikes of monzogabbro with the geochemical characteristics of OIB and of alkali aegirine granites and by the formation of associated metasomatites enriched in Zr, Nb, Y, and REE. Based on the geological, mineralogical, and geochemical data, we substantiate the hypothesis of the formation of Li-bearing granite-pegmatite melts from a mixed source resulted from the influence of fluids of an alkaline igneous complex of mantle genesis on the crustal protolith.