Three—Phase Uplift of the Qinghai—Tibet Plateau Druing the Cenozoic Period：Igneous Petrology Constraints

In northern Qinghai-Tibet plateau there are developed Cenozoic volcanic rocks. They constitute a trachybasalt-shoshonite-latite-trachydacite assemblage. According to the forming ages, three Cenozoic volcanic rock lithozones can be distinguished in the northern part of the plateau. Cenozoic volcanic rocks and muscovite/two-mica granites forming the three belts in pairs represent the northern and southern margins of the plateau in different periods. In fact, the tectonic setting of the northern part of the Qinghai-Tibet plateau is significantly different from that of the southern part—Himalayas. The southern part has experienced subduction and continent-continent collision. There are developed the Cenozoic S-type granites (muscovite/ two-mica granites) there. But the northern part is characterized by Cenozoic basaltic magmatism which obviously comes from the upper mantle. Slight doming of the upper mantle is recognized underneath the northern part of the plateau, which is the result of resistance of the Tarim plate to the north direction-sense movement of the Tibetan plate. And at the same time, the uplift machanism shows that the formation of the Qinghai-Tibet plateau involved three orogenic stages (35−23 Ma, 23−10 Ma and <2 Ma) of uplift in the vertical direction and extension in the horizontal direction with the Gangdise-Qiangtang orogenic belt as its core.     

THE EARLY UPLIFT IN NORTHERN TIBETAN PLATEAU: EVIDENCE FROM THE STUDY ON CENOZOIC VOLCANIC ROCKS IN QIANGTANG REGION

THE EARLY UPLIFT IN NORTHERN TIBETAN PLATEAU: EVIDENCE FROM THE STUDY ON CENOZOIC VOLCANIC ROCKS IN QIANGTANG REGION     

青藏高原新生代三阶段造山隆升模式:火成岩岩石学约束

从岩石从地构造学的角度,分析讨论了青藏高原新生代岩浆作用的特点、差异、成对性及其对高魇隆升深部动力学过程的岩石约束,在此基础上是提出青藏高原是以冈底斯－羌塘造山带为核心,通过三次造山幕事件而形成的高原隆升新模式。     

青藏高原新生代火山岩矿物化学及其岩石学意义--以玉门、可可西里及芒康岩区为例

本文系统地讨论了青藏高原玉门、可可西里及芒康岩区新生代火山岩中橄榄石、辉石、长石以及石榴子石巨晶和透长石巨晶的矿物化学持征,并利用矿物学资料探讨了火山岩形成的温度及压力条件．指出青藏高原新生代火山岩主体乃是一套陆内造山带钾玄岩系列火山岩,其矿物化学、主元素及同位素特征表明,这套火山岩应起源于加厚陆亮底部的特殊的富集型壳幔混合带。     

Quaternary Volcanic Activities in Shandong Peninsula and Northern Parts of Jiangsu and Anhui Provinces

Quaternary volcanic rocks often coexist with loess,as observed in the same geologic sections in the Shandong Peninsula and northern parts of Jiangsu and Anhui provinces.The development age of Shandong loess in close to that in the middle reaches of the Yellow River.Loess strata are of synchronous implication in the loess belt of North China.So the ages of volcanic activities can be es-timated approximately from the stratigraphic relations between loess layers and volcanic rocks.The re-sults of dating of the Quaternary volcanic rocks,baked layers and the TL dates of loess samples sug-gest that the Quaternary volcanic activity can be divided into 4 stages in the region studied,with the ages being 1.15-1.03,0.86-0.72,0.55-0.33 and 0.02 Ma B.P.respectively .The occurrence of tephra in the Shandong loess sections is possible due to multiple episodes of volcanism during the Quaternary time.     

藏北羌塘戈木错北部新生代钾质火山岩40Ar/39Ar定年

1∶25万玛依岗日幅区域地质调查期间,在藏北戈木错北部发现了一套新生代钾质火山岩。对保存较好的3处火山岩的样品进行40Ar/39Ar年代学研究,获得了30.6Ma±0.4Ma、30.0Ma±0.2Ma和29.8Ma±0.3Ma三个坪年龄,代表该地区火山岩的喷溢时代。戈木错北部火山岩的地球化学特征与钾质火山岩的类似,它与鱼鳞山、走构由茶错、多格错仁等地区的新生代火山岩共同构成了羌塘地区钾质—超钾质火山岩带,它们的形成与印度大陆同亚洲大陆的碰撞和青藏高原的隆升密不可分。     

Geochemical Characteristics of Cenozoic Basaltic High-K Volcanic Rocks from Maguan Area, Eastern Tibet

The major element, trace element and Nd-Sr isotopic composition of Cenozoic basaltic volcanic rocks from the Maguan area, eastern Tibet, indicates that the volcanic rocks are enriched in alkalis, especially K (K2O up to 3.81%) and depleted in Ti (TiO2 = 1.27%-2.00%). These rocks may be classified as two groups, based on their Mg# numbers: one may represent primary magma (Mg# numbers from 68 to 69), and the other, the evolved magma(Mg# numbers from 49 to 57). Their REE contents are very high (∑REE = 155.06-239.04μg/g). Their REE distribution patterns are of the right-inclined type, characterized by LREE enrichment [(La/Yb)N =12.0-19.2], no Ce anomaly (Ce/Ce*=1.0), and weak negative Eu anomaly (Eu/Eu*=0.9). The rocks are highly enriched in Rb, Sr and Ba (59.5-93.8μg/g, 732-999 μg/g, and 450-632 g/g, respectively), high in U and Th (1.59-2.31μg/g and 4.73-8.16 μg/g, respectively), and high in Nb, Ta, Zr and Hf (70-118 μg/g,3.72-5.93 μg/g, 215-381 μg/g, and 5.47-9.03 μg/g, respectively). In the primitive mantle-normalized incompatible element spidergram, Nb, Ta, Zr, Hf and P show positive anomalies, whereas Ba, Ti and Y show negative anomalies. The 87Sr/86Sr ratios range from 0. 704029 to 0.704761; 143Nd/144Nd from 0. 512769 to 0. 512949; and εNd from 2.6 to 6.1. These geochemical features might suggest that the potential source of the basaltic high-K volcanic rocks in the Maguan area is similar to the OIB-source mantle of Hawaii and Kergeulen volcanic rocks.     

DISCUSSION ABOUT THE PETROGENESIS OF THE CENOZOIC VOLCANIC ROCKS FROM YUMEN AND HOH XIL AREA, QINGHAI-TIBET PLATEAU

DISCUSSION ABOUT THE PETROGENESIS OF THE CENOZOIC VOLCANIC ROCKS FROM YUMEN AND HOH XIL AREA, QINGHAI-TIBET PLATEAU     

Geochemical evolution of Middle—Late Cenozoic magmatism in the northern part of the Rio Grande Rift,Western United States

Geochemical studies of the Middle—Late Cenozoic succession of volcanic rocks from the northern part of the Rio Grande Rift were conducted. The initial activation of the rift structure was coeval with voluminous eruptions of lava and pyroclastic material of mainly intermediate and acid compositions in the San Juan volcanic field 35–27 Ma. The composition of the volcanic products after the rifting was dominated by basic and intermediate lavas. It is shown that the basanites and alkali basalts of the territory had geochemical characteristics of sublithospheric slab and above–sl ab sources. The processes of the riftogenic thinning of lithosphere are expressed by geochemical parameters that reflect the interaction between the liquids from the sublithospheric mantle and the rocks from different levels of both the lithospheric mantle and lower crust. In the 35–18 Ma interval, melts of different–depth sublithospheric and lithospheric sources erupted simultaneously in the northern part of the rift. However, the products of interaction between the sublithospheric and lithospheric materials dominated later in the past 15 Ma, although the sublithospheric magmatic liquids erupted at the northern structural termination of the rift within the Yampa volcanic field at about 10 Ma.     

青藏高原及邻区新生代火山岩Sr-Nd-Pb同位素特征

笔者在综合分析最近十多年来的Sr、Nd、Pb同位素资料基础上,重点研究了青藏高原及邻区新生代火山岩岩浆源区在时空上的变化规律。结果表明:①冈底斯中段火山岩的岩浆源区逐渐从普通地幔向EMⅡ方向演化;西段晚期火山岩源区的演化方向为俯冲带壳幔混合源→造山带上地壳源→下地壳源。②西羌塘岩浆源区主要为不具富集或亏损的幔源物质;囊谦盆地、大理海东火山岩源区较深,为大洋型软流圈地幔+消减组分混合源;藏北羊湖、雄鹰台鲸鱼湖、西昆仑以及北羌塘巴毛穷宗火山岩的岩浆源区为EMⅡ;鱼鳞山超钾质火山岩为经历了大陆地壳物质强烈交代作用的EMⅡ型岩浆源区;西秦岭火山岩源于亏损地幔,腾冲新生代火山岩源区为受到地壳物质交代的EMⅡ。③西羌塘、可可西里、西昆仑和腾冲新生代火山岩具两种演化趋势——鱼鳞山、普鲁、雄鹰台鲸鱼湖岩区和腾冲火山群向EMⅡ方向演化,而泉水沟、黑石北湖、阿什库勒则分别沿0Ma的地幔上地壳混合线方向演化。④青藏高原及邻区新生代火山岩至少存在4种不同的岩浆源区。     

青海可可西里地区新生代火山岩的岩石特征与时代

可可西里地区的新生代火山岩属于藏北火山岩带的东段。火山岩主要以熔岩台地、桌状山的形式产出，熔岩厚约４０—１００ｍ。除少量的高钾流纹岩、粗面岩和粗面英安岩外，在数量和分布上以普遍含二辉石斑晶的安粗岩占优势。岩石以富碱（尤其富钾）和富ＬＲＥＥ为特征。火山活动发生在中新世，根据Ｋ／Ａｒ定年结果划分为早、中、晚三期。本区火山岩的特征与西藏境内的同时代岩石完全可以对比。火山活动与高原新生代以来的岩石圈演化有密切的关系     

青海拉鸡山:一个多阶段抬升的构造窗

拉鸡山断裂带位于祁连山褶皱带内,呈北西-南东向延伸.后者构成青藏高原的东北边缘,由三个主要构造单元组成:北部是一条早古生代的板块缝合带,中部是一个元古代的结晶地块,南部由一套晚古生代到三叠纪的被动大陆边缘沉积物组成.对拉鸡山及其邻区的构造研究结果表明,祁连山褶皱带在古生代加里东期发生过大规模的缩短,北祁连的早古生代蛇绿岩和岛弧火山岩沿祁连山中央冲断层向南,陆内俯冲到中祁连元古界变质杂岩之下.由于发生在晚古生代和晚中生代的陆内变形,位于中祁连之下的北祁连的蛇绿岩和岛弧火山岩发生褶皱,并被抬升到地表.到新生代,由于印度板块和欧亚大陆之间的碰撞和陆内汇聚作用,拉鸡山断裂带再次活动,这些下古生界蛇绿岩和岛弧火山岩通过冲断作用快速抬升,将中祁连地块一分为二.因此,拉鸡山是一个抬升的构造窗,不是一个中祁连结晶地块中的早古生代大陆裂谷.     

青藏高原北部的碰撞造山及深部动力学——中法地学合作研究新进展

本文展示了中法1995～2000年青藏高原北部地学研究的如下主要新进展：①完成8000km长的青藏高原北部及中部天然地震岩石圈探测剖面，确定若干条岩石圈断裂，发现与新生代火山喷发有关的青藏高原中部深处的低速、低密度体，塔里木地块俯冲于阿尔金山之下；②提出阿尔金断裂形成于220～240Ma和左行平移400km的科学依据及确定其新生代变形量；③确定祁连南缘350km长的高压-超高压变质带，提出其可能代表早古生代时期北中国板块与扬子板块之间西部界限的新认识；④根据加里东期蛇绿岩、花岗岩及俯冲杂岩带的新发现，初步建立了古碰撞造山格架；⑤提出高原隆升的“地幔底辟和内向陆内俯冲”的新假设。     

Geochemistry of the Caledonian basic volcanic rocks at the south margin of the Qinling orogenic belt, and its tectonic implications

The geochemistry of the basic volcanic rocks at the south margin of the Qinling orogenic belt(SMQOB) suggests that they were formed in an intraplate tectonic setting.The REE distribution patterns show these rocks are strongly enriched in LREE with high ∑REE, and their trace elements geochemistry is similar to that of contimental flood basalt.All the above evidence suggests that the Caledonian basic volcanic rocks in the SMQOB were tholeiitic basalts formed in an intraplate spreading-initial rift tectonic setting.The characteristics of regional geology and geochemistry indicate that there was an intraplate spreading-rift tectonic setting between the South Qingling block and the Yangtze block in the Caledonian epoch.The dynamic spreading in this district began in the Early Caledonian and then the intraplate spreadinginitial rifts were formed in the Late Caledonian.As a result of spreading of the Tethys and geodynamic processes in deep mantle ,the Mianlue-Huashan oceanic basin was formed between the Qinling block and the Yangtze block in Devonian,and the Qinling microplate was separated from the northern part of the Yangtze plate.     

羌塘盆地新构造活动与环境地质效应

本文将羌塘盆地新生代构造运动划分为三个阶段:古近纪为剥蚀、夷平和地壳加厚阶段;中新世为强烈挤压、褶皱阶段;上新世-全新世为高原缓慢整体抬升阶段。羌塘盆地的环境变迁和地质灾害与新生代构造活动密切相关。本区的强烈隆起、半荒漠化、沙尘暴、山洪、泥石流、冰川崩塌和雪崩、地震等均受新构造活动控制。     

长江源区新生代火山岩的年代学研究

长江源区的火山岩包含了青藏高原北部新生代火山岩形成及演化的全部信息，其年代学研究对查明青藏高原北部新生代火山活动时空演化具有重要意义。通过K—Ar同位素年代学研究，将长江源区新生代的火山活动划分为3期：第Ⅰ期(40．1-35．1Ma)火山喷发较弱，形成小范围分布的细粒安粗岩和斑状粗面岩；第Ⅱ期(26．5～17．6Ma)火山喷溢最为强烈，形成大面积厚层黑色气孔状安粗岩；第Ⅲ期(5．5-4．61Ma)由潜火山作用形成球粒状、斑状粗面岩岩丘。长江源区3个期次的火山喷发与青藏高原北部火山活动的阶段性相对应。长江源区新生代火山岩的演化特征为：从早到晚，岩石系列由高钾钙碱性系列→钾玄岩系列演化；岩性由安粗岩→粗面岩演化。     

Minerogenesis of Shilu iron ores with special reference to Sm-Nd isotope geochemical characteristics of Shilu Group bimodal volcanic rocks in Hainan Island

Presented in this paper are Sm-Nd isotope and major, trace and rare-earth element analyses of bimodal volcanic rocks of the Shilu Group and other stratigraphic units in northwestern Hainan Island, South China. It is shown that there are some N-MORB-type basalts (spilites) in the western part of the bimodal volcanic belt, in addition to some E-MORB-type and initial rift-type tholeiites (IRT) in the middle and eastern parts. Sm-Nd model ages of these basalts range from 545 Ma to 460 Ma. The other extremes of the bimodal volcanics are porphyritic quartz rhyolites. which are characteristic of crustal material source. Sm-Nd model ages of the rhyolites range from 1562 Ma to 1371 Ma. The bimodal volcanic rocks are almost distributed in rifts or faulted depressions, as well as in the Upper Paleozoic rift of Hainan Island. Tholeiites of the Shilu Group can be compared with Cenozoic basalts in the middle and southern parts of the Red Sea Rift Belt in petrology, elemental geochemistry and Sm-Nd isotope geology. Shilu iron ores are closely associated with N-MORB-type basalts located in the western bimodal volcanic belt. It is very interesting to note that the Shilu Fe-Co-Cu deposit can also be compared with Atlantis II Deep in the Red Sea Rift Belt. Therefore, the present authors believe that the Shilu deposit is a kind of hydrothermal deposit related to ocean volcanic belt, where the geotectonic setting belongs to initial extensional rifts in the oceanic crust. On the other hand, the largest Fe-Co-Cu ore deposit in China used to be influenced by Hercynian granites after mineralization, as is clearly observed on both ε Nd (T)-1/Nd and ε Nd (T)-¹⁴⁷Sm/¹⁴⁴Nd diagrams. This project was jointly funded by the National Natural Science Foundation of China and Research School of Earth Sciences. Australian National University, Australia.     

滇西腾冲更新世粗面安山岩Ar-Ar年代学、地球化学特征及其构造意义

腾冲芒棒地区广泛发育新近纪以来的火山岩,本文首次对该区粗面安山岩进行的高精度40Ar/39Ar同位素定年,其坪年龄分别为2.1±0.1Ma和2.0±0.1Ma,代表其喷溢时代为早更新世。岩石地球化学特征研究显示,粗面安山岩属高钾钙碱性系列,富集大离子亲石元素、亏损高场强元素,具有弧火山岩与大陆板内火山岩的双重属性,推测其形成于后造山环境。综合研究表明,腾冲地块更新世火山岩的形成与印度-欧亚板块俯冲-碰撞造山隆升后的伸展垮塌、富集地幔部分熔融作用密切相关,而印支陆块向东南逃逸以及腾冲弧形走滑断裂带(龙川江断裂带、大盈江断裂带)的活化促使了该期火山岩的喷发与侵位。     

Monzonitoid association of the Kavalerovo ore district (Primorye): geochronology and some genetic problems

This paper is dedicated to the isotope-geochronological study of the rocks that compose two large intrusions and a separate group of minor intrusions in the western part of the Kavalerovo ore district. In most publications, these rocks are considered as monzonitic or trachyandesite-monzonitic association. On the basis of the amphibole and biotite K-Ar ages and the Rb-Sr whole-rock and mineral datings, the studied association was formed within the interval of 113–98 Ma. A wider interval of 115–95 Ma was obtained with allowance for other isotope data, including those on the rocks of the volcanic facies. This is consistent with the concepts that the studied association belongs to a single magmatic complex. No significant and systematic age differences have been established between the compositionally similar rocks from the different massifs. In compliance with the scheme of the geodynamic evolution of the region, the chambers of latitic melts of the volcanic and most intrusive rocks of the complex were formed prior to the initiation of the Sikhote-Alin subduction volcanic belt. The initial stage of the formation of the latter is presumably constrained by the data on the biotite from the quartz diorites from the Uglovaya VTS (90 Ma), which is located in the central part of the region, and on the late amphibole from the monzonitoids of its western part (91–92 Ma). The geochemical differences between rocks from the different intrusive bodies could be caused by the specifics of the melt evolution in the intermediate or crystallization chambers.     

青藏高原北部黑石北湖新生代钾质火山岩的成因

昆仑岩带新生代钾质火山活动是青藏高原北缘深部动力学过程的重要记录。有关岩浆源区的性质和岩浆产生的机制一直存在较大的认识分歧。阐述了昆仑岩带黑石北湖钾质火山岩的岩石学和地球化学特征,并与西昆仑康西瓦和泉水沟新生代火山岩进行了成因对比分析。研究表明,昆仑火山岩带玄武质岩石的K2O和Na2O含量变化较大,从钠质过渡到钾质,硅碱图显示玄武质初始岩浆向钾质安粗岩方向演化。黑石北湖火山岩的高场强元素和Sr、Nd同位素组成显示岩浆源区具有EMⅡ的性质。岩石LREE的强烈富集和HREE的强烈分馏指示岩浆来自富集型含石榴子石地幔源区。不相容元素K/Nb、Ba/La等比值具有岛弧火山岩与OIB型玄武岩的过渡特征,指示源区为曾遭受软流圈流（熔）体交代的古俯冲地幔楔。