COUPLING RELATIONSHIPS BETWEEN OROGENS AND BASINS,LOWER CRUST AND UPPER CRUST IN THE QINGHAI—TIBET PLATEAU

COUPLING RELATIONSHIPS BETWEEN OROGENS AND BASINS,LOWER CRUST AND UPPER CRUST IN THE QINGHAI—TIBET PLATEAU     

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。     

青藏高原北部新生代火山岩岩石化学特征及其构造意义

青藏高原北部东西向展布的以安山岩为主的新生代火山岩带,以黑石湖—亚克错—多格错仁一线为界可分为北侧的钙碱性岩系亚带和南侧的碱性岩带亚带。火山岩明显富钾。其形成与塔里木—柴达木板块向高原的楔入作用有关,是消减带上物质重熔上升的结果。     

Heterogeneity of the Lithosphere in Tibetan Plateau on the Constraints of Magmatism

HETEROGENEITY OF THE LITHOSPHERE IN TIBETAN PLATEAU ON THE CONSTRAINTS OF MAGMATISM     

TWO TYPES OF XENOLITH—MANTLE XENOLITH AND CRUSTAL XENOLITH FOUND IN THE CENOZOIC VOLCANIC ROCKS FROM HOH XIL, NORTHERN TIBET PLATEAU

TWO TYPES OF XENOLITH—MANTLE XENOLITH AND CRUSTAL XENOLITH FOUND IN THE CENOZOIC VOLCANIC ROCKS FROM HOH XIL, NORTHERN TIBET PLATEAU1　YangJingsui,XuZhiqin ,BaiWenji,etal.CenozoicvolcanismontheQinghai Tibetplateauanditsgenesis[J].ContinentalGeodynamics ,1997(2 ) :1～ 11. 2　XuZhiqin ,JiangMei,etal.Mantlediapirandinwardintracontinentalsubduction :AdiscussiononthemechanismofupliftoftheQinghai TibetPlateau[A].MacfarlaneA ,Sorkabi,RB ,…     

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     

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。     

Sources of Magmas and Conditions of Rock Formation in the Late Cenozoic Udokan Volcanic Plateau

Doklady Earth Sciences - The Udokan volcanic plateau differs from other volcanic regions of the Late Cenozoic volcanic province of East Asia in the high alkalinity of volcanic rocks, their...     

青藏高原北羌塘榴辉岩质下地质及富集型地幔源区——来自新生代火山岩的岩石地球化学证据

利用岩石地球化学的方法，研究了北羌塘新生代火山岩，结果表明，北羌塘第三纪火山岩可区分为碱性（钾玄岩质）和高钾钙碱两套不同的火山岩组合，它们分别起源于一个特殊的，不均一的富集型上地幔和一个加厚陆壳的榴辉岩质下地壳，由于青藏陆块之下软流层物质的上涌而形成幔源碱性岩浆活动，而幔源岩浆在Mobo面的底侵作用又为下地壳中酸性高钾钙碱系列火山岩的起源提供了热动力条件，该区两套不同系列和源区类型的火山岩正是在这种特殊的构造环境中形成。     

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     

Spatial gaps in arc volcanism: The effect of collision or subduction of oceanic plateaus

One of the major processes in the formation and deformation of continental lithosphere is the process of arc volcanism. The plate-tectonic theory predicts that a continuous chain of arc volcanoes lies parallel to any continuous subduction zone. However, the map pattern of active volcanoes shows at least 24 areas where there are major spatial gaps in the volcanic chains (> 200 km). A significant proportion (~ 30%) of oceanic crust is subducted at these gaps. All but three of these gaps coincide with the collision or subduction of a large aseismic plateau or ridge.The idea that the collision of such features may have a major tectonic impact on the arc lithosphere, including cessation of volcanism, is not new. However, it is not clear how the collision or subduction of an oceanic plateau perturbs the system to the extent of inhibiting arc volcanism. Three main factors necessary for arc volcanism are (1) source materials for the volcanics—either volatiles or melt from the subducting slab and/or melt from the overlying asthenospheric wedge, (2) a heat source, either for the dehydration or the melting of the slab, or the melting within the asthenosphere and (3) a favorable state of stress in the overlying lithosphere. The absence of any one of these features may cause a volcanic gap to form.There are several ways in which the collision or subduction of an oceanic plateau may affect arc volcanism. The clearest and most common cases considered are those where the feature completely resists subduction, causing local plate boundaries to reorganize. This includes the formation of new plate-bounding transform faults or a flip in subduction polarity. In these cases, subduction has slowed down or stopped and the lack of source material has created a volcanic gap.There are a few cases, most notably in Peru, Chile, and the Nankai trough, where the dip of subduction is so shallow that effectively no asthenospheric wedge exists to produce source material for volcanism. The shallow dip of the slab may be a buoyant effect of the plateau imbedded in the oceanic lithosphere.The cases which are the most enigmatic are those where subduction is continuous, the oceanic plateau is subducted along with the slab, and the dip of the slab is clearly steep enough to allow arc volcanism; yet a volcanic gap exists. In these areas, the subducted plateau may have a fundamental effect on the physical process of arc volcanism itself. The presence of a large topographic feature on the subducting plate may affect the stress state in the are by increasing the amount of decoupling between the two plates. Alternatively, the subduction of the plateau may change the chemical processes at depth if either the water-rich top of the plateau with accompanying sediments are scraped off during subduction or if the ridge is compositionally different.     

The DEM or Mt. Etna: geomorphological and structural implications

Abstract

A Digital Elevation Model (DEM) of Mt. Etna is presented; it has altimetric and planimetric resolution of 1 m and 5 m, respectively, and covers an area of about 120 km . This 3-D view of Mt. Etna allowed both recognition and location of the main morphostructural and volcano-tectonic features of the volcano. A slope map has been generated from the DEM; on the basis of slope distributions and surface textures, five acclivity domains have been recognized. The largest domain, south of the summit craters, reflects the occurrence of old plateau lavas, distinct from central volcanoes which built the present Etnean volcanic system. Interaction between the central volcanoes, with their summit calderas and failed slopes, produced the other recognised domains. Furthermore, newly identified relevant morphostructural lines are discussed. © Elsevier, Paris     

The DEM of Mt. Etna: Geomorphological and structural implications

A Digital Elevation Model (DEM) of Mt. Etna is presented; it has altimetric and planimetric resolution of l m and 5 m, respectively, and covers an area of about 120 km². This 3-D view of Mt. Etna allowed both recognition and location of the main morphostructural and volcano-tectonic features of the volcano. A slope map has been generated from the DEM; on the basis of slope distributions and surface textures, five acclivity domains have been recognized. The largest domain, south of the summit craters, reflects the occurrence of old plateau lavas, distinct from central volcanoes which built the present Etnean volcanic system. Interaction between the central volcanoes, with their summit calderas and failed slopes, produced the other recognised domains. Furthermore, newly identified relevant morphostructural lines are discussed.     

TAKE ANOTHER VISION TO THE UPLIFT OF THE QING—ZANG (TIBETAN) PLATEAU BASED ON CENOZOIC VOLCANISM

TAKE ANOTHER VISION TO THE UPLIFT OF THE QING—ZANG (TIBETAN) PLATEAU BASED ON CENOZOIC VOLCANISM     

青藏高原东部贡觉盆地新生代火山岩的K-Ar稀释法年龄

通过新生代高钾钙碱性中、酸性火山岩的年代学研究来了解青藏高原的隆升特征,首次报道了藏东贡觉盆地新生代7个火山岩样品的K-Ar定年结果．全岩和黑云母的表面年龄均在40．8～46．2Ma间(平均值为44．2Ma)．样品中放射成因Ar与K构成了一条相关性良好的、几乎通过原点的线性等时线,表明它们有相同的成因和相近的形成时代。而且样品中可能既无过剩Ar,也无放射成因Ar的丢失,代表着真实的成岩年龄(始新世中期)．火山活动发生在印度—欧亚板块碰撞(50 Ma左右)后形成的构造环境中。受陆内水平剪切—走滑断裂带控制．结合前人对藏东地区岩浆活动的年代学研究成果．表明青藏高原东缘新生代岩浆活动具多期性．这种多期性可能反映着青藏高原阶段性隆升的壳—幔相互作用。     

青藏高原火山-沉积硼矿找矿的新发现与远景分析

本文报道了青藏高原火山-沉积硼矿找矿的新成果,首次发现和确认在青藏高原存在富硼的火山-沉积二元结构的地层,其构造位置、岩石地层组合和时代与同一成矿带西部的安纳托利亚高原的大型火山-沉积硼矿床都一致,且地层的稀碱金属元素含量高正异常,并已发现有团块或条带状的钠硼解石和硼砂等硼酸盐矿物,局部硼含量达边界品位。说明雄巴盆地具备形成火山-沉积硼矿床的构造地质、岩石矿物和地球化学的先决条件,具有形成大型火山-沉积硼矿的潜力。该发现是我国突破大型火山-沉积硼矿的先导性成果,为在青藏高原找寻该类型硼矿床提供重要科学依据。     

北京西山髫髻山组火山岩的地球化学特征与岩浆起源

对北京西山髫髻山组粗安岩斜长石Ar-Ar年龄测定获得全坪年龄和等时线年龄分别为148.91Ma±2.98Ma和146.60Ma±2.93Ma(相关系数r=0.9997),本文将其时代划为晚侏罗世.元素-同位素地球化学显示,西山髫髻山组火山岩主要为高钾钙碱性系列,低Ti\K,高Al\Ca和Na,轻稀土元素富集,Eu异常不明显,大离子亲石元素Rb\Sr\Ba等相对富集,高场强元素Nb\Ta\Ti\Zr\Hf相对亏损,Nd\Sr和Pb同位素比值较低,反映出火山岩形成于岛弧或活动大陆边缘,其源岩为富集地幔.据此认为髫髻山组火山岩形成于陆内挤压环境,由中生代玄武质岩浆底侵于下地壳-壳幔过渡带诱发古老(太古宙)的玄武质岩石部分熔融形成的.     

Petrogeochemical aspects of the Late Cretaceous and Paleogene ignimbrite volcanism of East Sikhote-Alin

The chemical and trace-element features of the Late Cretaceous and Early Paleogene ignimbrite complexes of East Sikhote Alin are discussed. The Turonian-Campanian volcanic rocks of the Primorsky Complex compose linear structure of the Eastern Sikhote Alin volcanic belt. They are represented by crystalrich rhyolitic, rhyodacitic, and dacitic S-type plateau ignimbrites produced by fissure eruptions of acid magmas. The Maastrichtian-Paleocene volcanic rocks occur as isolated volcanic depression and caldera structures, which have no structural and spatial relations with the volcanic belt. This period is characterized by bimodal volcanism. The Samarginsky, Dorofeevsky, and Severyansky volcanic complexes are made up of basalt-andesite-dacite lavas and pyroclastic rocks, while the Levosobolevsky and Siyanovsky complexes are comprised of rhyolitic and dacitic tuffs and ignimbrites. Petrogeochemically, the felsic volcanic rocks are close to the S-type plateau ignimbrites of the Primorsky Complex. The Paleocene-Early Eocene silicic volcanics of the Bogopolsky Complex are represented by S- and A-type dacitic and rhyolitic tuffs and ignimbrites filling collapsed calderas. The eruption of A-type ferroan hyaloignimbrites occurred at the final stage of the Paleogene volcanism (Bogopolsky Complex). The magmatic rocks show well expressed mineralogical and geochemical evidence for the interaction between the crustal magmas and enriched sublithospheric mantle. It was shown that the revealed differences in the mineralogical and geochemical composition of the ignimbrite complexes are indicative of a change in the geodynamic regime of the Asian active continental margin at the Mesozoic-Cenozoic transition.     

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.     

Characteristics and Zonation of the Cenozoic Volcanic Rocks on the Qinghai-Tibet Plateau

1.IntroductionCenozoicvolcanicrockshavebeenfoundinanumberoflocationsbothintheinteriorofandatthemarginsoftheQinghai-Tibetplateau.TheyhavebeenconsideredtObegeneticallyrelatedtOtheplatCsubduchon.Forexample,cafe-alkalinevolcedcrocksoftheLingzizongFormation(60-50Ma)occultingintheGangdisebelttothenorthoftheYarlungZangbosutUrezonehavebeenregardedtoberelatedwiththenorthwardsubduchonoftheboaplateandthecloseoftheNeo--Tethysocean(Wang,1984).StUdiesalsoindicatethattheseCenozoicvolcwhcrocksaredomina…