羌塘中部各拉丹冬一带鄂尔陇巴组火山岩特征及其构造环境

分布于羌塘中部各拉丹冬一带鄂尔陇巴组火山岩，锆石U—Pb同位素年龄值为212Ma，时代属晚三叠世。岩性主要为由玄武岩、安山岩、英安岩、流纹岩和凝灰岩等组成的一套基性一中性一中酸性一酸性岩石组合。主元素以低TiO2、富碱(K2O Na2O)为特征，为钙碱性系列至碱性系列，球粒陨石标准化的稀土元素配分模式为LREE中等富集型，MORB标准化的微量元素配分型式表现为大离子亲石元素K、Rb、Ba及高场强元素Th的高度富集和Ti的亏损，Ba／L平均为32．46，显示岩浆形成于岛弧构造环境。Sr、Nd同位素地球化学也支持这一结论。地质、地球化学及年代学综合分析研究表明，各拉丹冬一带鄂尔陇巴组火山岩形成于晚三叠世岛弧构造环境。     

新疆西天山大哈拉军山组火山岩岩石化学特征及地质意义

下石炭统大哈拉军山组主要分布于西天山伊犁盆地,不整合在志留纪地层或老地层之上,其上被阿克萨克组角度或平行不整合覆盖.火山岩组合为玄武岩、安山岩、流纹岩及安山岩、流纹岩组合,以安山岩发育为特征.玄武岩属岛弧拉斑玄武岩和钙碱性系列,属太平洋型钠质类型,稀土、微量元素显示具岛弧特征,大地构造位置为岛弧中心靠近大洋一侧,与南侧那拉提晚泥盆—早石炭世侵入岩共同组成火山弧,同为古亚洲洋向北俯冲的产物.     

冲绳海槽火山岩岩石特征及其地质意义

冲绳海槽火山岩目前发现有玄武岩、玄武安山岩、安山岩、粗面安山岩、粗面英安岩、英安岩和流纹岩。研究表明，冲绳海槽火山岩均属亚碱性系列，基性岩具有拉斑玄武岩系列和钙碱性系列的过渡性，中、酸性岩多属钙碱性系列；央石形成于上新世以来，大部分都是富集型地幔玄武质岩浆在分离结晶不同阶段的产物。岩石在分离结晶演化趋势上的一致性和岩石化学指数变异关系上的多样性是原来快速上升未发生混染的岩浆在断裂构造隔离下分枝独立     

《变质作用与大陆动力学学术讨论会》在北京召开

冲绳海槽火山岩目前发现有玄武岩、玄武安山岩、安山岩、粗面安山岩、粗面英安岩、英安岩和流纹岩。研究表明，冲绳海槽火山岩均属亚碱性系列，基性岩具有拉斑玄武岩系列和钙碱性系列的过渡性，中、酸性岩多属钙碱性系列；岩石形成于上新世以来，大部分都是富集型地幔玄武质岩浆在分离结晶不同阶段的产物。岩石在分离结晶演化趋势上的一致性和在岩石化学指数变异关系上的多样性是原来快速上升未发生混染的岩浆在断裂构造隔离下分枝独立演化的结果。     

乌纳哈绿岩带火山岩的岩石化学特征

阐述早元古代乌纳哈绿岩带及其邻近边缘中的火山岩岩石化学特点的解释结果。确定了火山岩原岩主要为玄武岩，少为安山岩和英安岩。火山岩为拉斑玄武岩系列和钙碱性系列。根据绿岩带玄武岩的一系列特征，划出了洋中脊拉斑辫武岩，岛弧拉斑玄武岩和钙碱弱武岩。     

黑龙江黑河地区早白垩世火山岩岩石地球化学特征及其构造环境意义

黑龙江省黑河地区广泛发育侏罗-白垩纪火山岩,但是该火山岩的岩石组合、成因和所表征的大地构造环境目前有很大的争议。本文对该套火山岩开展详细的岩石学、岩石地球化学等研究。该火山岩形成于早白垩世,主要以安山岩英安岩流纹岩为主,包含英安岩、安山岩、粗面岩、流纹岩、安粗岩、玄武安山岩、粗面英安岩、钾玄岩、歪长粗安岩,因此属于弧火山岩的组合。该区火山岩主要为亚碱性系列,岩石Na2O/K2O比值一般>1.2。A/CNK在1附近,为准铝质过铝质岩石。SiO2 TFeO/MgO图上既有钙碱性系列(包括低铁钙碱性系列),又有拉斑系列。SiO2 K2O图上主要为中钾钙碱高钾钙碱系列。SiO2 (Na2O+K2O-CaO)图上主要为钙碱系列、碱钙系列和碱性系列,在SiO2 MgO图中主要落入实验玄武岩的局部熔融范围和镁安山岩系列范围。痕量元素蛛网图显示富集大离子亲石元素,K、La、Zr、Hf、Tb、Tm为峰,亏损Nb、Ta、Ti、Y、Yb等高场强元素。稀土元素球粒陨石标准化配分模式为缓右倾型的模式,轻稀土相对富集,重稀土内部分馏不明显,具有微弱负Eu异常。大部分岩石具有高Sr低Y的特征,其中一些岩石具有adakite岩的特征。上述特征均指示弧火山岩的特征。结合构造环境判别认为该火山岩形成于与洋俯冲有关的环境。推测岩浆可能的源区为俯冲的洋壳、上覆的地幔楔、兴安弧的下地壳。     

西天山查岗诺尔铁矿区石炭纪火山岩地球化学特征及岩石成因

对伊犁地块东北缘查岗诺尔铁矿区石炭纪火山岩进行了系统的岩石学,锆石U-Pb年代学,岩石地球化学,Nd、Sr同位素地球化学研究.该区火山岩包括玄武岩(少量)、粗面岩、安山岩、流纹岩以及火山碎屑岩,它们的化学组成绝大多数属于钾玄岩系列和高钾钙碱性系列,少数玄武岩和安山岩属于钙碱性和低钾拉斑玄武岩系列.微量元素方面,它们相对...     

哀牢山构造岩浆带晚二叠世-早三叠世火山岩特征及其构造环境

本文对中国云南哀牢山构造岩浆带内的雅轩桥、帽盒山、绿春火山岩等开展了相关研究.雅轩桥附近的火山岩为晚二叠世,岩性主要为橄榄粗安岩-玄武岩(少量安山岩),在TAS图上既有碱性又有亚碱性.钾含量较低(＜1.19％),为低钾钙碱-中钾钙碱性,Peacock碱钙指数以钙碱性为主.与MORB相比,其痕量元素蛛网图亏损Nb、Ta,而富集Pb,从Zr-V曲线呈平坦型,并且整体比MORB亏损.稀土元素配分模式与MORB相近,但略显轻稀土元素富集和重稀土元素亏损.在构造环境判别图上均位于火山弧环境.他郎河边(雅轩桥地区)火山岩为英安岩,属亚碱性,中钾钙碱性,Peacock指数为钙性.痕量元素蛛网图、REE模式图以及大地构造环境判别图,均表明其属于弧的构造环境.由上推测雅轩桥火山岩在晚二叠世属于弧火山岩.帽盒山玄武岩的锆石SHRIMP U-Pb测年结果为249±1.6Ma,为早三叠世.岩性为亚碱性钠长玄武岩,低钾钙碱性系列,Peacock碱钙指数以钙性为主.痕量元素蛛网图和REE配分模式图与MORB相比,LREE略微富集.在构造环境判别图中位于从E-MORB向岛弧过渡的构造环境.绿春地区流纹岩的锆石SHRIMP U-Pb年龄为247.3±1.8Ma,为早三叠世,属亚碱性,钾玄岩系列,Peacock碱钙指数为碱钙性.痕量元素蛛网图、REE配分模式图及大地构造环境判别图显示其为成熟岛弧向陆陆碰撞的过渡环境.结合前人研究,推测哀牢山洋在晚泥盆世形成,可能在石炭世-早二叠世(?)处于洋的扩张期.晚二叠世时,在哀牢山洋的西侧出现了雅轩桥的初始孤火山岩,预示着至少在这一时期,哀牢山洋已经开始俯冲.到三叠世早期(249±1.6Ma),在哀牢山洋的东侧出现了具有弧和MORB的双重特性的帽盒山玄武岩,可能指示此时哀牢山洋盆已经变小,或已转化为孤间或弧后盆地,洋的演化进入了晚期阶段,并且在局部地段,如绿春地区,此时(247.3±1.8Ma)已经进入到成熟岛弧向陆陆碰撞的过渡阶段.因此支持哀牢山洋在晚三叠世闭合的结论,亦符合上三叠统一碗水组不整合在哀牢山蛇绿混杂岩之上的事实.     

东天山觉罗塔格地区晚石炭世岛弧火山岩

东天山觉罗塔格地区土古土布拉克组火山岩是晚石炭世火山活动的产物,火山岩与一套陆相碎屑岩互层产出,岩石组合为岛弧拉斑玄武岩、钙碱性(高铝)玄武岩、高铝玄武安山岩、英安岩和流纹岩,火山活动总体上具有由早期中基性火山岩向晚期中酸性火山岩演化的规律.岩石化学和地球化学特征表明,火山岩的w(SiO2)基本上连续变化于47.68%～75.19%之间,无明显的成分间断,安山岩所占的比重最大,并不具有双峰式火山岩的特点.其中w(SiO2)小于57.48%的中基性火山岩具有高w(Al2O3)(16.34%～20.22%),较富钾,富集大离子亲石元素,具明显的Nb、Ta负异常;w(SiO2)介于62.11%～75.19%之间的安山岩、英安岩和流纹岩岩石化学特征与准铝质的Ⅰ型花岗质岩石相似,其地球化学特征也反映出岛弧花岗岩的特点,表明东天山觉罗塔格地区路白山一带在晚石炭世仍处于古亚洲洋向南俯冲的岛弧环境.     

藏南羊卓雍错南部桑秀组火山岩的特征及构造环境

羊卓雍错南部桑秀组中分布有由玄武岩-安山岩-英安岩构成的海相火山岩组合，区域露头上玄武岩占绝对优势，喷发时代为晚侏罗世晚期-早白垩世早期。区域资料显示，这一时期该地区处于冈瓦纳大陆的被动陆缘。地球化学特征表明，本区火山岩与洋脊玄武岩和洋岛型玄武岩有明显区别，显示大陆拉张带或大陆裂谷亚碱性拉斑玄武岩的特征。     

Geochemical constraints on Carboniferous volcanic rocks of the Yili Block (Xinjiang,NW China): Implication for the tectonic evolution of Western Tianshan

The Yili Block is important for understanding the Late Paleozoic geodynamic evolution of Central Asia. It is bounded to the north by the Northern Tianshan Carboniferous flysch and ophiolitic mélange. The center of the Block is dominated by Carboniferous sedimentary rocks with intercalation of volcanic rocks. Petrological and geochemical features of these Carboniferous volcanic rocks show that: (1) they belong to the calc-alkaline series, (2) they display prominent Nb–Ta negative anomalies consistent with subduction-related magmas, and (3) HFSE-based discriminations place these volcanic rocks in the field of continental arcs. The depositional evolution of the sedimentary series shows evidence for Carboniferous sedimentation in a basin instead of rifting as previously proposed. All these evidences, together with the occurrence of contemporaneous turbidites and ophiolitic mélange along the northern boundary of the Yili Block, allow us to infer that the northern border of the Yili Block was a continental active margin during the Carboniferous. The Late Carboniferous southward subduction that finally closed the Late Devonian to Early Carboniferous North Tianshan oceanic basin was followed by Permian–Mesozoic polyphase transcurrent faulting.     

云南德钦鲁春-红坡牛场上叠裂谷盆地“双峰式”火山岩的Rb-Sr年龄值

云南德钦鲁春－红坡牛场上叠裂谷盆地是金沙江构造带内中生代的重要赋矿盆地,位于金沙江结合带与昌都稳定陆块之间的活动边缘火山岩带中。由于该区火山岩的形成时代一直没有确切的年龄值,从而造 成对火山岩的性质和构造背景认识上的差异。笔者采用Rb-Sr同位素年代学方法对云南德钦鲁春－红坡牛场上叠裂谷盆地中玄武岩和流岩的年龄进行了测定,获得了“双峰式”火山岩的平均年龄值为224Ma,其形成于晚三叠世早期。玄武岩的^87Sr/^86Sr初始值为0．7065－0．7194,流纹岩的^87Sr/^86Sr初始值为0．7074－0．7199,二者十分相似,表明盆地中的玄武岩与流纹岩为同一岩浆源,从早期的基性岩浆演化为晚期的酸性岩浆。玄武岩和流纹岩组合的“双峰式”火山岩形成于金沙江弧－ 陆碰撞后的地壳伸展构造环境。     

Comendite-bearing subduction-related volcanic associations in the Khan-Bogd area,southern Mongolia: Geochemical data

The vertical section of volcanic rocks in the Khan-Bogd Late Paleozoic depression, southern Mongolia, in the belt of southern Mongolian Hercynides contains comendites. The basement of the depression is made up of Devonian ophiolites (older than 362 Ma) overlain by volcanic associations of an active continental margin (ACM) (dated at 330 Ma) and a bimodal association (dated at approximately 290 Ma), which is subdivided into a lower unit (BLU), dacites of the intermediate layer (IL), and a bimodal association of the upper unit (BUU). The volcanic associations of the Devonian and ACM are calc-alkaline and poor in TiO₂. The BLU rocks have higher alkalinity and TiO₂ concentrations and show a transition from the tholeiitic to calc-alkaline series in the course of differentiation with the origin of comendites and trachyrhyolites, including those with adakite characteristics. The IL dacites are analogues of calc-alkaline magmas of the ACM type. The BUU volcanic association is composed of tholeiite basalts with moderate Ti concentrations (of the MORB type), comendites, and trachyrhyolites, with a compositional gap at rocks of intermediate composition. The variations in the canonical ratios of incompatible trace elements and petrochemical parameters of the Khan-Bogd volcanic rocks show that their parental magmas were derived mostly from a source of basalts of the arc type (IAB) with the addition of variable proportions of a source of the MORB type. The greatest role of the latter is identified in the magmas of the bimodal association. BLU and BUU are separated by IL, a fact testifying that the bimodal volcanism occurred simultaneously with normal dacite continental-marginal volcanism. Although the geodynamic environments in which volcanic rocks were formed somewhat varied during the development of the Khan-Bogd depression, a subduction environment remained predominant, and the volcanic rocks were derived from an IAB-type source. The subduction volcanic associations produced thereby are differentiated and vary in composition from basites to dacite and rhyolite, which could be formed at the assimilation of continental crustal material (CC). Conceivably, the bimodal volcanic association was generated when the subduction zone was approached by a mid-oceanic ridge, whose material could be added in appreciable amounts to the subduction sources. The volcanic evolution of the Khan-Bogd depression shows an evolution of geodynamic environments and the composition of the volcanic rocks generally resembling those in the western margin of North America in the Cenozoic. The acid BLU and BUU rocks were most probably generated by different mechanisms. The BLU comendites and trachyrhyolites were likely formed by the crystallization differentiation of an arc basite magma of elevated alkalinity. The acid BUU rocks resulted from the anatexis of basites of this association, particularly spilitized ones (as well as any other basites) and the subsequent crystallization differentiation of the anatectic magmas.     

羌塘中生代(T3-K1)盆地演化新模式

在羌塘盆地上三叠统那底岗日组陆相火山岩—沉火山碎屑岩及冲洪积相砂砾岩之下,作者发现了一个十分重要的古风化壳。该风化壳穿时超覆于肖茶卡组(T3上三叠统?)及其以下的二叠系及石炭系地层之上,沉积超覆于古风化壳之上的那底岗日组陆相火山岩—沉火山碎屑岩及冲洪积相砂砾岩代表了羌塘中生代(T3—K1,晚三叠世卡尼期至早白垩世时期)新一轮沉积作用的开启。采用SHRIMP锆石U-Pb同位素定年方法,作者在羌塘盆地胜利河地区和望湖岭地区分别获得了一组那底岗日组玻屑凝灰岩和晶屑凝灰岩的年龄,其值为216.8±2.1 Ma和217.3±2.5 Ma;这些同沉积年龄证据证实了羌塘中生代盆地的开启时间应该为晚三叠世卡尼—若利期。羌塘中生代盆地早期沉积作用经历了一个由陆相至海相的沉积超覆过程。伴随着岩浆侵入、火山爆发及火山碎屑沉积作用,沉积超覆作用是从冲洪积相开始。总体上,表现为一个向上由浅变深的海侵序列,显示为被动陆缘裂陷盆地特征。     

皖南屯溪盆地火山岩的地球化学、年代学及其构造意义

安徽南部侏罗至白垩纪屯溪盆地位于NE向中下扬子火山岩带和NNE向中国东南部火山岩带的交接部位,其火山岩的年代学和成因研究可以提供华南晚中生代构造演化的信息。4个火山岩样品的LA-ICP-MS锆石U-Pb年龄及其岩石地球化学数据指示屯溪盆地发育两期火山岩:早期火山岩形成于156~152 Ma,为中、高钾钙碱性系列,稀土元素分布型式为轻稀土元素富集的右倾型,铕负异常不明显,富集轻稀土元素和大离子亲石元素,亏损高场强元素Nb、Ti、P;晚期火山岩形成于136~130 Ma,具有双峰式火山岩特征,其酸性组分属中钾钙碱性系列,稀土元素分布型式为右倾斜的"V"型,铕负异常明显,同样具有富集轻稀土元素、大离子亲石元素及亏损高场强元素Nb、Ti、P的特征。皖南屯溪盆地晚侏罗世-早白垩世火山活动类似于中国东南部火山岩带。结合前人资料,认为屯溪盆地晚侏罗世火山岩形成于挤压构造环境,而早白垩世火山岩形成于伸展环境,其成因与晚侏罗至早白垩世古太平洋板块俯冲角度变化和俯冲板片后撤作用有关。     

青藏高原羌塘盆地东部鄂尔陇巴组火山岩的锆石SHRIMP U—Pb年龄及其地质意义

藏北羌塘盆地东部地区三叠系巴贡组之上沉积超覆了一套火山岩-火山碎屑岩．该套地层下部玄武岩的锆石SHRIMPu—Pb年龄明显可以分为2组,一组年龄相对年轻（220．4Ma±2．3Ma）,代表了羌塘东部地区鄂尔陇巴组火山岩的喷发年龄;另外一组年龄相对较老（241．4Ma±3．6Ma）,可能与中三叠世羌塘地区普遍存在的碰撞隆升事件有关。羌塘中生代（晚三叠世-早白垩世）盆地演化早期的沉积作用经历了由陆相至海相的超覆过程,沉积超覆作用从冲洪积相开始,伴随着岩浆侵入、火山爆发及火山碎屑沉积作用,总体上表现为一个向上变深的海侵序列,显示裂谷盆地的特征。     

中国东北地区中生代构造体制的转变:来自火山岩时空分布与岩石组合的制约

东北地区中生代经历了蒙古-鄂霍茨克构造体系向太平洋构造体系的转换,形成了不同期次火山活动。本文归纳总结了露头区与覆盖区中生代火山岩的年代学、空间分布、岩石组合以及地球化学特征,揭示了两个构造域的时空分布范围。该区火山岩锆石U-Pb年龄统计结果表明中生代存在五期火山活动:早-中侏罗世(190~160Ma)、晚侏罗世(160~145Ma)、早白垩世早期(145~120Ma)、早白垩世晚期(120~100Ma)、晚白垩世早期(100~90Ma)。早-中侏罗世火山岩分布较少,火山岩仅分布在大兴安岭西部满洲里地区和东部张广才岭以及南侧辽宁北票-朝阳地区,火山岩属于高钾钙碱性系列,为蒙古-鄂霍茨克海闭合和法拉隆板块双俯冲作用的产物。晚侏罗世东北地区火山活动明显增强,主要分布在大兴安岭地区,张广才岭以及小兴安岭也有少量分布。西部大兴安岭地区以粗面安山岩、粗面岩为主,属于同碰撞造山成因,为蒙古-鄂霍茨克海闭合造山环境产物。东部以中酸性、酸性岩为主,为法拉隆板块背离欧亚大陆,岩石圈伸展引起的壳源物质熔融产物。早白垩世早期火山活动最为强烈,火山岩主要分布在大兴安岭地区。岩性以高钾钙碱性系列的粗面玄武安山岩、粗面安山岩、安山岩、粗面岩为主,为蒙古-鄂霍茨克海闭合造山后伸展环境产物。早白垩世晚期火山岩主要分布在松辽盆地内部。火山岩以中酸性岩为主,属于中钾-高钾钙碱性系列,为伊泽奈崎板块俯冲引起的弧后拉张,软流圈上涌导致年轻地壳熔融的产物。晚白垩世早期火山岩仅分布在小兴安岭及吉林、黑龙江省东部地区。火山岩为一套玄武岩、玄武安山岩、安山岩和英安岩组合,属于中钾钙碱性系列,是伊泽奈崎-库拉板块高角度俯冲的大陆边缘岩浆活动产物。东北地区中生代不同期次火山岩记录了蒙古-鄂霍茨克构造域向太平洋构造域转换过程及其时空影响范围。     

Extensional to compressive Mesozoic magmatism at the SE Eurasia margin as recorded from the Meratus ophiolite (SE Borneo,Indonesia)

The Meratus ophiolitic series (SE Borneo) present a specific assemblage that have recorded (1) a continental extensional episode mostly seen within the peridotites and 2) later subduction-related magmatic events marked by the emplacement of calc-alkaline magmas. These events relate the magmatic activity and geodynamic evolution of the SE Eurasia margin in Mesozoic times. The ophiolitic series comprise ultramafic rocks with minor metavolcanic rocks. The ultramafic rocks include dominant lherzolites and pyroxenites with rather scarce harzburgites and dunites. Spinel peridotite, mineral chemistry data and bulk rock Rare Earth Element (REE) abundances show that most rocks underwent a low degree of partial melting. However, a few samples display significant depletions in Light REE (LREE), which are interpreted as the result of fractional melting under shallow conditions. Plagioclase-bearing peridotites are characterized by high REE abundances which also point to a very low degree of melting followed by reequilibration in the plagioclase facies, as seen from phase chemistry data. These peridotites are locally crosscut by dikelets containing high-temperature K-and Cr-rich amphiboles. Lavas closely associated with the Meratus peridotites have REE compositions ranging from the ones typical of enriched MORB (E-MORB) to normal MORB (N-MORB) types. We believe that the Meratus peridotites represent a fragment of subcontinental lithospheric mantle that locally suffered a low degree of fractional melting during the last stages of a continental rifting phase, in agreement with the presence of metamorphic K- and Cr-rich amphiboles in the peridotites. The E-MORB basalts might result from the melting of an enriched subcontinental lithosphere thermally eroded during the rifting phase by rising asthenosphere which might have produced N-MORB volcanic rocks. Back-arc basin basalts (BABB) now associated with E-MORB and N-MORB have also been found in the metamorphic soles of the peridotites. These rocks would have formed in a back-arc basin now accreted to the eastern margin of Eurasia. The latter are partly covered by calc-alkaline magmatism (Alino Formation). The ophiolitic series was later crosscut by calc-alkaline melts (Manunggul Formation). The Meratus ophiolitic series hence displays a dual origin. They witness 1) a continental episode mostly seen within the peridotites. and 2) later subductionrelated events marked by the emplacement of calc-alkaline magmas.     

Geochemistry of the ophiolite and island-Arc volcanic rocks in the Mianxian-Lueyang suture zone, southern Qinling and their tectonic significance

Ultrabasic rocks in the Mianxian-Lueyang ophiolitic melange zone include harzburgite and dunite which exhibit LREE depletion with remarkable positive Eu anomaly.The diabase dike swarm shows LREE enrichment but slightly negative Eu anomaly.Metamorphosed volcanic rocks can be divided into two groups in terms of their REE geochemistry and trace element ratios of Ti/V,Th/Ta,Th/Yb and Ta/Yb.One is ths MORB-type basalt with LREE depletion,representing the fragments of oceanic crust and implying an association of the MORB-type ophiolite and an ancient ocean basin between the Qinling and Yangtze plates during the Middle Paleozoic-Early Mesozoic era.The oter comprises the island-arc volcanic rocks including tholeiitic basalt and a large amount of calc-alkaline intermediate-acic volcanic rock,which could not be the component of the ancient oceanic crust but the result of magmatism at the continental margin.This indicates that the Mianxian-Lueyang limited ocean basin had undergone a whole process of development,evolution and vanishing from Devonian-Cretaceous to Permian.And the Qinling area had becone an independent lithospheric microplate,on the southern side of which there were exhibited the tectonic characteristics of active continental margins during the Late Paleozoic-Early Mesozoic.That is to say.the Qinling cannot be simply considered as a result of collision between the Yangtze and North China plates.     

西藏羌塘地区印支期火山岩构造地球化学特征

西藏羌塘地区印支期火山岩主要分布在盆地北缘若拉岗日和羌塘中央隆起南缘肖茶卡—香琼火山岩地区。主要元素和稀土元素地球化学特征分析表明 ,若拉岗日区火山岩属富钠型的碱性系列玄武岩 ,肖茶卡—香琼火山岩为拉斑玄武岩。两区岩石系列和构造发育部位虽不同 ,却都是在海西期末闭合的裂陷带上再扩张过程中形成的 ,反映盆地北部和中央隆起处的两条板块缝合带有相似的演化特点。