天山东段1.4Ga花岗闪长质片麻岩SHRIMP锆石U-Pb年龄及其地质意义

天山最东段星星峡地区出露的片麻岩、混合岩和斜长角闪岩等,一直被看作是东天山最老的地层星星峡群,实际上是中—新元古代变质杂岩体。用SHRIMP锆石U-Pb定年技术分析了星星峡花岗闪长质片麻岩中19颗锆石,由其中谐和性较好的14个锆石的分析结果得到206Pb/238U和207Pb/206Pb加权平均年龄分别为(1436±13)Ma(2σ)和(1405.2±7.8)Ma(2σ),为天山东段星星峡花岗闪长岩的形成年龄,从而确定了天山造山带中元古代基底岩浆岩形成的时间,与北美及欧洲大陆广泛存在的1.4Ga岩浆活动具有同时性,对进一步思考天山造山带中1.4Ga岩浆活动形成的古陆块在前Rodinia大陆时期的归属有重要意义。主元素和微量元素研究结果显示星星峡1.4Ga花岗闪长岩具有岛弧岩浆岩特征,与北美中部大陆和欧洲大陆Fennoscandia的中元古代非造山作用形成的岩浆岩有所不同。另外,片麻岩中有的锆石具有新的生长边,并给出年轻化和较大的不一致年龄,说明1.4Ga片麻岩不同程度地受到新元古代(0.9～1.1Ga)变质作用和岩浆活动的改造,同时形成一些混合岩和花岗片麻岩。19颗锆石分析数据中有1个锆石的207Pb/206Pb比值年龄为(1845±23)Ma,与该片麻岩的Nd模式年龄相一致,可能代表更古老地壳物质中的残留锆石。     

河北平山英云闪长质片麻岩锆石SHRIMP年代学

平山板桥沟地区的英云闪长质片麻岩常量元素具有高硅、高铝、高钠和低钾的特点,稀土元素显示强烈分异,具有较高的(La／Yb)。值(34),同时具有明显的Nb,Ta,Ti和P负异常,与太古宙TTG的特征完全一致。阴极发光和背散射研究表明,英云闪长质片麻岩中锆石具有密集震荡环带和较高的Th／U值,表现典型岩浆锆石的特点,但其外侧都有一高亮度(CL)的狭窄变质增生边。SHRIMP测试结果表明TTG的形成年龄为2536．5±9．8Ma,变质年龄为1802±43Ma。推测2500Ga西部块体向东部陆块俯冲形成了TTG,并导致五台陆块与太行山陆块拼合,使华北克拉通化,1．8Ga则为陆内的另一次构造事件。     

新疆中天山地块星星峡群形成的构造背景及峰期变质条件

中天山地块是天山造山带的重要组成部分,其前寒武纪基底的年龄自西向东逐渐变老。星星峡群位于中天山地块最东端,是天山造山带最古老的前寒武纪基底。目前为止,有关星星峡群原岩形成的构造背景与后期发生的变形变质作用尚无详细研究。文章重点对星星峡群的变质片岩和片麻岩进行了野外观察和取样,室内开展了薄片观察、矿物电子探针分析以及全岩地球化学测试。全岩主量元素地球化学分析表明,星星峡群变质片岩和片麻岩的原岩主要为泥质岩和砂岩;微量与稀土元素结果显示,星星峡群沉积形成于大陆弧或活动大陆边缘环境。依据矿物电子探针成分分析数据结合全岩主量元素测试结果计算获得,星星峡群所经历的峰期变质温压条件大致为610~730℃,6.8~8.5 kbar。此外,通过最新的基底岩石变质年龄限定星星峡群发生峰期变质的时间大概在380 Ma。     

胶东地区基底长英质片麻岩的地球化学特征及其构造归属

通过对胶东地区基底长英质片麻岩的地球化学研究发现, 莱西－栖霞一带的基底长英质片麻岩具有太古宙长英质片麻岩的典型特征, 微量元素组成与板内花岗岩类相似。该区应该属于华北陆块的一部分。荣成地区是苏鲁超高压变质带的典型地区, 其基底长英质片麻岩与栖霞一带不同, 是过铝型花岗岩类, 具有火山弧花岗岩类的地球化学特征, 结合普遍存在的０．８Ｇａ 的同位素年代资料, 可以确定荣成地区原来是扬子陆块的一部分。文登－威海地区的长英质片麻岩的常量和微量元素组成都与栖霞地区相当, 很可能也是华北陆块的一部分。从长英质片麻岩代表的基底岩石的地球化学差异来看, 超高压变质带与华北板块的界线应该在五莲－青岛－荣成断裂。威海一带含柯石英超高压岩块的出现很可能是因为大陆碰撞过程中复杂的构造原因, 使超高压岩片中的一部分进入了华北基底分布区。     

新疆东天山地区星星峡群的解体及地质意义

新疆东天山地区星星峡一带的原星星峡群为一套岩性复杂、变质程度差异很大的变质岩系, 在该区进行的1:50000区调工作中, 通过详细的地表调查和地层剖面测量, 并参考了相关变质侵入体的同位素年龄后认为, 根据岩石组合、变质程度、同位素年龄等地质标志, 可将其初步解体为大致形成于晚太古代—古元古代的天湖岩群(Ar₃—Pt₁T.)和长城纪星星峡岩群(ChX.)两套时代不同的岩群。该岩群的解体和区域对比表明, 中天山星星峡一带和塔里木北缘库鲁克塔格一带的前南华系基底应该是一致的, 属于统一的塔里木北缘隆起带。      

塔里木地块东南缘新太古代安南坝石英闪长片麻岩的成因及其对地壳演化的启示

目前塔里木地块东南缘早前寒武纪岩石形成时代和成因机制研究较为薄弱,制约了人们对塔里木大陆地壳形成和早期演化的认识.岩石地球化学及锆石Hf同位素组成表明塔里木地块东南缘安南坝石英闪长片麻岩原岩岩浆为下地壳变玄武岩部分熔融形成,并有少量幔源物质的加入.LA-ICP-MS锆石U-Pb测年结果显示石英闪长片麻岩成岩年龄为2 662±12 Ma、2 676±15 Ma,结合已有资料综合说明塔里木东南缘太古宙岩石形成时代主要集中在2.55~2.70 Ga,变质年龄分别为1 980±30 Ma、1 828±20 Ma~2 087±29 Ma,是古元古代中晚期与造山作用有关的岩浆-变质事件的地质记录.石英闪长片麻岩中锆石两阶段模式年龄T_DM2为2 954~3 742 Ma,峰值为~3.24 Ga,据此认为~3.2 Ga是塔里木东南缘大陆地壳生长的主要时期,并于2.55~2.70 Ga发生地壳再造,古老地壳再循环可能是该地区新太古代中晚期大陆地壳演化的重要方式.      

喜马拉雅造山带东段错那洞片麻岩穹窿的变质作用及构造意义

错那洞穹窿是喜马拉雅造山带北部发育的一系列片麻岩穹窿之一,因其赋存有超大型稀有金属矿床而倍受关注。本文对错那洞穹窿核部产出的石榴石十字石蓝晶石白云母片岩进行了岩石学、相平衡模拟和锆石U-Pb年代学研究,为揭示穹窿的成因和成矿作用提供了重要限定。岩石学研究表明,石榴石蓝晶石十字石白云母片岩的共生矿物组合是石榴石+蓝晶石+十字石+白云母+斜长石+石英+钛铁矿+金红石,为典型的中压角闪岩相变质岩。相平衡模拟表明岩石的变质温压条件为670℃和9. 0kbar,并未经历部分熔融。锆石U-Pb定年结果表明,片岩的变质作用发生在47～29Ma,即经历了一个较长期(～20Myr)的变质演化过程。结合现有研究成果,我们认为错那洞片麻岩穹窿具有与喜马拉雅造山带北部发育的其它片麻岩穹窿相同的成因,穹窿核部的中级变质岩为高喜马拉雅结晶岩系的上部构造层位,其变质作用发生在印度大陆向拉萨地体之下低角度俯冲过程中;穹窿核部淡色花岗岩是高分异的异地花岗岩,是高喜马拉雅结晶岩系下部高温高压麻粒岩部分熔融所形成的熔体经历高程度分离结晶产物。此外,本文研究成果为印度与亚洲大陆的碰撞时间和性质提供了进一步约束。     

苏鲁造山带胶南区段片麻岩原岩的成因:地球化学及Nd同位素证据

出露于苏鲁造山带胶南区段的片麻岩主要包括三种类型黑云斜长片麻岩、二长花岗片麻岩和A型花岗质片麻岩,地球化学判别结果表明它们的原岩均为火成岩.不同类型片麻岩的地球化学特征各不相同,反映它们的原岩具有不同的形成与演化历史.其中黑云斜长片麻岩以负Eu异常弱,甚至出现明显的正异常(δEu=0.60～1.45)、强的Ba正异常、无明显的Sr异常为特征而明显不同于其它类型的片麻岩.其地球化学的总体特征类似于扬子克拉通北缘新元古代双峰式火山岩的酸性端元;与黑云斜长片麻岩类似,二长花岗片麻岩中轻、重稀土元素之间的分馏程度也较强(LaN/YbN=6.3～17.2),但以强的负Eu异常(δEu=0.27～0.54)、强的Sr负异常和弱的Ba负异常为特征明显不同于黑云斜长片麻岩;A型花岗片麻岩的稀土模式及蛛网图的形态类似于二长花岗片麻岩,所不同的是前者Nb、Ta负异常相对较弱.区内几种类型片麻岩的εNd(t)值差别不大,反映它们的原岩之间可能有一定的成因联系.它们的Nd同位素模式年龄TDM都集中在2.0Ga左右,表明它们的源区主要为早元古代的地壳物质,且岩性比较均一.推测二长花岗片麻岩与黑云斜长片麻岩的原岩是同源异相,而A型花岗岩是在大规模Ⅰ型花岗质岩浆形成后,由脱水的紫苏辉石质残留下地壳物质再次发生部分熔融形成的.     

新疆东部卡瓦布拉克地区古生代岩浆活动对中天山地块构造归属的指示意义

卡瓦布拉克地区位于中天山地块南缘。该区古生代侵入岩类广泛发育,是探究中天山构造演化及地壳生长历史的重要窗口。本文获得该区两件二长花岗岩样品的LA-ICP-MS锆石U-Pb定年结果分别为447.4±4.9Ma、422.6±5Ma。LA-MC-ICP-MS锆石Hf同位素原位分析结果显示,其εHf(t)值分别为7.1～11.9、5.8～11.8,对应的二阶段模式年龄为674～963 Ma、514～1043 Ma。侵入于晚古生代花岗岩中的中—基性岩脉携带多期捕获锆石,其εHf(t)介于-7.4～4.8,对应的模式年龄变化范围为1.47～2.54Ga。卡瓦布拉克地区古生代花岗岩及中—基性岩脉中捕获锆石所反映的基底信息表明,中天山与塔里木在中元古代(～1.4Ga)、新元古代(～800Ma)以及古生代(～400Ma)期间岩浆活动具有截然不同的源区特征。结合前人研究成果,认为中天山与塔里木不具有构造亲缘性。     

The petrogenesis and tectonic implications of the granitoid gneisses from Xingxingxia in the eastern segment of Central Tianshan

As part of Central Asian Orogenic Belt (CAOB), the Central Tianshan zone plays a crucial role in the reconstruction of the tectonic evolution of the CAOB. Furthermore, it is bordered by the Tarim Craton to the south, and the comparable evolutionary history between them enables the Central Tianshan zone to provide essential information on the crustal evolution of the Tarim Craton. The eastern segment of the Central Tianshan tectonic zone is characterized by the presence of numerous Precambrian metamorphic rocks, among which the Xingxingxia Group is the most representative one. The granitoids gneisses, intruded into the Xingxingxia Group, consist of two major lithological assemblages: (1) biotite-monzonitic gneisses and (2) biotite-plagioclase gneisses. These metamorphosed granitoid rocks are characterized by enrichment in SiO₂, Al₂O₃ and K₂O and depletion in MgO and FeO_T. The Rittmann index (σ) spreads between 1.44 and 2.21 and ACNK (Al₂O₃/(CaO + Na₂O + K₂O)) ranges from 1.03 to 1.08, indicating that these granitoid gneisses are high-K calc-alkaline and peraluminous. Trace element data indicate that the studied samples are enriched in LREE with moderate REE fractionated patterns ((La/Yb)_N = 10.5–75.3). The concentrations of HREE of the garnet-bearing gneisses are significantly higher than those of garnet-free gneisses. The former show pronounced negative Eu anomalies (Eu/Eu^* = 0.32–0.57), while the latter are characterized by negligible negative Eu anomalies to moderate positive Eu anomalies (Eu/Eu^* = 0.80–1.35). In addition, the enrichment of LILE (Rb, Th, K, Pb) and depletion of HFSE (Ta, Nb, P, Ti) of the examined granitoid gneisses are similar to typical volcanic-arc granites. Zircons U–Pb dating on the biotite monzonitic gneiss yields a weighted mean ²⁰⁶Pb/²³⁸U age of 942.4 ± 5.1 Ma, suggesting their protoliths were formed in the early Neoproterozoic, which is compatible with the time of the assembly of supercontinent Rodinia. The zircons have a large ε_Hf(t) variation from −5.6 to +3.2, suggesting that both old crust-derived magmas and mantle-derived juvenile materials contributed to the formation of their protoliths. Based on field observation, and petrological, geochemical and geochronological investigations, we infer that the granitoid gneisses from Xingxingxia were probably formed on a continental arc that resulted from the interaction of Australia and the Tarim Craton during the assembly of the Rodinia supercontinent, and that the Central Tianshan zone was a part of the Tarim Craton during that time. Besides, the Grenvillian orogenic events may have developed better in the Tarim Craton than previously expected.     

Tectonic Framework of Late Paleozoic Intrusions in Xingxingxia: Implications for Final Closure of South Tianshan Ocean in East Tianshan

This work carried out systematic geological field investigation, petrography observation, zircon geochronology and whole rock geochemistry on Late Paleozoic intrusions in the Xingxingxia region near the Xinjiang-Gansu provincial boundary, western China, aiming to constrain the Late Paleozoic tectonic framework of the Xingxingxia region and the final closure time of South Tianshan Ocean in the East Tianshan. The Xingxingxia area is located in the east part of the Tianshan orogen, and adjacent to the north of the Tarim Basin. The Late Paleozoic magma activities in the Xingxingxia region can be mainly divided into three stages. The first stage includes intrusive magma activities under a collision setting between Late Ordovician to the Late Devonian. The second stage is intrusive magma activities under a subduction setting during(304±3)–(278±3) Ma, and the third stage involves intrusive magma activities under a collision and post-collision setting during(268±5)–(259.9±2.6) Ma. The final suture zone of South Tianshan Ocean should be between the Central Tianshan Block and South Tianshan accretionary complex. Based on previous work, both the first stage magma activities(i.e., intrusive magmatic activities between the Late Ordovician to Late Devonian) and the Hongliuhe ophiolitic complex indicate a close event between Central Tianshan Block and South Tianshan Accretionary Complex. The 304±3 Ma dioritic metamorphic gneiss of the XingX ingxia complex and the 278±3 Ma diorite are all island arc calc-alkaline rocks, the 289±3 Ma gabbro is island arc tholeiitic gabbro formed by magma from metasomatic enrichment mantle. All these results indicate that the second stage of magmatic activities is under a subduction setting. The third stage magma activities i.e. the granitic magma activities of(268±5)–(259.9±2.6) Ma occurred at a transitional setting from compressional to post-collision extensional tectonic setting. Thus, around(268±5)–(260±3) Ma, the final closure of the South Tianshan Ocean occurred and the Tianshan orogen shifted into the intracontinental evolution stage. During and after the closure process, a wide range of metamorphism and large dextral strike-slip faults developed.     

Geochronology and Geochemistry of the Xingxingxia Triassic A-type Granites in Central Tianshan, NW China: Petrogenesis and Tectonic Implications

The Triassic granitoids in Central Tianshan play a key role in determining the petrogenesis and tectonic evolution on the southern margin of the Central Asian orogenic belt. In this study, we present SHRIMP zircon U-Pb ages, Hf isotopic and geochemical data on the Xingxingxia biotite granite, amazonite granite and granitic pegmatite in Central Tianshan, NW China. Zircon U-Pb dating yielded formation ages of 242 Ma for the biotite granite and 240 Ma for the amazonite granite. These granitoid rocks have high K2O with low MgO and CaO contents. They are enriched in Nb, Ta, Hf and Y, while being depleted in Ba and Sr, showing flat HREE patterns and negative Eu anomalies. They have typical A-type granite geochemical signatures with high Ga/Al (8–13) and TFeO/(TFeO + MgO) ratios, showing an A2 affinity for biotite granite and an A1 affinity for amazonite granite and granitic pegmatite. Zircon εHf(t) values of the granitoids are 0.45–2.66, with Hf model ages of 0.99–1.17 Ga. This suggests that these A-type granites originated from partial melting of the lower crust. We propose that Xingxingxia Triassic A-type granites formed under lithospheric extension from post-orogenic to anorogenic intraplate settings and NE-trending regional strike-slip fault-controlled magma emplacement in the upper crust.     

阿拉善北部宗乃山地区片麻岩锆石U-Pb年龄、Hf同位素特征及其构造归属探讨

阿拉善北部宗乃山地区出露少量前寒武纪岩石,主要为一套变质表壳岩和变质深成侵入岩组成的变质杂岩,其形成时代和同位素特征对于了解该地区的基底性质和探讨阿拉善北部构造格架具有重要意义。本文对宗乃山西南缘阿尔滕托亚副片麻岩和嘎顺呼都格正片麻岩开展了详细的岩石学、锆石U-Pb年代学和Hf同位素研究,并对其构造意义进行了初步探讨。阿尔滕托亚副片麻岩包括黑云二长片麻岩和变斑状黑云斜长片麻岩,两套岩石中分选出来的锆石具有典型岩浆锆石特征,LA-ICPMS分析结果显示这些锆石的207Pb/206Pb年龄相对集中,并分别获得了1459±11Ma(MSWD=3.3)和1458±3Ma(MSWD=0.13)的年龄。初步研究认为阿尔滕托亚副片麻岩的源区存在~1.46Ga的岩浆事件,这些副片麻岩形成时代稍晚于该期岩浆事件。嘎顺呼都格正片麻岩以角闪黑云二长片麻岩为代表,其锆石结晶年龄为1433±17Ma(MSWD=0.25)。锆石Hf同位素分析结果显示,阿尔滕托亚副片麻岩和嘎顺呼都格正片麻岩具有一致的锆石εHf(t)值(+0.1~+11.9),二阶段模式年龄为2.19~1.44Ga,反映了片麻岩原岩岩浆可能来自当时相对年轻的地壳物质。结合前人研究成果,宗乃山前寒武纪岩石可能主要形成于中元古代1.4~1.5Ga,而不是以往认为的中太古代-古元古代。截至目前,宗乃山-沙拉扎山构造带暂未发现类似阿拉善地块内部的太古代-古元古代基底岩石,因而其与阿拉善地块在早前寒武纪的亲缘性存有疑问。     

西天山造山带晚古生代构造演化和成矿作用

西天山是我国重要的内生金属矿床集中区,其矿种包括有铜、镍、钼、铁、金、锌等,这些矿产在前寒武纪和显生宙的地质历史中分别形成了大量的成矿体系。通过对西天山成矿地质背景和成矿类型的研究,厘定了5种内生金属矿床类型：1）岩浆型铜镍矿床;2）斑岩铜钼矿床;3）火山岩型铁矿床;4）浅成低温热液型金矿床;5）造山型金铜矿床。典型矿床有菁布拉克铜镍矿床、达巴特铜钼矿床、喇嘛苏铜矿床、敦德铁锌矿床、备战铁矿床、阿希金矿、伊尔曼得金矿床和卡特巴阿苏金矿床等。从构造上看,这些矿床的发育与西天山造山带的增生和汇聚作用密切相关。矿床的形成经历了3个主要阶：早志留世,南天山洋北向俯冲于伊犁—中天山地块之下,形成与铜镍矿床有关的菁布拉克岩体;早-晚石炭世,由于北向俯冲作用,形成了斑岩型铜金矿床、低温热液型金矿床和火山岩型铁矿床;晚石炭世早期,南天山洋壳可能被消耗殆尽,导致了塔里木克拉通与南天山造山带的碰撞。大花岗岩体广泛分布于北天山增生楔和伊犁—中天山地块,并伴随造山型的金矿床形成。     

西南天山前寒武纪基底时代和特征：锆石U—Pb年龄和Nd—Sr同位素组成

采用锆石U-Pb定年方法,精确测定了西南天山木扎尔特群花岗片麻岩的结晶锆石年龄为（707±13）Ma(MSWD=0.33)。元素地球化学特征和低的ε     

西天山阿吾拉勒西段麻粒岩相片麻岩锆石Cameca U-Pb年龄及其地质意义

岩相学和岩石地球化学特征表明,西天山阿吾拉勒西段低压麻粒岩相片麻岩的原岩为杂砂岩,具有近源、快速沉积的特点。在稀土元素的球粒陨石标准化图解上,片麻岩具轻稀土元素陡倾、重稀土元素平坦的分布型式,并具明显的Eu负异常,Nb、Ta、Ti、Ba、P、Sr均相对亏损。片麻岩中Cameca离子探针锆石U-Pb年代学结果显示,上交点年龄为（1609±40）Ma,代表了原岩的岩浆结晶年龄;下交点年龄为（764±72）Ma,代表了引起Pb丢失的热事件的时代,可能代表麻粒岩相变质事件的年龄。该麻粒岩相片麻岩的产出表明伊犁地块可能具有中元古代的结晶基底,也表明伊犁地块经历了764Ma的热事件。该热事件可能是伊犁地块对全球Rodinia超大陆解体事件的响应。     

Mesoproterozoic Continental Arc Type Granite in the Central Tianshan Mountains: Zircon SHRIMP U-Pb Dating and Geochemical Analyses

The Central Tianshan belt in northwestern China is a small Precambrian block located in the southern part of the Central Asia Orogenic Belt （CAOB）, which is considered as ＂the most voluminous block of young continental crust in the world＂ that comprises numerous small continental blocks separated by Paleozoic magmatic arcs. The Precambrian basement of the central Tianshan Mountains is composed of volcanic rocks and associated volcano-sedimentary rocks that were intruded by granitic plutons. Geochemical analyses demonstrate that the granitic plutons and volcanic rocks were generated in the Andean-type active continental arc environment like today＇s Chile, and the zircon U-Pb SHRIMP dating indicates that they were developed at about 956 Ma, possibly corresponding to the subduction of the inferred Mozambique Ocean under the Baltic-African super-continent.     

东天山马庄山金矿区赋矿石英斑岩的岩石成因和构造背景:元素地球化学、U-Pb年代学和Sr-Nd-Hf同位素约束

马庄山金矿位于东天山东段,矿区出露有大量的石英斑岩,总体上呈北东走向,沿矿区中部断裂侵入。石英斑岩呈灰白色,具斑状结构,斑晶主要为石英,少量正长石和斜长石,基质为长英质和少量暗色矿物。石英斑岩的Na_2O+K_2O含量为3. 55%～9. 67%,Al_2O_3含量(10. 37%～14. 28%),K_2O/Na_2O比值为2. 57～66. 5,显示富碱高钾、过铝质特征;稀土含量中等(65×10~(-6)～161×10~(-6)),轻重稀土分异中等([La/Yb]N=6. 15～12. 5),相对富集轻稀土元素、具弱的负Eu异常。微量元素总体富集Rb、K、Th、U和Pb,亏损Sr、Ba、P、Nb和Ti等元素,与活动大陆边缘弧火成岩的微量元素特征一致。马庄山石英斑岩的SiO_2与P_2O_5呈现负相关关系,Y、Th与Rb均呈现正相关的关系,说明研究区的次火山岩属于I型花岗岩类。对马庄山石英斑岩内岩浆锆石进行LA-ICP-MS U-Pb定年,获得一致曲线年龄为315. 4±0. 6Ma(MSWD=0. 67),加权平均年龄为316. 0±2. 0Ma(MSWD=0. 23),将矿区内以石英斑岩为主的次火山岩侵位时间限定在314～318Ma。石英斑岩具有较高的(87Sr/86Sr)i值(0. 7077～0. 7102),较低的εNd(t)值(-1. 62～1. 82),Nd的二阶段模式年龄(tDM2)为0. 9～1. 2Ga,εHf(t)值为-3. 2～0. 4,tDM2在1. 28～1. 51Ga之间,暗示岩石来自于下地壳物质重熔,可能有部分地幔物质加入。综合石英斑岩的地质、地球化学和年代学特征,认为东天山东段,在晚石炭世,马庄山地区处于与俯冲相关的活动陆缘弧环境。     

东天山博格达造山带石炭纪火山岩及其形成地质环境

东天山博格达造山带早、中石炭世海相火山地具有双峰式特征,主要岩性为富钠的玄武岩和流纹岩,其次是英安岩,安山质岩石极少出现。玄武岩的特征是：少数岩石含有实际矿物石英,个别岩石含橄榄石斑晶;辉石主要是透辉石和次透辉石,其成分富含铝（Ａｌ２Ｏ３＝４．１７～５．９９）和钛（ＴｉＯ２＝２．８０～４．７８）;基质中的长石主要是钠－更长石,斑晶中有相当数量的中长石和拉长石;全岩化学成分ＣＩＰＷ计算结果绝大部分含