俯冲带部分熔融

俯冲带是地幔对流环的下沉翼,是地球内部的重要物理与化学系统。俯冲带具有比周围地幔更低的温度,因此,一般认为俯冲板片并不会发生部分熔融,而是脱水导致上覆地幔楔发生部分熔融。但是,也有研究认为,在水化的洋壳俯冲过程中可以发生部分熔融。特别是在下列情况下,俯冲洋壳的部分熔融是俯冲带岩浆作用的重要方式。年轻的大洋岩石圈发生低角度缓慢俯冲时,洋壳物质可以发生饱和水或脱水熔融,基性岩部分熔融形成埃达克岩。太古代的俯冲带很可能具有与年轻大洋岩石圈俯冲带类似的热结构,俯冲的洋壳板片部分熔融可以形成英云闪长岩-奥长花岗岩-花岗闪长岩。平俯冲大洋高原中的基性岩可以发生部分熔融产生埃达克岩。扩张洋中脊俯冲可以导致板片窗边缘的洋壳部分熔融形成埃达克岩。与俯冲洋壳相比,俯冲的大陆地壳具有很低的水含量,较难发生部分熔融,但在超高压变质陆壳岩石的折返过程中可以经历广泛的脱水熔融。超高压变质岩在地幔深部熔融形成的熔体与地幔相互作用是碰撞造山带富钾岩浆岩的可能成因机制。碰撞造山带的加厚下地壳可经历长期的高温与高压变质和脱水熔融,形成S型花岗岩和埃达克质岩石。     

西昆仑库地蛇绿岩地质、地球化学及其成因研究

西昆仑库地蛇绿混杂岩由方辉橄榄岩和纯橄榄岩等地幔变质橄榄岩、豆荚状铬铁矿、堆晶橄榄岩、堆晶辉石岩和辉长岩、辉绿岩墙、块状和枕状玄武岩等组成。强亏损方辉橄榄岩为主的地幔岩组合,二辉石的低Al含量和铬尖晶石的高Cr^#,以及岩石的富Mg、Ni和贫Al、Ca特征一致表明地幔橄榄岩类是经较高程度部分熔融后的地幔残余,与消减带之上蛇绿岩中的同类岩石相近。岩石富Rb、Ba、U、Th、LREE,说明地幔残余岩石受到了来自消减带的洋壳重熔组分的混染。堆晶岩以辉石岩和辉长岩为主,可能属PPG系列,指示岩浆是在消减带环境和含水条件下熔融的。辉长岩为低Ti蛇绿岩型,代表洋内弧后盆地早期环境或弧前环境。辉绿岩和玄武岩为洋中脊拉斑玄武岩和岛弧拉斑玄武岩的过渡类型;玄武岩和辉绿岩相比富Ba、Th、LREE,贫Ta,指示玄武岩较辉绿岩更多地受到来自消减带洋壳重熔组分的影响。库地蛇绿岩形成时的古构造环境是消减带之上的弧间或弧后盆地。     

蛇绿岩中辉长岩的形成和变质过程研究

系统论述了扩张脊之下的洋壳增生模式、辉长岩地球化学特征及其对岩浆源区及岩浆过程的反映,总结了辉长岩在洋底环境和俯冲带中的变质作用及微量元素地球化学行为,并探讨了蛇绿混杂岩带中辉长岩的特点。对典型蛇绿岩的研究表明,在席状岩墙根部区域存在熔体透镜,来自地幔的岩浆在此贮存、分异。蛇绿岩中不同层位辉长岩的成分差异及结构、构造特点反映了该分异过程。辉长岩以及辉长岩中单斜辉石的地球化学特征可以反演岩浆的源区特征和岩浆分异、混合过程。辉长岩发生的洋底变质包括与洋脊附近热液对流相关的绿片岩相-麻粒岩相变质作用和与超镁铁岩蛇纹石化相关的异剥钙榴岩化作用。辉长岩在变质过程中不相容元素的活动性与温度、流体性质以及构造作用密切相关。     

新疆西准噶尔达尔布特蛇绿岩套柳树沟镁铁质杂岩SHRIMP锆石U-Pb年龄及地球化学特征

对新疆西准噶尔达尔布特蛇绿岩套柳树沟镁铁质杂岩中橄榄辉长岩、蛇纹石化橄榄辉长岩、辉长岩和蚀变辉长岩地球化学分析表明:辉长岩和蚀变辉长岩具有钙碱性和拉斑玄武岩的双重特征,橄榄辉长岩和蛇纹石化橄榄辉长岩属镁铁质堆积岩,为蛇绿岩组成单元;稀土总量较高,具微弱正Eu异常,稀土元素配分模式为略左倾平坦型,与SSZ型镁铁质堆晶岩稀土配分模式相同;微量元素蛛网图上,富集大离子亲石元素Cs、K、Th、U,相对亏损高场强元素Nb、Ta,可能代表俯冲板片的流体交代上覆地幔楔使地幔岩石发生部分熔融。地球化学构造环境判别柳树沟镁铁质岩石岩浆源区为亏损型地幔向富集型地幔过渡的适度富集型地幔,其形成的最佳模型是在成熟岛弧基础上裂谷化形成的一个不成熟的类似边缘海性质弧后盆地,不具成熟大洋或盆地那样的洋壳-上地幔结构,在盆地扩张初期岩浆具岛弧特征,随着盆地被进一步打开,镁铁质岩石具N-MORB特征。对辉长岩采用SHRIMP锆石U-Pb同位素年龄测试,获得特柳树沟镁铁质岩石的结晶时间为314.9±1.7 Ma。     

阿尔泰造山带玛因鄂博蛇绿混杂岩俯冲-折返拼贴式就位的特征

阿尔泰山南缘原划下石炭统姜巴斯套组实为一套具有洋壳性质的变质岩组成,由玄武岩、辉长岩和少量硅质岩组成,并混杂岩了前寒武纪基底残残块。该洋壳组分位于增生岩楔之中,构造楔形体的形成是俯冲作用一次次"脉冲式"推进的产物,大体可以分为7个岩片,在增生楔下部(南部)见有滑混岩出露。角闪岩相变质的洋壳又经历了退变质作用的影响,显微镜下可见到辉石转变为阳起石、绿帘石交代斜长石的现象。显示折返过程中经历了由角闪岩相绿片岩相的退变质作用演化过程,俯冲的洋壳残片又被仰冲盘携带上升,发生俯冲-折返拼贴式就位,与弧火山岩共同形成了SSZ型蛇绿混杂岩。蛇绿混杂增生岩楔的特征表明洋壳由南向北俯冲,记录了古亚洲洋中支早古生代晚期的演化特点。     

南羌塘增生过程的中-晚三叠世岩浆记录:藏北玛依岗日-角木日地区基性岩墙

古特提斯洋向北俯冲形成增生杂岩,它们向南增生构成了南羌塘增生地体,且增生期内发育的岩浆岩可以用来研究南羌塘的增生过程。在南羌塘增生杂岩带内,由北向南,发育有玛依岗日(MG)辉长岩墙、角木日(JM)辉长辉绿岩墙。锆石U-Pb测年结果显示,两者分别形成于237. 1±2. 3Ma和230. 7±1. 8Ma,为南羌塘增生期内岩浆岩。它们的岩石地球化学特征均介于OIB与E-MORB之间,富集Ti、Nb,以及LREE和LILE。Nd-Pb同位素结果显示两者均起源于富集地幔源区。Sm/YbLa/Yb图解显示,两者均起源于尖晶石-石榴石二辉橄榄岩源区,相对于JM辉长辉绿岩MG辉长岩部分熔融程度较高。两者Mg#和Ni、Cr特征表明,MG辉长岩分异程度高于JM辉长辉绿岩。Th/Nb-La/Nb图解显示,相对于JM辉长辉绿岩MG辉长岩经历了一定程度的地壳混染。综合研究认为,MG辉长岩和JM辉长辉绿岩为古特提斯洋壳俯冲过程中软流圈上涌的两次岩浆活动的产物,并受俯冲洋壳和地幔楔影响。MG辉长岩和JM辉长辉绿岩记录了南羌塘的增生过程,它们为相关研究提供了岩浆岩证据。     

西天山特克斯北中酸性火成岩地球化学特征及成因意义

新疆西天山特克斯县城北部伊特公路沿线和库勒萨依出露大量中酸性火成岩,伊特公路沿线为石英钠长斑岩,库勒萨依为石英闪长斑岩和花岗闪长斑岩。岩石地球化学和同位素组成研究表明,前者为典型的岛(陆)弧带火成岩,而后者具有埃达克岩的成分特征,两者均为古亚洲洋壳在俯冲过程中岩浆活动的产物。早先俯冲的较冷洋壳板片在深处脱水诱发上覆地幔楔熔融,熔体上升并经历壳幔相互作用等过程引发伊特公路一带弧岩浆活动; 由于洋壳持续俯冲,后来新形成的靠近洋脊的年轻板片由于高热在较浅处直接发生部分熔融形成埃达克岩浆,并上侵至库勒萨依一带。库勒萨依斑岩体SIMS锆石 U-Pb年龄为342.5±2.3Ma,属于早石炭世。两组中酸性火成岩的地球化学特征表明,古亚洲洋(南天山洋)在早石炭世还未完全闭合,洋壳向北的持续俯冲过程造成伊犁-中天山板块南缘广泛的岩浆活动,此时西天山陆壳增生方式主要为侧向增生,增生物质主要为洋壳板片(埃达克岩)和洋壳板片流体交代的地幔楔成分。     

南阿尔金地区早古生代中酸性侵入岩的岩石成因及其对构造演化的指示意义

南阿尔金造山带位于塔里木盆地和柴达木盆地之间,是中国西北地区重要的俯冲-碰撞杂岩带,其早古生代构造演化过程是近年来的研究热点之一,然而,洋壳俯冲的时限一直存在争议。本文对茫崖石英二长岩开展岩石学、地球化学、锆石U-Pb年代学和锆石Lu-Hf同位素地球化学研究,探讨其岩石成因及成岩时的构造环境。样品显示高碱、富钾、低钛、贫铁及Nd-Ta-Ti异常等与钾玄岩相似的地球化学特征,成岩年龄为511～495 Ma, ε_Hf(t)主要为-3.51～-0.08,少量介于0.04～1.69之间。我们认为俯冲洋壳到达角闪岩相边界时释放大量水并上升进入地幔楔,导致地幔楔橄榄岩发生角闪石化交代作用,由于地幔楔沿俯冲带向下拖曳而温度升高,角闪石化橄榄岩熔融形成的熔体在上升过程诱发上地壳物质部分熔融,壳源岩浆混合少量幔源岩浆形成了石英二长岩,该期花岗岩是对造山带从大洋岛弧环境向活动大陆边缘过渡的岩石学响应。因此,南阿尔金洋壳可能在约517 Ma前已经开始俯冲。     

对富铝型豆荚状铬铁矿矿床成因的新认识一一以新疆萨尔托海铬铁矿矿床为例

萨尔托海铬铁矿矿床产于萨尔托海蛇绿岩块的地幔橄榄岩中,属于富铝型豆荚状铬铁矿床。该矿床与一套橄长岩和辉长岩类岩石紧密伴生,矿体周围常被一薄的绿泥石壳所包裹。本区铬铁矿的形成包括两个阶段:第一阶段是原始地幔岩经高度熔融形成富铬铬铁矿;第二阶段形成富铝铬铁矿。交代作用伴随着新生单斜辉石和斜长石的形成。原始地幔岩的高度熔融以及基性熔体在地幔橄榄岩中的形成和存在是萨尔托海铬铁矿形成的先决条件。     

延吉地区古新世埃达克岩成因的岩浆混合证据

本文通过年代学、矿物学、主量元素、微量元素和同位素的研究,指出延吉地区古新世富镁埃达克岩起源于被俯冲板片熔体交代的地幔楔。单斜辉石和角闪石斑晶所显示的反环带结构为幔源富镁埃达克熔体于壳源中酸性岩浆混合的结果,而非前人普遍认为的熔体—地幔的反应产物;其地球化学特征表现出的岩浆演化趋势可以很好地用地壳混染/AFC过程来解释。延吉古新世埃达克岩形成于俯冲后岩石圈伸展作用背景,与太平洋板块的俯冲后撤作用有关。因此,我们认为富镁埃达克岩的形成不必强调同期洋脊的俯冲作用,只要早先或同时有俯冲板片熔体交代,在合适的p-t条件下交代地幔并发生熔融作用,就能形成这一类岩石。     

强烈亏损重稀土元素的中酸性火成岩(或埃达克质岩)与Cu、Au成矿作用

文中概述了强烈亏损重稀土元素的中酸性火成岩(或埃达克质岩)的研究历史、现状和意义,列出了扬子地块东部、青藏高原以及新疆北部与铜金成矿有关的同类岩石的一些特征,重点分析了当前强烈亏损重稀土元素的中酸性火成岩(或埃达克质岩)的研究中所存在的问题,并提出了一些初步的设想。强烈亏损重稀土元素的中酸性火成岩(或埃达克质岩)不仅具有重要的地球动力学意义(可能与俯冲、拆沉、底侵、板片窗或地幔交代等深部过程有关),而且具有极其重要的Cu、Au成矿意义。俯冲洋壳熔融形成的埃达克岩及其成矿作用已有相当深入的研究,但是来自大陆内部的强烈亏损重稀土元素的中酸性火成岩的成因、岩石组合及其成矿作用是否类似于俯冲洋壳熔融形成的埃达克岩,还需要深入的研究。一些强烈亏损重稀土元素的中酸性火成岩(或埃达克质岩)的所表现出的高钾特征很可能与高压(>1 GPa)条件下的熔融或源岩的高钾有关。文中提出了一个有别于俯冲洋壳熔融+埃达克岩+Cu、Au成矿的新工作模型——拆沉洋壳或下地壳熔融+强烈亏损重稀土元素的中酸性火成岩(或埃达克质岩)+Cu、Au成矿。拆沉洋壳或下地壳熔融形成熔体的Fe_2O_3对地幔的交代(氧化)作用可能是Cu、Au从地幔迁出并最终成矿的一个重要原因,但是增厚下地壳环境中流体的作用也不?     

Chronology and Geochemistry of the Nadingcuo Volcanic Rocks in the Southern Qiangtang Region of the Tibetan Plateau: Partial Melting of Remnant Ocean Crust along the Bangong-Nujiang Suture

<正>The Nadingcuo high-K calc-alkaline rocks mainly composed of trachyte and trachyandesite are the largest outcrop area of volcanic rocks in southern Qiangtang terrane in the Tibetan plateau. However,their exact source and peterogenesis are still debated.~(40)Ar-~(39)Ar and LAM-ICPMS zircon U-Pb isotopic dating confirm that these rocks erupted in Eocene.In addition,the Nadingcuo volcanic rocks are characterized by high Sr/Y content ratios,similar with the adakite derived from partial melting of oceanic crust.They can be further classified as high Mg~#(Mg~#=48-57) and low Mg~# (Mg~#=33-42) subtypes.The Nadingcuo adakitic rocks have relatively low(~(87)Sr/~(86)Sr)_i and highε_(Nd)(t), showing a trend of similarity to the Dongcuo ophiolite present in the Bangong-Nujiang oceanic crust. Simple modeling indicates that the Nadingcuo adakitic rocks are a mix resulting from the basalt of Bangong-Nujiang Ocean with 10%-20%crustal material of Lhasa terrane.On these bases we suggest that the low Mg~# Nadingcuo adakitic rocks are the product of partial melting of remnant oceanic crust with small sediment,and the high Mg~# rocks are the result of reaction between rising melt of remnant oceanic crust with subducted sediment and mantle wedge.Therefore,the origin of Nadingcuo adakitic rocks may be related to intracontinental subduction triggered by collision of India-Asia during Cenozoic.     

Oxygen isotope composition of xenoliths from the oceanic crust and volcanic edifice beneath Gran Canaria (Canary Islands): consequences for crustal contamination of ascending magmas

Xenolith samples of marine terrigenous sediments and altered Jurassic MORB from Gran Canaria (Canary Islands) represent samples of sub-island oceanic crust. These samples are postulated to define end-members for crustal contamination of basaltic and felsic ocean island magmas. The meta-igneous rocks show great heterogeneity in oxygen isotope compositions (δ¹⁸O 3.3–8.6‰), broadly correlating with their stratigraphic position in the oceanic crust. Gabbros interpreted as fragments of oceanic crust layer 3 have δ¹⁸O values of 3.3–5.1‰, which is lower than MORB (5.7–6.0‰). Layer 2 lavas and dykes show a broader range of δ¹⁸O of 4.1–8.6‰. Therefore, high-temperature metamorphism seems to have been the dominant process in layer 3, while both high- and low-temperature alteration have variably affected layer 2 rocks. Siliciclastic sediments have high δ¹⁸O values (14.1–16.4‰), indicating diagenesis and low-temperature interaction with seawater. The oxygen isotope stratigraphy of the crust beneath Gran Canaria is typical for old oceanic crust and resembles that in ophiolites. The lithologic boundary between older oceanic crust and the igneous core complex at 8–10 km depth—as postulated from geophysical data—probably coincides with a main magma stagnation level. There, the Miocene shield phase magmas interacted with preexisting oceanic crust. We suggest that the range in δ¹⁸O values (5.2–6.8‰) [Chem. Geol. 135 (1997) 233] found for shield basalts on Gran Canaria, and those in some Miocene felsic units (6.0–8.5‰), are best explained by assimilation of various amounts and combinations of oceanic and island crustal rocks and do not necessarily reflect mantle source characteristics.     

Geochronology of the Duguer range metamorphic rocks,Central Tibet: implications for the changing tectonic setting of the South Qiangtang subterrane

The Duguer area represents one of the few occurrences of high-grade metamorphic rocks in the ‘Central Uplift’ zone of the Qiangtang terrane, central Tibet. The metamorphic rocks consist mainly of orthogneiss, paragneiss, and schist. To better understand the formation of these rocks, seven samples of gneiss and schist from the Duguer area were selected for in situ zircon U–Pb analysis and Ar–Ar dating of metamorphic minerals. The results suggest two distinct metamorphic stages, during the Late Triassic (229–227 Ma) and Late Jurassic (150–149 Ma). These stages correspond to the closure of the Palaeo-Tethys Ocean and northward subduction of the Bangong–Nujiang Neo-Tethys oceanic crust, respectively. We suggest that the Late Triassic metamorphic rocks of the Duguer area in the central South Qiangtang subterrane provide evidence of continental collision between the North and South Qiangtang subterranes, following the subduction of oceanic crust. It is likely that deep subduction of oceanic crust occurred along the Longmu Co–Shuanghu–Lancangjiang suture zone (LSLSZ), which would have hindered exhumation owing to the high density of oceanic crust. Subsequent break-off and delamination of the subducted oceanic slab at ~220 Ma may have resulted in exhumation of high-pressure and high-grade metamorphic rocks in the South Qiangtang subterrane. The Late Jurassic ages of metamorphism and deformation obtained in this study indicate the occurrence of an Andean-type orogenic event within the South Qiangtang subterrane. This hypothesis is further supported by an apparent age gap in magmatic activity (150–130 Ma) along the magmatic arc, and the absence of Late Jurassic sediments.     

The building blocks of continental crust: Evidence for a major change in the tectonic setting of continental growth at the end of the Archean

Oceanic arcs are commonly cited as primary building blocks of continents, yet modern oceanic arcs are mostly subducted. Also, lithosphere buoyancy considerations show that oceanic arcs (even those with a felsic component) should readily subduct. With the exception of the Arabian–Nubian orogen, terranes in post-Archean accretionary orogens comprise < 10% of accreted oceanic arcs, whereas continental arcs compose 40–80% of these orogens. Nd and Hf isotopic data suggest that accretionary orogens include 40–65% juvenile crustal components, with most of these (> 50%) produced in continental arcs.Felsic igneous rocks in oceanic arcs are depleted in incompatible elements compared to average continental crust and to felsic igneous rocks from continental arcs. They have lower Th/Yb, Nb/Yb, Sr/Y and La/Yb ratios, reflecting shallow mantle sources in which garnet did not exist in the restite during melting. The bottom line of these geochemical differences is that post-Archean continental crust does not begin life in oceanic arcs. On the other hand, the remarkable similarity of incompatible element distributions in granitoids and felsic volcanics from continental arcs is consistent with continental crust being produced in continental arcs.During the Archean, however, oceanic arcs may have been thicker due to higher degrees of melting in the mantle, and oceanic lithosphere would be more buoyant. These arcs may have accreted to each other and to oceanic plateaus, a process that eventually led to the production of Archean continental crust. After the Archean, oceanic crust was thinner due to cooling of the mantle and less melt production at ocean ridges, hence, oceanic lithosphere is more subductable. Widespread propagation of plate tectonics in the late Archean may have led not only to rapid production of continental crust, but to a change in the primary site of production of continental crust, from accreted oceanic arcs and oceanic plateaus in the Archean to primarily continental arcs thereafter.     

The formation of SiO<Subscript>2</Subscript>-rich melts within the deep oceanic crust by hydrous partial melting of gabbros

Small amounts of felsic, evolved plutonic rocks, often called oceanic plagiogranites, always occur as veins or small stocks within the gabbroic section of the oceanic crust. Four major models are under debate to explain the formation of these rocks: (1) late-stage differentiation of a parental MORB melt, (2) partial melting of gabbroic rocks, (3) immiscibility in an evolved tholeiitic liquid, and (4) assimilation and partial melting of previously altered dikes. Recent experimental data in hydrous MORB-type systems are used to evaluate the petrogenesis of oceanic plagiogranites within the deep oceanic crust. Experiments show that TiO₂ is a key parameter for the discrimination between different processes: TiO₂ is relatively low in melts generated by anatexis of gabbros which is a consequence of the low TiO₂ contents of the protolith, due to the depleted nature of typical cumulate gabbros formed in the oceanic crust. On the other hand, TiO₂ is relatively high in those melts generated by MORB differentiation or liquid immiscibility. Since the TiO₂ content of many oceanic plagiogranites is far below that expected in case of a generation by simple MORB differentiation or immiscibility, these rocks may be regarded as products of anatexis. This may indicate that partial melting processes triggered by water-rich fluids are more common in the deep oceanic crust than believed up to now. At slow-spreading ridges, seawater may be transported via high-temperature shear zones deeply into the crust and thus made available for melting processes.     

哀牢山缝合带中两类火山岩地球化学特征及其构造意义

在哀牢山构造带的哀牢山断裂与花山－雅邑断裂之间出路大量不同构造环境的岩浆岩。除双沟蛇绿岩外,尚发现有景东火山岩和墨江火山岩。地球化学研究表明,景东火山岩具有类似于富集型洋中脊玄武岩（Ｐ－ＭＯＲＢ）地球化学特征,形成于以双沟蛇绿岩为代表的哀牢山洋盆先期的陆内裂谷构造环境;墨江火山岩具有岛弧火山岩地球化学特征,形成于哀牢山洋盆向西俯冲消减作用下的岛弧构造环境。景东裂谷型火山岩和墨江岛弧火山岩分别代表了     

Hydrothermal alteration vs. ocean-floor metamorphism. A comparison between two case histories: the TAG hydrothermal mound (Mid-Atlantic Ridge) vs. DSDP/ODP Hole 504B (Equatorial East Pacific)

This article presents a review of hydrothermal alteration of the various basaltic rocks forming the oceanic crust, emphasizing especially on the water–rock interaction processes, the petrography and secondary mineralogy of hydrothermally altered rocks from the present-day ocean, hence excluding the ophiolitic complexes. A brief summary of the history of the first studies of hydrothermally altered oceanic rocks leads to a comparison between Miyashiro's concept of ‘ocean-floor metamorphism’ and that of hydrothermal alteration that warrant caution when applying Eskola's metamorphic facies of regional metamorphism to hydrothermally altered oceanic rocks. The functioning of mid-oceanic ridge axial hydrothermal systems, and the role of oceanic Layer-3 gabbros are discussed in detail. The mechanisms of the various alteration processes of the rocks forming the oceanic crust are presented. The case histories of the two examples more particularly studied by the author and his collaborators, are compared, i.e., the DSDP-ODP Hole 504B reference section South of the Costa Rica Ridge, and the TAG active mound at the Mid-Atlantic Ridge. The significance of the paragonitic phyllosilicate in highly altered rocks form the TAG Mound is compared to the other known occurrences of ‘white micas’ in the oceanic crust. The importance of metabasites as major components of the oceanic crust is emphasized. The elemental fluxes resulting from hydrothermal alteration of oceanic rocks in regulating seawater chemistry are only briefly alluded, because this topic is covered by the last article of this thematic issue by J.C. Alt, who assesses the chemical budgets resulting from ocean hydrothermal activity. To cite this article: J. Honnorez, C. R. Geoscience 335 (2003).     

岛弧火山岩成因和地球化学特征

岛弧火山岩主要为俯冲带的俯冲板片脱水形成的富大离子亲石元素流体交代地幔楔,并使其发生部分熔融,产生岛弧岩浆作用而形成的,岩石组合通常为玄武岩—安山岩—英安岩—流纹岩及相应侵入岩组合。它以Al2O3、K2O高,低Ti O2,且K2ONa2O为特征,相对富集LILE,亏损HFSE,特别是Ti、Nb、Ta等。本文主要从岛弧岩浆作用的起因着手,分析流体和熔体对地幔楔的交代作用,以及岛弧岩浆作用过程,进而分析岛弧火山岩的地球化学特征。