Geochemistry and petrogenesis of intrusive and extrusive ophiolitic plagiogranites, Central Anatolian Crystalline Complex, Turkey

Plagiogranites associated with the Sarikaraman ophiolite of the Central Anatolian Crystalline Complex, Turkey, closely resemble other plagiogranites from supra-subduction zone-type ophiolites of Neotethys. The ophiolite is remarkable in displaying a higher proportion of the plagiogranite suite (ca. 10% by volume) than is usually associated with such bodies. The Sarikaraman plagiogranites are represented by intrusive sheets and netvein trondhjemites largely developed at the top of the upper gabbros and as multiphase dykes within the sheeted dyke complex. The plagiogranite dykes are considered to feed extrusive silicified rhyolites associated with the basaltic lavas in the volcanic section of the ophiolite. Field relations suggest that the trondhjemites were probably generated from the roof section of a dynamic and evolving gabbroic magma chamber. Both the deep-seated trondhjemites and the volcanic rhyolites constitute the Sarikaraman plagiogranite suite. Geochemically there is complete overlap between the intrusive trondhjemites and extrusive rhyolites, which are characterised by (MORB-normalized) low HFS element contents with small negative Nb---Ta anomalies and variably enhanced LIL element abundances. Unlike other plagiogranites, however, the Sarikaraman suite is not characterized by consistently low K₂O contents; a feature that reflects the variable mobilization of the LIL elements under lower greenschist facies conditions. The REE are uniformly enriched relative to the basic components of the complex, but have similar normalized patterns exhibiting mild light REE depletion. In terms of their origin, the initial or most primitive plagiogranite melts could have been generated by either fractional crystallization (70–85% of clinopyroxene-feldspar ± amphibole) or partial melting (5–15% batch melting) of a gabbroic ‘source material’, although only the first process can produce most of the range of the plagiogranite compositions. As a group the plagiogranites exhibit some degree of internal variation which can be generated by further fractionation largely dominated by feldspar with minor apatite and amphibole.     

http://www.sciencedirect.com/science/article/pii/S1674987114000401

In this paper, a new discrimination diagram using absolute measures of Th and Nb is applied to post-Archean ophiolites to best discriminate a large number of different ophiolitic basalts. This diagram ...     

Boninitic and tholeiitic basaltic lavas and dikes from dispersed Jurassic East Othris ophiolitic units,Greece: petrogenesis and geodynamic implications

ABSTRACT

Pillow lavas, massive lava flows, and sub-volcanic dikes of tholeiitic basaltic composition are found to be members of the Vrinena, Aerino, Eretria, and Velestino dispersed Middle–Upper Jurassic ophiolitic units in East Othris. The Vrinena and Eretria ophiolitic units appear to have been emplaced onto the Pelagonian continental margin during the Upper Jurassic–Lower Cretaceous, whereas the Aerino and Velestino units seem to have been finally emplaced during post-Palaeocene times. Geochemically these are divided into two groups: Group I includes subduction-related boninites and low-Ti basalts from the Vrinena and Aerino units, and Group II high-Ti basalts show spreading-type characteristics occurring in the Eretria and Velestino units. Primary magma of the Group I volcanics appears to have been formed after high partial melting degrees (~18%) of a highly depleted harzburgitic mantle source, under relatively high temperatures (mantle potential temperature ~1372°C). Petrogenetic modelling also suggests that the primary magma of the Group II volcanics were formed after lower partial melting degrees (~7%) of a moderately depleted mantle source. The petrological and geochemical data from the East Othris dispersed and diversely emplaced ophiolitic units provide evidence of a common intra-oceanic supra-subduction zone (SSZ) origin within the Pindos oceanic strand of the Western Tethys. Specifically, Group I lavas and dikes from Vrinena seem to represent the extrusive part of an almost complete fore- to island-arc ophiolitic sequence. Dikes of Aerino most likely correspond to fore-arc magmatic material that intruded within exhumed serpentinized ultramafic rocks through a subduction channel that developed close to the slab and towards the fore-arc and the accretionary prism. The Group II volcanics either corresponded to a fore-arc magmatic expression, which extruded earlier than Group I volcanics and prior to the establishment of a mature subduction zone, or represent back-arc to island-arc magmatism that was contemporaneous to the fore-arc magmatic activity during rollback subduction.     

The geochemistry and petrogenesis of an ophiolitic sequence from Pindos,Greece

The ophiolites of Northern Pindos have been studied in a section close to the village of Perivoli (Grevena District). The section comprises cumulus rocks ranging from ultramafics to gabbros, overlain by dolerites (non-cumulus microgabbro) capped by thick frequently pillowed lava flows. The sequence is cut by basaltic dykes. While the cumulus rocks and the dolerites are mostly fresh, the lavas and dykes are strongly transformed.Major and trace element (Ni, Cr, Sc, Y, Zr, Nb, Sr, Ba, Zn, Cu, V, Li) data are presented for selected samples from the sequence. For some elements, the volcanic/subvolcanic rocks (flows, dykes, dolerites) exhibit wide chemical characteristics which are considered to mainly reflect variations within the parent magmas. Some lavas appear to be closely comparable with the present-day ocean-floor basalts, while other flows and most of the dykes are strongly depleted in some incompatible elements and are similar to some rocks from immature island arcs. The dolerites have transitional chemical features. The Pindos lavas differ from Western Mediterranean ophiolites in that the former have lower Ti,P,Zr,Y, higher Fe tot. and normally higher Ti/Zr ratio.The volcanic/subvolcanic rocks from Pindos have been derived from separate magmas. Some lavas were possibly produced by variable partial melting of an already depleted mantle source, while the lavas exhibiting ocean-floor affinity were probably generated by partial melting of a less depleted source. The wide chemical variations of the Pindos lavas cannot be easily explained by an ocean-ridge system. An island arc-marginal basin system could better account for the observed chemical features.     

锆石形态的定量研究：福州花岗质复式岩体的成岩机制

在浙闽粤沿海地区出露了一系列中生代的钙碱性－碱性侵入杂岩,其中福州花岗质复式岩体为该区最有代表性的岩体。本文试通过该岩体中早期原生锆石的大小与晶型的形态学研究,揭示这类侵入杂岩的岩石学特征及其成岩机制。锆石的形态学研究表明,钙碱性岩系中锆石群的晶体大小及晶型指数随岩体的定位次序而呈现连续变化的趋势,而碱性岩系中锆石群的形态的分布范围与钙碱性岩系的不连续,其Ｉｐｙ值远远大于钙碱性岩系锆石群的Ｉｐｙ值,它们代表了两个相对独立的成岩作用的产物。电子探针分析发现,福州花岗质复式岩体中锆石晶型的演化基本上是由其内部的微量元素含量控制的,表现为锆石的ＨｆＯ２含量越低,它的Ｉｐｒ值越高;而锆石的（ＴｈＯ２＋Ｙ２Ｏ３）含量越高,它的Ｉｐｙ值越高。锆石的形态学和微量元素地球化学特征表明,三个钙碱性岩体各自经历了非常相似的成岩过程,可能属于同一源区多阶段部分熔融作用的产物,而碱性岩体则来源于该区抽取了钙碱性花岗质岩浆以后残留物质再次部分熔融作用而分离出来的熔体,后者的形成显示了该区的构造背景已经由强烈挤压为主转化为引张、减压为主的造山期后的特征     

Geochemistry and petrogenesis of Cretaceous oceanic plateau lavas in eastern Jamaica

Basaltic lavas of Turonian to Coniacian age belonging to the Bath–Dunrobin Formation occur with intercalated island arc tuffs in the south of the Blue Mountain inlier, have been interpreted as being derived from the Caribbean oceanic plateau. This study presents new major and trace element and Sr–Pb–Nd–Hf isotopic data for these igneous rocks. The Jamaican rocks are altered by tropical weathering, hydrothermal and metamorphic processes, which have mobilised many of their elements (e.g. K and Ba). Consequently, the basalts and dacitic tuffs have been classified by using immobile trace elements. The trace element and _Hf(i)–_Nd(i) geochemistry suggests that the basaltic lavas are derived from a chemically similar source region by variable degrees of partial melting. The Caribbean plateau basalts lie on a mixing line between a depleted plume component and HIMU in Nd–Hf isotopic space. The Pb isotope data also demonstrate that the Jamaican plateau lavas are composed of a larger HIMU component than the other plateau lavas within the Caribbean region. The intercalated island arc tuffs are the first to be found in any oceanic plateau succession in the Caribbean and imply that the Caribbean oceanic plateau at  90 Ma was relatively close to the subduction zone along South America and the Great Arc of the Antilles.     

Geochronology and geochemistry of the Hegenshan ophiolitic complex: Implications for late-stage tectonic evolution of the Inner Mongolia-Daxinganling Orogenic Belt, China

The Hegenshan ophiolite in the Inner Mongolian-Daxinganling Orogenic Belt (IMDOB), northern China, consists of several discontinuous blocks composed dominantly of serpentinized ultramafic rocks with subordinate cumulate gabbros, mafic lavas and dikes, intruded by younger granodiorite dikes. The ultramafic rocks are highly depleted, serpentinized harzburgites with minor dunite, characterized by relative enrichment in large ion lithophile elements (LILE, e.g., Ba and Rb) and light rare earth elements (LREE). They are interpreted to be oceanic mantle that has undergone extensive melt extraction and variable degrees of metasomatism. The cumulate rocks consist mainly of gabbro and troctolite with LREE-depleted chondrite-normalized REE patterns showing significant positive Eu anomalies. They are enriched in LILE, depleted in Nb, and have high positive ε_Nd(t) (+8 to +11), suggesting derivation from a subduction-modified N-MORB-like source. The gabbros and mafic dikes have essentially the same age (295 ± 15 and 298 ± 9 Ma, respectively). The mafic dikes have flat to LREE-depleted, chondrite-normalized REE patterns, are depleted in Nb, enriched in LILE and have N-MORB-type Nd isotopic signatures (ε_Nd(t) = +8.1 to +10). The mafic lavas, erupted at 293 ± 1 Ma, can be divided into two groups; one composed of strongly deformed metabasalts similar in chemical and Nd–Sr isotopic compositions to the mafic dikes, and the other composed of undeformed and unmetamorphosed basalts with oceanic island basalt (OIB)-like trace element signatures and Nd isotopic compositions. The granodiorite dikes, which were intruded at 244 ± 4 Ma, have LREE-enriched, chondrite-normalized REE patterns with no Eu anomalies. Their abnormally high ε_Nd(t) values (+6.3 to +6.8) and low I_Sr (0.70412 to 0.70450) suggest formation from melts derived from thickened oceanic crust during or shortly after closure of the Paleo-Asian Ocean. The structure, lithology and geochemistry of the Hegenshan ophiolite suggest that it is a Cordilleran-type body formed in a supra-subduction zone (SSZ) environment and amalgamated by collision of several fragments of Paleo-Asian lithosphere. Final emplacement and amalgamation occurred in the latest Permian or earliest Triassic.     

Cretaceous tectonic evolution of the Neo-Tethys in Central Iran:Evidence from petrology and age of the Nain-Ashin ophiolitic basalts

The Nain and Ashin ophiolites consist of Mesozoic melange units that were emplaced in the Late Cretaceous onto the continental basement of the Central-East Iran microcontinent(CEIM).They largely consist of serpentinized peridotites slices;nonetheless,minor tectonic slices of sheeted dykes and pillow lavas-locally stratigraphically associated with radiolarian cherts-can be found in these ophiolitic melanges.Based on their whole rock geochemistry and mineral chemistry,these rocks can be divided into two geochemical groups.The sheeted dykes and most of the pillow lavas show island arc tholeiitic(IAT)affinity,whereas a few pillow lavas from the Nain ophiolites show calc-alkaline(CA)affinity.Petrogenetic modeling based on trace elements composition indicates that both IAT and CA rocks derived from partial melting of depleted mantle sources that underwent enrichment in subduction-derived components prior to melting.Petrogenetic modeling shows that these components were represented by pure aqueous fluids,or sediment melts,or a combination of both,suggesting that the studied rocks were formed in an arc-forearc tectonic setting.Our new biostratigraphic data indicate this arc-forearc setting was active in the Early Cretaceous.Previous tectonic interpretations suggested that the Nain ophiolites formed,in a Late Cretaceous backarc basin located in the south of the CEIM(the so-called Nain-Baft basin).However,recent studies showed that the CEIM underwent a counter-clockwise rotation in the Cenozoic,which displaced the Nain and Ashin ophiolites in their present day position from an original northeastward location.This evidence combined with our new data and a comparison of the chemical features of volcanic rocks from different ophiolites around the CEIM allow us to suggest that the Nain-Ashin volcanic rocks and dykes were formed in a volcanic arc that developed on the northern margin of the CEIM during the Early Cretaceous in association with the subduction,below the CEIM,of a Neo-Tethys oceanic branch that was existing between the CEIM and the southern margin of Eurasia.As a major conclusion of this paper,a new geodynamic model for the Cretaceous evolution of the CEIM and surrounding Neo-Tethyan oceanic basins is proposed.     

坦桑尼亚伦圭新生代火山岩的地球化学特征及岩石成因

伦圭新生代火山岩位于东非裂谷西支最南端,已有的大量地质与地球化学证据表明伦圭火山岩是典型的碱性双峰式火山岩,其SiO2含量在46％～56％之间出现明显的间断.基性火山岩和酸性火山岩均表现出富集轻稀土元素,轻、重稀土元素强烈分馏,无明显Eu异常的特征.基性岩大离子亲石元素Rb、Ba、Th、U、Sr富集,高场强元素Zr、H...     

洞错盆地蛇绿岩地球化学特征及大地构造意义

本文以改则的洞错盆地蛇绿岩为研究对象,开展了洞错盆地蛇绿岩的岩石学、岩相学及地球化学方面的研究工作。结果表明：地幔橄榄岩以方辉橄榄岩为主,为烟斗型稀土元素配分型式;形成于熔融程度较高的地幔残余物质,具有Nb、Ta负异常。辉绿岩稀土元素配分型式与N-MORB类似,其稀土元素来自亏损的软流圈地幔;Ta、Ti、Y等高场强元素分布特征与N-MORB相似;辉绿岩既有MORB特征又有IAT特征,在洋内弧后盆地扩张环境中形成。辉长岩稀土配分曲线与N-MORB的类似;微量元素中K、Rb、Ba等富集,Nb、Ta亏损,有岛弧火山岩的特征,与典型的N-MORB特征有区别;既有MORB特征,也显示了俯冲带物质的参与,为消减带上弧后盆地次级扩张产生的新洋壳。因此,洞错蛇绿岩为SSZ型蛇绿岩。     

The Koshrabad granite massif in Uzbekistan: petrogenesis, metallogeny, and geodynamic setting

The Koshrabad massif, referred to as the Hercynian postcollisional intrusions of the Tien Shan, is composed of two rock series: (1) mafic and quartz monzonites and (2) granites of the main phase. Porphyritic granitoids of the main phase contain ovoids of alkali feldspar, often rimmed with plagioclase. Mafic rocks developed locally in the massif core resulted from the injections of mafic magma into the still unconsolidated rocks of the main phase, which produced hybrid rocks and various dike series. All rocks of the massif are characterized by high f (Fe/(Fe + Mg)) values and contain fayalite, which points to the reducing conditions of their formation. Mafic rocks are the product of fractional crystallization of alkali-basaltic mantle melt, and granitoids of the main phase show signs of crustal-substance contamination. In high f values and HFSE contents the massif rocks are similar to A-type granites. Data on the geochemical evolution of the massif rocks confirm the genetic relationship of the massif gold deposits with magmatic processes and suggest the accumulation of gold in residual acid melts and the rapid formation of ore quartz veins in the same structures that controlled the intrusion of late dikes. The simultaneous intrusion of compositionally different postcollisional granitoids of the North Nuratau Ridge, including the Koshrabad granitoids, is due to the synchronous melting of different crustal protoliths in the zone of transcrustal shear, which was caused by the ascent of the hot asthenospheric matter in the dilatation setting. The resulting circulation of fluids led to the mobilization of ore elements from the crustal rocks and their accumulation in commercial concentrations.     

Sanukite（赞岐岩）的地球化学特征、成因及其地球动力学意义

赞岐岩 (サヌカイト ,sanukite)是指发现于日本四国北部的一种富Mg的火山岩 ,主要产于日本中新世 (11～14Ma)Setouchi火山岩带 ,是一种黑色玻璃质的火山岩。其化学成分以富Si质 (安山英安质 )、具很高的Mg# 值 (>0 .6 )、高的Cr、Ni丰度和K/Na值 (0 .33～ 0 .5 2 )为特征。赞岐岩的形成与菲律宾海板块年轻的热的岩石圈俯冲和四国盆地的张开有关 ,产于岛弧的弧前或弧后盆地环境。赞岐岩不只代表火山岩 ,也包括侵入岩。Shirey和Hanson(1984 )将该术语引入太古宙 ,将太古宙具上述赞岐岩特征 (Si过饱和、Mg# 高和Ni、Cr、LILE含量高 )的深成岩和火山岩称为sanukite岩套。赞岐岩与埃达克岩具有大体类似的地球化学特征 ,但前者更富Mg、Cr和Ni,表明赞岐岩可以直接由地幔岩部分熔融形成 ,而埃达克岩只能由玄武岩部分熔融形成。现代的赞岐岩很少见 ,而太古宙的赞岐岩比较常见 ,暗示太古宙导致板片熔融的消减的岩石圈本身或上地幔可能具有更高的温度。赞岐岩集中出现在晚太古代 (<3.0Ga) ,表明板块消减作用可能在 3.0Ga之后才成为一个重要的过程 ,晚太古代赞岐岩的出现可能标志着现代类型板块构造的开始     

西准噶尔蛇绿混杂岩中的白云石大理岩和石榴角闪岩：早古生代残余洋壳深俯冲的证据

本文在描述达拉布特和克拉玛依蛇绿岩中四个典型剖面(达拉布特、萨尔托海、白碱滩和百口泉)的基础上,通过研究变白云石大理岩和石榴角闪岩的形成和演化过程,展示西准噶尔蛇绿混杂岩的复杂性。白碱滩白云石大理岩是尖晶石二辉橄榄岩变质反应的产物。变质反应导致单斜辉石转变为白云石+石英+磁铁矿,橄榄石和斜方辉石先转变为蛇纹石+磁铁矿,蛇纹石再转变为白云石+石英+磁铁矿。透辉石+CO₂=白云石+石英+磁铁矿以及蛇纹石+CaCO₃=白云石+石英 +磁铁矿+H₂O这两个变质反应基本同时发生,他们以及石英—柯石英相变关系所限定的P-T空间(660~670℃,26.5~27.5 kbar)代表白云石大理岩的形成温度和压力。白云石大理岩与尖晶石二辉橄榄岩在一个不大的区域共存,说明循环到地球深部的尖晶石二辉橄榄岩(即：白云石大理岩的原岩)折返到地壳浅部后又与蛇绿岩中未俯冲的尖晶石二辉橄榄岩混杂在一起。因此,克拉玛依蛇绿混杂岩代表古俯冲带的位置。变辉长岩和尖晶石二辉橄榄岩中的单斜辉石均发育出溶结构(出溶尖晶石和斜方辉石)。这些出溶结构是蛇绿岩快速上升就位时由于温度和压力突然降低辉石发生分解反应的产物。因此,西准噶尔蛇绿混杂岩中的岩石组合记录着蛇绿岩形成时期、以及之后部分岩块通过俯冲带循环到地幔深处(最大深度~70km)并折返到地壳浅部的全过程。西准噶尔蛇绿混杂岩带是一个多时期、多阶段和多成因岩石的混杂体。     

桂北罗城地区云煌岩成因——地球化学及U-Pb年龄约束

对桂北罗城地区云煌岩开展系统的地球化学研究及LA-ICP-MS锆石U-Pb测年,获得锆石U-Pb年龄为248 ±1 Ma。其富钾（K2O/Na2O=4.23~136.2）,富碱（K2O+Na2O=6.86%~8.03%）,钾的含量显著高于大陆地壳平均值,富集轻稀土元素及大离子亲石元素,亏损高场强元素,具有较低的La/Nb值,Nb/U值低于洋中脊玄武岩、岛弧玄武岩及上地壳值,与全球平均俯冲沉积物接近,表明源区可能为早期俯冲交代作用形成的富集地幔。结合区域构造背景分析,推测桂北罗城地区云煌岩形成在中生代三叠纪（248±1 Ma）华南陆内岩石圈伸展减薄的背景下,软流圈上涌促使交代富集地幔发生部分熔融形成云煌岩岩浆,区域上NNE向的深大断裂为岩浆喷发提供通道。     

蛇绿岩就位机制及时限

蛇绿岩就位机制可以划分出4种:1)碰撞仰冲型:被动大陆边缘或岛弧与洋壳碰撞时,俯冲到一定深度的硅铝质物质在浮力作用下折返,并上驮相对完整的大洋岩石圈残片到达地表;2)增生底垫型:洋底、海沟沉积物及海底较高地形的上层物质从俯冲板块上刮削下来,持续底垫到上覆板块之下,使大洋岩石圈残片逐渐被动抬高;3)俯冲剥离型:断裂发育相...     

喜马拉雅造山带新生代花岗岩中两类石榴石的地球化学特征及其在地壳深熔作用中的意义

在喜马拉雅碰撞造山带中,石榴石是变泥质岩的主要造岩矿物,也是花岗岩或淡色体的重要副矿物,保存了有关地壳深熔作用的关键信息,是揭示大型碰撞造山带中-下地壳物质的物理和化学行为的重要载体。在喜马拉雅造山带内,新生代花岗质岩石(淡色花岗岩和混合岩中的淡色体)含两类石榴石,大多数为岩浆型石榴石,自形-半自形,不含包裹体,但淡色体中含有港湾状的混合型石榴石。岩浆型石榴石具有以下地球化学特征:(1)从核部到边部,显示了典型的"振荡型"生长环带;(2)富集HREE,亏损LREE,从核部到边部,Hf、Y和HREE含量降低;(3)显著的Eu负异常;(4)相对于源岩中变质石榴石,Mn和Zn的含量显著增高。岩相学和地球化学特征都表明:变泥质岩熔融形成的熔体(淡色体)捕获了源岩的变质石榴石,熔体与石榴石反应导致大部分元素的特征被改变,只在核部保留了源岩的部分信息。同时,在花岗质熔体结晶过程中,形成少量的岩浆型石榴石。这些石榴石摄取了熔体中大量的Zn,浓度显著升高,在斜长石和锆石同步分离结晶作用的共同影响下,石榴石中Eu为明显负异常,Hf、Y和HREE浓度从核部到边部逐渐降低。上述数据和结果表明,花岗岩中石榴石的矿物化学特征记录了精细的有关花岗岩岩浆演化的重要信息。     

The geochemistry and petrogenesis of the lavas of the Vulsinian District,Roman province,Central Italy

The Vulsinian lavas are dominated by a suite of undersaturated leucite-bearing basic to intermediate compositions. The remaining lavas are mainly oversaturated and have shoshonitic affinities. One hundred and thirty-five samples have been analysed for major elements and most for 20 trace elements. Twenty-seven lavas have been analysed for REE. They are all perpotassic (for the undersaturated lavas: K₂O/Na₂O=2–8) and have very high LIL element concentrations, (e.g. Rb=400–800 ppm, Th=25–150 ppm, REE/REE_cho=c.200, (LREE/HREE)_cho=c.20) even in the most basic rocks.The undersaturated lavas appear to be interrelated by fractional crystallization of cpx±olivine (from 14 to 11 wt.% CaO), cpx+leu±plg±mica (from 11 to 8 wt.% CaO), cpx+leu+plg+apa+magnetite±mica (from 8 to 5 wt.% CaO), and additional sanidine (or hyalophane)±haüyne (from 5 to 3 wt.% CaO). The saturated lavas and the few slightly undersaturated shoshonite basalts are thought to be evolved from the undersaturated magma(s) by crustal contamination or mixing with silica-rich magmas. The parental Vulsinian magma having: Mg-value=c.73, Cr=300–700 ppm, Ni=100–125 ppm, Sc= 40–50 ppm, Fo_89–92, Di_77–97 approximates a primary, mantle-derived liquid. Enrichment in LIL elements (incl. REE) and LREE/HREE suggest a small degree of partial melting from fertile mantle; whereas the low concentrations of Na, Ti and P suggest larger degrees of partial melting. This indicates that either the primary magma or the parental mantle was metasomatized by a fluid, which previously equilibrated with subducted continental material. This model agrees with published high ¹⁸O, high ⁸⁷Sr/⁸⁶Sr and low ¹⁴³Nd/¹⁴⁴Nd.     

Late Paleozoic-Mesozoic subduction and accretion of the Paleo-Pacific Plate:Insights from ophiolitic rocks in the Wandashan accretionary complex,NE China

The Wandashan accretionary complex(AC),consisting of the Raohe and Yuejinshan complexes,is located on the continental margin of Northeast Asia and represents an excellent source of information about Paleo-Pacific subduction and accretion.However,the protolith nature and tectonic evolution of the Wandashan AC are under debate.This contribution reports new geochronological,geochemical,and Sr-Nd-Pb-Hf isotopic data for ophiolitic rocks from the Wandashan AC.The 169-166 Ma plagioclasites and homogeneous gabbros from the Raohe complex are OIBs while 228-214 Ma homogeneous gabbros are continental VABs.Cumulate gabbros from the Yuejinshan complex formed at 280-278 Ma and～220 Ma and have similar characteristics with E-MORB and N-MORB,respectively.They are BABBs and their primary magma was derived from a source region between EMI and EMII that was affected by con-tinental crustal contamination as well as subduction-zone metasomatism.Combined with previous stud-ies,we suggest that the onset of subduction of the Paleo-Pacific Plate was in the Early Permian.Subsequently,a back-arc basin,whose present suture is on the eastern margin of the Jiamusi Massif,formed and widened during 280-232 Ma,after which the basin closed and BABBs were emplaced to form the Yuejinshan complex during 210-180 Ma.The formation of VABs of the Raohe complex is coincident with the closure of the back-arc basin,and together with the 169-166 Ma OIBs,they constitute a major part of the Raohe complex.The accretionary process was completed during 133-131 Ma.Taken together,the ophiolitic rocks indicating multistage magmatism in the Paleo-Wandashan region recorded the formation-closure process of back-arc basin and the accretionary process of the Wandashan AC,during the westward subduction of the Paleo-Pacific plate.The back-arc basin identified in our study sheds new lights on geodynamic evolution model of subduction and accretion of the Paleo-Pacific Plate on the continental margin of NE Asia.     

油源对比微量元素地球化学研究进展

原油中的微量元素地球化学组成可以应用于油源对比,指标可以归纳为3类:①所含元素的聚类分析及其所反映的元素分布总体特征;②不同族、不同类型元素的组成,特别是过渡族金属元素;③稀土元素。但对于哪些微量元素可以应用于油源对比,哪些具有普遍意义,在不同地区是否具有适用性,影响其油源对比应用有效性的因素有哪些,主控因素是什么,仍然不甚清楚,由此导致很多方面的认识还不甚成熟,成功应用的实例相对常规的有机地球化学研究不多。原油中的微量元素主要来源于外部成油和运聚环境,在原油生成和运聚过程中,通过烃—水—岩之间的复杂有机—无机相互作用以金属卟啉螯合物、有机络合物或吸附态的形式聚集于原油中,并且沥青质是原油中微量元素的主要载体,元素组成在此过程中发生分异。此外,原油在自身形成与演化过程中也会发生元素组成的分异,影响因素包括油源母质类型、成熟度、次生变化等。在这些过程中,元素地球化学性质的不同会使原油中的元素组成出现差异,基本不发生/少发生变化的元素即可能是好的油源对比指标,这是应用微量元素进行油源对比的原理和理论基础。