新疆北山罗东岩体橄榄石特征对岩浆演化和硫化物熔离的指示

 罗东岩体是新疆北山地区沿北山裂谷带的一个典型镁铁质—超镁铁质岩体,研究表明坡北杂岩带与东天山杂岩带的产出时代具有时间上的耦合性,并且其大地构造产出背景与东天山镁铁质—超镁铁质杂岩也具有一定的关系,可能与碰撞背景下幔源物质的上侵有关,并且受到俯冲板片的影响。该岩体具有较完整的岩相分异,包括橄榄岩、辉石岩、辉长岩。镁橄榄石指数Fo值为81~88,属于贵橄榄石,橄榄石具有环带结构,从橄榄石边缘到中心,Mg逐渐升高,说明橄榄石在岩浆演化过程中发生了与残余岩浆的交换反应。通过主量元素反演,得到原始岩浆中w(MgO)=8%、w(FeO)=6%,属于拉斑玄武岩。通过橄榄石的定量模拟计算,显示罗东岩体的橄榄石为正常岩浆演化的产物,橄榄石中Ni的质量分数没有发生明显亏损,这些证据表明岩浆可能没有经历过显著的硫化物熔离作用。     

咸沟岩体地质地球化学特征及成岩机制探讨

咸沟岩体位于华北地台北缘西段．主岩体为二云母花岗岩，成岩时代为３９９．８±１．８２．１Ｍａ，内有岩浆演化晚期的白云母花岗岩侵入，与主岩体有迥然不同的地球化学特点．前者显示出不同地壳物质混合的岩浆特征，后者属典型的Ｓ型花岗岩．结合区域构造演化分析，认为咸沟岩体形成于拉张环境，源岩可能为下地壳的英云闪长岩．下地壳的深熔岩浆在上升迁移过程中，遭受了富含泥质的陆壳物质的强烈混染，混染岩浆向Ｓ型岩浆方向演化．     

甘肃北山白山堂斑岩型铜铅矿床成矿地质特征

白山堂铜铅矿大地构造位置位于哈萨克斯坦板块、马鬃山中间地块、马鬃山地体东南裂谷边缘,营毛沱-铅炉子沟-白山堂构造岩浆带东段的白山堂半圆形构造岩浆弧上。处于方山口-七角井-白山堂金、铜、镍、钨、铁、锰和钒-磷-铀Ⅳ级成矿带内。铜铅矿自下而上具有斑岩型-矽卡岩型-热液脉型成矿系列的斑岩型成矿地质特征。     

新疆黄山含铜镍矿镁铁-超镁铁杂岩体的岩石学特征及其形成演化规律

新疆黄山含铜镍矿镁铁-超镁铁杂岩体热侵位于下石炭统干洞组变余砂岩、砂质灰岩、细碧玢岩中。杂岩体分为三个侵入期,其中第二期岩石构成了黄山岩体主体。分异较好,由下向上、由西向东可分出辉石橄榄岩相、橄榄二辉岩相、二辉岩相、苏长辉长岩相、辉长岩相。杂岩体是原始岩浆经过深部液态分异和金属硫化物熔离后的派生岩浆结晶形成。这种派生岩浆具富镁、贫碱、低钙特征,归属于橄榄拉斑玄武岩系列。杂岩体结晶温度为1500—860℃,压力为0.26—0.250GPa,fo_2为10~(-11)—10~(-13)。     

米易新街层状基性超基性侵入体的岩石学特征及其成因探讨

一、岩体地质概况新街岩体位于米易县城北八公里,新街附近。它是一个小型的、但具有明显分异韵律的单斜层状岩体,长约1.2公里,宽在0.5—0.8公里,面积约一平方公里,总体总厚约580米,四周和底板都为玄武岩包围。据接触带玄武岩的角岩化及岩体边缘形成3—6米厚的边缘相细粒辉长岩(照片1),可以证明岩体侵入玄武岩。层状系列主要由超基性出到辉绿辉长岩     

内蒙古阿巴嘎旗北部侵入岩体地质地球化学特征及成因

内蒙古阿巴嘎旗北部位于西伯利亚板块东南大陆边缘晚古生代陆缘增生带,地处二连—贺根山板块对接带的西北侧.通过对三类侵入岩体样品主微量元素地球化学特征的分析,结果显示正长花岗岩体(包括中细粒正长花岗岩、条纹正长花岗岩、钠长正长花岗岩)和碱长花岗岩体(中粗粒钠闪正长花岗岩、钠闪条纹正长花岗岩)都具有A型花岗岩的特征,碎裂岩化花岗斑岩岩体兼具A型和S型花岗岩的特征.三类侵入岩体岩浆成因与陆壳变杂砂岩部分熔融有关,均产于后造山构造环境.     

富宁基性岩区尾硐铜镍硫化物矿床矿化特征及矿床成因探讨

通过对尾硐铜镍硫化物矿床矿区地质特征、矿体分布特征、矿床矿化特征和S同位素分析,认为该矿区内各岩相带呈渐变过渡关系,为同期侵入岩体,存在深部岩浆熔离作用。橄榄苏长辉长岩和辉长苏长岩是矿区内主要赋矿岩体。S同位素分析显示其主要为幔源原生硫;但也可能有硫通过地壳混染作用加入。含矿岩浆深部熔离和岩体侵位后的岩浆分异结晶是导致金属硫化物富集成矿的主要过程。岩浆期后热液的叠加改造作用对部分地段的成矿物质富集有重要贡献。     

塔里木北山地区橄榄岩-辉石岩的微量元素地球化学特征及其深部过程

橄榄岩—辉石岩是塔里木北山地区镁铁一超镁铁岩体中非常重要的岩石类型．橄榄岩一辉石岩的主元素特征表明其主要为准铝质岩石，同时存在过碱质系列岩石．在稀土元素CI标准化配分图上，表现为LREE富集，HREE配分曲线平坦；在微量元素N-MORB标准化的蛛网图上，表现为C8，U，Pb等大离子低场强元素强烈富集，Nb，Ta，Zr，Ti等高场强元素明显亏损；w（Sm）／w（Nd）值特征表明研究区橄榄一辉石岩源于地幔源区．微量元素地球化学研究表明，塔里木北山地区橄榄岩一辉石岩形成于活动大陆边缘弧后张裂构造环境，为构造应力释放阶段的产物．本文及前期研究结果表明：橄榄岩、辉石岩和辉长岩的地球化学特征研究在解决深部地质过程方面具有较大潜力．     

智利MG矿区辉长岩-二长闪长岩地球化学特征研究及其构造意义

智利MG矿区位于安塔卡玛断裂南部,该断裂带发育大量的铁铜金多金属矿床,是智利重要的铁氧化物铜金矿成矿带。MG矿区Kiet(gd)单元岩体与成矿关系密切,该岩体主要由一套辉长岩-二长闪长岩组成。岩石化学成分显示,岩石具有高Al_2O_3(6.71%~19.63%)、高CaO(7.24%~11.54%、富Na(Na_2O/K_2O=0.99~3.21)、高Mg~#(40~58)、低K_2O(0.62%~2.24%)、低TiO_2(Ti O20.5%)和低P_2O_5(P2O50.1%)的特点。微量元素中大离子亲石元素Rb,Ba,Th,U元素相对富集,而高场强元素Ta,Nb,Zr,Fh呈明显亏损,δEu值介于0.71~1.15之间,具有轻微负铕异常;研究表明,该区岩浆演化过程中可能存在岩浆分异作用,但以平衡部分熔融作用为主。该区辉长岩-二长闪长岩形成于活动大陆边缘或岛弧环境,该区成岩、成矿作用与中生代太平洋板块的俯冲密切相关。     

长江中下游铜金成矿岩体稀土地球化学特征

长江中下游铜金成矿岩体的岩浆作用机理研究对于岩体含矿性评价和铜金找矿具有重要意义。代表性岩体的稀土地球化学研究表明本区铜金成矿岩体是壳幔混合型岩浆岩，其岩浆作用过程是导源于地幔的岩浆与导源于地壳的岩浆沿超壳断裂混合上侵，金主要富集于幔源岩浆，铜主要富集于壳源岩浆，由于铜金成矿岩体都是壳幔混合型岩浆岩，故铜金矿化总是形影相随；又因为它们的壳幔物质比例各异，故铜金矿化又适度分离。     

Contrasting origins of the upper mantle revealed by hafnium and lead isotopes from the Southeast Indian Ridge

The origin of the isotopic signature of Indian mid-ocean ridge basalts has remained enigmatic, because the geochemical composition of these basalts is consistent either with pollution from recycled, ancient altered oceanic crust and sediments, or with ancient continental crust or lithosphere. The radiogenic isotopic signature may therefore be the result of contamination of the upper mantle by plumes containing recycled altered ancient oceanic crust and sediments, detachment and dispersal of continental material into the shallow mantle during rifting and breakup of Gondwana, or contamination of the upper mantle by ancient subduction processes. The identification of a process operating on a scale large enough to affect major portions of the Indian mid-ocean ridge basalt source region has been a long-standing problem. Here we present hafnium and lead isotope data from across the Indian-Pacific mantle boundary at the Australian-Antarctic discordance region of the Southeast Indian Ridge, which demonstrate that the Pacific and Indian upper mantle basalt source domains were each affected by different mechanisms. We infer that the Indian upper-mantle isotope signature in this region is affected mainly by lower continental crust entrained during Gondwana rifting, whereas the isotope signature of the Pacific upper mantle is influenced predominantly by ocean floor subduction-related processes.     

Continental subduction channel processes: Plate interface interaction during continental collision

The study of subduction-zone processes is a key to development of the plate tectonic theory. Plate interface interaction is a basic mechanism for the mass and energy exchange between Earth＇s surface and interior. By developing the subduction channel model into continental collision orogens, insights are provided into tectonic processes during continental subduction and its products. The continental crust, composed of felsic to mafic rocks, is detached at different depths from subducting continental lithosphere and then migrates into continental subduction channel. Part of the subcontinental lithospheric mantle wedge, composed of perido- tile, is offscrapped from its bottom. The crustal and mantle fragments of different sizes are transported downwards and upwards inside subduction channels by the corner flow, resulting in varying extents of metamorphism, with heterogeneous deformation and local anatexis. All these metamorphic rocks can be viewed as tectonic melanges due to mechanical mixing of crust- and man- lie-derived rocks in the subduction channels, resulting in different types of metamorphic rocks now exposed in the same orogens. The crust-mantle interaction in the continental subduction channel is realized by reaction of the overlying ancient subcontinental lithospheric mantle wedge peridotite with aqueous fluid and hydrous melt derived from partial melting of subducted continental basement granite and cover sediment. The nature of premetamorphic protoliths dictates the type of collisional orogens, the size of ultrahigh-pressure metamorphic terranes and the duration of ultrahigh-pressure metamorphism.     

北祁连直河蛇绿岩的地质和地球化学特征

直河蛇绿岩是在北祁连造山带中新发现的,该蛇绿岩由地幔橄榄岩、辉长辉绿岩、玄武岩、硅质岩等组成,以构造岩片为接触关系.蛇绿岩中岩石地球化学特征表明,该蛇绿岩具有大洋拉斑玄武岩的特征,同时具有某些岛弧特征,基性岩类的REE球粒陨石标准化配分模式为平坦型和LREE亏损型,超基性岩为亏损地幔源和富集地幔物质加入的混合成因,稀土分配型式不同于典型洋脊玄武岩,源区为亏损地幔和富集地幔的混合源.北祁连自寒武纪末大陆裂解,完成大陆裂陷向洋盆的转化,至奥陶纪形成沟弧盆体系.直河蛇绿岩属于弧后盆地扩张环境的产物.     

东濮凹陷北部沙三段泥页岩岩相特征

东濮凹陷北部沙三段泥页岩厚度大、分布广,具有良好的页岩气生烃潜力;但陆相湖盆泥页岩非均质性强,不同岩相生烃能力和储集性能差异较大。为厘清不同岩相的含油气性特征,通过偏光显微镜、X衍射等手段研究泥页岩微观岩相类型,发现东濮凹陷北部沙三段主要发育块状粉砂质泥岩相、纹层状膏质泥岩相、纹层状灰质泥岩相三种典型岩相及多种过渡岩相。通过对比不同泥页岩相地球化学特征、荧光特征、试油试气数据,发现深湖-半深湖环境中的纹层状灰质泥岩相是页岩油气赋存的优势岩相。     

Continental mantle signature of Bushveld magmas and coeval diamonds

The emplacement of the 2.05-billion-year-old Bushveld complex, the world's largest layered intrusion and platinum-group element (PGE) repository, is a singular event in the history of the Kaapvaal craton of southern Africa, one of Earth's earliest surviving continental nuclei. In the prevailing model for the complex's mineralization, the radiogenic strontium and osmium isotope signatures of Bushveld PGE ores are attributed to continental crustal contamination of the host magmas. The scale of the intrusion and lateral homogeneity of the PGE-enriched layers, however, have long been problematical for the crustal contamination model, given the typically heterogeneous nature of continental crust. Furthermore, the distribution of Bushveld magmatism matches that of seismically anomalous underlying mantle, implying significant interaction before emplacement in the crust. Mineral samples of the ancient 200-km-deep craton keel, encapsulated in macrodiamonds and entrained by proximal kimberlites, reveal the nature of continental mantle potentially incorporated by Bushveld magmas. Here we show that sulphide inclusions in approximately 2-billion-year-old diamonds from the 0.5-billion-year-old Venetia and 1.2-billion-year-old Premier kimberlites (on opposite sides of the complex) have initial osmium isotope ratios even more radiogenic than those of Bushveld sulphide ore minerals. Sulphide Re-Os and silicate Sm-Nd and Rb-Sr isotope compositions indicate that continental mantle harzburgite and eclogite components, in addition to the original convecting mantle magma, most probably contributed to the genesis of both the diamonds and the Bushveld complex. Coeval diamonds provide key evidence that the main source of Bushveld PGEs is the mantle rather than the crust.     

Whole-mantle convection and the transition-zone water filter

Because of their distinct chemical signatures, ocean-island and mid-ocean-ridge basalts are traditionally inferred to arise from separate, isolated reservoirs in the Earth's mantle. Such mantle reservoir models, however, typically satisfy geochemical constraints, but not geophysical observations. Here we propose an alternative hypothesis that, rather than being divided into isolated reservoirs, the mantle is filtered at the 410-km-deep discontinuity. We propose that, as the ascending ambient mantle (forced up by the downward flux of subducting slabs) rises out of the high-water-solubility transition zone (between the 660 km and 410 km discontinuities) into the low-solubility upper mantle above 410 km, it undergoes dehydration-induced partial melting that filters out incompatible elements. The filtered, dry and depleted solid phase continues to rise to become the source material for mid-ocean-ridge basalts. The wet, enriched melt residue may be denser than the surrounding solid and accordingly trapped at the 410 km boundary until slab entrainment returns it to the deeper mantle. The filter could be suppressed for both mantle plumes (which therefore generate wetter and more enriched ocean-island basalts) as well as the hotter Archaean mantle (thereby allowing for early production of enriched continental crust). We propose that the transition-zone water-filter model can explain many geochemical observations while avoiding the major pitfalls of invoking isolated mantle reservoirs.     

Helium isotopic evidence for episodic mantle melting and crustal growth

The timing of formation of the Earth's continental crust is the subject of a long-standing debate, with models ranging from early formation with little subsequent growth, to pulsed growth, to steadily increasing growth. But most models do agree that the continental crust was extracted from the mantle by partial melting. If so, such crustal extraction should have left a chemical fingerprint in the isotopic composition of the mantle. The subduction of oceanic crust and subsequent convective mixing, however, seems to have largely erased this record in most mantle isotopic systems (for example, strontium, neodymium and lead). In contrast, helium is not recycled into the mantle because it is volatile and degasses from erupted oceanic basalts. Therefore helium isotopes may potentially preserve a clearer record of mantle depletion than recycled isotopes. Here I show that the spectrum of 4He/3He ratios in ocean island basalts appears to preserve the mantle's depletion history, correlating closely with the ages of proposed continental growth pulses. The correlation independently predicts both the dominant 4He/3He peak found in modern mid-ocean-ridge basalts, as well as estimates of the initial 4He/3He ratio of the Earth. The correspondence between the ages of mantle depletion events and pulses of crustal production implies that the formation of the continental crust was indeed episodic and punctuated by large, potentially global, melting events. The proposed helium isotopic evolution model does not require a primitive, undegassed mantle reservoir, and therefore is consistent with whole mantle convection.     

The return of subducted continental crust in Samoan lavas

Substantial quantities of terrigenous sediments are known to enter the mantle at subduction zones, but little is known about their fate in the mantle. Subducted sediment may be entrained in buoyantly upwelling plumes and returned to the Earth's surface at hotspots, but the proportion of recycled sediment in the mantle is small, and clear examples of recycled sediment in hotspot lavas are rare. Here we report remarkably enriched 87Sr/86Sr and 143Nd/144Nd isotope signatures in Samoan lavas from three dredge locations on the underwater flanks of Savai'i island, Western Samoa. The submarine Savai'i lavas represent the most extreme 87Sr/86Sr isotope compositions reported for ocean island basalts to date. The data are consistent with the presence of a recycled sediment component (with a composition similar to the upper continental crust) in the Samoan mantle. Trace-element data show affinities similar to those of the upper continental crust--including exceptionally low Ce/Pb and Nb/U ratios--that complement the enriched 87Sr/86Sr and 143Nd/144Nd isotope signatures. The geochemical evidence from these Samoan lavas significantly redefines the composition of the EM2 (enriched mantle 2; ref. 9) mantle endmember, and points to the presence of an ancient recycled upper continental crust component in the Samoan mantle plume.     

Some new ideas about the deep subduction of continental crust

The discovery of coesite in metasedimentary rocks not only implies that the materials of continental crust with low density could subduct down to mantle depth, but also initiates a series of studies on continent-deep-sub-duction. Could continental crust be subducted down to the depth of more than 300 km? Water played a role in ultra-high-pressure (UHP) metamorphism although limited. Was the fluid really limited within meter-scale, as the authors suggested, at mantle depth? Erosion and extension could remove the overburden of the UHP rocks, while squeezing and buoyancy could lift up the UHP rocks through the overburden. What, however, is the main process and mechanism with which the UHP rocks have exhumed from mantle depth? All progress of these studies will eventually form and complete a new paradigm of geodynamics.     

东秦岭松树沟长英质高压麻粒岩的原岩性质

地球化学特征研究表明,东秦岭松树沟长英质高压麻粒岩的原岩性质主体为杂砂岩或长石砂岩,少量为亚碱性的酸性火山岩或岩浆岩并具慢源成因;其古构造环境类似于活动大陆边缘。