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雅鲁藏布江缝合带西段普兰蛇绿岩中地幔橄榄岩的岩石学研究 总被引：14，自引：10，他引：4
西藏雅鲁藏布江缝合带西段普兰蛇绿岩以出现面积约600余平方千米的特大型地幔橄榄岩体而引人注目.该地幔橄榄岩以方辉橄榄岩为主体,含有少量的二辉橄榄岩和纯橄榄岩,岩体中另有一些橄榄单斜辉石岩、辉长岩和辉绿岩等侵入体.地幔橄榄岩的主要造岩矿物橄榄石的Fo 90～93,其中呈包裹体的橄榄石的Fo略高,斜方辉石为顽火辉石(En 88～90),单斜辉石主要为顽透辉石和透辉石,以低铝(0.48％～3.96％)和高Mg#(91～96)为特征,铬尖晶石的Cr#值为18～69,其中方辉橄榄岩和二辉橄榄岩中的铬尖晶石属富铝型尖晶石,而纯橄岩中为富铬型尖晶石.橄榄单斜辉石岩的橄榄石Fo值一致较低,平均为88.4,斜方辉石En平均87,单斜辉石以透辉石为主,铬尖晶石的Cr#值为45～69.普兰地幔橄榄岩及橄榄单斜辉石岩都具有相似的稀土元素和微量元素配分模式,表现为LREE相对富集,Eu亏损不明显,微量元素中大离子亲石元素含量较低,部分样品高场强元素亏损,另一些则相对富集,显示地幔橄榄岩具有亏损地幔源区特征,但也具有俯冲带流体的交代特征,表明普兰岩体可能经历了MOR和SSZ两种构造环境,该特征与雅鲁藏布江缝合带东段的罗布莎地幔橄榄岩的特征可以对比. 相似文献
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二叠纪镁铁-超镁铁质岩体在北山造山带广泛分布,其中多发育铜镍硫化物矿化,并集中在新疆北山坡北和甘肃北山柳园地区。本文对柳园地区二叠纪骆驼山(283Ma)和西南山(277Ma)矿化岩体中早期结晶的造岩矿物开展矿物化学分析,并对甘-新北山地区矿化岩体的主要造岩矿物进行系统对比研究。骆驼山和西南山岩体主要由单辉橄榄岩、二辉橄榄岩、橄榄辉石岩、橄榄辉长岩和辉长岩组成,主要造岩矿物为橄榄石、单斜辉石、斜方辉石、斜长石和角闪石,及少量铬尖晶石和金云母。铬尖晶石Cr#值范围为52.2～70.4,TiO2含量为1.1%～4.0%,Al2O3含量为8.1%～18.9%。橄榄石Fo值范围为78～86,Ni含量为856×10-6～2121×10-6,Ca含量为71.3×10-6～720×10-6。斜方辉石主要为顽火辉石和少量古铜辉石;单斜辉石为透辉石和普通辉石,Mg#范围为86～88,AlⅣ... 相似文献
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东波超镁铁岩体:西藏雅鲁藏布江缝合带西段一个甚具铬铁矿前景的地幔橄榄岩体 总被引：11，自引：5，他引：6
东波超镁铁岩体产在雅鲁藏布江缝合带的西段,与周边白垩纪沉积岩地层和火山岩以断层接触.航磁资料显示该岩体约400km2规模,地表出露连续,地下有一定延深.超镁铁岩体由亏损的地幔橄榄岩组成,主要有高镁的方辉橄榄岩、纯橄岩和少量二辉橄榄岩.方辉橄榄岩和二辉橄榄岩中橄榄石和斜方辉石属高镁型,分别为Fo=89.5～91.5和Mg#=90～91.5.但二辉橄榄岩中的Al2O3和CaO含量明显高于方辉橄榄岩.方辉橄榄岩中单斜辉石Mg#=92～95,二辉橄榄岩的Mg#=92～93,两者的值也重叠.二辉橄榄岩中的Al2O3和CaO含量要明显高于方辉橄榄岩.这些均为阿尔卑斯型地幔橄榄岩的典型特征.纯橄岩中的橄榄石Fo=92～93.2,其斜方辉石和单斜辉石的Mg#=～93,但Al2O3和CaO的含量比方辉橄榄岩和二辉橄榄岩的低.三种岩石的成分变化规律,反映了地幔部分熔融程度的差异.二辉橄榄岩铬尖晶石的Cr#值20～30,反映为典型深海橄榄岩特征,指示MOR环境.与其不同的是,方辉橄榄岩的铬尖晶石的Cr#=20～75,指示MOR和SSZ两者兼有环境.岩石的原始地幔标准化的REE和微量元素蛛网图模式支持了上述的认识.东波地幔橄榄岩中的岩石学特征与产有大型铬铁矿床的罗布莎地幔橄榄岩可对比,岩体中已多处发现块状铬铁矿石,其铬铁矿的Cr2O3含量56％～59％,表明东波是寻找铬铁矿大矿和富矿甚具前景的一个超镁铁岩体. 相似文献
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PP3超镁铁岩主要岩石类型有纯橄岩和石榴石橄榄岩,两者为渐变,主要矿物为橄榄石、铬尖晶石、石榴石、单斜辉石和斜方辉石.铬尖晶石的Cr#[Cr/(Cr+Mg) ×100]从51~89变化,TiO2和MnO2值分别低于0.26%和0.46%.铬尖晶石矿物表现为4期次演化的特点,反映了从岩浆期、榴辉岩相、角闪岩相和绿片岩相演化特征.随着超镁铁岩的演化,铬尖晶石表现为Cr#不断增大,而Mg#[Mg×100/(Mg+Fe2+) ]不断减少、氧逸度不断增加的过程.PP3铬尖晶石反映了地幔来源,为大陆岩石圈超镁铁岩特征,后期随折返而演化.从石榴石与铬尖晶石相互转变过程看出,PP3超镁铁岩经历了深度加大的过程,超镁铁岩曾经到达100km以上的岩石圈地幔深处.在绿片岩相-绿片角闪岩相变质过程中,铬尖晶石中Cr、Mg和Al减少,Fe相对增加,产生富Cr尖晶石变质作用样式.晚期剪切变形等次生变化影响了铬尖晶石矿物成分. 相似文献
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坡十Ni矿化超镁铁侵入体的矿化岩相主要为第二侵入期次的（斜长）单辉橄榄岩、（斜长）二辉橄榄岩、 纯橄岩等岩相。坡十超镁铁岩的橄榄石成分变化范围较大, 橄榄石的Fo值在76.8～89.6之间, Ni含量为767×10-6～4 580×10-6。铬尖晶石的Mg#值和Cr#值变化范围分别为19.4～41.9和49.8～64.8, 原生铬尖晶石中Cr2O3和Al2O3表现为负相关, 蚀变改造的铬尖晶石则表现为正相关。橄榄石成分剖面显示坡十母岩浆处于一个动态的岩浆系统中, 成分稳定的新鲜岩浆的补给、 持续向上的动力及浅部橄榄石快速分离结晶,造成了不同深度橄榄石成分的不同变化。坡十侵入体母岩浆估算结果为MgO=14.49％, FeO=10.01％,模拟结果显示橄榄石中Ni含量的变化主要受橄榄石结晶分异和硫化物不混溶作用共同控制,其中橄榄石与硫化物熔体发生明显的Fe-Ni交换反应。坡十母岩浆中橄榄石分离结晶造成的硫饱和,是坡十硫化物熔离的重要因素。橄榄石高Fo值、母岩浆高MgO、超镁铁岩中斜长石发育、矿物高结晶温度和铬尖晶石成分的弧岩浆特征显示,塔里木东北缘坡十侵入体是俯冲交代的岩石圈地幔部分熔融形成的母岩浆的产物,表现出低压高温的演化特征,其中源区熔融机制可能与塔里木二叠纪地幔柱提供的热源或该区大规模拆沉作用造成的软流圈上涌有关。 相似文献
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西藏雅鲁藏布江缝合带东段泽当地幔橄榄岩特征及其意义 总被引：1，自引：1，他引：0
泽当岩体位于雅鲁藏布江缝合带东段,主要由地幔橄榄岩、辉长辉绿岩和基性火山岩等组成。地幔橄榄岩主要为方辉橄榄岩和二辉橄榄岩,有少量透镜状纯橄岩。地幔橄榄岩经历了强烈的塑性变形作用。地幔橄榄岩中橄榄石的Fo值为89.6~91.8,属镁橄榄石;斜方辉石为顽火辉石,En 87.8~90.3;单斜辉石En 44.1~50.0,主要为顽透辉石和透辉石。铬尖晶石的Cr#值(=100×Cr/(Cr+Al))为17.0~93.6,其中,二辉橄榄岩和方辉橄榄岩中的铬尖晶石为富铝型尖晶石,纯橄岩中的铬尖晶石Cr#最高,为富铬型尖晶石。地幔橄榄岩的部分熔融程度为17%~34%,表明泽当地幔橄榄岩可能经历了多阶段的过程。亏损的主量元素组成和低于原始地幔的稀土元素含量(0.15×10-6~0.61×10-6)指示泽当地幔橄榄岩为经历过部分熔融和熔体抽取的亏损残余地幔岩石。REE配分型式为中稀土亏损的"V"型或"U"型,原始地幔标准化元素比值(La/Sm)N为0.5~8.0,表明泽当地幔橄榄岩经历过交代作用。矿物化学与地球化学数据表明泽当地幔橄榄岩形成于MOR环境,后受到SSZ环境的改造。 相似文献
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甘肃龙首山岩带西井镁铁质岩体成因及其构造意义 总被引：2，自引：0，他引：2
西井岩体位于北祁连造山带以北,阿拉善地块西南缘的龙首山隆起带。以往的研究多以沿龙首山断裂分布的镁铁-超镁铁质岩带作为和金川岩体相关的岩浆事件进行,而本次选择西井镁铁质岩体进行了精确的地质年代学和地球化学研究,确定了西井岩体岩性主要为橄榄辉石岩和辉长岩,成岩时代为 (421.0±9.0) Ma,可以和北祁连高压变质带榴辉岩年龄相对应;εNd(t)为4.06~5.52,(87Sr/86Sr)i为0.704 548~0.707 575,具有地幔岩石圈特征;微量元素及其同位素计算表明西井岩体经历了约10%的下地壳物质混染。据此得出西井岩体及其龙首山岩带早志留世镁铁质侵入岩体成因模式为:祁连洋壳连续俯冲过程中洋壳与陆壳分离,热的软流圈物质持续冲击地幔岩石圈的底部;由于热传导效应,大地热流沿着地幔岩石圈上升,使得80 km深度的湿的橄榄岩层发生熔融,产生玄武质岩浆作用,玄武质岩浆上升过程中与下地壳物质发生约10%混染,形成西井岩体及其龙首山镁铁超镁铁质岩带。 相似文献
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1958年袁棨林在我国北部一地槽区曾注意到有两类超基性岩体。第Ⅰ类有橄长岩-异剥辉长岩分异脉岩(以下简称分异脉岩)的岩体,其造矿铬尖晶石为较富铝的富铬尖晶石亚种和富铁富铬尖晶石亚种,组成低品位冶金级矿石;第Ⅱ类为无分异脉岩的岩体,其中合富铬贫铝的铬铁矿亚种和富铁铬铁矿亚种,组成高品位冶金级矿石。它们虽然都是镁质超基性岩,同样是以斜辉辉撖岩为主的纯橄榄岩-辉橄岩杂岩体,而且都显示了较强的动力分异作用,只是由于出现或不出现与晚期岩浆铬铁矿有成因关系的分异脉岩,而使造矿铬失晶石成分有明显地不同。 相似文献
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北秦岭松树沟超镁铁质岩体接触变质带中锆石特征及其地质意义 总被引：1，自引：0，他引：1
松树沟超镁铁质岩体位于秦岭商丹断裂以北,是该地区出露最大的超基性岩体,以侵位方式与秦岭杂岩接触.该岩体主要由细粒纯橄榄岩、中粗粒纯橄榄岩和斜辉橄榄岩组成.对松树沟超镁铁质岩体接触变质带榴闪岩中锆石包裹体成分及锆石微量元素含量进行了研究,结果表明松树沟超镁铁质岩体与相邻的镁铁质岩(主要是斜长角闪岩)不是同一构造旋回的地质体.斜长角闪岩先形成,之后松树沟岩体侵位其中.斜长角闪岩的地球化学特征显示其具有MORB和IAT两个端员组分特征,很可能是秦岭群的组成部分. 相似文献
11.
藏北班公湖—怒江缝合带中—西段康穷地区发现铬铁矿 总被引：2，自引：1，他引：1
班公湖—怒江缝合带中—西段康穷地区发育一套各端元出露比较齐全的蛇绿岩岩石组合,向东与八乌错、米素、赤日、孜如错、桑日一带的超基性岩共同构成了班公湖—怒江缝合带中—西段基性超基性岩带。2012年,于康穷地区变质橄榄岩岩体边部发现一处铬铁矿体,首次证实这一巨大的超基性岩带内存在铬铁矿。铬铁矿露头良好,地表见有2条矿体,在露头西侧还见有大片残坡积铬铁矿,残坡积之下的深部情况尚难确定。矿体以冶金级富铬矿石为主,Cr2O3含量最高可达59.11%,矿体围岩主要为方辉橄榄岩,见有少量纯橄榄岩。初步研究认为,康穷铬铁矿类型为豆荚状铬铁矿。该矿体的发现为班公湖—怒江缝合带中—西段铬铁矿的找矿工作提供了重要线索,对区域找矿具有重要的指示意义。 相似文献
12.
Zoned chromites with high Mn-contents in the Fe-Ni-Cr-laterite ore deposits from the Edessa area in Northern Greece 总被引：1，自引：0，他引：1
K. M. Michailidis 《Mineralium Deposita》1990,25(3):190-197
The mineralogy of the transported Fe-Ni-Cr-laterite ore bodies from the Edessa area in Northern Greece was studied. The special emphasis was on the textural features and chemistry of chromite. The chromite was residually inherited in laterites from weathered ultramafic rocks and it displays zonation. Three main zones were optically distinguished: an inner chromite zone, an intermediate ferritechromite zone and a magnetite rim. These three zones have distinct compositions. The major oxides MgO and Al2O3 decrease from the chromite core to the ferritechromite zone, while FeOt increases and Cr2O3 either increases or decreases. A characteristic chemical feature of the chromite is the very high Mn-content in the ferritechromite zone, up to 20%wt MnO. Chemical zonation has, however, been detected in optically unzoned chromite cores rimmed by magnetite.The zoning and the high Mn-content of the chromite is a result of serpentinization in the presence of Mn-rich fluids, following lateritic weathering and finally Alpine low-grade metamorphism. 相似文献
13.
Among the dominant species of chromium, the trivalent form widely occurs in nature in chromite ores or in silicate minerals and is extremely immobile. The higher oxidation state Cr(VI), is, however, rarely found in nature, is more mobile, and several times more toxic than Cr(III). Cr(VI) occurs in chromates and dichromates manufactured from chromite ores. The hexavalent state is stable in an oxidizing alkaline environment, whereas the trivalent state is stable in a reducing acidic environment. Serpentinization and Mg release during deuteric alteration of ultramafic rocks create alkaline pore water and lateritization is an intensive oxidation process. Chromite ore bodies in oxidized serpentinite therefore may generate hexavalent chromium from the inert chromites and cause hazardous chromium pollution of the water. With this end in view, a combined field and laboratory study has been made on chromite-bearing oxidized serpentinite rocks of Sukinda in Orissa, India. Laboratory leaching studies on mine overburden samples, chemical analyses of streamwater, and hydrolysate incrustation on detrital grains taken from stream beds have indicated the possibility of chromium mobilization from the chromite ores into the waterbodies. 相似文献
14.
Demantoid is a rare gem mineral. The Xinjiang Cr-bearing demantoid reported in this paper has been discovered for the first time in China. It contains more than 90% end-member molecule of andradite, close to the pure end-member composition, as revealed by chemical analysis, X-ray powder diffraction, Mössbauer spectrometry and both infrared and optical absorption spectrometry. The Fe2+ content lies beyond the detection limit of Mössbauer spectrometry. It was found that the green color of demantoid is directly related geological occurrence and mineral association the genesis of demantoid is inferred as follows. In ultramafic to Fe3+ in the octahedral site and that the presence of Cr3+ greatly enhances its inferred as follows. In ultramafic rocks olivine and pyroxene were replaced by serpentine under the reaction of residual volatiles, creating an Fe-rich and Al-poor environment. In such an environment late-stage hydrothermal metasomatism was developed along the fissures of serpentine, resulting in the crystallization and precipitation of demantoid in asbestos veins. On the other hand, local tectonic compression and dislocation gave rise to the formation of demantoid aggregates cemented by serpentine asbestos. Evidence has shown that the trace Cr was derived from chromite and Cr-spinel in the ultramafic rock bodies. 相似文献
15.
现在岩石学、矿床学的实验一般用样品是几十毫克、甚至十几毫克,其目的是要精确化。但是许多事实说明,这种精密的实验工作并不能完全解决矿床的成因。要解决矿床成因的问题,至少必须回答下面三个问题:(1)有用金属矿物是在什么条件下形成的;(2)有用金属矿物是如何富集为矿石的;(3)矿石如何具有一定的量,并达到经济上可开采的要求。实验岩石学和实验矿床学的资料一般只说明了第一个问题。 相似文献
16.
M. F. El-Sharkawy 《Mineralium Deposita》2000,35(4):346-363
Petrographical and petrochemical studies of the talc host rocks of Rod Umm El-Farag and Wadi Thamil in the Eastern Desert
of Egypt reveal that they consist mainly of metavolcanic rocks, whilst the geology, petrography, mineralogy, chemistry and
quality of the enclosed talc lenses reveal that the ore has ultramafic affinity. The setting of the talc ore is similar to
that hosted by metavolcanic rocks in terms of the type of host rocks, but it differs in its ultramafic affinity, resembling
the talc ore hosted by ultramafic rocks. The parent ultramafic rocks occur in the form of small bodies obducted later along
a tectonized fault plane within metavolcanic host rocks (Precambrian) and their tuffaceous equivalents. The metavolcanic host
rocks consist mainly of metabasalts, meta-andesites and metatuffs with a smaller amount of dacite, rhyolite and tuffaceous
lava. The metamorphic grade is low corresponding to greenschist facies. The calc-alkaline and tholeiitic characters of the
volcanic rocks are determined by the behaviour of trace elements on some chemical discrimination diagrams. After the emplacement
of the ultramafic bodies, they underwent regional metamorphism which was accompanied by further serpentinization. Metasomatic
changes, related to regional metamorphism (corresponding to the emplacement of granitic plutons at a distance) include talc,
carbonate, tremolite and chlorite formation. SiO2, H2O and CO2 have been supplied from hydrothermal solutions but all other constituents are considered indigenous to the ultramafic bodies,
and none of the metavolcanic components have been added during talc formation. Mineralogically, the talc ore is relatively
simple, including talc, tremolite, actinolite, chlorite and chromite. On the basis of mineral abundances, pure talc (>90%
talc), chlorite-rich and tremolite-actinolite-rich (50–70% talc) ore types have been recognized. Chromite is largely zoned
and occurs as disseminated grains within the talc matrix. Cr, Al and Mg were released during the formation of ferrite chromite
and accommodated in the talc and chlorite structures. The chemical data show that there is very little variation in the contents
of MgO, Fe2O3, FeO, NiO, Cr2O3, and Co between the parent ultramafic rocks and talc ore. Al2O3, CaO, Fe2O3 and FeO are the main impurity oxides in the talc ore. They decrease the whiteness of the ore and consequently limit the use
of talc.
Received: 26 March 1999 / Accepted: 10 October 1999 相似文献
17.
扬子地块北缘周庵超镁铁质岩体矿物学特征及其对铜镍矿化的启示 总被引：2，自引：0，他引：2
扬子地块北缘~635 Ma周庵超镁铁质岩体是一个新发现的含铜镍硫化物矿化的隐伏岩体,主要由二辉橄榄岩组成。文章通过研究周庵岩体中橄榄石、铬铁矿和辉石的矿物成分变化探讨了岩浆演化过程和含矿岩体成因。根据岩石的矿物组合和蚀变程度,岩体从上到下分为3个部分:上部绿泥石-蛇纹石化二辉橄榄岩相带、中部二辉橄榄岩相带和下部绿泥石-角闪石化二辉橄榄岩相带。根据岩体中部带橄榄石和铬铁矿的成分,计算得到母岩浆的Mg#值为0.63,MgO/FeO摩尔比值为1.72,w(Al2O3)为10.2%~11.7%,w(Ni)为476×10-6,说明其为高镁玄武质岩浆;岩体中部带原生铬铁矿和粒间相铬铁矿核部的Cr2O3和Al2O3呈正相关关系,说明铬铁矿与粒间硅酸盐熔体发生了平衡交换,铬铁矿的高w(TiO2) 和Cr#值与拉张环境中层状岩体的铬铁矿特征一致;根据辉石温压计得到岩体中部单斜辉石和斜方辉石的共结温度为1 017~1 077℃,压力为(3.6~4.5)×108 Pa,暗示形成岩体的浅部岩浆房深度约为12 km。岩体上部和中部带的橄榄石Fo值大部分集中在80 mol%~85 mol%,w(Ni)介于2 255×10-6~4 455×10-6,说明这些橄榄石是从没有经过强烈分离结晶和硫化物熔离的岩浆中结晶出来的。岩体下部带橄榄石的Fo值(67 mol%~68 mol%)和w(Ni) (1 500×10-6~2 000×10-6)都低于岩体上部和中部带的橄榄石相应值,说明岩体下部带的橄榄石可能形成于演化程度较高、并经历了硫化物熔离的岩浆。因此,笔者认为周庵岩体是由相对原始的和演化了的高镁玄武质岩浆两期侵位形成的。 相似文献
18.
《International Geology Review》2012,54(12):1466-1483
Chromitites (>80% volume chromite) hosted in two ultramafic bodies (Lavanderos and Centinela Bajo) from the Palaeozoic metamorphic basement of the Chilean Coastal Cordillera were studied in terms of their chromite composition, platinum-group element (PGE) abundances, and Re-Os isotopic systematics. Primary chromite (Cr# = 0.64–0.66; Mg# = 48.71–51.81) is only preserved in some massive chromitites from the Centinela Bajo ultramafic body. This chemical fingerprint is similar to other high-Cr chromitites from ophiolite complexes, suggesting that they crystallized from arc-type melt similar to high-Mg island-arc tholeiites (IAT) and boninites in supra-subduction mantle. The chromitites display enrichment in IPGE (Os, Ir, Ru) over PPGE (Rh, Pt, Pd), with PGE concentrations between 180 and 347 ppb, as is typical of chromitites hosted in the mantle of supra-subduction zone (SSZ) ophiolites. Laurite (RuS2)-erlichmanite (OsS2) phases are the most abundant inclusions of platinum-group minerals (PGM) in chromite, indicating crystallization from S-undersaturated melts in the sub-arc mantle. The metamorphism associated with the emplacement of the ultramafic bodies in the La Cabaña has been determined to be ca. 300 Ma, based on K-Ar dating of fuchsite. Initial 187Os/188Os ratios for four chromitite samples, calculated for this age, range from 0.1248 to 0.1271. These isotopic compositions are well within the range of chromitites hosted in the mantle section of other Phanaerozoic ophiolites. Collectively, these mineralogical and geochemical features are interpreted in terms of chromite crystallization in dunite channels beneath a spreading centre that opened a marginal basin above a supra-subduction zone. This implies that chromitite-bearing serpentinites in the metamorphic basement of the Coastal Cordillera are of oceanic-mantle origin and not oceanic crust as previously suggested. We suggest that old subcontinental mantle underlying the hypothetical Chilenia micro-continent was unroofed and later altered during the opening of the marginal basin. This defined the compositional and structural framework in which the protoliths of the meta-igneous and meta-sedimentary rocks of the Eastern and Western Series of the Chilean Coastal Cordillera basement were formed. 相似文献
19.
《Journal of Asian Earth Sciences》1999,17(4):423-442
The Hegenshan ophiolite in Inner Mongolia is a remnant of oceanic lithosphere of probable Devonian age. The ophiolite consists of several blocks composed chiefly of serpentinized ultramafic rocks with lesser amounts of troctolite and gabbro, and sparse lavas and dikes. The ultramafic rocks consist chiefly of depleted harzburgite and minor dunite and are interpreted as mantle tectonites. In the Hegenshan block dunite is relatively abundant and is typically associated with podiform chromitite. Both the chromite ore and the residual chromites in this body are relatively aluminous with average Cr numbers of 44–54. A few small chromite bodies and some of the residual chromites have much higher Cr numbers (72–76). Several blocks have well-layered cumulate sequences of gabbro and troctolite. Sheeted dikes are absent but small mafic dikes are common in some of the ultramafic sections. Most of the mafic dikes have flat chondrite-normalized REE patterns and are strongly depleted in incompatible elements, similar to depleted tholeiites from immature island arcs. The basaltic lavas of the Hegenshan ophiolite have two distinctly different chemical signatures—one similar to the mafic dikes and one similar to ocean island basalts. The entire complex was probably formed within an island arc–marginal basin system that was later accreted to the southern margin of the Siberian Altaids. 相似文献
20.
试论与布什维尔德杂岩体有关的铂族元素-铬铁矿矿床成矿系列及其对中国西南部的意义 总被引：12，自引：0，他引：12
布什维尔德杂岩体中铂族元素成矿作用具有多样性的特点,既有主岩体岩浆结晶分异形成的UG2和Merensky层,有晚期小岩体结晶分异产生的块状铜镍硫化物矿石中伴生的铂族元素矿床（如Nkomati）,也有岩体侵入过程中产于接触带的热液成因硫化物-铂族元素矿床（如Potgietersrust）,以及岩筒型矿床（如Mooihoek和Driekop）、剪切带热液型硫化物矿床（如TweefonteinHill）和石英脉型铂族元素矿床.这些矿床虽然产出部位不同（矿体可以分布在岩体内部也可以出现在接触带甚至远离岩体）,矿石类型也不同（有的是铬铁矿型,有的是硫化物型,有的是硅酸盐型,甚至还有石英脉型）,但铂族元素的富集都与布什维尔德基性超基性岩杂岩体密切有关,实际上构成一个完整的由布什维尔德地幔柱形成的矿床成矿系列。类似的矿床成矿系列在深受峨眉地幔柱影响的我国西南部地区也存在,这对于在我国寻找多种类型的铂族元素矿床无疑具有重要的启示意义.除了金宝山和杨柳坪等地的岩浆型铂矿外,近年来在杨柳坪、大岩子等地也先后发现了热液型铂族元素矿床. 相似文献