大别山北部饶拔寨超镁铁岩体微量元素地球化学   总被引：3，自引：4，他引：3  

支霞臣  靳永斌孟庆 高天山 《岩石学报》2004,20(3):463-472

本文报道了饶拔寨超镁铁岩体的5个钻孔15个岩心样品的主量元素和微量元素成分。该岩体由上、下两部分构成。岩性以方辉橄榄岩为主，纯橄榄岩和二辉橄榄岩次之。主量元素成分表明岩体由饱满地幔经过不同程度部分熔融，形成了亏损程度不同的大陆岩石圈地幔。总体上下部岩体较上部亏损程度大。原始地幔标准化REE等不相容微量元素丰度模式表明岩体在熔融作用后又经过了地幔交代作用，形成不同程度LREE和LILE的富集。样品中有角闪石和金云母等含水矿物，表明有实性地幔交代作用。对比LREE与LILE的富集特征，表明可能有两类地幔交代作用，有两种不同性质的交代介质，LREE和Sr等的富集可能与硅酸盐熔体有关，而Rb、Ba、K等的富集可能与俯冲带流体活动有关。总体上下部岩体的交代作用较上部岩体的强。  相似文献   

Silicate, Hydrous and Carbonate Metasomatism at Lherz, France: Contemporaneous Derivatives of Silicate Melt-Harzburgite Reaction   总被引：4，自引：0，他引：4  

BODINIER  JEAN-LOUIS; MENZIES  MARTIN A.; SHIMIZU  NOBUMICHI; FREY  FREDERICK A.; McPHERSON  ELAINE 《Journal of Petrology》2004,45(2):299-320

Complex multi-stage models involving silicate, hydrous and carbonatemelts of distinct provenance have been invoked to explain themetasomatism observed in mantle rocks. In contrast, relativelysimple models requiring polybaric crystallization of alkalinesilicate melts have been proposed to explain the occurrenceof veined mantle rocks. To address the spatial and temporalrelationships between veins and wall-rocks, a sequence of drillcores was obtained from Lherz, France. In outcrop the vein (amphibole–garnetpyroxenite dyke) is spatially associated with hornblendite veinlets(lherzite), and proximal amphibole-bearing and distal apatite-bearingwall-rock peridotite. Considerable elemental and isotopic heterogeneityexists in these wall-rock peridotites, in many instances equivalentto, or greater than, that observed in mantle xenoliths fromworldwide localities. A single stage of reactive porous flowbest explains the elemental and isotopic heterogeneity in thewall-rock. In essence it is proposed that emplacement of thesilicate melt (dyke) was inextricably linked to chromatographicfractionation/reaction of derivatives which led to the coexistence,in space and time, of silicate, hydrous and carbonate melts.This model elegantly and simply describes the formation of complexmetasomatic aureoles around mantle veins and negates the need,in the case of basalt-hosted (and kimberlite-hosted) xenoliths,for complex multi-stage models involving several episodes ofmelt influx with each melt being of different provenance. KEY WORDS: mantle metasomatism; trace-element enrichment; isotopic contamination; wall-rock peridotite; Lherz peridotite  相似文献   

Contrasting Enrichments in High- and Low-Temperature Mantle Xenoliths from Nushan, Eastern China: Results of a Single Metasomatic Event during Lithospheric Accretion?   总被引：9，自引：1，他引：9  

XU  YI-GANG; BODINIER  JEAN-LOUIS 《Journal of Petrology》2004,45(2):321-341

Distinct equilibration temperatures, deformation and trace elementcharacteristics are observed in amphibole-bearing and amphibole-freeperidotite xenoliths from Nushan, Sino-Korean Craton, easternChina. Amphibole-free peridotites are predominantly deformed,fine-grained (  相似文献   

Interactions between serpentinite devolatilization, metasomatism and strike-slip strain localization during deep-crustal shearing in the Eastern Alps   总被引：4，自引：0，他引：4  

J. D. Barnes  J. Selverstone  Z. D. Sharp 《Journal of Metamorphic Geology》2004,22(4):283-300

The Greiner shear zone in the Tauern Window, Eastern Alps, changes from a zone of distributed (dominantly sinistral) shear in supracrustal rocks to a series of narrow, gully forming dextral splays where it enters basement gneisses. Within these splays, granodiorite is transformed into quartz‐poor biotite and/or chlorite schists, reflecting hydration, removal of Si, Ca and Na, and concentration of Fe, Mg and Al. Stable isotope analyses show a prominent increase in δD and a decrease in δ¹⁸O from granodiorite into the shear zones. These changes indicate significant channelized flow of an externally derived, low‐δ¹⁸O, high‐δD fluid through the shear zones. The shear zone schists are chemically similar to blackwall zones developed around serpentinite bodies elsewhere in the Greiner zone and the stable isotope data support alteration via serpentinite‐derived fluid. Monazite in schist from one shear zone yields spot dates of 29–20 Ma, indicating that the fluid influx and switch from sinistral to dextral shear occurred at or shortly after the thermal peak of the Alpine orogeny (c. 30 Ma). We suggest that Alpine metamorphism of serpentinites released large amounts of high‐δD, low‐δ¹⁸O, Si‐undersaturated, Fe + Mg‐saturated fluids that became channelized along prior zones of weakness in the granodiorite. Infiltration of this fluid facilitated growth of chlorite and biotite, which in turn localized later dextral strain in the narrow splays via cleavage‐parallel slip. This dextral strain event can be linked to other structures that accommodated tectonic escape of major crustal blocks during dextral transpression in the Eastern Alps. This study shows that serpentinite devolatilization can play an important role in modifying both the chemistry and rheology of surrounding rocks during orogenesis.  相似文献   

Origin of early Cretaceous calc-alkaline lamprophyres from the Sulu orogen in eastern China: implications for enrichment processes beneath continental collisional belt   总被引：13，自引：0，他引：13  

Feng Guo  Weiming Fan  Ming Zhang 《Lithos》2004,78(3):291-305

K-Ar dating, major- and trace-element and Sr-Nd isotopic analyses were carried out for early Cretaceous (122-127 Ma) lamprophyres from the Sulu orogen in eastern China. The results show strong fractionation in rare-earth elements with (LREE) >100 times chondrite, but HREE <10 times chondrite, indicating the presence of residual garnet in the melting source. These rocks are characterized by significant LILE and LREE enrichment but Nb and Ta depletion with moderate Zr/Hf (39.8-50.8 with regard to 36 for primitive mantle) and Nb/Ta (17.8-23.0, compared with 17.5 for primitive mantle) fractionations, probably as a consequence of carbonate- and rutile-rich melt metasomatism induced by dehydration and/or melting of subducted continental slab at mantle depths. Age-correlated Sr-Nd isotope ratios show moderate ranges of ⁸⁷Sr/⁸⁶Sr(i) from 0.70787 to 0.70934 and −17.2 to −11.6 of ε_Nd(t). The lamprophyres from the Sulu orogen were derived from decompression melting of such a metasomatized lithospheric mantle that was mainly composed of phlogophite garnet peridotites and experienced crystal fractionation of a mineral assemblage of olivine+clinopyroxene±plagioclase en route to the surface. Such geochemical and isotopic signatures are also prevalent in the contemporaneous basaltic lavas in the Dabie-Sulu belt, suggesting predominant enrichment processes by carbonate- and rutile-rich metasomatic assemblage beneath the continental collisional belt.  相似文献   

A Simple Approach to Account for Radial Flow and Boundary Conditions When Kriging Hydraulic Head Fields for Confined Aquifers   总被引：2，自引：0，他引：2  

Y. Brochu  D. Marcotte 《Mathematical Geology》2003,35(2):111-139

The estimation and mapping of realistic hydraulic head fields, hence of flow paths, is a major goal of many hydrogeological studies. The most widely used method to obtain reliable head fields is the inverse approach. This approach relies on the numerical approximation of the flow equation and requires specifying boundary conditions and the transmissivity of each grid element. Boundary conditions are often unknown or poorly known, yet they impose a strong signature on the head fields obtained by inverse analysis. A simpler alternative to the inverse approach is the direct kriging of the head field using the measurements obtained at observation wells. The kriging must be modified to incorporate the available information. Use of the dual kriging formalism enables simultaneously estimating the head field, the aquifer mean transmissivity, and the regional hydraulic gradient from head data in steady or transient state conditions. In transient state conditions, an estimate of the storage coefficient can be obtained. We test the approach on simple analytical cases, on synthetic cases with solutions obtained numerically using a finite element flow simulator, and on a real aquifer. For homogeneous aquifers, infinite or bounded, the kriging estimate retrieves the exact solution of the head field, the exact hydrogeological parameters and the flow net. With heterogeneous aquifers, kriging accurately estimates the head field with prediction errors of the same magnitude as typical head measurement errors. The transmissivities are also accurately estimated by kriging. Moreover, if inversion is required, the kriged head along boundaries can be used as realistic boundary conditions for flow simulation.  相似文献   

广东长坑大型-超大型金银矿床的地球化学与成因带   总被引：12，自引：0，他引：12  

张生  李统锦  王联魁 《矿床地质》1998,17(2):125-134

对长坑金银矿床的化学组成、同位素特征、流体性质、成矿物理化学条件和机理的系统研究表明,与矿化最密切的硅质岩应主要为热液交代成因;金、银矿体的稀土和微量元素特征既有共性又有异性;矿床的硫、铅、碳、锶同位素组成特征反映它们均为壳源物质或沉积成因;成矿流体相对富Ｃａ、Ｋ,主要来自演化了的加热大气水或建造水;矿床形成于中低温的热液条件,矿化机制包括热液沸腾、流体混合与水岩反应。总之,长坑矿床为微细浸染型金矿与碳酸盐岩交代型银矿构成的新颖矿床组合,金、银矿体是统一的热液作用在不同的成矿环境和控矿条件下的产物,它们与区域内的铅锌（银）矿床应属于一个成矿系列。  相似文献   

碳酸岩是大陆岩石圈构造背景和地幔交代作用的指示岩石   总被引：2，自引：0，他引：2       下载免费PDF全文

杨学明  杨晓勇  M．J．LeBas 《地球物理学报》1998,41(Z1):228-235

根据已知碳酸岩的地质产状、岩石学特征、Nd-Sr-Pb同位素及痕量元素地球化学特征,结合高温高压实验岩石学资料,论述了其地幔源区的物质成分、交代过程、软流圈地幔部分熔融机制和碳酸岩岩浆的演化模型碳酸岩既可以产生于裂谷环境,由起源于软流圈地幔的霞石质超基性-基性岩浆经液态不混溶作用而形成,与硅酸不饱和过碱性杂岩构成环状碳酸岩-碱性杂岩;也能够产生于碰撞造山过程中派生的引张岩石圈断裂带,直接导源于岩石圈地幔的低程度部分熔融作用,形成单一的透镜状、条带状和似层状碳酸岩体  相似文献   

羊拉地区含矿夕卡岩流体包裹体特征及其成因意义带   总被引：8，自引：2，他引：6  

路远发  战明国  陈开旭  黄惠兰 《矿床地质》1998,17(4):331-342

羊拉铜矿化集中区共有４个夕卡岩体,按成因分为喷流－沉积和接触交代夕卡岩两大类,前者呈层状,是铜的主要赋矿围岩。层状夕卡岩中包裹体以类型多、组分复杂、均一温度（１００～６２０℃,一般大于３００℃）和盐度（８．３％～５５．０％ＮａＣｌ,一般≥２０％ＮａＣｌ）高且变化范围大、密度高（一般大于１．００ｇ／ｃｍ３）、捕获压力低（１０～２５ＭＰａ）为特征;交代夕卡岩则以包裹体类型简单、组分单一、均一温度（一般小于２５０℃）和盐度中—低（９．０％～２０．０％ＮａＣｌ）、密度低（一般小于１．００ｇ／ｃｍ３）且变化范围大、捕获压力高（１５０ＭＰａ）为特征。这些包裹体特征反映了两类夕卡岩的流体来源和演化机制是不同的,其中层状夕卡岩之流体为深部源与海水源的二元混合特征;交代夕卡岩为岩浆（体）源等组分自然冷却演化趋势。  相似文献   

会理小青山铜(金)矿区钠长石岩的地质地球化学特征及交代作用机制     

王奖臻  陆彦  肖渊甫  温春齐 《四川地质学报》1998,(3)

应用稀土元素及微量元素方法和Ｇｒｅｓｅｎｓ方程,研究了小青山铜（金）矿区交代成因钠长石岩,区分出了两类不同原岩性质的钠长石岩。Ａ类钠长石的原岩为绢云母千枚岩,它们的ΣＲＥＥ为３０．１３～１０１．０９,ΣＣｅ／ΣＹ＝１．８～７．８,δＥｕ＝０．２３～０．９１,稀土配分曲线为右倾型;Ｒｂ等大离子亲石元素强烈亏损。Ｂ类钠长石岩的原岩为辉长岩,它们的ΣＲＥＥ＝２９．０６,ΣＣｅ／ΣＹ＝２．０４,δＥｕ＝０．９３,配分曲线为平坦型,大多数微量元素均为负异常。两类钠长石岩形成过程中Ｋ２Ｏ、Ｆｅ２Ｏ３、ＦｅＯ及ＭｇＯ等带出,Ｎａ２Ｏ及ＳｉＯ２带入。  相似文献