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1.
绿岩带型金矿研究的进展   总被引：1，自引：0，他引：1  
本文介绍了近年来国外绿岩型带金矿在成矿模式，构造控制，成矿物化条件研究方向的某些进展，我国绿岩带与国外经典绿岩带有一定的差异，因而表现在成矿作用上也独树一帜，初步提出我国绿岩带型金矿研究中应注意的问题。  相似文献   

2.
本文通过对胶东地区早前寒武变质地层和花岗岩的研究，提出胶东绿岩带在变质地层、同位素年龄、变质程度、韧性剪切带和矿产等方面存在的证据，与世界典型绿岩带相比，胶东绿岩带具有５个方面的显著特征：①胶东绿岩带下部层位未发现完整科马提岩地层；②胶东绿岩带变质程度较高，一般可达角闪岩相，少数达麻粒岩相；③胶东绿岩带分布面积不大；④胶东绿岩带形成时间在２８．５８～２６亿ａ；⑤胶东绿岩带主要产出Ａｕ，Ａｇ，Ｚｎ，Ｃｕ等矿产。  相似文献   

3.
A large-scale high-pressure granulite belt (HPGB), more than 700 km long, is recognized within the metamorphic basement of the North China craton. In the regional tectonic framework, the Hengshan-Chengde HPGB is located in the central collision belt between the western block and eastern block, and represents the deep crustal structural level. The typical high-pressure granulite (HPG) outcrops are distributed in the Hengshan and Chengde areas. HPGs commonly occur as mafic xenoliths within ductile shear zones, and underwent multipile deformations. To the south, the Hengshan-Chengde HPGB is juxtaposed with the Wutai greenstone belt by several strike-slip shear zones. Preliminary isotopic age dating indicates that HPGs from North China were mainly generated at the end of the Neoarchaean, assocaited with tectonic assembly of the western and eastern blocks.  相似文献   

4.
Regional recumbent folds, inverted stratigraphy, nappes and olistostromes are described from the southern part of the 3.3–3.5 Ga Barberton Greenstone Belt. Overthrusting of thin rigid silicified slabs with minimum dimensions of 25 km2 and up to 500 m in thickness, occurred over minimum distances of 86 km. More ductile and coherent units were overfolded up to at least 2 km during their emplacement. The glide planes on which these nappes travelled were zones of high fluid pressures related to hydrothermal fluid circulation patterns, driven by heat sources from igneous intrusions. The upwelling areas of the geothermal convection cells were sites of mud-pools and hydrothermal vents which may mark the trailing edges (pull aparts) of the overthrust units. Progressive silica and carbonate precipitation due to decreasing temperatures, within the zones of fluid migration distant from the areas of high heat flow, probably acted as built-in braking systems below the travelling slabs. Active sedimentation and metasomatism during this tectonism indicates a protracted history for the evolution of the greenstone belt. The recognition of nappe and overthrust tectonics in the Barberton Belt, processes which may have been commonplace in Archaean terrains, necessitates a re-evaluation of the stratigraphy of this belt.  相似文献   

5.
The Archaean greenstone belt of Hidrolina (Central Goi?s, Brazil)is a severely tectonised and metamorphosed volcano-sedimentarysequence. It consists of a lower sequence (LS) with ultramaficand mafic flows (compositionally corresponding to komatiites),and an upper sequence (US) with intercalated mafic and felsicflows (compositionally corresponding to tholeiites, dacites,and rhyolites). Practically no primary structure or textureis preserved. Geochemical major and trace element modelling allow distinctionbetween liquid compositions and cumulates. Crustal contaminationdoes not seem to have been effective in controlling the geochemicalvariations. Batch partial melting models and CMAS plots indicatethat: (a) the komatiites probably resulted from moderate (28–30%)melting of a spinel peridotite rather than a garnet one; (b)the komatiites were formed by the mixing of a liquid of basalticcomposition with peridotite source material; (c) the mantlesource was heterogeneous, the flows higher in the stratigraphycoming from a more depleted source than the lower ones; and(d) US tholeiites resulted from lower degree melting of thesame depleted source that produced the upper LS flows.  相似文献   

6.
内蒙古中部地区太古宙绿岩带金矿找矿标志   总被引：3，自引：0，他引：3  
内蒙中部地区金矿集中分布在太古界花岗岩──—绿岩带中，并受区域深大断裂带及韧性剪切变质带的控制，构成内蒙中部金的矿化集中区。尽管人们对金矿化的成因有不同认识，但找矿标志是有规律可寻的，因而，总结内蒙中部地区金矿化的找矿标志是有重要意义的。本文着重通过内蒙古中部区的含金建造、容矿构造、岩浆活动、载金矿物、围岩蚀变及地球物理、地球化学、遥感影象和重砂等方面，总结本区的金矿找矿标志。  相似文献   

7.
Ｈｉｇｈ－ｐｒｅｓｓｕｒｅｍｅｔａｍｏｒｐｈｉｃｅｃｌｏｇｉｔｅ,ａｓａｗｉｎｄｏｗｏｆｓｔｕｄｙｆｏｒｄｅｐｔｈｌｅｖｅｌｏｆｌｏｗｅｒｍｏｓｔｃｒｕｓｔａｎｄｍａｎｔｌｅ,ｈａｓａｎｉｍｐｏｒｔａｎｔｉｎｄｉｃａｔｉｎｇｓｉｇｎｉｆｉｃａｎｃｅｔ...  相似文献   

8.
通过对华北地台北缘绿岩带型铁磷矿成矿构造环境、含矿建造、矿床地球化学等几个方面的研究认为,该类矿床含矿建造原岩主要为岛弧一拉斑玄武岩,变质后容矿岩石属碱性-铁质、铁镁质系列。容矿岩石中主微量元素明显不和谐,岩石中不相容元素明显富集（Ba、Sr、Zr、P）,相容元素（Cr、co、M）亏损。稀土元素含量高,模式图为向右倾斜平滑曲线,Ce轻度负异常。根据目前我国北方内生低品位共生铁磷矿开发利用情况,华北地台绿岩带型铁磷矿综合利用前景可观。  相似文献   

9.
Despite the fact that some greenstone belts preserve the record of contemporaneous komatiitic and tholeiitic volcanism, a genetic link between the two is not widely accepted. The significance of a compositional gap seperating these magma types and differences in their respective degree of light rare earth element (LREE) enrichment, cited as evidence against a derivative relationship, are complicated by the possibility of crustal assimilation by magmas of komatiitic affinity. In the Archean La Grande Greenstone belt of northern Quebec a succession of metamorphosed tholeiitic basalts and younger, high-Mg, LREE-enriched andesites are preserved. The tholeiites are differentiated basaltic rocks whose chemical compositions appear to have been controlled by low pressure, gabbroic fractional crystallization and are similar to Type 1 MORB. Parental magmas were probably high-Mg liquids of compositions similar to komatiitic basalts which also occur in the greenstone belt. These high-Mg liquids are believed to be themselves the product of high pressure, OLIV+OPX fractional crystallization of more magnesian primary liquids of komatiitic composition. The higher La/Sm ratios of komatiitic basalts and tholeiites relative to komatiites in this belt, can be explained by small degrees of crustal assimilation. In the central part of the belt, late-stage, mafic igneous rocks have chemical compositions similar to Archean examples of contaminated volcanic rocks (e.g., Kambalda, Australia). These late-stage lavas consist of basalts and andesites with high-Mg, Ni and Cr abundances, LREE-enriched profiles and low Ti abundances. They are believed to be the products of crustal assimilation and crystallization of OPX-PLAG-CPX from high-Mg liquids of komatiitic affinity. The volcanic stratigraphy records the progressive effects of crustal contamination through time. A light sialic crust may have initially acted as a density barrier, preventing the eruption of primary high-Mg liquids and forcing fractionation at depth which produced more buoyant compositions. With subsequent thinning of the crust, the density barrier presumably failed, and primary liquids migrated directly toward the surface. Reaction of these liquids with tonalitic crust produced contaminated differentiates.  相似文献   

10.
The very low-grade metamorphic sequence of volcano-sedimentary rocks, sandwiched between the platform sediments of the Vindhyan Supergroup to the east and the Banded Gneissic Complex (BGC) to the west, in the eastern fringe of the Aravalli-Delhi orogenic belt, has remained a stratigraphic enigma in the Precambrian geology of Rajasthan. This sequence known earlier as the Gwalior ‘series’ and in contemporary literature as the Hindoli Group, has been considered by several workers as a Proterozoic supracrustal unit and by some others, as an Archean secondary greenstone belt, based purely on geological considerations. U-Pb zircon geochronology was conducted to find an answer to this controversy on samples of felsic volcanics, conformably intercalated with the Hindoli sediments and hence, considered contemporaneous with them. Zircons from a sample of massive rhyodacite gave a concordia age of 1854k7 Ma though zircons from a sample of felsic tuff gave a wide range of ages between 3259-1877 Ma. Careful consideration of the nature of the samples and their constituent zircons suggests that the Hindoli Group rocks represent a low-grade Proterozoic supracrustal cover sequence in the eastern part of the Bhilwara belt, broadly synchronous to the Aravalli-Bhilwara sedimentation around 1.8 Ga.  相似文献   

11.
喜马拉雅造山带中段麻粒岩绝大多数呈透镜状、布丁体等弱应变域断续产出,强应变带围岩往往发育糜棱面理和构造片理。部分麻粒岩经历了强烈的韧性剪切构造变形,形成剪切透镜体,并且明显受韧性剪切带控制,显示成带分布、局部集中的特点。根据矿物组合可将产出的麻粒岩分为4种麻粒岩,其主要组成矿物如斜方辉石、单斜辉石、斜长石、角闪石以及石榴石等均不同程度地发生扭折、压扁、拉长扭曲、亚颗粒化及边缘强烈动态重结晶等强烈塑性显微构造变形特征。研究分析表明,麻粒岩的产出与重熔花岗岩的侵位及藏南伸展拆离断层活动有关,在喜马拉雅造山带强烈伸展快速抬升造山的绝热降压大陆动力学过程中,下地壳基性麻粒岩以较快的速率上升到地表,而下地壳层流作用、造山带伸展-隆升-造山导致麻粒岩相变质作用。  相似文献   

12.
鲁西泰山岩群是我国典型的新太古代绿岩带,发育并保存了良好的科马提岩,对其地质认识已基本趋于一致,但对鲁西地区绿岩带型金矿的认识还不够深入和全面.以往仅对韧性剪切带型金矿有所了解,对绿岩带层控型金矿很少重视,对矿源层的理解也较为模糊,笼统地将泰山岩群作为后期各种金矿成矿的矿源层.本文对鲁西绿岩带韧性剪切带型和层控型金矿做了系统介绍,认为绿岩带层控型金矿具有原生层状特征和矿源层意义,受绿岩带某特定层位控制十分明显,是超基性岩—基性火山岩—碎屑沉积岩建造旋回过程中发展到一定阶段的产物.对鲁西地区金矿源层成生发育机制进行了探讨,认为绿岩带中金初始沉积矿化层位十分狭窄,厚度一般仅1至十几米,但横向分布较广泛,一般长达5～10 km以上,初始沉积金品位一般在10×10-9～0.5×10-6,其金质来源于海底火山喷流(热液和喷气)作用.阐述了金矿源层与条带状硅铁建造(BIF)往往密切伴生的成因联系,并与硅铁矿层一样,也具有多旋回性沉积特点.韧性剪切带型金矿受矿源层内在控制,产于矿源层内或附近.  相似文献   

13.
The Palaeoproterozoic Lapland Granulite Belt is a seismically reflective and electrically conductive sequence of deep crustal (6–9 kbar) rocks in the northern Fennoscandian Shield. It is composed of garnet-sillimanite gneisses (khondalites) and pyroxene granulites (enderbites) which in certain thrust sheets form about 500 m thick interlayers. The structure was formed by the intrusion of intermediate to basic magmas into turbiditic sedimentary rocks under granulite facies metamorphism accompanied by shearing of the deep crust about 1.93–1.90 Gyr ago (Gal. Granulites were upthrust 1.90–1.87 Ga and the belt was divided by crustal scale duplexing into four structural units whose layered structure was preserved. The thrust structures are recognized by the repetition of lithological ensembles and by discordant structural patterns well distinguishable in airborne magnetic and electromagnetic data. Thrusting gave rise to clockwise pressure-temperature evolution of the belt. However, some basic rocks possibly record an isobaric cooling path. The low bulk resistivity of the belt (200–1000 Ωm) is caused by interconnected graphite and subordinate sulphides in shear zones. On the basis of carbon isotope ratios this graphite is derived mostly from sedimentary organic carbon. The seismic reflectivity of the belt may be caused by velocity and density differences between pyroxene granulites and khondalites, as well as by shear zones.  相似文献   

14.
The central part of the Carolina terrane in western South Carolina comprises a 30 to 40 km wide zone of high grade gneisses that are distinct from greenschist facies metavolcanic rocks of the Carolina slate belt (to the SE) and amphibolite facies metavolcanic and metaplutonic rocks of the Charlotte belt (to the NW). This region, termed the Silverstreet domain, is characterized by penetratively deformed felsic gneisses, granitic gneisses, and amphibolites. Mineral assemblages and textures suggest that these rocks formed under high‐pressure metamorphic conditions, ranging from eclogite facies through high‐P granulite to upper amphibolite facies. Mafic rocks occur as amphibolite dykes, as metre‐scale blocks of coarse‐grained garnet‐clinopyroxene amphibolite in felsic gneiss, and as residual boulders in deeply weathered felsic gneiss. Inferred omphacite has been replaced by a vermicular symplectite of sodic plagioclase in diopside, consistent with decompression at moderate to high temperatures and a change from eclogite to granulite facies conditions. All samples have been partially or wholly retrograded to amphibolite assemblages. We infer the following P‐T‐t history: (1) eclogite facies P‐T conditions at ≥ 1.4 GPa, 650–730 °C (2) high‐P granulite facies P‐T conditions at 1.2–1.5 GPa, 700–800 °C (3) retrograde amphibolite facies P‐T conditions at 0.9–1.2 GPa and 720–660 °C. This metamorphic evolution must predate intrusion of the 415 Ma Newberry granite and must postdate formation of the Charlotte belt and Slate belt arcs (620 to 550 Ma). Comparison with other medium temperature eclogites and high pressure granulites suggests that these assemblages are most likely to form during collisional orogenesis. Eclogite and high‐P granulite facies metamorphism in the Silverstreet domain may coincide with a ≈570–535 Ma event documented in the western Charlotte belt or to a late Ordovician‐early Silurian event. The occurrence of these high‐P assemblages within the Carolina terrane implies that, prior to this event, the western Carolina terrane (Charlotte belt) and the eastern Carolina terrane (Carolina Slate belt) formed separate terranes. The collisional event represented by these high‐pressure assemblages implies amalgamation of these formerly separate terranes into a single composite terrane prior to its accretion to Laurentia.  相似文献   

15.
The features of the structure and tectonic evolution of granulite gneiss belts (GGBs) are analyzed and summarized from the present-day data. Their continent–continent collision tectonic origin is supported, as well as multicycle and an inherited style of evolution expressed in multiple manifestations of granulite facies metamorphism of the belt separated by few 100 Ma. GGBs are permanently mobile structures that exhibit endogenic activity during all stages of their evolution, including intraplate conditions. Their relationship with supercontinental cyclicity is evident from (i) the spatial location of most GGBs in the margins of young oceans that originated during the breakup of Pangea, (ii) the amalgamation and breakup of ancient supercontinents along the GGBs, and (iii) the correlation between various types of granulite metamorphism of these belts and stages of supercontinental cycle. The evolution of these belts leads to complex interaction of plate and mantle plume tectonics, which is expressed in combination of continent–continent collision and underplating. The possible use of GGBs in paleotectonic analysis along with other indicators of geodynamic settings is shown.  相似文献   

16.
The normative mineral composition is reported on source rocks of metasediments from the granulite belt of the Baltic Shield. The primary composition, CIA index, and position of data points of studied rocks in discriminant diagrams indicate that a significant part of the studied rocks formed from immature sediments (graywackes and subgraywackes). The material supplied to sedimentation paleobasins was obtained from different (ultrabasic, basic, intermediate, and acid) rocks. The paleobasin was characterized by organic activity and reducing environment in the bottom layer. Correlation found between some elements, e.g., (Rb, Ba, Pb)–K; Sr–(Na, Ca), and so on, is also typical of Phanerozoic deposits. The possible contents of OM (Corg) and U were reconstructed in source rocks of metasediments of the Lapland–Kolvitsa granulite belt of the Baltic Shield.  相似文献   

17.
Doklady Earth Sciences - Data on the carbon isotope composition of graphite and CO2 from inclusions in quartz of granitoids of the Southern Marginal Zone (SMZ) of the Limpopo granulite belt, South...  相似文献   

18.
《International Geology Review》2012,54(12):1166-1181
Geological and isotope-geochemical studies of acid volcanics in the Verkhovtsevo greenstone belt and surrounding tonalite-trondhjemite plutons within the central Dnieper gneiss-green- stone terrain were conducted in the search for genetic relationships and increased understanding of the petrogenesis of acid melts. The acid volcanic and plutonic rocks are similar in mineral composition and form a unified calc-alkaline-like trend from dacite/tonalite to rhyolite/ trondhjemite. Dacites and tonalites have the same rare-earth element (REE) patterns with moderately fractionated light and heavy REE as well as small negative Eu anomalies. Rhyolite and trondhjemites have less-fractionated REE patterns with larger negative Eu anomalies. Whole-rock data for the acid volcanic and plutonic rocks yielded a single isochron of 3117 ± 204 Ma, εNd = +1.14 ± 0.80.

The data suggest a temporal and genetic relationship between the acid volcanics of the greenstone sequences and the surrounding plutonic rocks; both appear to belong to a single suite. The positive eNd value tends to suggest that a source of their melts can be traced to mafic materials rather than to older sialic crust. Petrochemical data and REE-model calculations suggest that dacite/tonalite liquids might have formed during partial melting of a mafic source, such as Archaean tholeiite TH-1 in equilibrium with hornblende-pyroxene-plagioclase restite. Subsequent differentiation of these melts in equilibrium with titanoilmenite-pyroxene-plagioclase cumulate may have given rise to the trondhjemites and rhyolites. Such a mineralogy of the restite and cumulate phases suggests that felsic melts containing little water in the Verkhovtsevo greenstone belt were generated at depths up to 30 km, probably in the greenstone belt's mafic basement.  相似文献   

19.
Estimating the undiscovered mineral resources of a terrane is a challenging, yet essential, task in mineral exploration. We apply Zipf’s law rank statistical analysis to estimate the undiscovered nickel sulphide resources in the Norseman-Wiluna Greenstone Belt, Western Australia. The analysis suggests that about 3.0 to 10.0 Mt of nickel sulphide resources are yet to be discovered in this belt, compared to the currently known total nickel sulphide endowment of 10.8 Mt. This undiscovered nickel sulphide endowment is likely to be hosted by incompletely delineated deposits and undiscovered deposits in less explored komatiites in the belt. Using the more detailed data subset of the Kambalda domain, this study manipulates Zipf’s law to estimate the sizes of undiscovered deposits, in addition to the domain’s total nickel sulphide endowment estimate. Importantly, regression analysis shows that the gradient of the line of best fit through the logarithmic rank-size plot for the detailed Kambalda data subset is −1. This gradient, which is the key Zipf’s law constant k, has the value of −0.92 for the Norseman-Wiluna Greenstone Belt which is collectively less mature than the Kambalda domain. This result corroborates the use of k = −1 in Zipf’s law predictive analyses of mineral resources for deposit populations for which the value of k = −1 has not yet been attained due to exploration immaturity.  相似文献   

20.
ＲｅｃｏｇｎｉｔｉｏｎｏｆＯｐｈｉｏｌｉｔｅＢｅｌｔａｎｄＧｒａｎｕｌｉｔｅｉｎＮｏｒｔｈｅｒｎＡｒｅａｏｆＭｉａｎ－Ｌｕｅ，ＳｏｕｔｈｅｒｎＱｉｎｌｉｎｇ，ＣｈｉｎａａｎｄＴｈｅｉｒＩｍｐｌｉｃａｔｉｏｎ￥ＸｕＪｉｆｅｎｇ（Ｄｅｐａｒｔｍｅｎｔｏｆ...  相似文献   

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