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1.
《Gondwana Research》2002,5(2):453-465
The Kunduru Betta Ring Complex (KRC), at the southern margin of Dharwar craton, South India, comprises metaluminous sub-solvus syenites and quartz monzonite with a concentric disposition younging towards the center. An outer mafic syenite (of lamprophyric affinity) is followed by porphyritic monzonite, quartz monzodiorite and finally a quartz monzonitic stock at the centre.SiO2, Al2O3 and Na2O increase from the primitive lamprophyric mafic syenite to the quartz monzonite through the intermediate members, while CaO, MgO, Fe2O3T, TiO2, P2O5 and MnO show an opposite trend suggesting fractionation of hornblende, clinopyroxene, biotite, apatite, sphene, and iron oxide minerals. Rb, Th and U increase with a complementary decrease in Sc, V, Cr, Co, Cu, Sr and Ba from the outer mafic syenite to the inner quartz monzonite. Y, Zr and Hf decrease from lamprophyric mafic syenite to quartz monzodiorite and the trend is reversed in the final quartz monzonite phase. However, the suite is characterised by a compositional gap between quartz monzodiorite and quartz monzonite. Total REE gradually decrease from the mafic syenite to quartz monzonite and the REE distribution patterns show LREE-enriched and HREE-depleted parallel distributions with negligible Eu anomalies.The geochemical data suggest that the rock types were formed as products of progressive differentiation by crystal fractionation of calc-alkaline lamprophyric parent magma which was derived by partial melting of metasomatically enriched mantle in the Kabini lineament. Although the quartz monzonites conform to the trend of differentiated Kunduru Betta suite, the compositional gap between them and the quartz monzodiorite precludes their origin by simple differentiation. It is suggested that convective liquid fractionation might have resulted in the discrete body of quartz monzonite.  相似文献   

2.
Biotite-rich syenitic stocks in the Mont-Laurier area of the southwestern Grenville Province are shown to belong to the first recorded Proterozoic example of an ultrapotassic, K-rich alkaline and shoshonitic rock association with clear arc affinities. The plutons investigated were previously considered mostly syenitic, typical of nepheline syenite alkaline suites, slightly metamorphosed and late-tectonic with respect to the Grenville orogeny. We find that they postdate the regional metamorphism and comprise a felsic to ultramafic range of rock types belonging to two series: (1) a potassic-to-ultrapotassic, silica-undersaturated series of biotite-rich nepheline-bearing syenite, syenite, monzonite, diorite and pyroxenite, and (2) a shoshonitic, critically silicasaturated series of quartz syenite and amphibole-bearing syenite, with rare monzonite and diorite. The ubiquitous biotite, previously regarded as metamorphic, is reinterpreted as igneous and diagnostic of the potassic character. The shoshonitic and potassic series display the strong enrichment in Al, Ca, K and large-ion-lithophile elements relative to the high-field-strength elements (e.g. Ba/Nb722, La/YB45) and the low contents in Mg that are characteristic of arc-related magmas. The syenitic rocks consistently share the distinctive arc-related geochemical signature of their mafic counterparts. Syenites may thus represent a potential source of paleotectonic information for high grade terranes. Geochemical discriminants (NbN/TaN and HfN/TiN ratios) indicate that the shoshonitic and potassic series are unrelated by closedsystem fractionation processes. Rather, the chemical differences between the two series probably reflect differences in source characteristics and conditions of melting. Similar plutons occur throughout the Central Metasedimentary Belt of the southwestern Grenville Province. They define a 1089 to 1076 Ma, 450-km-long grenvillian potassic alkaline plutonic (PAP) province. The presence of this K-rich alkaline province indicates that the scarcity of K-rich rocks in the Precambrian could be only apparent and a consequence of misidentification of K-rich plutons in metamorphosed Precambrian terranes. These 1.1 Ga ultrapotassic to shoshonitic plutonic rocks are geochemically similar to shoshonites and leucitites of the Sunda arc. This similarity suggests that subduction-type enrichment processes were operating in the Proterozoic in ways similar to those of modern settings.  相似文献   

3.
《International Geology Review》2012,54(12):1074-1093
The mineral-fluid equilibria that govern silica redistribution by aqueous fluids in subduction zones were evaluated at constant pressure and temperature in the model system MgO-SiO2-H2O (MSH). At <20 kbar and <1000° C, model H2O-SiO2 fluids liberated via devolatilization in subducting crust will be buffered at or near quartz saturation along any specified subduction P-T path, whereas fluids in equilibrium with model metaperidotites, ranging from dunite to orthopyroxenite protoliths, have silica concentrations significantly below quartz saturation. Isothermalisobaric flow of fluid from the slab to the mantle wedge therefore drives metasomatic reactions that increase the bulk silica content of metaperidotites and decrease the silica content of the fluid. The potential for silica metasomatism increases with depth for all subduction paths and model bulk compositions. At a given depth, the capacity for silica metasomatism increases with temperature and with abundance of forsterite relative to enstatite. Water-rock ratios required to produce metasomatic mineral assemblages decrease with increasing pressure and temperature. Mineral assemblages diagnostic of silica metasomatism at shallow subduction levels require water-rock ratios of >100 moles fluid/cm3 rock; but at depth, flow of only several moles fluid/cm3 rock is sufficient to produce assemblages characteristic of silica metasomatism. Decreasing temperature with time in most subduction zones suggests that the potential for silica metasomatism is greatest at early stages of convergence. Subducted ultramafic rocks showing evidence of high-temperature silica metasomatism therefore may provide windows into early subduction processes. In general, temporal changes in subduction parameters favoring increasing temperatures will enhance the potential for silica metasomatism, whereas those leading to lower temperatures should be expected to decrease the capacity for silica transfer with time.  相似文献   

4.
Whole rock trace element and isotopic compositions of different HP–LT metamorphic rocks of the Ile de Groix were analysed to characterise geochemical fingerprints during subduction and exhumation in a late Palaeozoic HP metamorphic terrain. Massive metabasites of hydrothermally altered enriched mid-ocean ridge basalt (E-MORB) origin are in association with banded metabasic rocks of volcano-sedimentary origin and metapelites. Fluid-rock interactions that likely occurred during seafloor hydrothermal alteration and early subduction metasomatism increased δ18O values, as well as K2O, Na2O, MgO, and LILE contents and decreased CaO contents of metabasites. Most metabasites have retained their early-subduction and pre-HP trace element and isotopic composition, even for rocks metamorphosed to lower eclogite-facies P–T conditions. Micaschists also preserved apparent pelitic protolith trace element values and oxygen isotopic compositions. During retrograde metamorphism related to the exhumation, metabasites were rehydrated by fluids in equilibrium with the host rock compositions, which were likely derived from the basic rocks. This style of fluid–rock interaction formed a greenschist facies mineral assemblage. Metabasites that underwent pervasive alteration by seafloor hydrothermal and metasomatism processes prior to peak metamorphism, show greater effects of retrogression and albitisation, probably because they were richer in H2O and Na2O. The variety of metamorphic assemblages on the Ile de Groix is thus directly related to the pre-HP rock composition. The extent of retrogression in the western part of the Ile de Groix primarily reflects stronger metasomatic intensities than in the eastern part.  相似文献   

5.
The South Dehgolan pluton, in NW Iran was emplaced into the Sanandaj–Sirjan magmatic–metamorphic zone. This composite intrusion comprises three main groups: (1) monzogabbro–monzodiorite rocks, (2) quartz monzonite–syenite rocks, and (3) a granite suite which crops out in most of the area. The granites generally show high SiO2 content from 72.1%–77.6 wt.% with diagnostic mineralogy consisting of biotite and amphibole along the boundaries of feldspar–quartz crystals which implies anhydrous primary magma compositions. The granite suite is metaluminous and distinguished by high FeOt/MgO ratios (av. 9.6 wt.%), typical of ferroan compositions with a pronounced A‐type affinity with high Na2O + K2O contents, high Ga/Al ratios, enrichment in Zr, Nb, REE, and depletion in Eu. The quartz monzonite–syenites show intermediate SiO2 levels (59.8%–64.5 wt.%) with metaluminous, magnesian to ferroan characteristics, intermediate Na2O + K2O contents, enrichment in Zr, Nb, REE, Ga/Al, and depletion in Eu. The monzogabbro–monzodiorites show overall lower SiO2 content (48.5%–55.9 wt.%) with metaluminous and calc‐alkaline compositions, relatively lower Na2O + K2O contents, low Ga/Al ratios, and FeOt/MgO (av. 1.6 wt.%) ratios, low abundances of Zr, Nb, and lower REE element concentrations relative to the granites and quartz monzonite–syenites. These geochemical differences among the three different rocks suites are likely to indicate different melt origins. We suggest that the South Dehgolan pluton resulted from a change in the geodynamic regime, from compression to extension in the Sanandaj–Sirjan zone during Mesozoic subduction of the Neo‐Tethys oceanic crust beneath the Central Iranian microcontinent. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

6.
Chemical analyses suggest that the metavolcanic rocks of the Almas Greenstone Belt (AGB), Tocantins State, Brazil have a continental affinity, possibly related to a continental rift environment. They were metamorphosed to amphibolite facies during a regional tectono-metamorphic event (Dn), retrogressed to greenschist facies assemblages and then hydrothermally altered within dextral strike–slip shear zones (Dn+1). Fracture sets related to Dn+2 intersect Sn+1.The Paiol Gold Mine is one of several mineralised zones within metabasic and meta-intermediate rocks of the AGB. It exploits shoots of sulphide–Au–quartz mineralisation that occupy dilational zones approximately perpendicular to an elongation lineation (Ln+1) within mylonitic foliation Sn+1 (Sn+1=S within the S–C fabric). The dilational zones probably formed due to dextral displacement on sinistrally en echelon C surfaces. Minor amounts of gold may have been introduced or remobilised during Dn+2.Coexisting primary and pseudosecondary fluid inclusions in mineralised quartz veins from ore shoots comprise a high-salinity three-phase type (Type II) and a lower salinity two-phase type (Type I). Homogenisation temperatures for Type II inclusions range from 200 to 410 °C and Type I from 90 to 320 °C. The inclusions and their temperature ranges are believed to reflect heat exchange and some mixing between the two fluid types under relatively constant ambient temperatures, but variable (though broadly declining) fluid temperatures. This took place late in Dn+1 in conjunction with greenschist facies retrogression and localised hydrothermally induced metasomatism.  相似文献   

7.
Archaean granulites from the type charnockite locality of Pallavaram, Madras City, Tamil Nadu, southern India consist of a bimodal suite of basic and silicic orthogneisses, associated with metasedimentary gneisses (khondalites). Charnockite is the dominant rock type. Basic granulites display a tholeiitic trend of strong iron enrichment accompanied by an increase in the concentration of the rare earth elements (REE), and the development of appreciable negative europium anomalies. These trends are considered to reflect low pressure fractional crystallisation of pyroxene-plagioclase assemblages under conditions of lowf O 2. Ultramafic granulites may represent the cumulus material of such a process. The silicic granulites (charnockites) are generally K2O rich and in marked contrast to the low K2O (tonalitic) silicic gneisses which dominate most granulite facies terrains. Their REE abundances, however, embrace the complete range of patterns observed in both K-rich and K-poor Archaean gneisses. The presence of a large number of pre-granulite facies potassic pegmatites in the area suggests metasomatism of an originally less potassic suite of rocks. Trace element considerations lead to a model whereby metasomatism and partial fusion of silicic gneisses in the terrain preceded the granulite facies metamorphic event. This sequence of events is best related to fluctuations in the composition of metamorphic fluids in the lower crust.  相似文献   

8.
王伟  胡健民  陈虹  于根旺  赵越  刘晓春 《地质通报》2014,33(12):2023-2031
对采自南极罗斯造山带中北维多利亚地难言岛的侵入岩进行了岩石学和锆石U-Pb同位素分析。难言岛的主要侵入岩类型为石英二长岩,并有少量石英二长闪长岩。采用LA-ICP-MS对石英二长岩和石英二长闪长岩样品进行锆石UTh-Pb同位素分析,获得石英二长岩的侵位年龄为482.4Ma±4.2Ma和484.3Ma±2.5Ma,石英二长闪长岩的侵位年龄为484.0Ma±3.0Ma,均为早奥陶世早期。难言岛石英二长岩和石英二长闪长岩岩浆应在伸展背景下侵位结晶,结合已有区域资料可以推测,在北维多利亚地罗斯造山运动应主要发生在寒武纪,并在早奥陶世早期之前趋于结束。  相似文献   

9.
河北东坪金矿区水泉沟岩体的地球化学特征   总被引：17，自引：0，他引：17       下载免费PDF全文
魏菊英  苏琪 《地质科学》1994,29(3):256-266
水泉沟岩体主要由二长岩构成。主要矿物是碱性长石和斜长石,它们的含量高达80%以上。石英不多见,暗色矿物含量少。副矿物主要是磁铁矿、石榴石、榍石和锆石。交代结构发育,蚀变现象普遍。主要化学组分和微量元素含量及δ18O值变化范围大。该二长岩体是由老片麻岩经热液碱交代作用而成。  相似文献   

10.
The central, northwestern and western Anatolian magmatic provinces are defined by a large number of late Mesozoic to late Cenozoic collision‐related granitoids. Calc‐alkaline, subalkaline and alkaline intrusive rocks in central Anatolia are mainly metaluminous, shoshonitic, I‐ to A‐types. They cover a petrological range from monzodiorite through quartz monzonite to granite/syenite, and are all enriched in LILE. Their geochemical characteristics are consistent with formation from a subduction‐modified mantle source. Calc‐alkaline plutonic rocks in northwestern Anatolia are mainly metaluminous, medium‐ to high‐K and I‐types. They are monzonite to granite, and all are enriched in LILE and depleted in HFSE, showing features of arc‐related intrusive rocks. Geochemical data reveal that these plutons were derived from partial melting of mafic lower crustal sources. Calc‐alkaline intrusive rocks in western Anatolia are metaluminous, high‐K and I‐types. They have a compositional range from granodiorite to granite, and are enriched in LILE and depleted in HFSE. Geochemical characteristics of these intrusive rocks indicate that they could have originated by the partial melting of mafic lower crustal source rocks.  相似文献   

11.
The Rio Espinharas pluton, northeastern Brazil, belongs to the shoshonitic series and consists mainly of syenogranite, quartz–monzonite and porphyritic quartz–monzonite, but diorite, quartz–monzodiorite, quartz–syenite and microsyenogranite also occur containing microgranular enclaves, except for the diorite. Most variation diagrams of rocks, amphiboles, biotites and allanites show linear trends, but K, Zr, Sr and Ba of rocks display curved scattered trends. The rocks ranging from diorite to syenogranite define a pseudo-errorchron and have similar REE patterns. Syenogranite and microsyenogranite are derived from two distinct pulses of granite magma with initial 87Sr/86Sr ratio of 0.7083±0.0003 and 0.7104±0.0007, respectively. Modelling of major and trace elements shows that the syenogranite evolved by fractional crystallization of plagioclase, microcline, edenite, biotite and titanite, whereas quartz–monzonite, porphyritic quartz–monzonite, quartz–monzodiorite and quartz–syenite resulted from simple mixing between an upper mantle-derived dioritic magma and the upper crust-derived syenogranite magma. Dioritic enclaves are globules of a mafic magma from the upper mantle.  相似文献   

12.
The In Ouzzal granulitic unit (IOGU) consists predominantly of felsic orthogneisses most of which correspond to granitoids emplaced during the Archaean, plus metasediments, including olivine-spinel marbles, of late Archaean age. All units were metamorphosed at granulite facies during the Eburnean (2 Ga). The stable isotope signature of the marbles (δ13C=–0.8 to –4.2‰/PDB; δ18O = 7.9 to 18.9‰/SMOW) does not record a massive streaming of C-bearing fluids during metamorphism. Most of the isotopic variation in the marbles is explained in terms of pregranulitic features. Metasomatic transformation of granulites into layered potassic syenitic rocks and emplacement of carbonate veins and breccias occurred during retrogressive granulite facies conditions. The chemistry of these rocks is comparable with that of fenites and carbonatites with high contents of (L)REEs, Th, U, F, C, Ba and Sr but, with respect to these elements, a relative depletion in Nb, Ta, Hf, Zr and Ti. The isotopic compositions of Nd (?Nd(T)=–6.3 to –9.9), of Sr (87Sr/86Sr(T)= 0.7093–0.7104), and the O isotopic composition of metasomatic clinopyroxene (δ18O = 6.9 to 8‰), all indicate that the fluid had a strong crustal imprint. On the basis of the C isotope ratios (δ13C =–3.5 to –9.7‰), the fluid responsible for the crystallization of carbonates and metasomatic alteration is thought to be derived from the mantle, presumably through degassing of mantle-derived magmas at depth. Intense interaction with the crust during the upward flow of the fluid may explain its chemical and isotopic signatures. The zones of metasomatic alteration in the In Ouzzal granulites may be the deep-seated equivalents of the zones of channelled circulation of carbonated fluids described at shallower levels in the crust.  相似文献   

13.
The Hämeenkyrö batholith is a round-shaped plutonic body of an areal size of 147 km2. It is composed of calc-alkaline to alkaline rocks that intruded previously metamorphosed Svecofennian volcanogenic and sedimentary schists 1860 Ma ago. The Cu-W bearing tourmaline breccia of the Ylörvi deposit occurs in metavolcanic rocks close to the eastern contact of the batholith.The average sampling density in the batholith was 1 sample per km2, and 175 samples were analyzed for Cu, Au, Ag, Ni, Pb, Co, Zn, S by AAS for SiO2, TiO2, Al2O3, FeO, MnO, MgO, CaO, Na2O, K2O, As, Sn and P by X-ray fluorescence. Mo and W were determined colorimetrically. Barth mesonorms were calculated for each sample and the rock type was determined according to Streckeisen's classification. Element distributions are displayed on contour maps.The rock types of the batholith exhibit an asymmetric concentric arrangement, the order from the center towards the margin being alkali-feldspar granite, syenogranite, monzogranite, quartz monzonite, quartz syenite, alkali-feldspar, quartz syenite, syenite and alkali-feldspar syenite. Anomalously high Cu, As, Sn, S, K2O and Na2O contents have been found at the eastern margin of the batholith in a N—S-trending zone, which is characterized by hydrothermal alteration phenomena, propylitization, tourmalinization and scapolitization. Three anomalous areas have been defined within this zone, one of them is associated with the Ylöjärvi deposit and the other two are regarded as exploration targets.  相似文献   

14.
The structural study of the Saint-Laurent – La Jonquera pluton (Eastern Pyrenees), a Variscan composite laccolithic intrusion emplaced in metasedimentary and gneissic rocks of the Roc de Frausa dome, by means of the anisotropy of magnetic susceptibility (AMS) technique has allowed the determination of the nature and orientation of its magmatic fabrics. The magmatic foliation has a predominant NE–SW strike and the mean lineation is also NE–SW trending with a shallow plunge. A strain gradient is measured so that the tonalites to granodiorites that form the basal parts of the pluton, and are intruded into amphibolite-facies metamorphic rocks, recorded the highest anisotropies, whereas the monzogranites and leucogranites, emplaced into upper crustal, low-grade metamorphic rocks, are weakly deformed. These results point to the synkinematic sequential emplacement of multiple granitoid sheets, from less to more differentiated magmatic stages, during the Late Carboniferous D2 event characterized by an E–W-trending dextral transpression. The magmatic foliation appears locally disturbed by the effects of two tectonic events. The first of them (D3) produced mylonitization of granitoids along NW–SE retrograding shear zones and open folds in the host Ediacaran metasediments of the Roc de Frausa massif, likely during late Variscan times. Interference between D2 and D3 structures was responsible for the dome geometry of the whole Roc de Frausa massif. The second and last perturbation consisted of local southward tilting of the granitoids coupled to the Mesozoic–Cenozoic cover during the Alpine.  相似文献   

15.
锦州-迁安太古宙赞岐岩类片麻岩成因及其动力学意义   总被引：2，自引：2，他引：0  
详细的野外地质调查和综合研究表明冀东-辽西南部地区太古宙变质基底主要由富钾花岗质岩石组成,由锦州至迁安构成一条NEE向延伸200余千米的富钾花岗质岩石带。这些富钾花岗质岩石主要由似斑状/中粒石英二长闪长质-花岗闪长质-二长花岗质片麻岩和中粒二长花岗岩-正长花岗岩构成。全岩地球化学分析表明这些石英二长闪长质-花岗闪长质-二长花岗质片麻岩具有高FeO~T、MgO、K_2O和Mg~#值的地球化学特征,与全球范围内中-新太古宙赞歧岩类相似。LA-ICP-MS锆石U-Pb同位素定年结果表明这些岩石形成于2546~2543Ma。岩石成因研究表明这些赞歧岩类片麻岩形成于俯冲板片及其拖曳的洋壳沉积物、增生楔物质的熔体和受俯冲流体、熔体交代的地幔楔之间相互作用引发的一系列的岩浆作用。这一多样化的赞岐岩类岩浆作用形成了一条新太古代赞岐岩类带,该赞岐岩类带反映了冀东-辽西南部地区新太古代从NNW向SSE向板片热俯冲的动力学体制。  相似文献   

16.
In the Sanandaj-Sirjan zone of metamorphic belt of Iran, the area south of Hamadan city comprises of metamorphic rocks, granitic batholith with pegmatites and quartz veins. Alvand batholith is emplaced into metasediments of early Mesozoic age. Fluid inclusions have been studied using microthermometry to evaluate the source of fluids from which quartz veins and pegmatites formed to investigate the possible relation between host rocks of pegmatites and the fluid inclusion types. Host minerals of fluid inclusions in pegmatites are quartz, andalusite and tourmaline. Fluid inclusions can be classified into four types. Type 1 inclusions are high salinity aqueous fluids (NaCleq >12 wt%). Type 2 inclusions are low to moderate salinity (NaCleq <12 wt%) aqueous fluids. Type 3 and 4 inclusions are carbonic and mixed CO2-H2O fluid inclusions. The distribution of fluid inclusions indicate that type 1 and type 2 inclusions are present in the pegmatites and quartz veins respectively in the Alvand batholith. This would imply that aqueous magmatic fluids with no detectable CO2 were present during the crystallization of these pegmatites and quartz veins. Types 3 and 4 inclusions are common in quartz veins and pegmatites in metamorphic rocks and are more abundant in the hornfelses. The distribution of the different types of fluid inclusions suggests that CO2 fluids generated during metamorphism and metamorphic fluids might also contribute to the formation of quartz veins and pegmatites in metamorphic terrains.  相似文献   

17.
The geological position, composition of mineral assemblages, and typomorphism of major minerals from garnet-bearing rocks at the Berezitovoe gold-base-metal deposit in the Upper Amur Region have been studied in detail. These are ore-bearing metasomatic rocks and metamorphosed porphyritic dikes. The garnet-bearing metasomatic rocks reveal zoning, which is caused by various degrees of metasomatic transformation of the Paleozoic porphyritic granodiorite that hosts the ore zone. The metasomatic replacement of granodiorite was accompanied by loss of Na, Ca, Ba, Sr and gain of K, Mn, and Rb. Garnet-bearing metamorphosed intermediate dikes occur within the metasomatic zone. The PT conditions of metamorphism and metasomatism are similar and estimated at 3.9 kbar and 500°C from various mineral equilibria. The results of physicochemical simulation of garnet-bearing mineral assemblages carried out by minimizing the Gibbs free energy and the geological data show that garnet-bearing mineral assemblages arose at the Berezitovoe deposit as a result of local high-temperature thermal metamorphism of previously formed low-temperature metasomatic rocks close in composition to classic beresite. In this connection, we propose considering garnet-bearing metasomatic rocks as high-temperature metamorphosed beresites.  相似文献   

18.
通过详细的野外地质填图和岩石地球化学研究,发现分布在皖浙两省交界处的天目山一带的石英二长闪长岩、石英二长斑岩、石英正长(斑)岩体不仅在空间上相伴,且岩石化学、地球化学特征相近,又都与燕山期黄尖旋回的火山岩密切共生,亲缘关系较密切,将其归并为天目山超单元。该超单元为高钾钙碱性—钾玄岩系列,地球化学特点表明岩浆由造山带的山根或者加厚的双倍陆壳的下部熔融产生,为同源岩浆成分与结构演化序列,其侵位机制不仅受区域构造控制,而且还受火山机构制约,以被动式就位为主,少数可能兼有主动就位机制。  相似文献   

19.
雄村特大型斑岩铜金矿床主要以细脉浸染状产于强烈蚀变岩石中,赋矿岩石原岩成因类型存在争议。本文对多个赋矿蚀变岩石作了系统光薄片显微鉴定,在多个蚀变较弱的矿化样品中发现赋矿岩石具斑状结构,其基质主要为钾长石,斑晶主要为斜长石、钾长石及少量石英,显示石英正长斑岩及二长斑岩(少量)矿物组成特征。结合前人工作,可以认为雄村铜金矿床赋矿岩石为正长斑岩、火山岩及少量二长斑岩。正长斑岩发育斑岩铜金矿床成矿早期常见的钾硅化蚀变及磁铁矿化蚀变,锆石具高的Ce4+/Ce3+比值(334~3084,平均值为1169),显示高氧逸度岩浆特征,和世界斑岩铜金矿床成矿岩体一致;这表明石英正长斑岩为雄村铜金矿床成矿岩体。石英正长斑岩锆石LA-ICP-MS U-Pb年龄为173.7±2.1Ma(MSWD=0.23),石英正长斑岩钾化阶段形成的黑云母40Ar/39Ar坪年龄为48.3±0.9Ma(MSWD=1.58),远小于锆石U-Pb年龄却与矿区东北部始新世花岗岩基的年龄一致,显示Ar-Ar年龄受后期地质事件影响而发生重置。通过上述研究,可以认为雄村铜金矿床为与石英正长斑岩有关的斑岩型矿床,形成时代约173Ma,和新特提斯洋洋壳向北俯冲诱发的岩浆事件有关,矿区内云母受后期地质事件影响重置,不能记录其形成时代。  相似文献   

20.
This paper presents the results of a study of the Paleoproterozoic basal garnet-kyanite-staurolite-two-mica paraschists from the Kukasozero structure of the Karelides of Northern Karelia, Baltic Shield, underlying Neoarchean acid metavolcanic rocks, and schists with quartz, phengite, kyanite, staurolite, garnet, and tschermakite located in the Paleoproterozoic rocks and considered to be metasomatic in origin. It was established that the sedimentary protolith of the Paleoproterozoic paraschists contains detritus of Neoarchean igneous rocks as follows from detrital 2737 ± 11 Ma zircons with oscillatory magmatic zoning. Metavolcanic 2757 ± 13 Ma rocks, close in age and composition, are known directly in the framework of the Kukasozero structure and are considered to be the most likely source of the sedimentary schist protolith. The coincidence of the Nd-model ages of paraschists (t DM is 2.73–2.76 Ga) with the age of detrital zircons indicates no contribution of older rocks to the protolith composition. The age of magmatic crystallization of metavolcanic rocks directly underlying the Paleoproterozoic paraschists is 2681 ± 18 Ma and coincides with the age of porphyry granites in the western framework of the structure (2680.3 ± 3.6 Ma). No detrital zircons of similar age were found in basal paraschists, but the restricted amount of dated zircons does not allow us to draw a final conclusion about the absence of detritus of the underlying metavolcanic rocks in the paraschist protolith. It was confirmed that phengite-bearing schists are the products of acid metasomatism of the Paleoproterozoic amphibolites and amphibole schists (metavolcanic rocks). The metasomatic features were revealed in garnet-kyanite-staurolite-two-mica paraschists, so the strict identification of their sedimentary protolith is impossible. The paraschists do not represent metamorphosed weathering crust, because acid metasomatism gives a false impression of the greater maturity of the primary sedimentary rocks.  相似文献   

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