The Jayachamarajapura schist belt in western Dharwar craton, southern India, is predominantly an ultramafics dominant terrain. These rocks have been extensively metamorphosed and altered to serpentinite. The komatiite...The Jayachamarajapura schist belt in western Dharwar craton, southern India, is predominantly an ultramafics dominant terrain. These rocks have been extensively metamorphosed and altered to serpentinite. The komatiite nature of ultramafics is conspicuous. In most of the areas of the belt these ultramafics are massive in nature. However, some of the ultramafic units show layered nature. But, their outcrops are encompassed within the massive komatiitic bodies. These komatiitic ultramafics are predominantly Mg-rich in nature. The layered rocks are also Mg-rich, and their field setting and geochemistry suggest their intermittent occurrence as sills, during the differentiation of peridotitic magma. The layered rocks, which have been intensely serpentinisation show homogenous nature. They are almost wholly made of serpentine with occasional relics of pyroxene. Secondary carbonate mineral is often noticed. Their higher MgO content indicates Mg-rich ultramafic magmatism during Archaean orogeny.展开更多
It has been suggested that eclogites in the Dabie orogenic be lt are exhumation products, which had subducted into the deep-seated mantle and undergone ultra-high pressure metamorphism during the Triassic. But no dire...It has been suggested that eclogites in the Dabie orogenic be lt are exhumation products, which had subducted into the deep-seated mantle and undergone ultra-high pressure metamorphism during the Triassic. But no direct evidence supports this process except the calculated p-T conditions from mineral thermobarometers. The Late Cretaceous basalts studied in the prese nt paper, however, have provided some geochemical evidence for crust-mantle int eraction in the area. These basalts are distributed in Mesozoic faulted basins i n central and southern Dabie orogenic belt. Since little obvious contamination f rom continental crust and differentiation-crystallization were observed, it is suggested, based on a study of trace elements, that the basalts are alkaline and resultant from batch partial melting of the regional mantle rocks, and share th e same or similar geochemical features with respect to their magma source. In th e spider diagram normalized by the primitive mantle, trace element geochemistry data show that their mantle sources are enriched in certain elements concentrate d in the continental crust, such as Pb, K, Rb and Ba, and slightly depleted in s ome HFSE such as Hf, P and Nb. Pb-Sr-Nd isotopic compositions further suggest the mantle is the mixture of depleted mantle and enriched one . T his interaction can explain the trace element characteristics of basaltic magmas , i.e., the enrichment of Pb and the depletion of Hf, P and Nb in basalts can be interpreted by the blending of the eclogites in DOB (enriched in Pb and deplete d in Hf, P and Nd) with the East China depleted mantle (As compared to the primi tive mantle, it is neither enriched in Pb nor depleted in Hf, P and Nb). It is a lso indicated that the eclogites in the Dabie orogenic belt were surely derived from the exhumation materials, which had delaminated into the deep-seated mantl e. Moreover, the process subsequently resulted in compositional variation of the mantle (especially in trace elements and isotopes), as revealed by the late man tle-derived basalts in the Dabie orogenic belt.展开更多
This paper focuses on the effect of the later hydrotherm on uraniferous leucogranites and the stages of uranium mineralization. Here, we review C-H-O stable isotope, elements and fluid geochemistry of uraniferous leuc...This paper focuses on the effect of the later hydrotherm on uraniferous leucogranites and the stages of uranium mineralization. Here, we review C-H-O stable isotope, elements and fluid geochemistry of uraniferous leucogranites in Gaudeanmus, Namibia. The results show that there is significant increasing amount of rare earth element from non-mineralized to uraniferous leucogra-nites, indicating the synchronization of REE enrichment and uranium mineralization. Uranium enrichment may have close relations with Pb, Th, Co, Ni, REE in this region, so REE and U evidently exist homology. There are at least two stages of uranium mineralization by later hydrothermal alteration: firstly, due to magnatic residual high temperature and low salinity fluid, the temperature of main metallogenetic epoch ranges from 470°C to 530°C, salinity ranges from 3.55% to 9.60% NaCleq, and C, H, O stable isotope is -23‰ - -13.6‰, -53.3‰ - -46.4‰, 7.71‰ - 8.81‰, respectively. Secondly, due to superim-posed hydrothermal fluid, the temperature, salinity, and C, H, O stable isotope is 150°C - 220°C, 4.65% - 19.05% NaCleq, -20.3‰ -?-3.7‰, -64.7‰ - -53.6‰, 1.49‰ - 1.99‰, respectively. The fluid for reformation is derived from postmagmatic fluid, mixed with a number of meteoric water.展开更多
文摘The Jayachamarajapura schist belt in western Dharwar craton, southern India, is predominantly an ultramafics dominant terrain. These rocks have been extensively metamorphosed and altered to serpentinite. The komatiite nature of ultramafics is conspicuous. In most of the areas of the belt these ultramafics are massive in nature. However, some of the ultramafic units show layered nature. But, their outcrops are encompassed within the massive komatiitic bodies. These komatiitic ultramafics are predominantly Mg-rich in nature. The layered rocks are also Mg-rich, and their field setting and geochemistry suggest their intermittent occurrence as sills, during the differentiation of peridotitic magma. The layered rocks, which have been intensely serpentinisation show homogenous nature. They are almost wholly made of serpentine with occasional relics of pyroxene. Secondary carbonate mineral is often noticed. Their higher MgO content indicates Mg-rich ultramafic magmatism during Archaean orogeny.
文摘It has been suggested that eclogites in the Dabie orogenic be lt are exhumation products, which had subducted into the deep-seated mantle and undergone ultra-high pressure metamorphism during the Triassic. But no direct evidence supports this process except the calculated p-T conditions from mineral thermobarometers. The Late Cretaceous basalts studied in the prese nt paper, however, have provided some geochemical evidence for crust-mantle int eraction in the area. These basalts are distributed in Mesozoic faulted basins i n central and southern Dabie orogenic belt. Since little obvious contamination f rom continental crust and differentiation-crystallization were observed, it is suggested, based on a study of trace elements, that the basalts are alkaline and resultant from batch partial melting of the regional mantle rocks, and share th e same or similar geochemical features with respect to their magma source. In th e spider diagram normalized by the primitive mantle, trace element geochemistry data show that their mantle sources are enriched in certain elements concentrate d in the continental crust, such as Pb, K, Rb and Ba, and slightly depleted in s ome HFSE such as Hf, P and Nb. Pb-Sr-Nd isotopic compositions further suggest the mantle is the mixture of depleted mantle and enriched one . T his interaction can explain the trace element characteristics of basaltic magmas , i.e., the enrichment of Pb and the depletion of Hf, P and Nb in basalts can be interpreted by the blending of the eclogites in DOB (enriched in Pb and deplete d in Hf, P and Nd) with the East China depleted mantle (As compared to the primi tive mantle, it is neither enriched in Pb nor depleted in Hf, P and Nb). It is a lso indicated that the eclogites in the Dabie orogenic belt were surely derived from the exhumation materials, which had delaminated into the deep-seated mantl e. Moreover, the process subsequently resulted in compositional variation of the mantle (especially in trace elements and isotopes), as revealed by the late man tle-derived basalts in the Dabie orogenic belt.
文摘This paper focuses on the effect of the later hydrotherm on uraniferous leucogranites and the stages of uranium mineralization. Here, we review C-H-O stable isotope, elements and fluid geochemistry of uraniferous leucogranites in Gaudeanmus, Namibia. The results show that there is significant increasing amount of rare earth element from non-mineralized to uraniferous leucogra-nites, indicating the synchronization of REE enrichment and uranium mineralization. Uranium enrichment may have close relations with Pb, Th, Co, Ni, REE in this region, so REE and U evidently exist homology. There are at least two stages of uranium mineralization by later hydrothermal alteration: firstly, due to magnatic residual high temperature and low salinity fluid, the temperature of main metallogenetic epoch ranges from 470°C to 530°C, salinity ranges from 3.55% to 9.60% NaCleq, and C, H, O stable isotope is -23‰ - -13.6‰, -53.3‰ - -46.4‰, 7.71‰ - 8.81‰, respectively. Secondly, due to superim-posed hydrothermal fluid, the temperature, salinity, and C, H, O stable isotope is 150°C - 220°C, 4.65% - 19.05% NaCleq, -20.3‰ -?-3.7‰, -64.7‰ - -53.6‰, 1.49‰ - 1.99‰, respectively. The fluid for reformation is derived from postmagmatic fluid, mixed with a number of meteoric water.
