The Brazilian shield was assembled from a few Archean and Paleoproterozoic cratonic nuclei surrounded by Pan-African-Brasiliano mobile belts of Neoproterozoic age. While some of these mobile belts display a typical fr...The Brazilian shield was assembled from a few Archean and Paleoproterozoic cratonic nuclei surrounded by Pan-African-Brasiliano mobile belts of Neoproterozoic age. While some of these mobile belts display a typical frontal collision tectonic style, others are dominated by transcurrent regimes, clearly indicating oblique collisional systems. This paper is an attempt to determine the mean orientation of the principal horizontal compressive stresses for each mobile belt, considering either the frontal or oblique convergence character. From these general observations a scheme with WNW - ESE to NWSE trends of the main compressive stress is proposed. We suggest that this trend represents the mean displacement vectors, according to a coherent kinematic picture for the amalgamation of the West Gondwana during the final stages of convergence of the Brasiliano belts, where WNW-ESE to NW-SE are the main directions of final closure.展开更多
Considering its central position in East Gondwana reconstructions, the Indian subcontinent figures prominently in the studies, which were envisaged under the recently conceptualized international project—""...Considering its central position in East Gondwana reconstructions, the Indian subcontinent figures prominently in the studies, which were envisaged under the recently conceptualized international project—""LEGENDS"" (Lithospheric Evolution of Gondwana East from interdisciplinary Deep Surveys), a major initiative by international scientific community to study continents of the southern hemisphere. The CC-8 subcommittee of the International Lithospheric Programme (ILP) has also accepted the LEGENDS initiative.展开更多
Graphites which occur in the Early Precambrian banded iron formation (BIF)(3.1×10^9 yr, Algoma type) at Gongchangling, Anshan, China can be divided into two genetie types on the basis of their modes of occurrence...Graphites which occur in the Early Precambrian banded iron formation (BIF)(3.1×10^9 yr, Algoma type) at Gongchangling, Anshan, China can be divided into two genetie types on the basis of their modes of occurrence: biogenic and inorganic; the former occurs in garnet-mica-quartz schist and the latter in rich magnetite ore. The garnet-mica-quartz schist is located at the bottom of the formation. Its original rock is a volcanic tuff-bearing clayey siltstone. Graphite disseminates fairly uniformly in the schist. Chemical analysis of 20 samples of graphite yields an average content of 0.29±0.22%. The average δ^13C value of 4 samples is -26.6±0.6‰ (PDB). Rich magnetite ore bodies occur in the form of lens and layer within the banded magnetite quartzite, and wall-rock alteration is also noticed. Graphite-bearing rich magnetite ore is composed of magnetite, maghemite and minor graphite. Late chlorite and siderite are recognized locally. Disseminated graphite is generally distributed in scaly aggregates interstitial to the grains of magnetite, occasionally found within the grains of magnetite. It is non-uniformly distributed in the horizon of shoot, mainly in the core of the shoot. No graphite is found in the outer part of the shoot, poor ore in the same horizon, wallrock near the shoot and altered rock, indicating that graphite has a great bearing on the shoot. Chemical analysis of 15 samples gives an average graphite content of 0.89±0.51%. The average δ^23C value of 18 samples is-4.7±2.1‰(PDB). This kind of graphite seems to have been formed by the following reaction:6 FeCO3=2 Fe3O4+5 CO2+C in the primary sedimentary siderite under condition of amphibole-facies regional metamorphism.展开更多
鲁西地区中生代有2个岩浆活动时期,中侏罗世岩浆活动规模较小,形成铜石杂岩体,锆石SHRIMP U Pb年龄167.9-183Ma,加权平均值为（175.7±3.8）Ma;早白垩世岩浆活动范围较广,生成多种岩石系列,形成济南—埠村—邹平—淄博金岭一带杂岩...鲁西地区中生代有2个岩浆活动时期,中侏罗世岩浆活动规模较小,形成铜石杂岩体,锆石SHRIMP U Pb年龄167.9-183Ma,加权平均值为（175.7±3.8）Ma;早白垩世岩浆活动范围较广,生成多种岩石系列,形成济南—埠村—邹平—淄博金岭一带杂岩体和沂南县铜井、莱芜、蒙阴虎头崖、临朐铁寨等杂岩体,锆石SHRIMP和LA ICP MS U Pb测年结果为128-134Ma。展开更多
文摘The Brazilian shield was assembled from a few Archean and Paleoproterozoic cratonic nuclei surrounded by Pan-African-Brasiliano mobile belts of Neoproterozoic age. While some of these mobile belts display a typical frontal collision tectonic style, others are dominated by transcurrent regimes, clearly indicating oblique collisional systems. This paper is an attempt to determine the mean orientation of the principal horizontal compressive stresses for each mobile belt, considering either the frontal or oblique convergence character. From these general observations a scheme with WNW - ESE to NWSE trends of the main compressive stress is proposed. We suggest that this trend represents the mean displacement vectors, according to a coherent kinematic picture for the amalgamation of the West Gondwana during the final stages of convergence of the Brasiliano belts, where WNW-ESE to NW-SE are the main directions of final closure.
文摘Considering its central position in East Gondwana reconstructions, the Indian subcontinent figures prominently in the studies, which were envisaged under the recently conceptualized international project—""LEGENDS"" (Lithospheric Evolution of Gondwana East from interdisciplinary Deep Surveys), a major initiative by international scientific community to study continents of the southern hemisphere. The CC-8 subcommittee of the International Lithospheric Programme (ILP) has also accepted the LEGENDS initiative.
文摘Graphites which occur in the Early Precambrian banded iron formation (BIF)(3.1×10^9 yr, Algoma type) at Gongchangling, Anshan, China can be divided into two genetie types on the basis of their modes of occurrence: biogenic and inorganic; the former occurs in garnet-mica-quartz schist and the latter in rich magnetite ore. The garnet-mica-quartz schist is located at the bottom of the formation. Its original rock is a volcanic tuff-bearing clayey siltstone. Graphite disseminates fairly uniformly in the schist. Chemical analysis of 20 samples of graphite yields an average content of 0.29±0.22%. The average δ^13C value of 4 samples is -26.6±0.6‰ (PDB). Rich magnetite ore bodies occur in the form of lens and layer within the banded magnetite quartzite, and wall-rock alteration is also noticed. Graphite-bearing rich magnetite ore is composed of magnetite, maghemite and minor graphite. Late chlorite and siderite are recognized locally. Disseminated graphite is generally distributed in scaly aggregates interstitial to the grains of magnetite, occasionally found within the grains of magnetite. It is non-uniformly distributed in the horizon of shoot, mainly in the core of the shoot. No graphite is found in the outer part of the shoot, poor ore in the same horizon, wallrock near the shoot and altered rock, indicating that graphite has a great bearing on the shoot. Chemical analysis of 15 samples gives an average graphite content of 0.89±0.51%. The average δ^23C value of 18 samples is-4.7±2.1‰(PDB). This kind of graphite seems to have been formed by the following reaction:6 FeCO3=2 Fe3O4+5 CO2+C in the primary sedimentary siderite under condition of amphibole-facies regional metamorphism.
文摘鲁西地区中生代有2个岩浆活动时期,中侏罗世岩浆活动规模较小,形成铜石杂岩体,锆石SHRIMP U Pb年龄167.9-183Ma,加权平均值为（175.7±3.8）Ma;早白垩世岩浆活动范围较广,生成多种岩石系列,形成济南—埠村—邹平—淄博金岭一带杂岩体和沂南县铜井、莱芜、蒙阴虎头崖、临朐铁寨等杂岩体,锆石SHRIMP和LA ICP MS U Pb测年结果为128-134Ma。
