Many Propositions are made about the mechanism of emplacement of volcanoclastic material in the Bombay volcanic complex. The present paper deals exclusively with the physical features of the deposits laid by a complex...Many Propositions are made about the mechanism of emplacement of volcanoclastic material in the Bombay volcanic complex. The present paper deals exclusively with the physical features of the deposits laid by a complex tectono-magmatic process by making detailed inventory of the different kind of volcanic ejecta exposed in the Bomay Volcanic Complex (BVC), and an attempt has been made to classify the deposits genetically. A subsidenace which was hinted at earlier, may be a possible cauldron in BVC has been proposed, which might be responsible for producing such a varied and complex lithology.展开更多
The Colima Volcanic Complex trends in a nearly N-S direction in western Mexico, and one of its?structures, Colima volcano, is the most historically active volcano in the country. Immediately to the?N, there is another...The Colima Volcanic Complex trends in a nearly N-S direction in western Mexico, and one of its?structures, Colima volcano, is the most historically active volcano in the country. Immediately to the?N, there is another volcanic center called El Cántaro volcano, whose activity started around 1.7 Ma in its N portion and migrated to the S in various episodes. Volcanic activity migrated further south, from El Cántaro to the Colima Volcanic Complex where the southernmost manifestation, Hijos del Volcán domes, is located on the south slope of Fuego volcano. The above date appears to mark initiation of the rather continuous volcanic activity in the area. It has been noted that these volcanic manifestations lie on, or near the Rivera-Cocos inland plate boundary. Colima’s Fuego volcano is also the closest to the Middle America Trench, among the polygenetic volcanoes in Mexico. We submit that the anomalous location of volcanism in this area originates in an anomalous subduction process of the Rivera and Cocos plates and evoke a tectonic model, proposed elsewhere, to support the idea. Modeling gravimetric and aeromagnetic data we locate the magma chambers of the Fuego (active) and Nevado (extinct) volcanoes within a 65 mGals negative Bouguer anomaly elongated in a nearly N-S direction. The corresponding aeromagnetic map displays a magnetic high over the southern portion of the Fuego volcano edifice. We found two additional, associated structures whose anomalies have not been previously reported, which appear to follow the southward magmatic migration pattern. One of them is a collapse structure with a circular topographic expression, and the southernmost is a low-density intrusion ~1 km below sea level, associated with a moderate topographic bulge at the surface that we interpret as a magma body. Five lines cross the anomalies;gravimetric and magnetic fields are concurrently modeled along them to locate the magmatic bodies. In addition to the 2-D models we perform 3-D gravimetric and magnetic inversions. For each field a 3-D mesh is built under the area occupied by the Colima Volcanic Complex, the volume elements are then assigned density or magnetic susceptibility values and their surface contributions in various points are evaluated. The process is iterated until the difference between the measured and the calculated fields is less than a predetermined value. The results of each inversion adequately and independently define the location of the magmatic chambers although they cannot distinguish between the individual chambers of the Nevado and Fuego volcanoes. 2-D and 3-D results complement each other and consistently show the locations of potential magmatic regions. Our models support a multiple, complex magmatic system that appears to continue to spread southwardly, which can pose additional volcanic risks to an already threatened local population.展开更多
The Cu - An co - existence ore deposits related to intermediate- acidic volcanic - intrusive complexes are widespread in eastern China. They can be divided into 5 types: (1) sharn type, (2 )porphyry type, (3)vein type...The Cu - An co - existence ore deposits related to intermediate- acidic volcanic - intrusive complexes are widespread in eastern China. They can be divided into 5 types: (1) sharn type, (2 )porphyry type, (3)vein type, (4 )breccia pipe type and (5)stratabound type. All of those have intimate spatial, temporal and genetic relations formed by the Mesozoic tertonicmatic - hydrothermal activities in certain geological environments. The magmatic and Cu-An metallogenic ager were predominately in Late Mesozoic (179-90 Ma), and in the period of 150-120 Ma the ore-forming Processes reached the Peak. The main geological Settings of Cu-An ore-forming Processes are: (1) continental margins, including the Peripheral depression of the continental Plate, (2) deep fault zones in the continental Plate,(3)continental rift belt. The magmatic activities were under the combined control of basement fault (s )and superficial fault (s ), and mostly formed the continental volcanic basins. The regional Cu-An metallogenic zones occur along the deep fault zones in WNW - EW direction,such as the Tongling metallogenic subzone, or in NE-NNE direction, such as the Dexing metallogenic subzone. Most of Cu- An ore deposits are related to subvolcanic stocks consist of quartz diorite, granodiorite, quartz porphyry, andesite porphyry, trachyte porphyry and other rocks, which belong to the calc- alkaline series and the I - type granitoid. The spatial zoning of matals from the center to periphery of the stocks is: CU (Mo )→ Cu,Au→Cu, Ph, Zn,An →Ph, Zn, Ag →Ph, Ag. There is a typical venical metallic zoning (from surface to 3 000m in depth ) in Yinshan Cu-An-Ph-Zn-Ag ore deposit, northeastern Jianxi Province.展开更多
The Assam-Meghalaya Gneissic Complex(AMGC)of northeast India contains numerous Pan-African granitic bodies that have been attributed to post-collisional rift-related magmatism.The present study is concerned with the f...The Assam-Meghalaya Gneissic Complex(AMGC)of northeast India contains numerous Pan-African granitic bodies that have been attributed to post-collisional rift-related magmatism.The present study is concerned with the first appraisal of intermediate magmatism(diorite,monzonite,and monzodiorite)found in the Borjuri Pluton of Mikir Massif,which is the eastern extension of AMGC.The diorites are strongly metaluminous and exhibit enriched LREE([La/Yb]N=1.63–7.37)with respect to HREE([Gd/Yb]N=1.95–2.27).The studied rocks do not show any mineralogical or textural indication of metamorphism.Tectonic discrimination diagrams indicate that these rocks originated in a within-plate tectonic setting.The lower Mg#(33.49–38.69),low Cr(below detection limit),and Ni(27–41 ppm)contents along with elemental ratios such as Rb/Sr(0.32–0.95),La/Nb(0.49–4.21),and Nb/Ce(0.11–0.64)suggest a crustal source for the diorites.Discrimination diagrams coupled with elemental ratios suggest that these rocks originated due to partial melting of mafic components in the crust with possible contribution from mantle materials.The P–T conditions of diorite emplacement(7.4 kbar,688℃)were calculated using the amphibole-plagioclase geothermobarometer.Geochemical and geochronological data of the Pan-African felsic plutons reported from the AMGC indicate that these rocks were emplaced in a post-collisional extensional regime.The Borjuri Pluton is in close proximity with the Kathalguri Pluton,which has been reported as a product of PanAfrican magmatism.In view of the numerous extensional Pan-African felsic magmatism reported from the AMGC and based on the close vicinity of the Borjuri diorites with the Kathalguri granites,we speculate that the Borjuri diorites are products of the Pan-African post-collisional magmatism.展开更多
The Guidong granitic complex is constituted by Luxi pluton, Xiazhuang pluton, Maofeng pluton, Sundong pluton, Aizi pluton and Siqian pluton, which intruded in Indosinian and early Yanshanian Periods. These plutons var...The Guidong granitic complex is constituted by Luxi pluton, Xiazhuang pluton, Maofeng pluton, Sundong pluton, Aizi pluton and Siqian pluton, which intruded in Indosinian and early Yanshanian Periods. These plutons varies from each other not only in major element content, aluminium saturation index, but also in ∑REE, δEu, and LREE/HREE, （La/Yb）N, （La/Sm） N and （Gd/Yb） N ratios. Uranium mineralization is mainly hosted by strong peraluminous granites, which has undergone intense fluid-rock interaction, and their REE compositions are characterised by M-type tetrad effects and lower ∑REE, δEu value, LREE/HREE, （La/Yb） N, （La/Sm） N and （Gd/Yb） N ratios.展开更多
A detailed study of isotope and trace element on the volcanic-intrusive complex in Yanbei,Jiangxi Province is reported.All rocks of the complex have similar crystallization age,relatively high(<sup>87</sup>...A detailed study of isotope and trace element on the volcanic-intrusive complex in Yanbei,Jiangxi Province is reported.All rocks of the complex have similar crystallization age,relatively high(<sup>87</sup>Sr/<sup>88</sup>Sr)<sub>i</sub> and δ<sup>18</sup>O,high <sup>207</sup>Pb/<sup>204</sup>Pb,lower ε<sub>Nd</sub>and old Nd model age.They also possess high Rb/Sr and F/Cl,weak Ce and intense Eu negative anomalies.These characteristics clearly demonstrate that the volcanic-intrusive complex is the product of the evolution of cognate magma,and the initial magma was formed by thepartial melting of Early-Middle Proterozoic metasedimentary rocks.展开更多
文摘Many Propositions are made about the mechanism of emplacement of volcanoclastic material in the Bombay volcanic complex. The present paper deals exclusively with the physical features of the deposits laid by a complex tectono-magmatic process by making detailed inventory of the different kind of volcanic ejecta exposed in the Bomay Volcanic Complex (BVC), and an attempt has been made to classify the deposits genetically. A subsidenace which was hinted at earlier, may be a possible cauldron in BVC has been proposed, which might be responsible for producing such a varied and complex lithology.
文摘The Colima Volcanic Complex trends in a nearly N-S direction in western Mexico, and one of its?structures, Colima volcano, is the most historically active volcano in the country. Immediately to the?N, there is another volcanic center called El Cántaro volcano, whose activity started around 1.7 Ma in its N portion and migrated to the S in various episodes. Volcanic activity migrated further south, from El Cántaro to the Colima Volcanic Complex where the southernmost manifestation, Hijos del Volcán domes, is located on the south slope of Fuego volcano. The above date appears to mark initiation of the rather continuous volcanic activity in the area. It has been noted that these volcanic manifestations lie on, or near the Rivera-Cocos inland plate boundary. Colima’s Fuego volcano is also the closest to the Middle America Trench, among the polygenetic volcanoes in Mexico. We submit that the anomalous location of volcanism in this area originates in an anomalous subduction process of the Rivera and Cocos plates and evoke a tectonic model, proposed elsewhere, to support the idea. Modeling gravimetric and aeromagnetic data we locate the magma chambers of the Fuego (active) and Nevado (extinct) volcanoes within a 65 mGals negative Bouguer anomaly elongated in a nearly N-S direction. The corresponding aeromagnetic map displays a magnetic high over the southern portion of the Fuego volcano edifice. We found two additional, associated structures whose anomalies have not been previously reported, which appear to follow the southward magmatic migration pattern. One of them is a collapse structure with a circular topographic expression, and the southernmost is a low-density intrusion ~1 km below sea level, associated with a moderate topographic bulge at the surface that we interpret as a magma body. Five lines cross the anomalies;gravimetric and magnetic fields are concurrently modeled along them to locate the magmatic bodies. In addition to the 2-D models we perform 3-D gravimetric and magnetic inversions. For each field a 3-D mesh is built under the area occupied by the Colima Volcanic Complex, the volume elements are then assigned density or magnetic susceptibility values and their surface contributions in various points are evaluated. The process is iterated until the difference between the measured and the calculated fields is less than a predetermined value. The results of each inversion adequately and independently define the location of the magmatic chambers although they cannot distinguish between the individual chambers of the Nevado and Fuego volcanoes. 2-D and 3-D results complement each other and consistently show the locations of potential magmatic regions. Our models support a multiple, complex magmatic system that appears to continue to spread southwardly, which can pose additional volcanic risks to an already threatened local population.
文摘The Cu - An co - existence ore deposits related to intermediate- acidic volcanic - intrusive complexes are widespread in eastern China. They can be divided into 5 types: (1) sharn type, (2 )porphyry type, (3)vein type, (4 )breccia pipe type and (5)stratabound type. All of those have intimate spatial, temporal and genetic relations formed by the Mesozoic tertonicmatic - hydrothermal activities in certain geological environments. The magmatic and Cu-An metallogenic ager were predominately in Late Mesozoic (179-90 Ma), and in the period of 150-120 Ma the ore-forming Processes reached the Peak. The main geological Settings of Cu-An ore-forming Processes are: (1) continental margins, including the Peripheral depression of the continental Plate, (2) deep fault zones in the continental Plate,(3)continental rift belt. The magmatic activities were under the combined control of basement fault (s )and superficial fault (s ), and mostly formed the continental volcanic basins. The regional Cu-An metallogenic zones occur along the deep fault zones in WNW - EW direction,such as the Tongling metallogenic subzone, or in NE-NNE direction, such as the Dexing metallogenic subzone. Most of Cu- An ore deposits are related to subvolcanic stocks consist of quartz diorite, granodiorite, quartz porphyry, andesite porphyry, trachyte porphyry and other rocks, which belong to the calc- alkaline series and the I - type granitoid. The spatial zoning of matals from the center to periphery of the stocks is: CU (Mo )→ Cu,Au→Cu, Ph, Zn,An →Ph, Zn, Ag →Ph, Ag. There is a typical venical metallic zoning (from surface to 3 000m in depth ) in Yinshan Cu-An-Ph-Zn-Ag ore deposit, northeastern Jianxi Province.
基金DST-SERB grant vide Project No.CRG/2020/002635CSIR-JRF fellowship No.09/1236(11154)/2021-EMR-I。
文摘The Assam-Meghalaya Gneissic Complex(AMGC)of northeast India contains numerous Pan-African granitic bodies that have been attributed to post-collisional rift-related magmatism.The present study is concerned with the first appraisal of intermediate magmatism(diorite,monzonite,and monzodiorite)found in the Borjuri Pluton of Mikir Massif,which is the eastern extension of AMGC.The diorites are strongly metaluminous and exhibit enriched LREE([La/Yb]N=1.63–7.37)with respect to HREE([Gd/Yb]N=1.95–2.27).The studied rocks do not show any mineralogical or textural indication of metamorphism.Tectonic discrimination diagrams indicate that these rocks originated in a within-plate tectonic setting.The lower Mg#(33.49–38.69),low Cr(below detection limit),and Ni(27–41 ppm)contents along with elemental ratios such as Rb/Sr(0.32–0.95),La/Nb(0.49–4.21),and Nb/Ce(0.11–0.64)suggest a crustal source for the diorites.Discrimination diagrams coupled with elemental ratios suggest that these rocks originated due to partial melting of mafic components in the crust with possible contribution from mantle materials.The P–T conditions of diorite emplacement(7.4 kbar,688℃)were calculated using the amphibole-plagioclase geothermobarometer.Geochemical and geochronological data of the Pan-African felsic plutons reported from the AMGC indicate that these rocks were emplaced in a post-collisional extensional regime.The Borjuri Pluton is in close proximity with the Kathalguri Pluton,which has been reported as a product of PanAfrican magmatism.In view of the numerous extensional Pan-African felsic magmatism reported from the AMGC and based on the close vicinity of the Borjuri diorites with the Kathalguri granites,we speculate that the Borjuri diorites are products of the Pan-African post-collisional magmatism.
文摘The Guidong granitic complex is constituted by Luxi pluton, Xiazhuang pluton, Maofeng pluton, Sundong pluton, Aizi pluton and Siqian pluton, which intruded in Indosinian and early Yanshanian Periods. These plutons varies from each other not only in major element content, aluminium saturation index, but also in ∑REE, δEu, and LREE/HREE, （La/Yb）N, （La/Sm） N and （Gd/Yb） N ratios. Uranium mineralization is mainly hosted by strong peraluminous granites, which has undergone intense fluid-rock interaction, and their REE compositions are characterised by M-type tetrad effects and lower ∑REE, δEu value, LREE/HREE, （La/Yb） N, （La/Sm） N and （Gd/Yb） N ratios.
文摘A detailed study of isotope and trace element on the volcanic-intrusive complex in Yanbei,Jiangxi Province is reported.All rocks of the complex have similar crystallization age,relatively high(<sup>87</sup>Sr/<sup>88</sup>Sr)<sub>i</sub> and δ<sup>18</sup>O,high <sup>207</sup>Pb/<sup>204</sup>Pb,lower ε<sub>Nd</sub>and old Nd model age.They also possess high Rb/Sr and F/Cl,weak Ce and intense Eu negative anomalies.These characteristics clearly demonstrate that the volcanic-intrusive complex is the product of the evolution of cognate magma,and the initial magma was formed by thepartial melting of Early-Middle Proterozoic metasedimentary rocks.
