Objective The Gaoligongshan oblique collisional orogen is located in the southern section of the Hengduan Mountains, and belongs to one of the main Late Yanshanian-Himalayan oblique collisional orogens in the Sanjiang...Objective The Gaoligongshan oblique collisional orogen is located in the southern section of the Hengduan Mountains, and belongs to one of the main Late Yanshanian-Himalayan oblique collisional orogens in the Sanjiang area. Many researchers have studied the geology, geochemistry and geophysics of this region, and many research achievements have been obtained from deep geophysical exploration of the region, especially using the magnetotelluric （MT） sounding technique. However,展开更多
Saindak is one of the typical porphyry Cu deposits(PCDs)in the Chagai magmatic arc in Pakistan.Ore-forming porphyries at Saindak PCD are mainly composed of tonalite.Here,we use geochemistry of apatite enclosed in plag...Saindak is one of the typical porphyry Cu deposits(PCDs)in the Chagai magmatic arc in Pakistan.Ore-forming porphyries at Saindak PCD are mainly composed of tonalite.Here,we use geochemistry of apatite enclosed in plagioclase phenocrysts from the ore-forming tonalite to constrain the releasing and recharging processes of S and Cl in the underlying parental magma chamber during PCD mineralization.Although apatite inclusions have homogeneous intra-grain S and Cl compositions,there is significant inter-grain S and Cl variations in apatite inclusions located from core to rim in the hosting plagioclase.Such inter-grain S and Cl variation in apatites are coupled with the core-to-rim trends of An,FeO and Mg contents of the hosting plagioclase phenocryst.It indicates that the Saindak PCD likely formed by episodic injection of primitive magmas during the growth of an underlying magma chamber,rather than by one major injection or by addition of mafic melt derived from different source region.Each primitive melt injection introduced essential ore-forming materials such as S and Cl,which were rapidly and effectively released to the coexisting fluids,causing mineralization.Once primitive melt injection stops,signaling the end of growth of underlying magma chamber,mineralization will cease quickly although the hydrothermal system can still survive for a long time.However,the later released fluids are relatively depleted in ore-forming materials,and thus have lower capability to generate mineralization.Accordingly,predominant porphyry-type mineralizations occurred during the growth rather than waning stage of a magmatic system.展开更多
A systematic account of micro-textures and a few compositional profiles of plagioclase from high-alumina basaltic aa lava erupted during the year 1994-1995, from Barren Island Volcano, NE India ocean, are presented fo...A systematic account of micro-textures and a few compositional profiles of plagioclase from high-alumina basaltic aa lava erupted during the year 1994-1995, from Barren Island Volcano, NE India ocean, are presented for the first time. The identified micro-textures can be grouped into two categories： （i） Growth related textures in the form of coarse/fine-sieve morphology, fine-scale oscillatory zoning and resorption surfaces resulted when the equilibrium at the crystal-melt interface was fluctuated due to change in temperature or H20 or pressure or composition of the crystallizing melt; and （ii） morphological texture, like glomerocryst, synneusis, swallow-tailed crystal, microlite and broken crystals, formed by the influence of dynamic behavior of the crystallizing magma （convection, turbulence, degassing, etc.）. Each micro-texture has developed in a specific magmatic environment, accordingly, a first order magma plumbing model and crystallization dynamics are envisaged for the studied lava unit. Magma generated has undergone extensive fractional crystallization of An-rich plagioclase in stable magmatic environment at a deeper depth. Subsequently they ascend to a shallow chamber where the newly brought crystals and pre-existing crystals have undergone dynamic crystallization via dissolution-regrowth processes in a convective self- mixing environment. Such repeated recharge-recycling processes have produced various populations of plagioclase with different micro-textural stratigraphy in the studied lava unit. Intermittent degassing and eruption related decompression have also played a major role in the final stage of crystallization dynamics.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
基金the National Natural Science Foundation of China(grants No.41504061 and 41674078)the National Key Research and Development Project of China(grant No. 2016YFC0600302)
文摘Objective The Gaoligongshan oblique collisional orogen is located in the southern section of the Hengduan Mountains, and belongs to one of the main Late Yanshanian-Himalayan oblique collisional orogens in the Sanjiang area. Many researchers have studied the geology, geochemistry and geophysics of this region, and many research achievements have been obtained from deep geophysical exploration of the region, especially using the magnetotelluric （MT） sounding technique. However,
基金supported by the National Key Research and Development Program of China(Grant No.2016YFC0600310)the National Natural Science Foundation of China(Grant Nos.41872083 and 41702091)+2 种基金the Program of the China Geological Survey(Grant No.DD20160024-07)the China Fundamental Research Funds for the Central Universities(Grant No.2652018133)the 111 Project of the Ministry of Science and Technology(Grant No.BP0719021)。
文摘Saindak is one of the typical porphyry Cu deposits(PCDs)in the Chagai magmatic arc in Pakistan.Ore-forming porphyries at Saindak PCD are mainly composed of tonalite.Here,we use geochemistry of apatite enclosed in plagioclase phenocrysts from the ore-forming tonalite to constrain the releasing and recharging processes of S and Cl in the underlying parental magma chamber during PCD mineralization.Although apatite inclusions have homogeneous intra-grain S and Cl compositions,there is significant inter-grain S and Cl variations in apatite inclusions located from core to rim in the hosting plagioclase.Such inter-grain S and Cl variation in apatites are coupled with the core-to-rim trends of An,FeO and Mg contents of the hosting plagioclase phenocryst.It indicates that the Saindak PCD likely formed by episodic injection of primitive magmas during the growth of an underlying magma chamber,rather than by one major injection or by addition of mafic melt derived from different source region.Each primitive melt injection introduced essential ore-forming materials such as S and Cl,which were rapidly and effectively released to the coexisting fluids,causing mineralization.Once primitive melt injection stops,signaling the end of growth of underlying magma chamber,mineralization will cease quickly although the hydrothermal system can still survive for a long time.However,the later released fluids are relatively depleted in ore-forming materials,and thus have lower capability to generate mineralization.Accordingly,predominant porphyry-type mineralizations occurred during the growth rather than waning stage of a magmatic system.
文摘A systematic account of micro-textures and a few compositional profiles of plagioclase from high-alumina basaltic aa lava erupted during the year 1994-1995, from Barren Island Volcano, NE India ocean, are presented for the first time. The identified micro-textures can be grouped into two categories： （i） Growth related textures in the form of coarse/fine-sieve morphology, fine-scale oscillatory zoning and resorption surfaces resulted when the equilibrium at the crystal-melt interface was fluctuated due to change in temperature or H20 or pressure or composition of the crystallizing melt; and （ii） morphological texture, like glomerocryst, synneusis, swallow-tailed crystal, microlite and broken crystals, formed by the influence of dynamic behavior of the crystallizing magma （convection, turbulence, degassing, etc.）. Each micro-texture has developed in a specific magmatic environment, accordingly, a first order magma plumbing model and crystallization dynamics are envisaged for the studied lava unit. Magma generated has undergone extensive fractional crystallization of An-rich plagioclase in stable magmatic environment at a deeper depth. Subsequently they ascend to a shallow chamber where the newly brought crystals and pre-existing crystals have undergone dynamic crystallization via dissolution-regrowth processes in a convective self- mixing environment. Such repeated recharge-recycling processes have produced various populations of plagioclase with different micro-textural stratigraphy in the studied lava unit. Intermittent degassing and eruption related decompression have also played a major role in the final stage of crystallization dynamics.
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.
