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
The major earthquakes often trigger unrest of surrounding volcanic magma chambers.In recent years,three major earthquakes occurred around the Changbaishan volcano,but it was unclear whether these earthquakes triggered...The major earthquakes often trigger unrest of surrounding volcanic magma chambers.In recent years,three major earthquakes occurred around the Changbaishan volcano,but it was unclear whether these earthquakes triggered the unrest of the magma chamber.Based on geodetic data,we analyzed the volcanic activity according to the Global Position System(GPS)and leveling sites time-series and reestimated the location and volume change of magma chamber from 2002 to 2005.Meanwhile,we calculated the dilatational strain variations of the deep magma chamber resulting from coseismic deformations caused by the 1999 Mw7.0 and 2002 Mw7.3 Wangqing deep earthquakes and the 2011 Mw9.0 Tohoku-oki earthquake.Our results show:(1)Changbaishan has experienced four stages of unrest since 1999,and the biggest unrest of the shallow magma chamber occurred from 2002 to 2005;(2)the parameters of the shallow magma chamber simulated by the Mogi and Point Compound Dislocation Model(p DCM)show that the magma chamber is located in the northern part of the crater,with a depth of approximately 7 km.The volume of the magma chamber increased by 25-28×10^(6) m from 2002 to2005;(3)the strain variation beneath the Changbaishan volcano corresponding to the 1999 Wangqing earthquake was small.The 2002 Wangqing earthquake produced an expansion strain of about 4.4 nanostrain on the magma chamber at a depth of 550 km,and probably promoted the unrest of the Changbaishan volcano.The 2011 Tohoku earthquake induced the expansion of the shallow magma chamber and compression of the deep magma chamber.Although this event promoted shallow magma unrest,it inhibited deep magma unrest.This may explain why the Changbaishan did not show obvious unrest after the 2011 Tohoku earthquake.Therefore,more attention should be paid to earthquakes that can promote deep magma unrest in the Changbaishan volcano.展开更多
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.
基金support from the National Key Research and Development Program of China(2018YFC1503601)Scientific Research Fund of Institute of Seismology and Institute of Crustal Dynamics,China Earthquake Administration(IS201926297)。
文摘The major earthquakes often trigger unrest of surrounding volcanic magma chambers.In recent years,three major earthquakes occurred around the Changbaishan volcano,but it was unclear whether these earthquakes triggered the unrest of the magma chamber.Based on geodetic data,we analyzed the volcanic activity according to the Global Position System(GPS)and leveling sites time-series and reestimated the location and volume change of magma chamber from 2002 to 2005.Meanwhile,we calculated the dilatational strain variations of the deep magma chamber resulting from coseismic deformations caused by the 1999 Mw7.0 and 2002 Mw7.3 Wangqing deep earthquakes and the 2011 Mw9.0 Tohoku-oki earthquake.Our results show:(1)Changbaishan has experienced four stages of unrest since 1999,and the biggest unrest of the shallow magma chamber occurred from 2002 to 2005;(2)the parameters of the shallow magma chamber simulated by the Mogi and Point Compound Dislocation Model(p DCM)show that the magma chamber is located in the northern part of the crater,with a depth of approximately 7 km.The volume of the magma chamber increased by 25-28×10^(6) m from 2002 to2005;(3)the strain variation beneath the Changbaishan volcano corresponding to the 1999 Wangqing earthquake was small.The 2002 Wangqing earthquake produced an expansion strain of about 4.4 nanostrain on the magma chamber at a depth of 550 km,and probably promoted the unrest of the Changbaishan volcano.The 2011 Tohoku earthquake induced the expansion of the shallow magma chamber and compression of the deep magma chamber.Although this event promoted shallow magma unrest,it inhibited deep magma unrest.This may explain why the Changbaishan did not show obvious unrest after the 2011 Tohoku earthquake.Therefore,more attention should be paid to earthquakes that can promote deep magma unrest in the Changbaishan volcano.
