Past fifty years have seen mounting publications on the genesis of volcanic arc magmas.While details remain debated,it is generally agreed that arc magmas result from slab-dehydration induced mantle wedge melting foll...Past fifty years have seen mounting publications on the genesis of volcanic arc magmas.While details remain debated,it is generally agreed that arc magmas result from slab-dehydration induced mantle wedge melting followed by crustal level differentiation of varying extent and sophistication.Two recent arc magma studies deserve particular attention because they attempt to discuss globally unifying controls on arc magma composition.Both Harvard study(Turner and Langmuir,2015a,b)and Rice study(Farner and Lee,2017)show correlations of arc magma composition with crustal thickness and both ascribe the crustal thickness as the principal control on their observed magma compositional variations,yet the physical role of the crustal thickness in their interpretations is markedly different because of(1)the ambiguous use of“crust”and(2)their different magma compositional ranges chosen in discussion.The Harvard study only uses basaltic samples corrected to MgO=6.0 wt.%to discuss mantle processes and interprets the arc crustal thickness as restricting the mantle wedge melting,i.e.,the extent of melting decreases with increasing crustal thickness.The Rice study uses samples of all compositions(basaltic to rhyolitic),whose extent of differentiation increases with increasing crustal thickness,interpreted as Moho-crossing mantle wedge melts travelling greater vertical distance with greater degree of cooling and erupting more evolved compositions above thicker crust than melts erupted above thinner crust without need of invoking mantle wedge processes.We commend these efforts and approve their different approaches but emphasize that the unifying understanding of global arc magmatism requires clearly defined Moho(the base of the crust)and LAB(the lithosphere-asthenosphere boundary)and their intrinsic controls on mantle wedge melting(Harvard Study model)and crustal level magma differentiation(Rice Study model)beneath global arcs.In this study,we use chemical compositions of 36,945 global arc volcanic samples provided by the Rice s展开更多
P-wave and S-wave receiver function analyses have been performed along a profile consisted of 27 broadband seismic stations to image the crustal and upper mantle discontinuities across Northeast China. The results sho...P-wave and S-wave receiver function analyses have been performed along a profile consisted of 27 broadband seismic stations to image the crustal and upper mantle discontinuities across Northeast China. The results show that the average Moho depth varies from about 37 km beneath the Daxing＇anling orogenic belt in the west to about 33 km beneath the Songliao Basin, and to about 35 km beneath the Changbai mountain region in the east. Our results reveal that the Moho is generally flat beneath the Daxing＇anling region and a remarkable Moho offset （about 4 km） exists beneath the basin-mountain boundary, the Daxing＇anling-Taihang Gravity Line. Beneath the Tanlu faults zone, which seperates the Songliao Basin and Changbai region, the Moho is uplift and the crustal thick- ness changes rapidly. We interpret this feature as that the Tanlu faults might deeply penetrate into the upper mantle, and facilitate the mantle upwelling along the faults during the Cenozoic era. The average depth of the lithosphereasthenosphere boundary （LAB） is - 80 km along the profile which is thinner than an average thickness of a continental lithosphere. The LAB shows an arc-like shape in the basin, with the shallowest part approximately beneath the center of the basin. The uplift LAB beneath the basin might be related to the extensive lithospheric stretching in the Mesozoic. In the mantle transition zone, a structurally complicated 660 km discontinuity with a maximum 35 km depression beneath the Changbai region is observed. The 35 km depression is roughly coincident with the location of the stagnant western pacific slab on top of the 660 km discontinuity revealed by the recent P wave tomography.展开更多
基金started as a research project at Durham University by RABM(2018-2019)under the supervision of YNYN with RABM’s commentssupported by NSFC grant 91958215 and 111 Project(B18048).
文摘Past fifty years have seen mounting publications on the genesis of volcanic arc magmas.While details remain debated,it is generally agreed that arc magmas result from slab-dehydration induced mantle wedge melting followed by crustal level differentiation of varying extent and sophistication.Two recent arc magma studies deserve particular attention because they attempt to discuss globally unifying controls on arc magma composition.Both Harvard study(Turner and Langmuir,2015a,b)and Rice study(Farner and Lee,2017)show correlations of arc magma composition with crustal thickness and both ascribe the crustal thickness as the principal control on their observed magma compositional variations,yet the physical role of the crustal thickness in their interpretations is markedly different because of(1)the ambiguous use of“crust”and(2)their different magma compositional ranges chosen in discussion.The Harvard study only uses basaltic samples corrected to MgO=6.0 wt.%to discuss mantle processes and interprets the arc crustal thickness as restricting the mantle wedge melting,i.e.,the extent of melting decreases with increasing crustal thickness.The Rice study uses samples of all compositions(basaltic to rhyolitic),whose extent of differentiation increases with increasing crustal thickness,interpreted as Moho-crossing mantle wedge melts travelling greater vertical distance with greater degree of cooling and erupting more evolved compositions above thicker crust than melts erupted above thinner crust without need of invoking mantle wedge processes.We commend these efforts and approve their different approaches but emphasize that the unifying understanding of global arc magmatism requires clearly defined Moho(the base of the crust)and LAB(the lithosphere-asthenosphere boundary)and their intrinsic controls on mantle wedge melting(Harvard Study model)and crustal level magma differentiation(Rice Study model)beneath global arcs.In this study,we use chemical compositions of 36,945 global arc volcanic samples provided by the Rice s
文摘P-wave and S-wave receiver function analyses have been performed along a profile consisted of 27 broadband seismic stations to image the crustal and upper mantle discontinuities across Northeast China. The results show that the average Moho depth varies from about 37 km beneath the Daxing＇anling orogenic belt in the west to about 33 km beneath the Songliao Basin, and to about 35 km beneath the Changbai mountain region in the east. Our results reveal that the Moho is generally flat beneath the Daxing＇anling region and a remarkable Moho offset （about 4 km） exists beneath the basin-mountain boundary, the Daxing＇anling-Taihang Gravity Line. Beneath the Tanlu faults zone, which seperates the Songliao Basin and Changbai region, the Moho is uplift and the crustal thick- ness changes rapidly. We interpret this feature as that the Tanlu faults might deeply penetrate into the upper mantle, and facilitate the mantle upwelling along the faults during the Cenozoic era. The average depth of the lithosphereasthenosphere boundary （LAB） is - 80 km along the profile which is thinner than an average thickness of a continental lithosphere. The LAB shows an arc-like shape in the basin, with the shallowest part approximately beneath the center of the basin. The uplift LAB beneath the basin might be related to the extensive lithospheric stretching in the Mesozoic. In the mantle transition zone, a structurally complicated 660 km discontinuity with a maximum 35 km depression beneath the Changbai region is observed. The 35 km depression is roughly coincident with the location of the stagnant western pacific slab on top of the 660 km discontinuity revealed by the recent P wave tomography.
