1. Introduction The convergence plate margins, where lithospheric plates move each other and collide, are the most intense areas of magmatism, tectonism and metamorphism. The development of slab windows beneath conver...1. Introduction The convergence plate margins, where lithospheric plates move each other and collide, are the most intense areas of magmatism, tectonism and metamorphism. The development of slab windows beneath convergent margins, originally defined by Dickinson and Snyder （1979）, is one of the essential mechanisms of subduction- related tectonics. A slab window is a gap that forms in a subducting plate when a mid-oceanic ridge reaches a trench and is subducted. The opening of a slab window causes various geological processes including magmatism （e.g. Thorkelson, 1996; Kinoshita, 2002; Bradley et al., 2003; Thorkelson and Breitsprecher, 2005; Zhang et al., 2010; Eyuboglu et al., 2011a）, changes in plate kinematics and deformation （Hibhard and Karig, 1990）, mineralization （Haeussler et al., 1995; Eyuboglu et al., 2011b）, high temperature metamorphism （Sisson et al., 1989; Santosh and Kusky, 2010）, and changes in sedimentary basin evolution （Dostal et al., 2001; Wilson et al., 2005）. In this special issue of Geoscience Frontiers （GSF）, I assemble a set of contributions on the current understanding of petrogenesis of slab window-related arc magmas and also convergent margin tectonics.展开更多
We report here geochemical data, U-Pb zircon ages, and Hf isotopes for the high-Mg diorites (HMDs), Nb-enriched basaltic porphyrys (NEBPs) and plagiogranites (PLAGs) in the Pingshui segment of the Jiangshan-Shaoxing s...We report here geochemical data, U-Pb zircon ages, and Hf isotopes for the high-Mg diorites (HMDs), Nb-enriched basaltic porphyrys (NEBPs) and plagiogranites (PLAGs) in the Pingshui segment of the Jiangshan-Shaoxing suture zone. The HMDs are characterized by high Mg# (>60), high Na and LREE contents, depletion of HREE and HFSE, and pronounced positive εNd(t) values of 7.0 to 7.7, similar to some adakitic high-Mg andesites. The NEBPs are relatively Na-rich (Na2O/K2O>6) and display high abundances of P2O5 (～1.00%), TiO2 (～3.08%) and HFSE (e.g., Nb=9.53–10.27 ppm). Their Nd isotopic compositions (εNd(t)=6.8–8.0) are comparable to those of the HMDs. The PLAGs are metaluminous (A/CNK=0.84–0.89) and sodic (Na2O/K2O>10). Their depletion in HFSE (e.g., Nb, Ta) is consistent with “SSZ-type” plagiogranite. Zircon LA-ICP-MS U-Pb dating yields an age of 932±7 Ma for the HMD, 916±6 Ma for the NEBP, and 902±5 Ma for the PLAG, respectively, indicating that they were products of early Neoproterozoic magmatism. The PLAGs exhibit relatively high zircon Hf isotopes and positive εHf(t) values of 11.0 to 16.2, consistent with their Nd isotopic data (εNd(t)=7.5–8.4). Such features are similar to those of oceanic plagiogranites in ophiolites and distinct from those of crust-derived granites. The PLAGs were most likely derived from partial melting of subducted oceanic crust in an active continental margin. Considering these results in the context of the regional geology, we suggest that a slab window in the subducting oceanic crust between the Yangtze Block and Cathaysia Block was possibly the principal cause for the unique arc magmatism in the area. The upwelling asthenosphere below the slab window may have provided significant thermodynamic conditions.展开更多
The circum-Pacific convergent margin is known as"the Ring of Fire",with abundant volcano eruptions.Large eruptions are rare but very disastrous.It remains obscure how are large explosive volcanos formed and ...The circum-Pacific convergent margin is known as"the Ring of Fire",with abundant volcano eruptions.Large eruptions are rare but very disastrous.It remains obscure how are large explosive volcanos formed and where are the danger zones.Three largest eruptions since 1900,the Hunga Tonga-Hunga Ha’apai,the Mt.Pinatubo,and the Novarupta were found to be associated with subductions of volatile-rich sediments and located close to slab windows.Among them,the Hunga Tonga-Hunga Ha’apai is close to subducting seamount chains;the Mt.Pinatubo is right next to subducting fossil ridges.Both seamount chains and fossil ridges have water depths much shallower than the carbonate compensation depths(CCD)in the Pacific Ocean.Seismic image shows that a seamount is subducting towards the Novarupta volcano.Subduction of volatile-rich sediments and a slab window nearby are the two most important favorable conditions for catastrophic eruptions.Slab windows expose the mantle wedge to the hot asthenosphere,which increases the temperature and dramatically promotes the partial melting of the carbonate-fluxed domains,forming volatile-rich magmas that powered explosive eruptions.展开更多
文摘1. Introduction The convergence plate margins, where lithospheric plates move each other and collide, are the most intense areas of magmatism, tectonism and metamorphism. The development of slab windows beneath convergent margins, originally defined by Dickinson and Snyder （1979）, is one of the essential mechanisms of subduction- related tectonics. A slab window is a gap that forms in a subducting plate when a mid-oceanic ridge reaches a trench and is subducted. The opening of a slab window causes various geological processes including magmatism （e.g. Thorkelson, 1996; Kinoshita, 2002; Bradley et al., 2003; Thorkelson and Breitsprecher, 2005; Zhang et al., 2010; Eyuboglu et al., 2011a）, changes in plate kinematics and deformation （Hibhard and Karig, 1990）, mineralization （Haeussler et al., 1995; Eyuboglu et al., 2011b）, high temperature metamorphism （Sisson et al., 1989; Santosh and Kusky, 2010）, and changes in sedimentary basin evolution （Dostal et al., 2001; Wilson et al., 2005）. In this special issue of Geoscience Frontiers （GSF）, I assemble a set of contributions on the current understanding of petrogenesis of slab window-related arc magmas and also convergent margin tectonics.
基金Supported by China Geological Survey (Grant No. 1212010610611) the Ministry of Land and Resources (Grant No. 200811015)
文摘We report here geochemical data, U-Pb zircon ages, and Hf isotopes for the high-Mg diorites (HMDs), Nb-enriched basaltic porphyrys (NEBPs) and plagiogranites (PLAGs) in the Pingshui segment of the Jiangshan-Shaoxing suture zone. The HMDs are characterized by high Mg# (>60), high Na and LREE contents, depletion of HREE and HFSE, and pronounced positive εNd(t) values of 7.0 to 7.7, similar to some adakitic high-Mg andesites. The NEBPs are relatively Na-rich (Na2O/K2O>6) and display high abundances of P2O5 (～1.00%), TiO2 (～3.08%) and HFSE (e.g., Nb=9.53–10.27 ppm). Their Nd isotopic compositions (εNd(t)=6.8–8.0) are comparable to those of the HMDs. The PLAGs are metaluminous (A/CNK=0.84–0.89) and sodic (Na2O/K2O>10). Their depletion in HFSE (e.g., Nb, Ta) is consistent with “SSZ-type” plagiogranite. Zircon LA-ICP-MS U-Pb dating yields an age of 932±7 Ma for the HMD, 916±6 Ma for the NEBP, and 902±5 Ma for the PLAG, respectively, indicating that they were products of early Neoproterozoic magmatism. The PLAGs exhibit relatively high zircon Hf isotopes and positive εHf(t) values of 11.0 to 16.2, consistent with their Nd isotopic data (εNd(t)=7.5–8.4). Such features are similar to those of oceanic plagiogranites in ophiolites and distinct from those of crust-derived granites. The PLAGs were most likely derived from partial melting of subducted oceanic crust in an active continental margin. Considering these results in the context of the regional geology, we suggest that a slab window in the subducting oceanic crust between the Yangtze Block and Cathaysia Block was possibly the principal cause for the unique arc magmatism in the area. The upwelling asthenosphere below the slab window may have provided significant thermodynamic conditions.
基金Supported by the Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDA22050103)the Taishan Scholar Program of Shandong(No.ts201712075)。
文摘The circum-Pacific convergent margin is known as"the Ring of Fire",with abundant volcano eruptions.Large eruptions are rare but very disastrous.It remains obscure how are large explosive volcanos formed and where are the danger zones.Three largest eruptions since 1900,the Hunga Tonga-Hunga Ha’apai,the Mt.Pinatubo,and the Novarupta were found to be associated with subductions of volatile-rich sediments and located close to slab windows.Among them,the Hunga Tonga-Hunga Ha’apai is close to subducting seamount chains;the Mt.Pinatubo is right next to subducting fossil ridges.Both seamount chains and fossil ridges have water depths much shallower than the carbonate compensation depths(CCD)in the Pacific Ocean.Seismic image shows that a seamount is subducting towards the Novarupta volcano.Subduction of volatile-rich sediments and a slab window nearby are the two most important favorable conditions for catastrophic eruptions.Slab windows expose the mantle wedge to the hot asthenosphere,which increases the temperature and dramatically promotes the partial melting of the carbonate-fluxed domains,forming volatile-rich magmas that powered explosive eruptions.
