We conducted a detailed analysis of along-trench variations in the flexural bending of the subducting Pacific Plate at the Tonga-Kermadec Trench.Inversions were conducted to obtain best-fitting solutions of trench-axi...We conducted a detailed analysis of along-trench variations in the flexural bending of the subducting Pacific Plate at the Tonga-Kermadec Trench.Inversions were conducted to obtain best-fitting solutions of trench-axis loadings and variations in the effective elastic plate thickness for the analyzed flexural bending profiles.Results of the analyses revealed significant along-trench variations in plate flexural bending:the trench relief(W0)of 1.9 to 5.1 km;trench-axis vertical loading(V0)of-0.5×10^12 to 2.2×10^12 N/m;axial bending moment(M0)of 0.1×10^17 to 2.2×10^17 N;effective elastic plate thickness seaward of the outer-rise region(Te^M)of 20 to 65 km,trench-ward of the outer-rise(Te^M)of 11 to 33 km,and the transition distance(Xr)of 20 to 95 km.The Horizon Deep,the second greatest trench depth in the world,has the greatest trench relief(W0 of 5.1km)and trench-axis loading(V0 of 2.2×10^12N/m);these values are only slightly smaller than that of the Challenger Deep(W0 of 5.7km and V0 of 2.9×10^12N/m)and similar to that of the Sirena Deep(W0 of 5.2 km and V0 of 2.0×10^12 N/m)of the Mariana Trench,suggesting that these deeps are linked to great flexural bending of the subducting plates.Analyses using three independent methods,i.e.,the/inversion,the flexural curvature/yield strength envelope analysis,and the elasto-plastic bending model with normal faults,all yielded similar average Te reduction of 28%-36% and average Te reduction area S△Te of 1195-1402 km^2 near the trench axis.The calculated brittle yield zone depth from the flexural curvature/yield strength envelope analysis is also consistent with the distribution of the observed normal faulting earthquakes.Comparisons of the Manila,Philippine,Tonga-Kermadec,Japan,and Mariana Trenches revealed that the average values Te^M of Te^M and both in general increase with the subducting plate age.展开更多
Dehydration/melting of oceanic crusts during returning to the mantle in subduction zones are related to origin of arc lavas. The factors that influence arc magmatism include compositions of the subducting slabs, mantl...Dehydration/melting of oceanic crusts during returning to the mantle in subduction zones are related to origin of arc lavas. The factors that influence arc magmatism include compositions of the subducting slabs, mantle wedge and subduction rates. However, distinguishing these factors remains difficult and highly debated. Subducting rate is related to the total mass of inputs and controls thermal structure, thus plays a crucial role in arc magmatism. Here we explore the relationships between geochemical variations of arc lavas and convergence rates(increasing from 46 mm/a to the south to 83 mm/a to the northward) in the Tonga-Kermadec arc system. Data of geochemistry for lava samples from nine islands of this arc system are collected and compiled to investigate the role of subduction rate in arc magmatism. Lavas from the northern Tonga arc with a faster subduction rate show broadly lower concentrations of TiO_2 and highfield-strength elements(HFSEs, e.g. Nb, Ta, Zr, Hf), and higher Ba/Th, U/Th ratios than the Kermadec Arc to the south. Some of the Kermadec lavas show the highest values of Th/Nb ratio. We suggest that the northern Tonga arc with a higher subduction rate has been influenced by a stronger role of subductionreleased fluid, which results in stronger large-ion-lithophile elements(LILEs) and relatively weaker HFSEs contribution. It is interpreted that faster subduction rate tend to create a cooler subduction zone, leading to stronger dehydration subduction slab contribution with, thus, higher LILE/HFSE ratios of arc lavas. The conclusion contributes to a better understanding of arc magmatism, and ultimately the long-term chemical differentiation of the Earth. More supplementary geochemical data along Tonga-Kermadec arc and tests in other arcs are needed.展开更多
基金The National Natural Science Foundation of China under contract Nos 41976064,91958211,41890813,91858207,91628301,U1606401,41976066 and 41706056the Programs of the Chinese Academy of Sciences under contract Nos Y4SL021001,QYZDY-SSW-DQC005 and 133244KYSB20180029+1 种基金the National Key Research and Development Program of China under contract Nos2018YFC0309800 and 2018YFC0310100the China Ocean Mineral Resources R&D Association under contract No.DY135-S2-1-04
文摘We conducted a detailed analysis of along-trench variations in the flexural bending of the subducting Pacific Plate at the Tonga-Kermadec Trench.Inversions were conducted to obtain best-fitting solutions of trench-axis loadings and variations in the effective elastic plate thickness for the analyzed flexural bending profiles.Results of the analyses revealed significant along-trench variations in plate flexural bending:the trench relief(W0)of 1.9 to 5.1 km;trench-axis vertical loading(V0)of-0.5×10^12 to 2.2×10^12 N/m;axial bending moment(M0)of 0.1×10^17 to 2.2×10^17 N;effective elastic plate thickness seaward of the outer-rise region(Te^M)of 20 to 65 km,trench-ward of the outer-rise(Te^M)of 11 to 33 km,and the transition distance(Xr)of 20 to 95 km.The Horizon Deep,the second greatest trench depth in the world,has the greatest trench relief(W0 of 5.1km)and trench-axis loading(V0 of 2.2×10^12N/m);these values are only slightly smaller than that of the Challenger Deep(W0 of 5.7km and V0 of 2.9×10^12N/m)and similar to that of the Sirena Deep(W0 of 5.2 km and V0 of 2.0×10^12 N/m)of the Mariana Trench,suggesting that these deeps are linked to great flexural bending of the subducting plates.Analyses using three independent methods,i.e.,the/inversion,the flexural curvature/yield strength envelope analysis,and the elasto-plastic bending model with normal faults,all yielded similar average Te reduction of 28%-36% and average Te reduction area S△Te of 1195-1402 km^2 near the trench axis.The calculated brittle yield zone depth from the flexural curvature/yield strength envelope analysis is also consistent with the distribution of the observed normal faulting earthquakes.Comparisons of the Manila,Philippine,Tonga-Kermadec,Japan,and Mariana Trenches revealed that the average values Te^M of Te^M and both in general increase with the subducting plate age.
基金Supported by the National Natural Science Foundation of China(Nos.41376065,41522602)the National Program on Global Change and AirSea Interaction(No.GASI-GEOGE-02)+1 种基金the Strategic Priority Research Program of Chinese Academy of Sciences(No.XDA11030103)the Project of“Ao Shan”Excellent Scholar for Qingdao National Laboratory for Marine Science and Technology
文摘Dehydration/melting of oceanic crusts during returning to the mantle in subduction zones are related to origin of arc lavas. The factors that influence arc magmatism include compositions of the subducting slabs, mantle wedge and subduction rates. However, distinguishing these factors remains difficult and highly debated. Subducting rate is related to the total mass of inputs and controls thermal structure, thus plays a crucial role in arc magmatism. Here we explore the relationships between geochemical variations of arc lavas and convergence rates(increasing from 46 mm/a to the south to 83 mm/a to the northward) in the Tonga-Kermadec arc system. Data of geochemistry for lava samples from nine islands of this arc system are collected and compiled to investigate the role of subduction rate in arc magmatism. Lavas from the northern Tonga arc with a faster subduction rate show broadly lower concentrations of TiO_2 and highfield-strength elements(HFSEs, e.g. Nb, Ta, Zr, Hf), and higher Ba/Th, U/Th ratios than the Kermadec Arc to the south. Some of the Kermadec lavas show the highest values of Th/Nb ratio. We suggest that the northern Tonga arc with a higher subduction rate has been influenced by a stronger role of subductionreleased fluid, which results in stronger large-ion-lithophile elements(LILEs) and relatively weaker HFSEs contribution. It is interpreted that faster subduction rate tend to create a cooler subduction zone, leading to stronger dehydration subduction slab contribution with, thus, higher LILE/HFSE ratios of arc lavas. The conclusion contributes to a better understanding of arc magmatism, and ultimately the long-term chemical differentiation of the Earth. More supplementary geochemical data along Tonga-Kermadec arc and tests in other arcs are needed.
