The Late Jurassic Monviso ophiolite in the Western Alps is a multiply deformed,eclogite-facies metaophiolite that represents a remnant of the Alpine Tethyan oceanic lithosphere.The recent recognition of a pre-Alpine d...The Late Jurassic Monviso ophiolite in the Western Alps is a multiply deformed,eclogite-facies metaophiolite that represents a remnant of the Alpine Tethyan oceanic lithosphere.The recent recognition of a pre-Alpine detachment fault in the Lower Tectonic Unit of this ophiolite has led to the discovery of an oceanic core complex,which developed during the initial stages of the tectonic evolution of the Alpine Tethys.The NNWstriking,20–25-km-long shear zone(Baracun Shear Zone)contains ductilely to cataclastically deformed blocks and clasts of Fe-Ti and Mg-Al metagabbros in a matrix made of mylonitic serpentinite and talc-chlorite schist with high Ni–Cr concentrations and high Cl contents.Intensely sheared ophicarbonate rocks and brecciated serpentinite within this shear zone are deformed by the Alpine-phase S1 foliation and D2 folds,providing a critical age constraint for the timing of its formation.Metabasaltic–metasedimentary rocks in the hanging wall increase in thickness away from the shear zone,characteristic of syn-extensional rock sequences in supradetachment basins.展开更多
Large-scale detachment faults on mid-ocean ridges （MORs） provide a window into the deeper earth. They have megamullion on their corrugated surfaces, with exposed lower crustal and upper mantle rocks, rela- tively hi...Large-scale detachment faults on mid-ocean ridges （MORs） provide a window into the deeper earth. They have megamullion on their corrugated surfaces, with exposed lower crustal and upper mantle rocks, rela- tively high residual Bouguer gravity anomaly and P-wave velocity, and are commonly associated with ocean- ic core complex. According to 30 detachment faults identified on MORs, we found that their distances to the axis mostly range from 5 to 50 km, half-spreading rates range from 6.8 to 17 mm/a, and activity time ranges from recent to 3 Ma. Most of the detachment faults are developed on the slow spreading Mid-Atlantic Ridge （MAR） and ultra-slow spreading Southwest Indian Ridge （SWIRl, with the dominant half-spreading rates of 7-13 mm/a, especially 10-13 mm/a. Furthermore, they mostly occur at the inside corner of one segment end and result in an asymmetric seafloor spreading. The detachment faults on MORs are mainly controlled by the tectonism and influenced by the magmatism. Long-lived detachment faults tend to be formed where the ridge magma supply is at a moderate level, although the tectonism is a first-order controlling factor. At the slow spreading ridges, detachment faults tend to occur where local magma supply is relatively low, whilst at the ultra-slow spreading ridges, they normally occur where local magma supply is relatively high. These faults are accompanied by hydrothermal activities, with their relationships being useful in the study of hydrothermal polymetallic sulfides and their origin.展开更多
东南印度洋脊(Southeast Indian Ridge,简称SEIR)是中速扩张洋中脊,在其中的108°—134°E区域的全扩张速率为72~76 mm·a^-1。但在接近澳大利亚-南极洲不整合带(Australian-Antarctic Discordance,简称AAD)区内,海底地貌...东南印度洋脊(Southeast Indian Ridge,简称SEIR)是中速扩张洋中脊,在其中的108°—134°E区域的全扩张速率为72~76 mm·a^-1。但在接近澳大利亚-南极洲不整合带(Australian-Antarctic Discordance,简称AAD)区内,海底地貌沿洋中脊的变化强烈,其变化范围涵盖了从慢速到快速扩张洋中脊上常见的例子,且出现了明显的地球物理与地球化学异常,说明洋中脊在AAD区附近的岩浆供应量极不均匀。文章定量分析了高精度多波束测深数据,计算了洋中脊不同段的地形坡度、断层比例以及平面与剖面的岩浆参数M值,结合研究区内剩余地幔布格重力异常以及洋中脊轴部地球化学指标Na8.0、Fe8.0等资料,分析与讨论了研究区的断层构造与岩浆活动特征的关系。研究发现,东南印度洋脊108°—134°E区域的B区(在AAD区内)及C5段(在AAD区外西侧)发育有大量的海洋核杂岩,而且B区的海洋核杂岩单体规模更大,其中最大的位于B3区,沿洋中脊扩张方向延伸约50km。研究结果首次系统性地显示,相比东南印度洋的其他区域, B和C5异常区具有偏低的平面与剖面M值、偏高的断层比例、偏正的地幔布格重力异常以及偏高的Na8.0值与偏低的Fe8.0值,这些异常特征可能反映了B区和C5段的岩浆初始熔融深度较浅以及岩浆熔融程度较低,因此导致其岩浆供应量异常少,形成较薄的地壳。研究结果同时表明,在岩浆供应量极少的洋中脊,构造伸展作用有利于海洋核杂岩的发育,导致地壳进一步减薄。展开更多
The morphotectonic features and their evolution of the central Southwest Indian Ridge （SWIR） are dis- cussed on the base of the high-resolution flfll-coverage bathyraetric data on the ridge between 49°-51°...The morphotectonic features and their evolution of the central Southwest Indian Ridge （SWIR） are dis- cussed on the base of the high-resolution flfll-coverage bathyraetric data on the ridge between 49°-51°E. A comparative analysis of the topographic features of the axial and flank area indicates that the axial topogra- phy is alternated by the ridge and trough with en echelon pattern and evolved under a spatial-temporal mi- gration especially in 49°-50.17°E. It is probably due to the undulation at the top of the mantle asthenosphere, which is propagating with the mantle flow. From 50.17° to 50.7°E, is a topographical high terrain with a crust much thicker than the global average of the oceanic crust thickness. Its origin should be independent of the spreading mechanism of ultra-slow spreading ridges. The large numbers of volcanoes in this area indicate robust magmatic activity and may be related to the Crozet hot spot according to RMBA （residual mantle Bouguer anomaly）. The different geomorphological feature between the north and south flanks of the ridge indicates an asymmetric spreading, and leading to the development of the OCC （oceanic core complex）. The tectonic activity of the south frank is stronger than the north and is favorable to develop the OCC. The first found active hydrothermal vent in the SWIR at 37°47＇S, 49°39＇E is thought to be associated with the detach- ment fault related to the OCC.展开更多
We analyzed seafloor morphology and geophysical anomalies of the Southeast Indian Ridge(SEIR) to reveal the remarkable changes in magma supply along this intermediate fast-spreading ridge. We found systematic differen...We analyzed seafloor morphology and geophysical anomalies of the Southeast Indian Ridge(SEIR) to reveal the remarkable changes in magma supply along this intermediate fast-spreading ridge. We found systematic differences of the Australian-Antarctic Discordance(AAD) from adjacent ridge segments with the residual mantle Bouguer gravity anomaly(RMBA) being more positive, seafloor being deeper, morphology being more chaotic, M factors being smaller at the AAD. These systematic anomalies, as well as the observed Na8.0 being greater and Fe8.0 being smaller at AAD, suggest relatively starved magma supply and relatively thin crust within the AAD.Comparing to the adjacent ridges segments, the calculated average map-view M factors are relatively small for the AAD, where several Oceanic Core Complexes(OCCs) develop. Close to 30 OCCs were found to be distributed asymmetrically along the SEIR with 60% of OCCs at the northern flank. The OCCs are concentrated mainly in Segments B3 and B4 within the AAD at ~124°–126°E, as well as at the eastern end of Zone C at ~115°E. The relatively small map-view M factors within the AAD indicate stronger tectonism than the adjacent SEIR segments.The interaction between the westward migrating Pacific mantle and the relatively cold mantle beneath the AAD may have caused a reduction in magma supply, leading to the development of abundant OCCs.展开更多
基金“ex 60%–2013 and 2014”Universitàdegli Studi di Torino and PROGEO Piemonte(Universita degli Studi di Torino and Compagnia San Paolo)to A.Festa and G.Balestrothe Italian Ministry of University and Research Cofin-PRIN 2010/2011(“GEOPROB–GEOdynamic Processes of Oceanic Basins”)to A.Festa and P.Tartarotti“Subduction and exhumationof continental lithosphere:Implications on orogenic architecture,environment and climate”to G.Balestro.
文摘The Late Jurassic Monviso ophiolite in the Western Alps is a multiply deformed,eclogite-facies metaophiolite that represents a remnant of the Alpine Tethyan oceanic lithosphere.The recent recognition of a pre-Alpine detachment fault in the Lower Tectonic Unit of this ophiolite has led to the discovery of an oceanic core complex,which developed during the initial stages of the tectonic evolution of the Alpine Tethys.The NNWstriking,20–25-km-long shear zone(Baracun Shear Zone)contains ductilely to cataclastically deformed blocks and clasts of Fe-Ti and Mg-Al metagabbros in a matrix made of mylonitic serpentinite and talc-chlorite schist with high Ni–Cr concentrations and high Cl contents.Intensely sheared ophicarbonate rocks and brecciated serpentinite within this shear zone are deformed by the Alpine-phase S1 foliation and D2 folds,providing a critical age constraint for the timing of its formation.Metabasaltic–metasedimentary rocks in the hanging wall increase in thickness away from the shear zone,characteristic of syn-extensional rock sequences in supradetachment basins.
基金The National Natural Science Foundation of China under contract Nos 91028006 and 41206046the Dayang 115 under contact No.DYXM-115-02-3-01
文摘Large-scale detachment faults on mid-ocean ridges （MORs） provide a window into the deeper earth. They have megamullion on their corrugated surfaces, with exposed lower crustal and upper mantle rocks, rela- tively high residual Bouguer gravity anomaly and P-wave velocity, and are commonly associated with ocean- ic core complex. According to 30 detachment faults identified on MORs, we found that their distances to the axis mostly range from 5 to 50 km, half-spreading rates range from 6.8 to 17 mm/a, and activity time ranges from recent to 3 Ma. Most of the detachment faults are developed on the slow spreading Mid-Atlantic Ridge （MAR） and ultra-slow spreading Southwest Indian Ridge （SWIRl, with the dominant half-spreading rates of 7-13 mm/a, especially 10-13 mm/a. Furthermore, they mostly occur at the inside corner of one segment end and result in an asymmetric seafloor spreading. The detachment faults on MORs are mainly controlled by the tectonism and influenced by the magmatism. Long-lived detachment faults tend to be formed where the ridge magma supply is at a moderate level, although the tectonism is a first-order controlling factor. At the slow spreading ridges, detachment faults tend to occur where local magma supply is relatively low, whilst at the ultra-slow spreading ridges, they normally occur where local magma supply is relatively high. These faults are accompanied by hydrothermal activities, with their relationships being useful in the study of hydrothermal polymetallic sulfides and their origin.
基金The National Natural Science Foundation of China under contract No.91028006the Dayang 115 under contract No.DYXM115-02-3-01
文摘The morphotectonic features and their evolution of the central Southwest Indian Ridge （SWIR） are dis- cussed on the base of the high-resolution flfll-coverage bathyraetric data on the ridge between 49°-51°E. A comparative analysis of the topographic features of the axial and flank area indicates that the axial topogra- phy is alternated by the ridge and trough with en echelon pattern and evolved under a spatial-temporal mi- gration especially in 49°-50.17°E. It is probably due to the undulation at the top of the mantle asthenosphere, which is propagating with the mantle flow. From 50.17° to 50.7°E, is a topographical high terrain with a crust much thicker than the global average of the oceanic crust thickness. Its origin should be independent of the spreading mechanism of ultra-slow spreading ridges. The large numbers of volcanoes in this area indicate robust magmatic activity and may be related to the Crozet hot spot according to RMBA （residual mantle Bouguer anomaly）. The different geomorphological feature between the north and south flanks of the ridge indicates an asymmetric spreading, and leading to the development of the OCC （oceanic core complex）. The tectonic activity of the south frank is stronger than the north and is favorable to develop the OCC. The first found active hydrothermal vent in the SWIR at 37°47＇S, 49°39＇E is thought to be associated with the detach- ment fault related to the OCC.
基金The National Key R&D Program of China under contract Nos 2018YFC0310105 and 2018YFC0309800the China Ocean Mineral Resources R&D Association under contract No.DY135-S2-1-04+2 种基金the National Natural Science Foundation of China under contract Nos 41890813,91628301,41976066,41706056,41976064,91858207 and U1606401the Chinese Academy of Sciences under contract Nos Y4SL021001,QYZDY-SSW-DQC005 and 133244KYSB20180029the Southern Marine Science and Engineering Guangdong Laboratory(Guangzhou)under contract No.GML2019ZD0205
文摘We analyzed seafloor morphology and geophysical anomalies of the Southeast Indian Ridge(SEIR) to reveal the remarkable changes in magma supply along this intermediate fast-spreading ridge. We found systematic differences of the Australian-Antarctic Discordance(AAD) from adjacent ridge segments with the residual mantle Bouguer gravity anomaly(RMBA) being more positive, seafloor being deeper, morphology being more chaotic, M factors being smaller at the AAD. These systematic anomalies, as well as the observed Na8.0 being greater and Fe8.0 being smaller at AAD, suggest relatively starved magma supply and relatively thin crust within the AAD.Comparing to the adjacent ridges segments, the calculated average map-view M factors are relatively small for the AAD, where several Oceanic Core Complexes(OCCs) develop. Close to 30 OCCs were found to be distributed asymmetrically along the SEIR with 60% of OCCs at the northern flank. The OCCs are concentrated mainly in Segments B3 and B4 within the AAD at ~124°–126°E, as well as at the eastern end of Zone C at ~115°E. The relatively small map-view M factors within the AAD indicate stronger tectonism than the adjacent SEIR segments.The interaction between the westward migrating Pacific mantle and the relatively cold mantle beneath the AAD may have caused a reduction in magma supply, leading to the development of abundant OCCs.
