Geophysical studies point to a complex tectonic and geodynamic evolution of the Alboran Basin and Gulf of Cadiz. Tomograpbic images show strong seismic waves velocity contrasts in the upper mantle. The high velocity a...Geophysical studies point to a complex tectonic and geodynamic evolution of the Alboran Basin and Gulf of Cadiz. Tomograpbic images show strong seismic waves velocity contrasts in the upper mantle. The high velocity anomaly beneath the Alboran Sea recovered by a number of studies is now a well estab- lished feature. Several geodynamic reconstructions have been proposed also on the base of these images. We present and elaborate on restllts coming from a recent tomography study which concentrates on both the Alboran and the adjacent Atlantic region. These new results, while they confirm the existence of the fast anomaly below the Alboran region, also show interesting features of the lithosphere-asthenosphere system below the Atlantic. A high velocity body is imaged roughly below the Horseshoe Abyssal plain down to sub-lithospheric depths. This feature suggests either a possible initiation or relic subduction. Pronounced low velocity anomalies pervade the upper mantle below the Atlantic region and separate the lithospheres of the two regions. We also notice a strong change of the upper mantle velocity structure going from south to north across the Gorringe Bank. This variation in structure could be related to the different evolution in the opening of the central and northern Atlantic oceans.展开更多
The convergent plate margins of Paleo-Tethys Ocean and Neo-Tethys Ocean are the two orogenic belts in the eastern Tethyan realm with the best exposures of igneous rocks.Previous studies have revealed that both belts h...The convergent plate margins of Paleo-Tethys Ocean and Neo-Tethys Ocean are the two orogenic belts in the eastern Tethyan realm with the best exposures of igneous rocks.Previous studies have revealed that both belts have developed not only island arc basalts(IAB)-like mafic magmatism but also ocean island basalts(OIB)±mid-ocean ridge basalts(MORB)-like mafic magmatism in various stages of their formation and evolution.These different types of mafic igneous rocks show both similarity and difference that were acquired in the various stages from oceanic subduction through continental collision to intracontinental reworking.Comprehensive examination and comparison of these igneous rocks can provide insights into the tectonic evolution of the eastern Tethyan realm.This study integrates the spatiotemporal distribution and geochemical compositions of Mesozoic and Cenozoic primitive mafic igneous rocks in the eastern Tethyan realm within China.The results show:(1)in addition to the stage of oceanic subduction,the stages of continental collision and intracontinental reworking are the primary periods of mafic magmatic activity at convergent plate margins,consistent across the Paleo-Tethyan and Neo-Tethyan domains.(2)OIB(±MORB)-like mafic igneous rocks are present not only in the stage of continental collision in both domains but also in the stage of intracontinental reworking in the Paleo-Tethyan domain.(3)In the stages from oceanic subduction to continental collision,the compositions of IAB-like mafic igneous rocks in both domains exhibit continuous variations,with remarkable similarities in lithology,elemental and isotopic characteristics,indicating their formation through similar deep geodynamic processes—partial melting of the mantle wedge metasomatized by subducting slab-derived fluids in the forms of aqueous solution and/or hydrous melts.As a consequence,the mafic igneous rocks display more compositional inheritance than difference.In the stage of continental collision,the mantle sources of mafic igneous rocks did not acquire geochemical signatures from the subducting continental crust.(4)during the continental collision,some IAB-like and most OIB(±MORB)-like mafic igneous rocks show more depleted radiogenic isotope compositions than their counterparts generated during the oceanic subduction,suggesting an increased contribution from asthenospheric mantle components and a relatively diminished influence from subducting crustal components.(5)extensive mafic magmatism in the compressional regime of continental collision occurs in the overriding plate above continental subduction zones,indicating the local extension of the overlying lithosphere due to upwelling of the asthenospheric mantle in response to rollback or breakoff of the subducting oceanic slab.This upwelling induces simultaneous melting of various mantle sources,leading to high compositional diversity of the mafic igneous rocks during this period.(6)during the intracontinental reworking in both domains,the geochemical characteristics of IAB-like mafic igneous rocks differ significantly from those formed in the stages of continental collision and oceanic subduction,likely due to contributions from subducting continental crust components to their mantle sources.Delamination and thinning of the thickened lithosphere are the most plausible mechanisms for triggering of the mafic magmatism in this stage.The geochemical and petrogenetic similarities between the Mesozoic and Cenozoic mafic igneous rocks from the Paleo-Tethyan and Neo-Tethyan domains are evident in these periods from oceanic subduction through continental collision to intracontinental reworking,suggesting the common features of tectonic evolution across the convergent plate margins of different eras.These features are primarily reflected in the processes of crust-mantle interaction,particularly via the formation of mafic magma sources in the mantle wedge due to metasomatism by fluids derived from subducting oceanic or continental slabs.Moreover,after the formation of the mantle source regions,the key geodynamic processes involved in their partial melting are similar,namely,the rollback of subducting oceanic slabs in the stage of oceanic subduction,the rollback or breakoff of subducting oceanic slabs during the continental collision,and the delamination and thinning of the lithospheric mantle during the intracontinental reworking.The heating caused by upwelling of the asthenospheric mantle is always the most effective mechanism for partial melting of the metasomatic domains in the mantle wedge.Therefore,the occurrence of mafic magmatism always involves two stages in the tectonic evolution of convergent plate margins.The first is the chemical metasomatism of the mantle wedge during the subduction of oceanic or continental slabs,generating the mantle source regions.The second is the partial melting of the metasomatic mantle domains,giving rise to the mafic magmas.The differences between the different stages and types of mafic magmatism lie in the composition of metasomatic agents and the time interval between these two stages.展开更多
Paleoproterozoic subduction strongly occurred in the western margin of Yangtze plate. The basalticandesite volcanics of Ailaoshan Group and Dibadu Formation had been formed during paleo QinghaiTibet oceanic plate s...Paleoproterozoic subduction strongly occurred in the western margin of Yangtze plate. The basalticandesite volcanics of Ailaoshan Group and Dibadu Formation had been formed during paleo QinghaiTibet oceanic plate subduction under the paleoYangtze plate. Their trace element geochemistry suggests that their forming environments are continentalmarginarc and back arcbasin respectively. Consequently, the Paleoproterozoic subduction system in the western margin of Yangtze plate was established. Ailaoshan Group and Dibadu Formation came from an enriched mantle source that was contaminated by crustal sediments carried by subducted slab, and formed the Paleoroterozoic metamorphic basement of western margin of Yangtze plate. Ailaoshan Group is actually western boundary of Yangtze plate.展开更多
During subduction, continental margins experience shortening along with inversion of extensional sedimentary basins. Here we explore a tectonic scenario for the inversion of two-phase extensional basin systems, where ...During subduction, continental margins experience shortening along with inversion of extensional sedimentary basins. Here we explore a tectonic scenario for the inversion of two-phase extensional basin systems, where the Early-Middle Jurassic intra-arc volcano-sedimentary Oseosan Volcanic Complex was developed on top of the Late Triassic-Early Jurassic post-collisional sequences, namely the Chungnam Basin. The basin shortening was accommodated mostly by contractional faults and related folds. In the basement, regional high-angle reverse faults as well as low-angle thrusts accommodate the overall shortening, and are compatible with those preserved in the cover. This suggests that their spatial and temporal development is strongly dependent on the initial basin geometry and inherited structures.Changes in transport direction observed along the basement-sedimentary cover interface is a characteristic structural feature, reflecting sequential kinematic evolution during basin inversion. Propagation of basement faults also enhanced shortening of the overlying sedimentary cover sequences. We constrain timing of the Late Jurassic-Early Cretaceous(ca. 158-110 Ma) inversion from altered K-feldspar 40 Ar/39 Ar ages in stacked thrust sheets and K-Ar illite ages of fault gouges, along with previously reported geochronological data from the area. This "non-magmatic phase" of the Daebo Orogeny is contemporaneous with the timing of magmatic quiescence across the Korean Peninsula. We propose the role of flat/low-angle subduction of the Paleo-Pacific Plate for the development of the "Laramide-style" basement-involved orogenic event along East Asian continental margin.展开更多
Prior to the collision and accretion of the Kohistan arc terrane during the late Cretaceous and the Indian plate after the early Eocene, the southern margin of Asia along the Hindu Kush, Karakoram and Lhasa block terr...Prior to the collision and accretion of the Kohistan arc terrane during the late Cretaceous and the Indian plate after the early Eocene, the southern margin of Asia along the Hindu Kush, Karakoram and Lhasa block terranes was an active Andean\|type continental margin. In south Tibet this margin was dominated by the calc\|alkaline Ladakh—Gangdese granite batholith, associated andesitic volcanic rocks and continental red\|beds. In contrast, the southern Karakoram exposes deep crustal metamorphic rocks and crustal melt leucogranites. New U\|Pb age dating from the Hunza valley and Baltoro glacier region has revealed four spatially and temporally distinct metamorphic episodes. M1 sillimanite grade metamorphism in Hunza was a late Cretaceous event, probably caused by the accretion of the Kohistan arc to Asia. M2 was the major kyanite and sillimanite grade event during late Eocene—Oligocene crustal thickening and shortening, following India\|Asia collision. Numerous melting events resulted in the formation of crustal melt granites throughout the last 50Ma with multiple generations of dykes and very large scale crustal melting along the Baltoro monzogranite\|leucogranite ba tholith during the late Oligocene—early Miocene. M3 metamorphism was a high\| T , low\| p contact thermal metamorphism around the Baltoro granite. In Hunza, younger staurolite grade metamorphism has been dated by U\|Pb monazites at 16Ma, with the Sumayar leucogranite intruded at 9 5Ma cross\|cutting the metamorphic isograds. In the Baltoro region the youngest metamorphism, M4, is the sillimanite grade Dassu gneiss core complex dated by U\|Pb on monazites as late Miocene—Pliocene (5 4±0 25)Ma with Precambrian protolith zircon cores (1855±11)Ma. Numerous gem\|bearing pegmatite dykes cross\|cut these rocks and are thought to have been intruded within the last 2～3Ma. Structural mapping, combined with U\|Pb geochronology shows that major metamorphic events can be both long\|lasting (up to 20Ma) and very restrictive, both in time and space.展开更多
文摘Geophysical studies point to a complex tectonic and geodynamic evolution of the Alboran Basin and Gulf of Cadiz. Tomograpbic images show strong seismic waves velocity contrasts in the upper mantle. The high velocity anomaly beneath the Alboran Sea recovered by a number of studies is now a well estab- lished feature. Several geodynamic reconstructions have been proposed also on the base of these images. We present and elaborate on restllts coming from a recent tomography study which concentrates on both the Alboran and the adjacent Atlantic region. These new results, while they confirm the existence of the fast anomaly below the Alboran region, also show interesting features of the lithosphere-asthenosphere system below the Atlantic. A high velocity body is imaged roughly below the Horseshoe Abyssal plain down to sub-lithospheric depths. This feature suggests either a possible initiation or relic subduction. Pronounced low velocity anomalies pervade the upper mantle below the Atlantic region and separate the lithospheres of the two regions. We also notice a strong change of the upper mantle velocity structure going from south to north across the Gorringe Bank. This variation in structure could be related to the different evolution in the opening of the central and northern Atlantic oceans.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.92155306,42072061,92058211)the Shandong Excellent Young Scientist Grant(Grant No.ZR2022YQ32)。
文摘The convergent plate margins of Paleo-Tethys Ocean and Neo-Tethys Ocean are the two orogenic belts in the eastern Tethyan realm with the best exposures of igneous rocks.Previous studies have revealed that both belts have developed not only island arc basalts(IAB)-like mafic magmatism but also ocean island basalts(OIB)±mid-ocean ridge basalts(MORB)-like mafic magmatism in various stages of their formation and evolution.These different types of mafic igneous rocks show both similarity and difference that were acquired in the various stages from oceanic subduction through continental collision to intracontinental reworking.Comprehensive examination and comparison of these igneous rocks can provide insights into the tectonic evolution of the eastern Tethyan realm.This study integrates the spatiotemporal distribution and geochemical compositions of Mesozoic and Cenozoic primitive mafic igneous rocks in the eastern Tethyan realm within China.The results show:(1)in addition to the stage of oceanic subduction,the stages of continental collision and intracontinental reworking are the primary periods of mafic magmatic activity at convergent plate margins,consistent across the Paleo-Tethyan and Neo-Tethyan domains.(2)OIB(±MORB)-like mafic igneous rocks are present not only in the stage of continental collision in both domains but also in the stage of intracontinental reworking in the Paleo-Tethyan domain.(3)In the stages from oceanic subduction to continental collision,the compositions of IAB-like mafic igneous rocks in both domains exhibit continuous variations,with remarkable similarities in lithology,elemental and isotopic characteristics,indicating their formation through similar deep geodynamic processes—partial melting of the mantle wedge metasomatized by subducting slab-derived fluids in the forms of aqueous solution and/or hydrous melts.As a consequence,the mafic igneous rocks display more compositional inheritance than difference.In the stage of continental collision,the mantle sources of mafic igneous rocks did not acquire geochemical signatures from the subducting continental crust.(4)during the continental collision,some IAB-like and most OIB(±MORB)-like mafic igneous rocks show more depleted radiogenic isotope compositions than their counterparts generated during the oceanic subduction,suggesting an increased contribution from asthenospheric mantle components and a relatively diminished influence from subducting crustal components.(5)extensive mafic magmatism in the compressional regime of continental collision occurs in the overriding plate above continental subduction zones,indicating the local extension of the overlying lithosphere due to upwelling of the asthenospheric mantle in response to rollback or breakoff of the subducting oceanic slab.This upwelling induces simultaneous melting of various mantle sources,leading to high compositional diversity of the mafic igneous rocks during this period.(6)during the intracontinental reworking in both domains,the geochemical characteristics of IAB-like mafic igneous rocks differ significantly from those formed in the stages of continental collision and oceanic subduction,likely due to contributions from subducting continental crust components to their mantle sources.Delamination and thinning of the thickened lithosphere are the most plausible mechanisms for triggering of the mafic magmatism in this stage.The geochemical and petrogenetic similarities between the Mesozoic and Cenozoic mafic igneous rocks from the Paleo-Tethyan and Neo-Tethyan domains are evident in these periods from oceanic subduction through continental collision to intracontinental reworking,suggesting the common features of tectonic evolution across the convergent plate margins of different eras.These features are primarily reflected in the processes of crust-mantle interaction,particularly via the formation of mafic magma sources in the mantle wedge due to metasomatism by fluids derived from subducting oceanic or continental slabs.Moreover,after the formation of the mantle source regions,the key geodynamic processes involved in their partial melting are similar,namely,the rollback of subducting oceanic slabs in the stage of oceanic subduction,the rollback or breakoff of subducting oceanic slabs during the continental collision,and the delamination and thinning of the lithospheric mantle during the intracontinental reworking.The heating caused by upwelling of the asthenospheric mantle is always the most effective mechanism for partial melting of the metasomatic domains in the mantle wedge.Therefore,the occurrence of mafic magmatism always involves two stages in the tectonic evolution of convergent plate margins.The first is the chemical metasomatism of the mantle wedge during the subduction of oceanic or continental slabs,generating the mantle source regions.The second is the partial melting of the metasomatic mantle domains,giving rise to the mafic magmas.The differences between the different stages and types of mafic magmatism lie in the composition of metasomatic agents and the time interval between these two stages.
文摘Paleoproterozoic subduction strongly occurred in the western margin of Yangtze plate. The basalticandesite volcanics of Ailaoshan Group and Dibadu Formation had been formed during paleo QinghaiTibet oceanic plate subduction under the paleoYangtze plate. Their trace element geochemistry suggests that their forming environments are continentalmarginarc and back arcbasin respectively. Consequently, the Paleoproterozoic subduction system in the western margin of Yangtze plate was established. Ailaoshan Group and Dibadu Formation came from an enriched mantle source that was contaminated by crustal sediments carried by subducted slab, and formed the Paleoroterozoic metamorphic basement of western margin of Yangtze plate. Ailaoshan Group is actually western boundary of Yangtze plate.
基金supported by Basic Science Research Program through National Research Foundation of Korea funded by the Ministry of Education, Science and Technology (2018R1C 186003851)to S.-I. Park and 2015RIDlAIA09058914 and NRF2019R1A2C1002211 to S. Kwonsupported by the 2017RlA6A1A07015374(Multidisciplinary study forassessment of large earthquake potentials in the Korean Peninsula) through the National Research Foundation of Korea(NRF)funded by the Ministry of Science and ICT, Korea to S.K
文摘During subduction, continental margins experience shortening along with inversion of extensional sedimentary basins. Here we explore a tectonic scenario for the inversion of two-phase extensional basin systems, where the Early-Middle Jurassic intra-arc volcano-sedimentary Oseosan Volcanic Complex was developed on top of the Late Triassic-Early Jurassic post-collisional sequences, namely the Chungnam Basin. The basin shortening was accommodated mostly by contractional faults and related folds. In the basement, regional high-angle reverse faults as well as low-angle thrusts accommodate the overall shortening, and are compatible with those preserved in the cover. This suggests that their spatial and temporal development is strongly dependent on the initial basin geometry and inherited structures.Changes in transport direction observed along the basement-sedimentary cover interface is a characteristic structural feature, reflecting sequential kinematic evolution during basin inversion. Propagation of basement faults also enhanced shortening of the overlying sedimentary cover sequences. We constrain timing of the Late Jurassic-Early Cretaceous(ca. 158-110 Ma) inversion from altered K-feldspar 40 Ar/39 Ar ages in stacked thrust sheets and K-Ar illite ages of fault gouges, along with previously reported geochronological data from the area. This "non-magmatic phase" of the Daebo Orogeny is contemporaneous with the timing of magmatic quiescence across the Korean Peninsula. We propose the role of flat/low-angle subduction of the Paleo-Pacific Plate for the development of the "Laramide-style" basement-involved orogenic event along East Asian continental margin.
文摘Prior to the collision and accretion of the Kohistan arc terrane during the late Cretaceous and the Indian plate after the early Eocene, the southern margin of Asia along the Hindu Kush, Karakoram and Lhasa block terranes was an active Andean\|type continental margin. In south Tibet this margin was dominated by the calc\|alkaline Ladakh—Gangdese granite batholith, associated andesitic volcanic rocks and continental red\|beds. In contrast, the southern Karakoram exposes deep crustal metamorphic rocks and crustal melt leucogranites. New U\|Pb age dating from the Hunza valley and Baltoro glacier region has revealed four spatially and temporally distinct metamorphic episodes. M1 sillimanite grade metamorphism in Hunza was a late Cretaceous event, probably caused by the accretion of the Kohistan arc to Asia. M2 was the major kyanite and sillimanite grade event during late Eocene—Oligocene crustal thickening and shortening, following India\|Asia collision. Numerous melting events resulted in the formation of crustal melt granites throughout the last 50Ma with multiple generations of dykes and very large scale crustal melting along the Baltoro monzogranite\|leucogranite ba tholith during the late Oligocene—early Miocene. M3 metamorphism was a high\| T , low\| p contact thermal metamorphism around the Baltoro granite. In Hunza, younger staurolite grade metamorphism has been dated by U\|Pb monazites at 16Ma, with the Sumayar leucogranite intruded at 9 5Ma cross\|cutting the metamorphic isograds. In the Baltoro region the youngest metamorphism, M4, is the sillimanite grade Dassu gneiss core complex dated by U\|Pb on monazites as late Miocene—Pliocene (5 4±0 25)Ma with Precambrian protolith zircon cores (1855±11)Ma. Numerous gem\|bearing pegmatite dykes cross\|cut these rocks and are thought to have been intruded within the last 2～3Ma. Structural mapping, combined with U\|Pb geochronology shows that major metamorphic events can be both long\|lasting (up to 20Ma) and very restrictive, both in time and space.
