2019 Vol. 44, No. 5
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2019, 44(5): 1439-1440.
Abstract:
2019, 44(5): 1441-1451.
doi: 10.3799/dqkx.2019.970
Abstract:
In order to reveal the material composition and the structure of the orogenic belt, we propose the ocean plate geology, which is used to explain the process of continental formation and evolution and the source of dynamics. Based on the theory of plate tectonics and geological research methods, the subduction-accretionary complex, the ophiolite belt, and other oceanic lithospheric plate geological formations and structure construction in the orogenic belt are systematically studied in order to find the igneous rock association of the front arc in the subduction zone. In the initial subduction process of the ocean plate, the magmatism from the forearc basalts (FAB) to the boninite, high-Mg andesite (HMA), to the arc tholeiite and calc-alkaline lava and its different stage evolution, are studied in order to identify the characteristics of the original arc and front arc igneous rock association, which reveals the ocean-continent transition in the evolution process from ocean basin to the continent, laying a scientific foundation for the establishment and development of ocean plate geology.
In order to reveal the material composition and the structure of the orogenic belt, we propose the ocean plate geology, which is used to explain the process of continental formation and evolution and the source of dynamics. Based on the theory of plate tectonics and geological research methods, the subduction-accretionary complex, the ophiolite belt, and other oceanic lithospheric plate geological formations and structure construction in the orogenic belt are systematically studied in order to find the igneous rock association of the front arc in the subduction zone. In the initial subduction process of the ocean plate, the magmatism from the forearc basalts (FAB) to the boninite, high-Mg andesite (HMA), to the arc tholeiite and calc-alkaline lava and its different stage evolution, are studied in order to identify the characteristics of the original arc and front arc igneous rock association, which reveals the ocean-continent transition in the evolution process from ocean basin to the continent, laying a scientific foundation for the establishment and development of ocean plate geology.
2019, 44(5): 1452-1463.
doi: 10.3799/dqkx.2019.042
Abstract:
Gneiss domes develop in exhuming orogens, where they constitute an efficient mechanism for material and heat advection of continental crust during orogenesis, which is always related to magmatism (or migmatization). Dome formation may be accompanied by heterogeneous thinning of the upper crust that may occur as the ductile lower crust flows into a gneiss dome by convergent flow and lead to contraction strain in the core. During gneiss dome formation process, lithium-rich (with other rare earth elements) pegmatite is beneficial to form and hence, lead to lithium enrichment. Previous researches indicate that the Songpan-Ganzi-Tianshuihai Indosinian orogenic belt, located in the northern part of the Qinghai-Tibetan Plateau, is the "pegmatite-type" lithium mine resources base in China. The ultra-large pegmatite-type lithium belt in the southwestern of the Songpan-Ganzi occurs in the Triassic flysch which is the country rock of Barrow-type metamorphism with low/medium pressure-high temperature metamorphic traits. It has a genetic relationship with the Late Triassic granite and the lithium-bearing pegmatite intrusion. The authors suggest that future studies should focus on (1) exploring the formation process and tectonic mechanism of gneiss domes; (2) identifying the geochemical properties of granite-bearing pegmatites; (3) revealing the genetic relationship between the differentiation of granite and the evolution of ore-bearing pegmatite; (4) clarifying lithium migrating and enriching process in the melt; (5) delineating the distribution of the Barrow-type metamorphic facies belt in the Triassic strata; (6) proving the favorable metamorphic facies belts and P-T conditions where the lithium-rich pegmatite formed can reveal the space-time coupling of "deformation-metamorphism-magmatic deep-melting-metallogenesis". Moreover, the law of enrichment and preservation of lithium ore, used to establish the metallogenic kinetics model, is an important scientific aspect to reveal the relationships of gneiss dome and metallogenic regularity of pegmatite-type lithium deposits.
Gneiss domes develop in exhuming orogens, where they constitute an efficient mechanism for material and heat advection of continental crust during orogenesis, which is always related to magmatism (or migmatization). Dome formation may be accompanied by heterogeneous thinning of the upper crust that may occur as the ductile lower crust flows into a gneiss dome by convergent flow and lead to contraction strain in the core. During gneiss dome formation process, lithium-rich (with other rare earth elements) pegmatite is beneficial to form and hence, lead to lithium enrichment. Previous researches indicate that the Songpan-Ganzi-Tianshuihai Indosinian orogenic belt, located in the northern part of the Qinghai-Tibetan Plateau, is the "pegmatite-type" lithium mine resources base in China. The ultra-large pegmatite-type lithium belt in the southwestern of the Songpan-Ganzi occurs in the Triassic flysch which is the country rock of Barrow-type metamorphism with low/medium pressure-high temperature metamorphic traits. It has a genetic relationship with the Late Triassic granite and the lithium-bearing pegmatite intrusion. The authors suggest that future studies should focus on (1) exploring the formation process and tectonic mechanism of gneiss domes; (2) identifying the geochemical properties of granite-bearing pegmatites; (3) revealing the genetic relationship between the differentiation of granite and the evolution of ore-bearing pegmatite; (4) clarifying lithium migrating and enriching process in the melt; (5) delineating the distribution of the Barrow-type metamorphic facies belt in the Triassic strata; (6) proving the favorable metamorphic facies belts and P-T conditions where the lithium-rich pegmatite formed can reveal the space-time coupling of "deformation-metamorphism-magmatic deep-melting-metallogenesis". Moreover, the law of enrichment and preservation of lithium ore, used to establish the metallogenic kinetics model, is an important scientific aspect to reveal the relationships of gneiss dome and metallogenic regularity of pegmatite-type lithium deposits.
2019, 44(5): 1464-1475.
doi: 10.3799/dqkx.2019.971
Abstract:
From our long-term study on continental geology, it has been realized that the theory of plate tectonics is the main guiding principle, but it has limitations in the recognition and interpretation of continental geology. This paper presents firstly six specific examples of continental tectonics typified by orogens, by which it attempts to demonstrate that a continent is the tectonic collage comprising the components formed by plate tectonics (including the far field effect from plate active boundaries) and intracontinental mechanisms, respectively. It is proposed that the orogeny occurring in the intracontinental setting can be initiated by continent itself and more likely by the interaction of different blocks within a continent when there was no involvement of plate tectonics and the distant effect derived from plate tectonics. Furthermore, the authors raise a number of questions concerning the fundamental continental issues such as the origin of early continents, the mechanism of continental evolution in the form of supercontinent and the essential differences of oceanic and continental lithospheres and their tectonic cycles. These issues are not related to plate tectonics or cannot be solved by the theory of plate tectonics. In summary, besides plate tectonics works on continents, continents have their own law governing the origin, preservation and evolution of continents. Therefore, it is suggested to further develop the continental study while deepening the theory of plate tectonics.
From our long-term study on continental geology, it has been realized that the theory of plate tectonics is the main guiding principle, but it has limitations in the recognition and interpretation of continental geology. This paper presents firstly six specific examples of continental tectonics typified by orogens, by which it attempts to demonstrate that a continent is the tectonic collage comprising the components formed by plate tectonics (including the far field effect from plate active boundaries) and intracontinental mechanisms, respectively. It is proposed that the orogeny occurring in the intracontinental setting can be initiated by continent itself and more likely by the interaction of different blocks within a continent when there was no involvement of plate tectonics and the distant effect derived from plate tectonics. Furthermore, the authors raise a number of questions concerning the fundamental continental issues such as the origin of early continents, the mechanism of continental evolution in the form of supercontinent and the essential differences of oceanic and continental lithospheres and their tectonic cycles. These issues are not related to plate tectonics or cannot be solved by the theory of plate tectonics. In summary, besides plate tectonics works on continents, continents have their own law governing the origin, preservation and evolution of continents. Therefore, it is suggested to further develop the continental study while deepening the theory of plate tectonics.
2019, 44(5): 1476-1486.
doi: 10.3799/dqkx.2019.047
Abstract:
Since the late 1980s, the Qinling orogen has been considered an Indosinian collisional orogenic belt by some Chinese and foreign geologists. However, no trace of a Triassic oceanic basin or a Paleozoic oceanic basin that continued to Triassic has been found as yet in the Qinling area. It has been suggested that the Devonian-Triassic of the Qinling area is characterized by coastal to shallow marine sediments, and there are no pelagic sediments or ophiolites. There is a clear regional angular unconformity between the Devonian and its underlying rocks. The Shangdan fault is not an Indosinian but a Caledonian suture zone, both sides of which (i.e. the southern margin of the Sino-Korean plate and the northern margin of the Yangtze plate) have a clear record of the Caledonian orogeny. The Pb isotopic compositions of the Liuling Group of the Middle-Upper Devonian, deposited on the northern margin of the Yangtze plate, are similar to those of the North Qinling belt. The detrital zircon age spectrum also suggests that the sediments came from the North Qinling orogenic belt. Mafic rocks from the Mianlue and Sanligang ophiolitic melanges within the Mianlue Indosinian suture zone show a Proterozoic age, and the Sanligang ophiolitic melange is overlain by the sediments of the Nanhuan-Sinian. The so-called Mianlue suture zone is actually a huge regional fracture zone, to the north of which was the passive margin of the Yangtze plate in Early Paleozoic and to the south lay the Yangtze paraplatform (small craton), the core of the Yangtze plate. Therefore, the Indosinian orogen of the Qinling should be attributed to the thrusting and overlapping of the continental crust rather than the continent-continent collision after the disappearance of the oceanic basin. The ultrahigh pressure (UHP) metamorphic belt of the Dabieshan, the eastern extension of the Qinling orogen, is considered an important piece of evidence suggesting that the Qinling was an Indosinian collisional orogen. However, the Dabieshan UHP metamorphic rocks were formed under dynamic UHP conditions during the orogenic process. Therefore, it is inappropriate to convert the estimated thermodynamic pressure to depth by assuming that the pressure was static simply due to burial. Accumulating data from field geological observations, structural geology, metamorphic petrology, isotope geology, geochemistry, geophysics, and physical experiments all indicate that the UHP metamorphism did not occur in the upper mantle but in the earth crust. Structurally, the upper crust of the South Qinling-Dabie region can be subdivided, from top to bottom, into four layers:unmetamorphosed sedimentary rocks, epidote-glaucophane schists, high pressure metamorphic rocks, and UHP metamorphic rocks. The lower crust is represented by the upper amphibolite-granulite facies rocks which were not affected by the UHP metamorphism. The coesite-bearing metamorphic rocks are merely sheeted slices of about 10-12 km thick in the lower part of the upper crust. Based on these observations, our preliminary conclusion is that the low-high-ultrahigh pressure tectonic system of the upper crust in the South Qinling-Dabie region was the result of multilayered decollement above the lower crust, acting as a main shear slide plane during the Indosinian orogeny. The UHP metamorphic rocks of the lower part of the upper crust were formed in response to repeated transient UHP events in the focal area, where frequent earthquakes were likely caused by severe shearing.
Since the late 1980s, the Qinling orogen has been considered an Indosinian collisional orogenic belt by some Chinese and foreign geologists. However, no trace of a Triassic oceanic basin or a Paleozoic oceanic basin that continued to Triassic has been found as yet in the Qinling area. It has been suggested that the Devonian-Triassic of the Qinling area is characterized by coastal to shallow marine sediments, and there are no pelagic sediments or ophiolites. There is a clear regional angular unconformity between the Devonian and its underlying rocks. The Shangdan fault is not an Indosinian but a Caledonian suture zone, both sides of which (i.e. the southern margin of the Sino-Korean plate and the northern margin of the Yangtze plate) have a clear record of the Caledonian orogeny. The Pb isotopic compositions of the Liuling Group of the Middle-Upper Devonian, deposited on the northern margin of the Yangtze plate, are similar to those of the North Qinling belt. The detrital zircon age spectrum also suggests that the sediments came from the North Qinling orogenic belt. Mafic rocks from the Mianlue and Sanligang ophiolitic melanges within the Mianlue Indosinian suture zone show a Proterozoic age, and the Sanligang ophiolitic melange is overlain by the sediments of the Nanhuan-Sinian. The so-called Mianlue suture zone is actually a huge regional fracture zone, to the north of which was the passive margin of the Yangtze plate in Early Paleozoic and to the south lay the Yangtze paraplatform (small craton), the core of the Yangtze plate. Therefore, the Indosinian orogen of the Qinling should be attributed to the thrusting and overlapping of the continental crust rather than the continent-continent collision after the disappearance of the oceanic basin. The ultrahigh pressure (UHP) metamorphic belt of the Dabieshan, the eastern extension of the Qinling orogen, is considered an important piece of evidence suggesting that the Qinling was an Indosinian collisional orogen. However, the Dabieshan UHP metamorphic rocks were formed under dynamic UHP conditions during the orogenic process. Therefore, it is inappropriate to convert the estimated thermodynamic pressure to depth by assuming that the pressure was static simply due to burial. Accumulating data from field geological observations, structural geology, metamorphic petrology, isotope geology, geochemistry, geophysics, and physical experiments all indicate that the UHP metamorphism did not occur in the upper mantle but in the earth crust. Structurally, the upper crust of the South Qinling-Dabie region can be subdivided, from top to bottom, into four layers:unmetamorphosed sedimentary rocks, epidote-glaucophane schists, high pressure metamorphic rocks, and UHP metamorphic rocks. The lower crust is represented by the upper amphibolite-granulite facies rocks which were not affected by the UHP metamorphism. The coesite-bearing metamorphic rocks are merely sheeted slices of about 10-12 km thick in the lower part of the upper crust. Based on these observations, our preliminary conclusion is that the low-high-ultrahigh pressure tectonic system of the upper crust in the South Qinling-Dabie region was the result of multilayered decollement above the lower crust, acting as a main shear slide plane during the Indosinian orogeny. The UHP metamorphic rocks of the lower part of the upper crust were formed in response to repeated transient UHP events in the focal area, where frequent earthquakes were likely caused by severe shearing.
2019, 44(5): 1487-1493.
doi: 10.3799/dqkx.2019.972
Abstract:
This paper is written for commemorating the 100th anniversary of the birth of late Academician Ma Xingyuan. It briefly describes the general idea and significance of the earth system sciences, and it further indicates that magmatism is a result of interaction between geospheres, and magma is the media of transfer of mass and energy between geospheres. The paper discusses with emphasis on the geodynamic significance of magmatism with case studies. On one hand, igneous rocks and their carried deep-seated nodules could be served as lithoprobes and windows to explore the deep earth. On the other hand, igneous rocks are also the records of tectonic events so they could be used to retrace the paleo-tectonic pattern and the history of tectonic evolution.
This paper is written for commemorating the 100th anniversary of the birth of late Academician Ma Xingyuan. It briefly describes the general idea and significance of the earth system sciences, and it further indicates that magmatism is a result of interaction between geospheres, and magma is the media of transfer of mass and energy between geospheres. The paper discusses with emphasis on the geodynamic significance of magmatism with case studies. On one hand, igneous rocks and their carried deep-seated nodules could be served as lithoprobes and windows to explore the deep earth. On the other hand, igneous rocks are also the records of tectonic events so they could be used to retrace the paleo-tectonic pattern and the history of tectonic evolution.
2019, 44(5): 1494-1510.
doi: 10.3799/dqkx.2019.973
Abstract:
The sedimentary facies in the lower Yangtze area changed from the neritic facies to the delta facies in the Late Ordovician. This change of sedimentary facies is related to the orogenic event in the late Early Paleozoic. Based on the comprehensive study of sedimentology and detrital zircon geochronology from the Late Ordovician to the Silurian in the lower Yangtze area, this paper presents the nature and spatial-temporal evolution of the sedimentary basin and discusses the relationship between the basin evolution and the orogenic uplift and denudation. The lithology changed from lithic sandstone to quartz sandstone and grain size changed from coarse to fine from southeast to northwest in the lower Yangtze area. The basin morphology shows asymmetrical wedge shape in transverse cross-section. The sediments are thicker and the slope is steeper in the southeastern part than those in the northwestern part. The narrow subsidence center of the basin parallels to the orogenic belt and migrates from southeast to northwest. All these features indicate the characteristics of foreland basin for the late Early Paleozoic sedimentary basin in the lower Yangtze area. The 900-720 Ma detrital zircons from the Upper Ordovician to the Middle Silurian indicate that the provenance of these strata is the sediments deposited in the rift basin in the Late Neoproterozoic. Occurrence and gradual increase of the 450-420 Ma detrital zircons in the Early Silurian Gaojiabian Formation indicate that the synorogenic magmatic rocks were exposed to provide materials. The absence of 1.9-1.7 Ga detrital zircons which are widespread in the Cathaysia Block might imply that the Cathaysia Block was not the sediment provenance of the late Early Paleozoic basins in the lower Yangtze area. The foreland basin in the lower Yangtze area began to develop in the Late Ordovician. The tectonic subsidence rate exceeded the rate of sediment supply, so thick neritic mudstone interbedded with siltstone and sandstone deposited in the foredeep. The sediments in the foreland basin in the Yangtze area became coarser and the sedimentary facies changed from the neritic facies to the delta front facies with the increasing uplift and northwestward propagation of the orogenic belt in the end of the Late Ordovician. In the Early Silurian, more synorogenic magmatic rocks were eroded, resulting in the increase of the 450-420 Ma detrital zircons in the foreland basin.
The sedimentary facies in the lower Yangtze area changed from the neritic facies to the delta facies in the Late Ordovician. This change of sedimentary facies is related to the orogenic event in the late Early Paleozoic. Based on the comprehensive study of sedimentology and detrital zircon geochronology from the Late Ordovician to the Silurian in the lower Yangtze area, this paper presents the nature and spatial-temporal evolution of the sedimentary basin and discusses the relationship between the basin evolution and the orogenic uplift and denudation. The lithology changed from lithic sandstone to quartz sandstone and grain size changed from coarse to fine from southeast to northwest in the lower Yangtze area. The basin morphology shows asymmetrical wedge shape in transverse cross-section. The sediments are thicker and the slope is steeper in the southeastern part than those in the northwestern part. The narrow subsidence center of the basin parallels to the orogenic belt and migrates from southeast to northwest. All these features indicate the characteristics of foreland basin for the late Early Paleozoic sedimentary basin in the lower Yangtze area. The 900-720 Ma detrital zircons from the Upper Ordovician to the Middle Silurian indicate that the provenance of these strata is the sediments deposited in the rift basin in the Late Neoproterozoic. Occurrence and gradual increase of the 450-420 Ma detrital zircons in the Early Silurian Gaojiabian Formation indicate that the synorogenic magmatic rocks were exposed to provide materials. The absence of 1.9-1.7 Ga detrital zircons which are widespread in the Cathaysia Block might imply that the Cathaysia Block was not the sediment provenance of the late Early Paleozoic basins in the lower Yangtze area. The foreland basin in the lower Yangtze area began to develop in the Late Ordovician. The tectonic subsidence rate exceeded the rate of sediment supply, so thick neritic mudstone interbedded with siltstone and sandstone deposited in the foredeep. The sediments in the foreland basin in the Yangtze area became coarser and the sedimentary facies changed from the neritic facies to the delta front facies with the increasing uplift and northwestward propagation of the orogenic belt in the end of the Late Ordovician. In the Early Silurian, more synorogenic magmatic rocks were eroded, resulting in the increase of the 450-420 Ma detrital zircons in the foreland basin.
2019, 44(5): 1511-1525.
doi: 10.3799/dqkx.2019.974
Abstract:
In this paper, comprehensive structural analysis of the formation process and formation mechanism of the S-shaped anticline of Tongguanshan is carried out through systematical observation of folds, faults, joints and lineation. It is found that there have been three stages of structural deformation and two structures superimposed and compounded. The S-bend of the early NE-fold is due to the limitation of the EW-direction faults. Late S-shaped bending is the result of the near-horizontal twisting due to the Newcathaysian tectonic stress field. It also verifies the formation mechanics of restricted and twisted S-shaped structures by physical simulation and numerical simulation. It is worth noting that the structural synthesis analysis of the S-shaped anticline of Tongguanshan can be expanded to the geomechanics analysis of the formation and evolution of the whole Lower Yangtze platform fold belt, showing that the detailed structural synthesis analysis of the local typical structures is the scientific basis for studying the manner and direction of the movements.
In this paper, comprehensive structural analysis of the formation process and formation mechanism of the S-shaped anticline of Tongguanshan is carried out through systematical observation of folds, faults, joints and lineation. It is found that there have been three stages of structural deformation and two structures superimposed and compounded. The S-bend of the early NE-fold is due to the limitation of the EW-direction faults. Late S-shaped bending is the result of the near-horizontal twisting due to the Newcathaysian tectonic stress field. It also verifies the formation mechanics of restricted and twisted S-shaped structures by physical simulation and numerical simulation. It is worth noting that the structural synthesis analysis of the S-shaped anticline of Tongguanshan can be expanded to the geomechanics analysis of the formation and evolution of the whole Lower Yangtze platform fold belt, showing that the detailed structural synthesis analysis of the local typical structures is the scientific basis for studying the manner and direction of the movements.
2019, 44(5): 1526-1536.
doi: 10.3799/dqkx.2019.033
Abstract:
Geotectonics study is concerned with the evolution of earth materials in the time and space, and it is an important branch of the structural geology, which is related with many domains in the science. The future geotectonics must focus on quantitive studies of fixed type, orientation, time, position, which involves lots of travelling for field work, lots of reading for literature research, and lots of knowledge accumulated over a long period of time, in the pursuit of the science and the truth. The geosyncline and platform hypothesis has been out-of-date. The plate tectonics originated from oceanic geophysical survey is a developing tectonic theory, mainly emphasizing the horizontal movement of tectonic plates. However, the dynamic mechanics of plate tectonics has never been solved completely till now and remains an issue to be worked out.
Geotectonics study is concerned with the evolution of earth materials in the time and space, and it is an important branch of the structural geology, which is related with many domains in the science. The future geotectonics must focus on quantitive studies of fixed type, orientation, time, position, which involves lots of travelling for field work, lots of reading for literature research, and lots of knowledge accumulated over a long period of time, in the pursuit of the science and the truth. The geosyncline and platform hypothesis has been out-of-date. The plate tectonics originated from oceanic geophysical survey is a developing tectonic theory, mainly emphasizing the horizontal movement of tectonic plates. However, the dynamic mechanics of plate tectonics has never been solved completely till now and remains an issue to be worked out.
2019, 44(5): 1537-1543.
doi: 10.3799/dqkx.2019.975
Abstract:
The Songshan area of Henan Province is tectonically located in the southern part of the Sino-Korean craton. It is marked by the three groups of Precambrian separated by two unconformities. A master décollement horizon developed along the unconformity between the Dengfeng Group below and the Songshan Group above. The lower Songshan Group above the décollement horizon formed a nearly N-S trending folded belt. Therefore, Songshan Group structures have little relation with the Archaean Dengfeng Group below the décollement. The thickness of the master décollement horizon ranges from 4 to 30 m.Along this décollement horizon, the Denfeng Group amphibolite facies rock assemblage was strongly retrograded to that with superimposed greenschist facies mineral paragensis. The development of the décollment occurs near the brittle/ductle transition field. Our observations in various scales show that the formation of the décollement horizon is controlled by the rheological stratification which was induced by compositional layering of the crust. It is suggested that the weak interval or interface at the base of a stratigraphic sequence may be preferred structural level for the localization of sub-horizontal décollement zones. It is also clear that consideration of hydrolytic weakening is necessary to unravel the development of the décollement horizon.
The Songshan area of Henan Province is tectonically located in the southern part of the Sino-Korean craton. It is marked by the three groups of Precambrian separated by two unconformities. A master décollement horizon developed along the unconformity between the Dengfeng Group below and the Songshan Group above. The lower Songshan Group above the décollement horizon formed a nearly N-S trending folded belt. Therefore, Songshan Group structures have little relation with the Archaean Dengfeng Group below the décollement. The thickness of the master décollement horizon ranges from 4 to 30 m.Along this décollement horizon, the Denfeng Group amphibolite facies rock assemblage was strongly retrograded to that with superimposed greenschist facies mineral paragensis. The development of the décollment occurs near the brittle/ductle transition field. Our observations in various scales show that the formation of the décollement horizon is controlled by the rheological stratification which was induced by compositional layering of the crust. It is suggested that the weak interval or interface at the base of a stratigraphic sequence may be preferred structural level for the localization of sub-horizontal décollement zones. It is also clear that consideration of hydrolytic weakening is necessary to unravel the development of the décollement horizon.
2019, 44(5): 1544-1561.
doi: 10.3799/dqkx.2019.063
Abstract:
Oceanic subduction-accretion or back-arc oceanic subduction-accretion is the dominant geological process of continental crustal growth. Reconstructing the gradual extinction oceanic rock assemblage sequence of continent is a frontier of contemporary continental dynamics and geosciences. The determination of the oceanic crust subduction complex belt is the core of the reconstruction for the oceanic geological structure and the research of the global geotectonics, which is the core of the understanding for the evolution and dynamics of the regional geotectonics. Basic characteristics of the subduction accretion belt include:(1) the commonality of the material composition of the subduction accretionary complex:the pelagic siliceous rock, siliceous mudstone, siltstone, arc-trench turbidite as matrix, in highly tectonic deformation. Stratigraphic sequences of oceanic islands and seamounts are comprised of limestone and basalt, slided conglomerate, residual rock of intra-arc; ultramafic serpentine rocks, greenschists, and blueschists as mass. (2) Deformation style:synclinal overturned thrust imbricated structure, the gravity sliding structure of the accretionary prim front and the diapir structure of the argillaceous rock. The deformation and accretion form of the accretionary wedge front are controlled by the scale of oceanic crust or back-arc oceanic basina, and the subduction speed also depends on the amount of continent margin debris and the sediment thickness and lithology of ocean floor. (3) Width and thickness:the thickness is often several kilometers, the width is from several tens of kilometers to hundreds of kilometers, and the extension is thousands of kilometers. It is the result of the accumulation of oceanic basin system and continental margin sediments during the subduction of oceanic crust. (4) Formation mechanism:it is the product of the subduction of the lithosphere before the collision of the continent or back-arc oceanic basin. The early subduction accretionary belts in the jointing belt are often involved in late tectonic mélange.
Oceanic subduction-accretion or back-arc oceanic subduction-accretion is the dominant geological process of continental crustal growth. Reconstructing the gradual extinction oceanic rock assemblage sequence of continent is a frontier of contemporary continental dynamics and geosciences. The determination of the oceanic crust subduction complex belt is the core of the reconstruction for the oceanic geological structure and the research of the global geotectonics, which is the core of the understanding for the evolution and dynamics of the regional geotectonics. Basic characteristics of the subduction accretion belt include:(1) the commonality of the material composition of the subduction accretionary complex:the pelagic siliceous rock, siliceous mudstone, siltstone, arc-trench turbidite as matrix, in highly tectonic deformation. Stratigraphic sequences of oceanic islands and seamounts are comprised of limestone and basalt, slided conglomerate, residual rock of intra-arc; ultramafic serpentine rocks, greenschists, and blueschists as mass. (2) Deformation style:synclinal overturned thrust imbricated structure, the gravity sliding structure of the accretionary prim front and the diapir structure of the argillaceous rock. The deformation and accretion form of the accretionary wedge front are controlled by the scale of oceanic crust or back-arc oceanic basina, and the subduction speed also depends on the amount of continent margin debris and the sediment thickness and lithology of ocean floor. (3) Width and thickness:the thickness is often several kilometers, the width is from several tens of kilometers to hundreds of kilometers, and the extension is thousands of kilometers. It is the result of the accumulation of oceanic basin system and continental margin sediments during the subduction of oceanic crust. (4) Formation mechanism:it is the product of the subduction of the lithosphere before the collision of the continent or back-arc oceanic basin. The early subduction accretionary belts in the jointing belt are often involved in late tectonic mélange.
2019, 44(5): 1562-1569.
doi: 10.3799/dqkx.2019.071
Abstract:
We outlined the academic life of Academician Ma Xingyuan and some historical facts of the establishment of the Opening-Closing Tectonics theory. This theory was established during a special development stage of modern geosciences in China, when all schools of thoughts were proposed. Academicians Huang Jiqing, Zhang Wenyou, and Ma Xingyuan independently led their research teams working on frontier problems in the theory of plate tectonics. After the establishment of this uniform tectonic theory, the three academicians work together to better decipher this theory. Under the support of the Professional Committee of Geotectonics, the first academic seminar for the Opening-Closing Tectonic Theory was held in 2002. A research group on this theory was set up and results accumulated in the previous 20 plus years were summarized, and a special book collection was published after this seminar. The research group met again at Beijing in 2015, and new achievements using this theory and improved research methods were summarized. Advances in geophysics were combined to better define the Opening-Closing Tectonic Theory and its characteristics. This meeting proposed that the energy source of tectonism is from the Gutenberg discontinuity, and stressed the importance of transitional belt. More importantly, the research group all agree that the Opening-Closing Tectonic Theory should be extended to planetology and also passed on to young generations, so that this theory can be advocated to the world.
We outlined the academic life of Academician Ma Xingyuan and some historical facts of the establishment of the Opening-Closing Tectonics theory. This theory was established during a special development stage of modern geosciences in China, when all schools of thoughts were proposed. Academicians Huang Jiqing, Zhang Wenyou, and Ma Xingyuan independently led their research teams working on frontier problems in the theory of plate tectonics. After the establishment of this uniform tectonic theory, the three academicians work together to better decipher this theory. Under the support of the Professional Committee of Geotectonics, the first academic seminar for the Opening-Closing Tectonic Theory was held in 2002. A research group on this theory was set up and results accumulated in the previous 20 plus years were summarized, and a special book collection was published after this seminar. The research group met again at Beijing in 2015, and new achievements using this theory and improved research methods were summarized. Advances in geophysics were combined to better define the Opening-Closing Tectonic Theory and its characteristics. This meeting proposed that the energy source of tectonism is from the Gutenberg discontinuity, and stressed the importance of transitional belt. More importantly, the research group all agree that the Opening-Closing Tectonic Theory should be extended to planetology and also passed on to young generations, so that this theory can be advocated to the world.
2019, 44(5): 1570-1583.
doi: 10.3799/dqkx.2019.976
Abstract:
Based on the deep geophysical data, a comprehensive study is carried out by analyzing the tectonic environment, magma isotopic tracing and laws of distribution of mineral resources. The thermodynamic calculation indicates that the structure of the upper mantle lithosphere and asthenosphere of the eastern China which is near 200 Ma can be kept to now, and the time of Mesozoic and Cenozoic can be recognized. Results show the following asthenosphere upwelling and mineralization concentration regions. (1) Mesozoic metal deposit:(a) Craton area, asthenosphere upwelled along the plume body, above the plume head, there formed intermingling granitic rock of crust and mantle melts and corresponding Au, Cu, Mo, Pb-Zn etc mineralization concentrated region. And in the steep contact belt of the plume body and lithosphere body, there formed mediate-basic complex and corresponding Fe mineralization concentrated region. (b) Fold belt area, above the asthenosphere upwelling plume, there formed near mantle-source granitic rocks, and corresponding Cu, Au, Pb-Zn, Mo, Ag mineralization concentrated region. (c) Nanling belt, asthenosphere was "recumbent" at suitable depth, with adequate heat and to a great extent, for heat conduction, the interior of crust remelted partially, and the crust-source granitic rocks, corresponding W, Sn and rare elements mineralization concentrated regions were formed. (2) Cenozoic oil and gas field:(a) Asthenosphere upwelling related with the Pacific subduction, above them, there outcropped basalt, and formed large-scale oil field. (b) Asthenosphere upwelling related with the rift basin, above them, there formed large-scale oil fields, also medium- and small-scale oil fields. Asthenosphere upwelling and tectonic:at J-K of Mesozoic, through comprehensive analysis of tectonic force etc, the origin and influence of Yanshan movement are presented. For Cenozoic, the characters related with continental rift should be analyzed essentially. In conclusion, asthenosphere upwelling is the origin of lithosphere thinning and formation of Meso-Cenozoic structure-magma-mineralization concentration region.
Based on the deep geophysical data, a comprehensive study is carried out by analyzing the tectonic environment, magma isotopic tracing and laws of distribution of mineral resources. The thermodynamic calculation indicates that the structure of the upper mantle lithosphere and asthenosphere of the eastern China which is near 200 Ma can be kept to now, and the time of Mesozoic and Cenozoic can be recognized. Results show the following asthenosphere upwelling and mineralization concentration regions. (1) Mesozoic metal deposit:(a) Craton area, asthenosphere upwelled along the plume body, above the plume head, there formed intermingling granitic rock of crust and mantle melts and corresponding Au, Cu, Mo, Pb-Zn etc mineralization concentrated region. And in the steep contact belt of the plume body and lithosphere body, there formed mediate-basic complex and corresponding Fe mineralization concentrated region. (b) Fold belt area, above the asthenosphere upwelling plume, there formed near mantle-source granitic rocks, and corresponding Cu, Au, Pb-Zn, Mo, Ag mineralization concentrated region. (c) Nanling belt, asthenosphere was "recumbent" at suitable depth, with adequate heat and to a great extent, for heat conduction, the interior of crust remelted partially, and the crust-source granitic rocks, corresponding W, Sn and rare elements mineralization concentrated regions were formed. (2) Cenozoic oil and gas field:(a) Asthenosphere upwelling related with the Pacific subduction, above them, there outcropped basalt, and formed large-scale oil field. (b) Asthenosphere upwelling related with the rift basin, above them, there formed large-scale oil fields, also medium- and small-scale oil fields. Asthenosphere upwelling and tectonic:at J-K of Mesozoic, through comprehensive analysis of tectonic force etc, the origin and influence of Yanshan movement are presented. For Cenozoic, the characters related with continental rift should be analyzed essentially. In conclusion, asthenosphere upwelling is the origin of lithosphere thinning and formation of Meso-Cenozoic structure-magma-mineralization concentration region.
2019, 44(5): 1584-1601.
doi: 10.3799/dqkx.2019.977
Abstract:
The tectonic affinity between the Chinese Central Tianshan basement and the Tarim craton is pivotal for us to understand the tectonic framework of the Central Asian orogenic belt. Based on analyses of field investigation and stratigraphic sequences, it performed detrital zircon U-Pb dating analysis on the four Neoproterozoic meta-sandstone samples from the Gangou region of Hejing County and Alagou region of Baluntai Town, Chinese Central Tianshan. Stratigraphically, the Precambrian strata, rock assemblages, stratigraphical contacts, sedimentary environment in the Chinese Central Tianshan are very similar to those in the northern margin of the Tarim craton, revealing close tectonic affinity between them. All analyzed detrital zircons show oscillatory zoning and have Th/U ratios >0.1 (mainly ranging from 0.4 to 4.0), suggesting that they were mainly derived from igneous rocks. A total of about 165 detrital zircon analyses yielded four age peaks, namely, 950 Ma, 1 550 Ma, 1 920 Ma and 2 480 Ma, respectively, corresponding to four prominent tectonomagmatic events that occurred in the Tarim craton. In addition, these peak ages are remarkably consistent with age populations of detrital zircons in the Tarim craton and its neighbouring areas, and further corroborate that the Chinese Central Tianshan terrane has close tectonic affinity with the Tarim craton. Furthermore, some Proterozoic zircons have been found, showing ages of 2 600-3 260 Ma. Therefore, it is argued that the Chinese Central Tianshan belonged to the Tarim craton in the Precambrian time. Owing to the southward subduction of the Paleo-Tianshan oceanic lithosphere beneath the northern margin of the Tarim craton during the Neoproterozoic period, the remarkable arc-type magmatism occurred in the Chinese Central Tianshan terrane, which rifted away from the Tarim craton.
The tectonic affinity between the Chinese Central Tianshan basement and the Tarim craton is pivotal for us to understand the tectonic framework of the Central Asian orogenic belt. Based on analyses of field investigation and stratigraphic sequences, it performed detrital zircon U-Pb dating analysis on the four Neoproterozoic meta-sandstone samples from the Gangou region of Hejing County and Alagou region of Baluntai Town, Chinese Central Tianshan. Stratigraphically, the Precambrian strata, rock assemblages, stratigraphical contacts, sedimentary environment in the Chinese Central Tianshan are very similar to those in the northern margin of the Tarim craton, revealing close tectonic affinity between them. All analyzed detrital zircons show oscillatory zoning and have Th/U ratios >0.1 (mainly ranging from 0.4 to 4.0), suggesting that they were mainly derived from igneous rocks. A total of about 165 detrital zircon analyses yielded four age peaks, namely, 950 Ma, 1 550 Ma, 1 920 Ma and 2 480 Ma, respectively, corresponding to four prominent tectonomagmatic events that occurred in the Tarim craton. In addition, these peak ages are remarkably consistent with age populations of detrital zircons in the Tarim craton and its neighbouring areas, and further corroborate that the Chinese Central Tianshan terrane has close tectonic affinity with the Tarim craton. Furthermore, some Proterozoic zircons have been found, showing ages of 2 600-3 260 Ma. Therefore, it is argued that the Chinese Central Tianshan belonged to the Tarim craton in the Precambrian time. Owing to the southward subduction of the Paleo-Tianshan oceanic lithosphere beneath the northern margin of the Tarim craton during the Neoproterozoic period, the remarkable arc-type magmatism occurred in the Chinese Central Tianshan terrane, which rifted away from the Tarim craton.
2019, 44(5): 1602-1619.
doi: 10.3799/dqkx.2019.040
Abstract:
The core of the Himalayan orogen, resulting from the Cenozoic collision between the Indian and Asian continents, consists of high-pressure (HP) and ultrahigh-pressure metamorphic rocks. The ultrahigh-pressure (UHP) eclogites occur in the western segment of the Himalayan orogen, and contain garnet, omphacite, coesite, phengite, zoisite/epidote, kyanite and rutile. The UHP eclogites record a peak metamorphic condition of 2.6-2.8 GPa and 600-620℃, and a late stage of amphibolite-facies retrogression and slight partial melting. The prograde, peak and retrograde metamorphic times of the UHP eclogites are~50 Ma, ~45-47 Ma and~35-40 Ma, respectively, indicating that the UHP eclogites underwent a rapid subduction and rapid exhumation. The HP eclogites occur in the east-central segment of the Himalayan orogen, and contain garnet, omphacite, phengite, quartz and rutile. The HP eclogites have a peak metamorphic condition of > 2.1 GPa and > 750℃, and experienced a late stage of granulite-facies retrogression and extensive anataxis. The peak and retrograde metamorphic times of the HP eclotites are~38 Ma and~14-17 Ma, respectively, indicating that the HP eclogites underwent a slow subduction and slow exhumation. The presence of two contrasting eclogite types in the Himalayan orogen shows that, after the India collided with Asia at around 51-53 Ma, the north-western margin of Indian continental crust deeply subducted into the mantle, and underwent UHP metamorphism, and while the north-eastern margin of Indian continental crust shallowly subducted beneath the Asian continent, and experienced HP metamorphism.
The core of the Himalayan orogen, resulting from the Cenozoic collision between the Indian and Asian continents, consists of high-pressure (HP) and ultrahigh-pressure metamorphic rocks. The ultrahigh-pressure (UHP) eclogites occur in the western segment of the Himalayan orogen, and contain garnet, omphacite, coesite, phengite, zoisite/epidote, kyanite and rutile. The UHP eclogites record a peak metamorphic condition of 2.6-2.8 GPa and 600-620℃, and a late stage of amphibolite-facies retrogression and slight partial melting. The prograde, peak and retrograde metamorphic times of the UHP eclogites are~50 Ma, ~45-47 Ma and~35-40 Ma, respectively, indicating that the UHP eclogites underwent a rapid subduction and rapid exhumation. The HP eclogites occur in the east-central segment of the Himalayan orogen, and contain garnet, omphacite, phengite, quartz and rutile. The HP eclogites have a peak metamorphic condition of > 2.1 GPa and > 750℃, and experienced a late stage of granulite-facies retrogression and extensive anataxis. The peak and retrograde metamorphic times of the HP eclotites are~38 Ma and~14-17 Ma, respectively, indicating that the HP eclogites underwent a slow subduction and slow exhumation. The presence of two contrasting eclogite types in the Himalayan orogen shows that, after the India collided with Asia at around 51-53 Ma, the north-western margin of Indian continental crust deeply subducted into the mantle, and underwent UHP metamorphism, and while the north-eastern margin of Indian continental crust shallowly subducted beneath the Asian continent, and experienced HP metamorphism.
2019, 44(5): 1620-1646.
doi: 10.3799/dqkx.2019.036
Abstract:
This paper summarizes recent achievements in basic geological studies in NE China, with the aim of understanding the basement nature and the evolution and overprinting processes of multiple tectonic regimes within the Xing'an-Mongolian Orogenic Belt (XMOB). In this paper, the XMOB only includes the northeastern China which influenced by the Paleozoic orogenic processes, where the overprinting and modification of the Mesozoic tectonic processes took place. The XMOB mainly consists of microcontinental massifs and several orogenic belts between them. Although the so-called Precambrian basement has been dated as Paleozoic and Mesozoic terranes, the new discoveries of the Neoarchean and Paleoproterozoic terranes, together with the Paleoproterozoic mantle-derived xenoliths hosted in Cenozoic basalts, indicate that the microcontinental massifs in the XMOB have the Precambrian basement, and the mantle-crust is coupling within the microcontinental massifs. The crustal accretion within the microcontinental massifs mainly happened in the Neoproterozoic and Mesoproterozoic as well as Neoarchean and Paleozoic by vertical accretion. In contrast, the crustal accretion within intercontinental orogenic belts or island arc terranes mainly took place in the Neoproterozoic and Paleozoic by lateral accretion. The amalgamation of the Erguna and Xing'an massifs happened in the Early stage of Early Paleozoic. The collision between the Xing'an and Songnen massifs took place in the late Early Carboniferous. The amalgamation of the Songnen and Jiamusi massifs occurred in the late stage of Early Paleozoic, the breakup and second amalgamation of these two massifs happened in the Early Mesozoic (the Middle Triassic to Early Jurassic). The final collision between the accretionary belt of northern margin of the North China craton and northern massifs took place during the Late Permian to Middle Triassic. The scissor type closure of the Paleo-Asian Ocean finally happened in the Middle Triassic. The southward subduction of the Mongol-Okhotsk oceanic plate happened during the late stage of Late Paleozoic to Early Jurassic, which controlled the magmatic activities in the Great Xing'an Range and northern Hebei-western Liaoning provinces in this period. The closure of the Mongol-Okhotsk Ocean took place in the Middle Jurassic, and the post-closure extensional environment occurred in the Late Jurassic to Early Cretaceous. The onset of subduction of the Paleo-Pacific plate beneath the Eurasia continent took place in the Early Jurassic. The stike-slip tectonic nature in continental margin of northeastern Asia occurred in the Late Jurassic to early Early Cretaceous, resulting in the tectonic emplacement of accretionary complexes in continental margin from low latitude to high latitude. The eastward shrinking of extents of magmatic activities from the late Early Cretaceous to Paleogene reveals the subduction and subsequent roll-back processes of the Paleo-Pacific plate. The opening of the Japan Sea in the Late Paleogene marks the transformation from active continental margin to trench-arc-basin system and the formation of large mantle wedge in eastern Asia.
This paper summarizes recent achievements in basic geological studies in NE China, with the aim of understanding the basement nature and the evolution and overprinting processes of multiple tectonic regimes within the Xing'an-Mongolian Orogenic Belt (XMOB). In this paper, the XMOB only includes the northeastern China which influenced by the Paleozoic orogenic processes, where the overprinting and modification of the Mesozoic tectonic processes took place. The XMOB mainly consists of microcontinental massifs and several orogenic belts between them. Although the so-called Precambrian basement has been dated as Paleozoic and Mesozoic terranes, the new discoveries of the Neoarchean and Paleoproterozoic terranes, together with the Paleoproterozoic mantle-derived xenoliths hosted in Cenozoic basalts, indicate that the microcontinental massifs in the XMOB have the Precambrian basement, and the mantle-crust is coupling within the microcontinental massifs. The crustal accretion within the microcontinental massifs mainly happened in the Neoproterozoic and Mesoproterozoic as well as Neoarchean and Paleozoic by vertical accretion. In contrast, the crustal accretion within intercontinental orogenic belts or island arc terranes mainly took place in the Neoproterozoic and Paleozoic by lateral accretion. The amalgamation of the Erguna and Xing'an massifs happened in the Early stage of Early Paleozoic. The collision between the Xing'an and Songnen massifs took place in the late Early Carboniferous. The amalgamation of the Songnen and Jiamusi massifs occurred in the late stage of Early Paleozoic, the breakup and second amalgamation of these two massifs happened in the Early Mesozoic (the Middle Triassic to Early Jurassic). The final collision between the accretionary belt of northern margin of the North China craton and northern massifs took place during the Late Permian to Middle Triassic. The scissor type closure of the Paleo-Asian Ocean finally happened in the Middle Triassic. The southward subduction of the Mongol-Okhotsk oceanic plate happened during the late stage of Late Paleozoic to Early Jurassic, which controlled the magmatic activities in the Great Xing'an Range and northern Hebei-western Liaoning provinces in this period. The closure of the Mongol-Okhotsk Ocean took place in the Middle Jurassic, and the post-closure extensional environment occurred in the Late Jurassic to Early Cretaceous. The onset of subduction of the Paleo-Pacific plate beneath the Eurasia continent took place in the Early Jurassic. The stike-slip tectonic nature in continental margin of northeastern Asia occurred in the Late Jurassic to early Early Cretaceous, resulting in the tectonic emplacement of accretionary complexes in continental margin from low latitude to high latitude. The eastward shrinking of extents of magmatic activities from the late Early Cretaceous to Paleogene reveals the subduction and subsequent roll-back processes of the Paleo-Pacific plate. The opening of the Japan Sea in the Late Paleogene marks the transformation from active continental margin to trench-arc-basin system and the formation of large mantle wedge in eastern Asia.
2019, 44(5): 1647-1660.
doi: 10.3799/dqkx.2019.978
Abstract:
The break-up region of the North China craton is an area where historically destructive earthquakes have frequently occurred. The focal mechanism solutions and earthquake surface rupture zones indicate that these historical earthquakes were dominated by the newly-formed seismogenic strike-slip faults, which are incompatible with the crustal extensional tectonics. This research firstly examines the high-resolution seismic reflection profile and borehole stratigraphy on the hanging wall of the Xiadian fault, which resulted in the 1679 Sanhe-Pinggu M8.0 earthquake ruptures along the western boundary of the Dachang concealed sag. Then, two unconformity contacts (UC1 and UC2) are distinguished by careful checks on structural and stratigraphic features from a cross section of the Late Pleistocene lacustrine at the southern piedmont of the Daqingshan. Combined with the results of active fault mappings with 1:50 000 scale and urban active fault detection in recent years, we conclude that the listric normal faults, which represent crustal extension in the Early Cenozoic, had been weakening in the Pliocene to the Early Quaternary, and had ceased activity by the early Late Pleistocene. The Daqingshan tectonic movement has initiated since the middle of the Late Pleistocene, representing the latest tectonic movement in break-up region of the North China craton, in which new strike-slip faults have formed under a shear-strain crustal condition owing to continuous eastward extrusion of the Qinghai-Tibet Plateau and strong eastward push on the southwestern margin of the Ordos block. These new points of view have important academic value for understanding mechanism of earthquake occurrence and dynamics of the latest crustal deformation in intra-plate.
The break-up region of the North China craton is an area where historically destructive earthquakes have frequently occurred. The focal mechanism solutions and earthquake surface rupture zones indicate that these historical earthquakes were dominated by the newly-formed seismogenic strike-slip faults, which are incompatible with the crustal extensional tectonics. This research firstly examines the high-resolution seismic reflection profile and borehole stratigraphy on the hanging wall of the Xiadian fault, which resulted in the 1679 Sanhe-Pinggu M8.0 earthquake ruptures along the western boundary of the Dachang concealed sag. Then, two unconformity contacts (UC1 and UC2) are distinguished by careful checks on structural and stratigraphic features from a cross section of the Late Pleistocene lacustrine at the southern piedmont of the Daqingshan. Combined with the results of active fault mappings with 1:50 000 scale and urban active fault detection in recent years, we conclude that the listric normal faults, which represent crustal extension in the Early Cenozoic, had been weakening in the Pliocene to the Early Quaternary, and had ceased activity by the early Late Pleistocene. The Daqingshan tectonic movement has initiated since the middle of the Late Pleistocene, representing the latest tectonic movement in break-up region of the North China craton, in which new strike-slip faults have formed under a shear-strain crustal condition owing to continuous eastward extrusion of the Qinghai-Tibet Plateau and strong eastward push on the southwestern margin of the Ordos block. These new points of view have important academic value for understanding mechanism of earthquake occurrence and dynamics of the latest crustal deformation in intra-plate.
2019, 44(5): 1661-1687.
doi: 10.3799/dqkx.2019.979
Abstract:
Accretionary orogens record complicated geological processes during plate convergence, and are characterized by long evolutionary history with multi-stage orogenesis. This paper presents a brief summary and review on the characteristics and complexity of accretionary orogens, and also discusses the methods of analyzing the spatio-temporal evolution of accretionary orogeny. Accretionary orogeny is here defined as a collection of interactions between various types (convergent, transform and divergent) of plate boundaries along a host continental margin with multiple orogenic phases. The forearc region of an accretionary orogen includes accretionary complexes with overlying sedimentary basins such as forearc basin and wedge-top basin, which together constrain the spatio-temporal evolution of accretionary processes. Accretionary orogens are characterized by complicated archipelagic paleogeographic patterns with the development of different types of basins, diverse magmatism, wide accretionary complexes, multiple subduction polarity, multiple terrane accretion, secular evolution and planar accretion. By using the paleomagnetic, paleogeographic, paleontological and paleoclimate data, first-order tectonic units can be deciphered. Based on structural analysis and detailed geological mapping, in combination with material and geochronological analysis, second-order tectonic units can be divided. The lower time limit of accretionary events can be discriminated by defining the youngest components, unconformities, and high-pressure metamorphic events involved in the accretion; while the upper time limit relies on the oldest unconformities which are not involved in the accretion.
Accretionary orogens record complicated geological processes during plate convergence, and are characterized by long evolutionary history with multi-stage orogenesis. This paper presents a brief summary and review on the characteristics and complexity of accretionary orogens, and also discusses the methods of analyzing the spatio-temporal evolution of accretionary orogeny. Accretionary orogeny is here defined as a collection of interactions between various types (convergent, transform and divergent) of plate boundaries along a host continental margin with multiple orogenic phases. The forearc region of an accretionary orogen includes accretionary complexes with overlying sedimentary basins such as forearc basin and wedge-top basin, which together constrain the spatio-temporal evolution of accretionary processes. Accretionary orogens are characterized by complicated archipelagic paleogeographic patterns with the development of different types of basins, diverse magmatism, wide accretionary complexes, multiple subduction polarity, multiple terrane accretion, secular evolution and planar accretion. By using the paleomagnetic, paleogeographic, paleontological and paleoclimate data, first-order tectonic units can be deciphered. Based on structural analysis and detailed geological mapping, in combination with material and geochronological analysis, second-order tectonic units can be divided. The lower time limit of accretionary events can be discriminated by defining the youngest components, unconformities, and high-pressure metamorphic events involved in the accretion; while the upper time limit relies on the oldest unconformities which are not involved in the accretion.
2019, 44(5): 1688-1704.
doi: 10.3799/dqkx.2019.056
Abstract:
Ophiolites represent on-land fragments of paleo-oceanic crust and have been recognized as one of the key markers of suture zones. Here, we provide new insights into the emplacement of ophiolitic mélanges based on detailed geological mapping and structural analysis in the West Junggar and Songpan-Ganzi orogens. The results show that some ophiolitic mélange belts cannot be regarded as suture zones. The distribution of these ophiolitic mélange belts are usually associated with the structural processes during the closure of remnant oceanic basins. After the remnant oceanic basin is filled with thick clastic deposit, the oceanic lithosphere material as the base of the remnant basin can be injected into the overlying sedimentary strata through various faultings under the regional compressive stress, forming the remnant oceanic basin-type ophiolitic mélange system with dispersive distribution characteristics. Combining with previous researches, the emplacement mechanism of suture-zone type ophiolitic mélanges can be divided into three categories:subduction type, obduction type, and collision type.These different types of ophiolitic mélange belts will be superimposed and even re-emplaced by the tectonic processes of post-plate convergence, complicating their distribution. Therefore, identifying the ophiolitic mélanges formed in different tectonic processes and their backgrounds is of importance for understanding the process of ocean-continental transition and the tectonic evolution of orogenic belts.
Ophiolites represent on-land fragments of paleo-oceanic crust and have been recognized as one of the key markers of suture zones. Here, we provide new insights into the emplacement of ophiolitic mélanges based on detailed geological mapping and structural analysis in the West Junggar and Songpan-Ganzi orogens. The results show that some ophiolitic mélange belts cannot be regarded as suture zones. The distribution of these ophiolitic mélange belts are usually associated with the structural processes during the closure of remnant oceanic basins. After the remnant oceanic basin is filled with thick clastic deposit, the oceanic lithosphere material as the base of the remnant basin can be injected into the overlying sedimentary strata through various faultings under the regional compressive stress, forming the remnant oceanic basin-type ophiolitic mélange system with dispersive distribution characteristics. Combining with previous researches, the emplacement mechanism of suture-zone type ophiolitic mélanges can be divided into three categories:subduction type, obduction type, and collision type.These different types of ophiolitic mélange belts will be superimposed and even re-emplaced by the tectonic processes of post-plate convergence, complicating their distribution. Therefore, identifying the ophiolitic mélanges formed in different tectonic processes and their backgrounds is of importance for understanding the process of ocean-continental transition and the tectonic evolution of orogenic belts.
2019, 44(5): 1705-1715.
doi: 10.3799/dqkx.2019.009
Abstract:
This paper makes an overview on the continental extensional tectonics from the research history, basic concept, structural pattern, deformational mechanism and dynamic tectonic backgrounds. Extension is one of the major tectonics in continent, which forms many different structural patterns with normal faults, such as, grabens, rifts, detachment faults and metamorphic core complexes (MCC). Deformational mechanism for the continental extension includes models of pure shearing, simple shearing and delaminating shearing, which results in symmetric and asymmetric extensional structures, respectively. There are mainly two kinds of surface expressions for the continental extension, i.e., rifts or MCC, which depends on the rheological structure of the continental lithosphere. The dynamic tectonic backgrounds for continental extension include the upwelling plume, slab rollback and subduction retreat, gravitational collapse of thickened crust, and the extension derived from strike-slip system.
This paper makes an overview on the continental extensional tectonics from the research history, basic concept, structural pattern, deformational mechanism and dynamic tectonic backgrounds. Extension is one of the major tectonics in continent, which forms many different structural patterns with normal faults, such as, grabens, rifts, detachment faults and metamorphic core complexes (MCC). Deformational mechanism for the continental extension includes models of pure shearing, simple shearing and delaminating shearing, which results in symmetric and asymmetric extensional structures, respectively. There are mainly two kinds of surface expressions for the continental extension, i.e., rifts or MCC, which depends on the rheological structure of the continental lithosphere. The dynamic tectonic backgrounds for continental extension include the upwelling plume, slab rollback and subduction retreat, gravitational collapse of thickened crust, and the extension derived from strike-slip system.
2019, 44(5): 1716-1733.
doi: 10.3799/dqkx.2019.053
Abstract:
Amphibolite is an important component in middle to lower crustal rocks, and the deformation behavior and mechanical strength of rocks and minerals in it control the mechanical properties and state of middle to lower crustal rocks directly, so it's quite meaningful to study amphibole's deformation behavior and seismic anisotropy. we took deformed amphibolite from Red River-Ailao Shan shear zone as our studying object. Microstructure analysis of amphibolite shows three types of mylonites:coarse-grained banded mylonite, medium-grained banded mylonite and fine-grained banded ultramylonite. we carried out EBSD crystal preferred orientation analysis and seismic anisotropy calculation of three types of amphibole respectively. Results show that these three types of amphiboles have different initial orientations and typical crystal plastic deformation, (100)[001] is the dominant slip system, furthermore, two secondary slip systems (010)[001] and (110)[001] are also developed. It is concluded that in the process of shear deformation amphibole's twin slip and cleavage plane slip contribute to the grain size reduction together. As amphibole's grain size become finer from coarse-grained banded mylonite to fine-grained banded ultramylonite, AVps of amphiboles also tend to be smaller, it indicates that amphibole's deformation behavior, shape preferred orientation and crystal preferred orientation affect its seismic wave anisotropy together.
Amphibolite is an important component in middle to lower crustal rocks, and the deformation behavior and mechanical strength of rocks and minerals in it control the mechanical properties and state of middle to lower crustal rocks directly, so it's quite meaningful to study amphibole's deformation behavior and seismic anisotropy. we took deformed amphibolite from Red River-Ailao Shan shear zone as our studying object. Microstructure analysis of amphibolite shows three types of mylonites:coarse-grained banded mylonite, medium-grained banded mylonite and fine-grained banded ultramylonite. we carried out EBSD crystal preferred orientation analysis and seismic anisotropy calculation of three types of amphibole respectively. Results show that these three types of amphiboles have different initial orientations and typical crystal plastic deformation, (100)[001] is the dominant slip system, furthermore, two secondary slip systems (010)[001] and (110)[001] are also developed. It is concluded that in the process of shear deformation amphibole's twin slip and cleavage plane slip contribute to the grain size reduction together. As amphibole's grain size become finer from coarse-grained banded mylonite to fine-grained banded ultramylonite, AVps of amphiboles also tend to be smaller, it indicates that amphibole's deformation behavior, shape preferred orientation and crystal preferred orientation affect its seismic wave anisotropy together.
2019, 44(5): 1734-1748.
doi: 10.3799/dqkx.2018.119
Abstract:
The folds with near E-W-trending fold axis are widely developed in the Western Hills of Beijing, which are very important for understanding the tectonic evolution of the eastern part of North China craton (NCC). However, their deformation age and tectonic dynamic background are poorly understood. Taipingshan folds in the Fangshan area, Beijing, are typical folds with near E-W axial orientation. The detailed field structure observation and tectonic geochronology were carried out to determine the spatial distribution characteristics and tectonic style of Taipingshan folds and their deformation age. The detailed field structure observation and systematic β-diagrams study show that the Taipingshan folds consist of an upright capsized anticline and an inclined capsized syncline. A deformed lamprophyre sheet which is earlier than the folds structure gives a weighted zircon U-Pb age of 147.2±2.4 Ma, and the later porphyrite dyke that cuts strata of the folds gives a weighted zircon U-Pb age of 129.0±3.2 Ma, suggesting that the deformation time of the Taipingshan folds is between ca. 147 and 129 Ma, belonging to phase B of "Yanshanian movement". In addition, the extensional structure with NW-SE extensional direction is also developed in the Western Hills of Beijing. Fangshan dome (about 136 Ma), which is a typical product of the extensional tectonic, intruded into and cut the Taipingshan folds, further limiting the deformation age of the Taipingshan folds ranges from ca. 147 to 136 Ma. Thus, the folds with E-W-trending fold axis in the studied area are products of nearly N-S compressional tectonics in Early Cretaceous. The tectonic regime transformation from N-S compressional to NW-SE extensional tectonics provides a key understanding on tectonic dynamics of the eastern part of NCC in Late Mesozoic.
The folds with near E-W-trending fold axis are widely developed in the Western Hills of Beijing, which are very important for understanding the tectonic evolution of the eastern part of North China craton (NCC). However, their deformation age and tectonic dynamic background are poorly understood. Taipingshan folds in the Fangshan area, Beijing, are typical folds with near E-W axial orientation. The detailed field structure observation and tectonic geochronology were carried out to determine the spatial distribution characteristics and tectonic style of Taipingshan folds and their deformation age. The detailed field structure observation and systematic β-diagrams study show that the Taipingshan folds consist of an upright capsized anticline and an inclined capsized syncline. A deformed lamprophyre sheet which is earlier than the folds structure gives a weighted zircon U-Pb age of 147.2±2.4 Ma, and the later porphyrite dyke that cuts strata of the folds gives a weighted zircon U-Pb age of 129.0±3.2 Ma, suggesting that the deformation time of the Taipingshan folds is between ca. 147 and 129 Ma, belonging to phase B of "Yanshanian movement". In addition, the extensional structure with NW-SE extensional direction is also developed in the Western Hills of Beijing. Fangshan dome (about 136 Ma), which is a typical product of the extensional tectonic, intruded into and cut the Taipingshan folds, further limiting the deformation age of the Taipingshan folds ranges from ca. 147 to 136 Ma. Thus, the folds with E-W-trending fold axis in the studied area are products of nearly N-S compressional tectonics in Early Cretaceous. The tectonic regime transformation from N-S compressional to NW-SE extensional tectonics provides a key understanding on tectonic dynamics of the eastern part of NCC in Late Mesozoic.
2019, 44(5): 1749-1760.
doi: 10.3799/dqkx.2019.078
Abstract:
It reports for the first time the presence of a suite of high-Mg volcanic xenoliths in Jianshui area of Southeast Yunnan, western Yangtze platform, China, which provides new insights into mantle plume activity in the platform during the Permian. Zircon U-Pb dating, geochemistry and petrology of the xenoliths were studied to assess the petrogenetic origin and geodynamic setting of these high-Mg volcanic rocks in this paper. The high-Mg volcanic xenoliths are porphyritic texture and contain only large phenocrysts of olivine, which show as dense mass, develop as lenticulars in the Permian Emeishan basalts in Jianshui area, Southeast Yunnan. The igneous zircons from the volcanic xenoliths yield a weighted age of ca. 259±2 Ma that is interpreted to be the formation age of the magmatic protolith, which is the same as the host rocks of the Emeishan basalts. The volcanic xenoliths are characterized by low SiO2, moderate TiO2 and high Mg#. All the volcanic xenoliths are enriched in LREE but depleted in HREE. The geochemical characteristics of the xenoliths show that they belong to sub-alkali basalts and intra-plate tholeiitic basalts, suggesting that the primary magma of the high-Mg volcanic rock is likely produced by low partial melting of garnet lherzolite. The original magma may have undergone the process of fractional crystallization of olivines and clinopyroxenes. The original magma has not been affected obviously by crustal material contamination in the emplacement and uplifting. The high-Mg volcanic xenoliths may origin from riched-mantle and may be the product of the main stage of the mantle plume activity. All above indicates that there was a mantle branch developed in the study area in Late Permian. It is proposed that several mantle branches have not only ascending motion but also lateral movement while the thermal melting mantle plume arrives at the boundary of mantle and crust.
It reports for the first time the presence of a suite of high-Mg volcanic xenoliths in Jianshui area of Southeast Yunnan, western Yangtze platform, China, which provides new insights into mantle plume activity in the platform during the Permian. Zircon U-Pb dating, geochemistry and petrology of the xenoliths were studied to assess the petrogenetic origin and geodynamic setting of these high-Mg volcanic rocks in this paper. The high-Mg volcanic xenoliths are porphyritic texture and contain only large phenocrysts of olivine, which show as dense mass, develop as lenticulars in the Permian Emeishan basalts in Jianshui area, Southeast Yunnan. The igneous zircons from the volcanic xenoliths yield a weighted age of ca. 259±2 Ma that is interpreted to be the formation age of the magmatic protolith, which is the same as the host rocks of the Emeishan basalts. The volcanic xenoliths are characterized by low SiO2, moderate TiO2 and high Mg#. All the volcanic xenoliths are enriched in LREE but depleted in HREE. The geochemical characteristics of the xenoliths show that they belong to sub-alkali basalts and intra-plate tholeiitic basalts, suggesting that the primary magma of the high-Mg volcanic rock is likely produced by low partial melting of garnet lherzolite. The original magma may have undergone the process of fractional crystallization of olivines and clinopyroxenes. The original magma has not been affected obviously by crustal material contamination in the emplacement and uplifting. The high-Mg volcanic xenoliths may origin from riched-mantle and may be the product of the main stage of the mantle plume activity. All above indicates that there was a mantle branch developed in the study area in Late Permian. It is proposed that several mantle branches have not only ascending motion but also lateral movement while the thermal melting mantle plume arrives at the boundary of mantle and crust.
2019, 44(5): 1761-1772.
doi: 10.3799/dqkx.2018.245
Abstract:
Mesozoic to Cenozoic tectonic evolution of the South China Block was dominated jointly by the Pacific tectonic domain and the Tethys tectonic domain. Brittle faulting of the NE-SW-striking Jingdezhen-Shexian shear zone and the Qiuchuan-Xiaoshan fault was studied in the eastern Jiangnan area. Based on cross-cutting relations and inversion of fault-slip data, seven stages of structural deformation were identified and their paleostress fields were inverted. Their formation ages and geodynamics are also discussed. Cretaceous to Cenozoic paleostress fields that occurred in the eastern Jiangnan area are:(1) NW-SE extension during early stage of Early Cretaceous (136-125 Ma); (2) N-S compression and E-W extension during late stage of Early Cretaceous (125-107 Ma); (3) latest Early Cretaceous to early stage of Early Cretaceous (105-86 Ma) NW-SE extension; (4) middle Late Cretaceous (86-80 Ma) NW-SE compression and NE-SW extension; (5) N-S extension during late stage of Late Cretaceous to latest Eocene (80-36 Ma); (6) NE-SW compression and NW-SE extension during latest Eocene to early stage of Oligocene (36-30 Ma); (7) early stage of Oligocene to medium stage of Miocene (30-17 Ma) NE-SW extension. Combining these with regional geological evidences, the first to fourth paleostress fields were related to roll-back, subduction of the Pacific Plate and collision between micro-terrane (Philippine Sea plate) and the South China Block. The fifth paleostress field was attributed to the roll-back of Neo-Tethys oceanic plate whereas the sixth and seventh paleostress fields to the far-field effect of the India-Asia collision. Extensional regimes and strike-slip regimes alternately dominated Cretaceous to Cenozoic structural deformation in the South China Block. The predominated factor for the strike-slip regimes in the South China Block is re-existed faults occurred before Late Mesozoic.
Mesozoic to Cenozoic tectonic evolution of the South China Block was dominated jointly by the Pacific tectonic domain and the Tethys tectonic domain. Brittle faulting of the NE-SW-striking Jingdezhen-Shexian shear zone and the Qiuchuan-Xiaoshan fault was studied in the eastern Jiangnan area. Based on cross-cutting relations and inversion of fault-slip data, seven stages of structural deformation were identified and their paleostress fields were inverted. Their formation ages and geodynamics are also discussed. Cretaceous to Cenozoic paleostress fields that occurred in the eastern Jiangnan area are:(1) NW-SE extension during early stage of Early Cretaceous (136-125 Ma); (2) N-S compression and E-W extension during late stage of Early Cretaceous (125-107 Ma); (3) latest Early Cretaceous to early stage of Early Cretaceous (105-86 Ma) NW-SE extension; (4) middle Late Cretaceous (86-80 Ma) NW-SE compression and NE-SW extension; (5) N-S extension during late stage of Late Cretaceous to latest Eocene (80-36 Ma); (6) NE-SW compression and NW-SE extension during latest Eocene to early stage of Oligocene (36-30 Ma); (7) early stage of Oligocene to medium stage of Miocene (30-17 Ma) NE-SW extension. Combining these with regional geological evidences, the first to fourth paleostress fields were related to roll-back, subduction of the Pacific Plate and collision between micro-terrane (Philippine Sea plate) and the South China Block. The fifth paleostress field was attributed to the roll-back of Neo-Tethys oceanic plate whereas the sixth and seventh paleostress fields to the far-field effect of the India-Asia collision. Extensional regimes and strike-slip regimes alternately dominated Cretaceous to Cenozoic structural deformation in the South China Block. The predominated factor for the strike-slip regimes in the South China Block is re-existed faults occurred before Late Mesozoic.
