It is dominantly characterized that arc and back\|arc basin occur mutually in arc\|basin systems, Jomda arc and Sinda back\|arc basin located in Qamdo area are typical(Fig.1). Jomda arc covered by Triassic with thickn...It is dominantly characterized that arc and back\|arc basin occur mutually in arc\|basin systems, Jomda arc and Sinda back\|arc basin located in Qamdo area are typical(Fig.1). Jomda arc covered by Triassic with thickness about 10000m.Marine sediments predominate, and are Characterized by the largely thick turbidity rocks and arc volcanic rocks of calc\|alkali suite which frequent volcanic events raised. Sinda back\|arc basin with a land\|crust basement is filled by the Upper Triassic sedimentary strata of more than 5000m. The active marginal sediments are composed of terrigenous,basinal and volcanic turbidity deposits of bathyal to deep\|sea facies,Characteristic extensive alkali basalts and submarine spout hot water deposits. Based on investigation of the cutcrop pro\|file, isotime grillwork for Triassic sequence stratigraphy has been established. for example Jomda arc basin, including 6 type 1 and 4 type 2 boundaries.10 three\|order sequences are divided, including 6 type 1 and 4 type 2 sequences. These sequences evolves during 37Ma,the estimated average time of a sequences is 3～7Ma,with being generally 1～2Ma,the longest being about 10Ma. type 1 and type 2 sequence boundaries are identified, in Upper Triassic Sinda back\|arc basin two type 1 and one type 2 sequences are divided. Relations have been first concluded among mainly controlled factors of sequence stratigraphies in arc and back\|arc basin systems. First, more sequences product and three\|units of its structures are complete in arc systems of complicated tectonic\|volcanic topographies, for example Jomda arc area of island\|sea framework, because lots of deposits are supplied and accumulations are allowed. Secondly, tectonic control is very clear, type 1 boundaries of SQ1 and SQ7 are clearly unconformity interfaces stressed by tectonism.Thirdly,volcanic rocks is greatly related with sequences, and there are various volcanic rocks in mang sequences,for example Jomda sequence stratigraphies,volcanic rocks of calc alkaline suite occurs in LST which thickness occupying in LST is middle; both tholeiite and calc\|alkaline,alkaline suite (Sinda back\|arc area) in TST, thickness smallest; calc\|alkaline suite in HST, Thickness biggest. It proves that intra\|genetic association between volcanic and relative sea\|level changes, which is gained by the concordance of thick curves of volcanic rock and sea\|level in different systematic traces. When thickness of volcanic rocks growing or progressing, relative sea\|level falls; otherwise, when reducing, it rises. There are larger differences in quantities, structures and types of sequences by comparing sequence stratigraphies of arc, back\|arc with craton area. Those varieties are responses for interactions among tectonic\|volcano, sediment and eustacy. It is pointed out that tectonic and arc volcanic processes are crucial.展开更多
The Yamansu belt,an important tectonic component of Eastern Tianshan Mountains,of the Central Asian Orogenic Belt,NW China hosts many Fe-(Cu)deposit.In this study,we present new zircon U-Pb geochronology and geochemic...The Yamansu belt,an important tectonic component of Eastern Tianshan Mountains,of the Central Asian Orogenic Belt,NW China hosts many Fe-(Cu)deposit.In this study,we present new zircon U-Pb geochronology and geochemical data of the volcanic rocks of Shaquanzi Formation and diorite intrusions in the Yamansu belt.The Shaquanzi Formation comprises mainly basalt,andesite/andesitic tuff,rhyolite and sub-volcanic diabase with local diorite intrusions.The volcanic rocks and diorites contain ca.315-305 Ma and ca.298 Ma zircons respectively.These rocks show calc-alkaline affinity with enrichment in large-ion lithophile elements(LILEs),light rare-earth elements(LREEs),and depletion in high field strength elements(HFSEs)in primitive mantle normalized multi-element diagrams,which resemble typical back-arc basin rocks.They show depleted mantle signature with ε_(Nd)(t)ranging from+3.1 to +5.6 for basalt;+2.1 to+4.7 for andesite;-0.2 to+1.5 for rhyolite and the ε_(Hf)(t)ranges from-0.1 to +13.0 for andesites;+5.8 to +10.7 for andesitic tuffs.We suggest that the Shaquanzi Formation basalt might have originated from a depleted,metasomatized lithospheric mantle source mixed with minor(3-5%)subduction-derived materials,whereas the andesite and rhyolite could be fractional crystallization products of the basaltic magma.The Shaquanzi Formation volcanic rocks could have formed in an intracontinental back-arc basin setting,probably via the southward subduction of the Kangguer Ocean beneath the Middle Tianshan Massif.The Yamansu mineralization belt might have undergone a continental arc to back-arc basin transition during the Late Carboniferous and the intra-continental back-arc basin might have closed in the Early Permian,marked by the emplacement of dioritic magma in the Shaquanzi belt.展开更多
The Napo-Qinzhou Tectonic Belt （NQTB） lies at the junction of the Yangtze, Cathaysia and Indochina （North Vietnam） Blocks, which is composed of five major lithotectonic subunits： the Qinzhou-Fangcheng Suture Zone...The Napo-Qinzhou Tectonic Belt （NQTB） lies at the junction of the Yangtze, Cathaysia and Indochina （North Vietnam） Blocks, which is composed of five major lithotectonic subunits： the Qinzhou-Fangcheng Suture Zone （QFSZ）, the Shiwandashan Basin （SB）, the Pingxiang-Nanning Suture Zone （PNSZ）, the Damingshan Block （DB） and the Babu-Lingma Suture Zone （BLSZ）. On the basis of geochemical compositions, the Permian mafic igneous rocks can be divided into three distinct groups： （1） mafic igneous rocks （Group 1） from the Longjing region in the PNSZ and Hurun region in the BLSZ, which are characterized by intermediate Ti, P and Zr with low Ni and Cr contents; （2） mafic igneous rocks （Group 2） from the Naxiao and Chongzuo region in the DB, characterized by low-intermediate Ti, P and Zr with high Ni and Cr concentrations; and （3） mafic igneous rocks （Group 3） from the Siming region in the Jingxi carbonate platform of the northwestern margin of the NQTB, with intermediate-high Ti, P and Zr and low Ni and Cr contents. The Group 1 rocks yield a weighted mean 206 Pb/ 238 U age of 250.5±2.8 Ma and are geochemically similar to basalts occurring in back-arc basin settings. The Group 2 rocks exhibit geochemical features to those basalts in island arcs, whereas the Group 3 rocks show geochemical similarity to that of ocean island basalts. All three groups are characterized by relatively low ε Nd （t） values （-2.61 to ＋1.10） and high initial 87 Sr/ 86 Sr isotopic ratios （0.705309-0.707434）, indicating that they were derived from a subduction-modified lithospheric mantle and experienced assimilation, fractional crystallization, and crustal contamination or mixing during magmatic evolution. Accordingly, we propose the existence of an arc-back arc basin system that developed along the NQTB at the border of SW Guangxi Province （SW China） and northern Vietnam, and it was formed by continued northwestward subduction of the Cathaysian （or Yunkai） Block under the Yangtze Block, and northeastward subduction of the Indochina Block beneath the Yangtze Block during Permian time.展开更多
The Qom Formation comprises Oligo-Miocene deposits from a marine succession distributed in the Central Basin of Iran. It is composed of five members designated as A-F. Little previous work exists on the sequence strat...The Qom Formation comprises Oligo-Miocene deposits from a marine succession distributed in the Central Basin of Iran. It is composed of five members designated as A-F. Little previous work exists on the sequence stratigraphy. Based on an integrated study of sequence stratigraphy with outcrop data, wells and regional seismic profiles, the Qom Formation is interpreted as a carbonate succession deposited in a mid.Tertiary back-arc basin. There are two second-order sequences （designated as SS1 and SS2） and five third-order sequences （designated as S1-S5）. Five distinct systems tracts including transgressive, highstand, forced regressive, slope margin and Iowstand have been recognized. The relationship between the sequences and lithologic sub-units has been collated and defined （S1 to S5 individually corresponding to A-C1, C2--C4, D-E, the lower and upper portions of F）; a relative sea level change curve and the sequence stratigraphic framework have been established and described in detail. The coincidence of relative sea level change between that of the determined back-arc basin and the world indicates that the sedimentary cycles of the Qom Formation are mainly controlled by eustatic cycles. The variable combination of the systems tracts and special tectonic-depositional setting causally underpin multiple sequence stratigraphic framework styles seen in the carbonates of the back-arc basin revealing： （1） a continental margin basin that developed some form of barrier, characterized by the development of multiple cycles of carbonate-evaporites; （2） a flat carbonate ramp, which occurred on the southern shelf formed by the lack of clastic supply from nearby magmatic islands plus mixed siliciclastics and carbonates that occurred on the northern shelf due to a sufficient clastics supply from the land; and （3） a forced regressive stratigraphic stacking pattern that occured on the southern shelf and in basin lows due to the uplifting of the southern shelf. Thick and widespread aggradational framework limestone usually occurs in the initial sequences （S1 and S3） of the supersequence, which led to preferential oil reservoir deposition but a lack of source and cap rocks, whereas the retrogradational and progradational framework limestone usually occurs in the later sequences （S2 and S4-S5） of the supersequence, which results in two perfect sets of source, reservoir and cap rock assemblies, so that the limestone in sub-member C2-C4 and the F-Member can be predicted as important objects for oil exploration.展开更多
To look for gas hydrate, 22 multi-channel and 3 single-channel seismic lines on the East China Sea （ECS） shelf slope and at the bottom of the Okinawa Trough were examined. It was found that there was indeed bottom s...To look for gas hydrate, 22 multi-channel and 3 single-channel seismic lines on the East China Sea （ECS） shelf slope and at the bottom of the Okinawa Trough were examined. It was found that there was indeed bottom simulating reflector （BSR） occurrence, but it is very rare. Besides several BSRs, a gas seepage was also found. As shown by the data, both the BSR and gas seepage are all related with local geological structures, such as mud diapir, anticline, and fault-controlled graben-like structure. However, similar structural ＂anomalies＂ are quite common in the tectonically very active Okinawa Trough region, but very few of them have developed BSR or gas seepage. The article points out that the main reason is probably the low concentration of organic carbon of the sediment in this area. It was speculated that the rare occurrence of gas hydrates in this region is governed by structure-controlled fluid flow. Numerous faults and fractures form a network of high-permeability channels in the sediment and highly fractured igneous basement to allow fluid circulation and ventilation. Fluid flow in this tectonic environment is driven primarily by thermal buoyancy and takes place on a wide range of spatial scales. The fluid flow may play two roles to facilitate hydrate formation： to help gather enough methane into a small area and to modulate the thermal regime.展开更多
The evolution of the Mediterranean area since the Oligocene-Lower Miocene has been driven by the convergence of the surrounding plates. This implies that the observed deformation pattern in that region must be the mos...The evolution of the Mediterranean area since the Oligocene-Lower Miocene has been driven by the convergence of the surrounding plates. This implies that the observed deformation pattern in that region must be the most convenient shortening pattern, i.e. the one controlled by the minimum action principle. To understand why the fulfilment of such condition has required a complex spatio-temporal distribution of major tectonic events, such as uplift, lateral displacement and bending of orogenic belts, consumption of large lithospheric domains and formation of back arc basins, it may be very useful to take into account a basic tectonic concept, which helps to identify the process that can minimize the resistance of tectonic forces. Such concept starts from the fact that the most convenient consumption process is the one that involves low buoyancy oceanic lithosphere (Tethyan domains). However, such process is highly favoured where the oceanic lithosphere is stressed by vertical forces, a situation that develops when orogenic wedges are forced to over thrust and load the oceanic domain to be consumed. This interpretation can provide plausible and coherent explanations for the complex pattern of the observed deformations. In this view, the generation of back arc basins is taken as a side effect of an extrusion process, as suggested by numerical and mechanical experiments.展开更多
There are three cases of variation of trench location possible to occur during subduction: trench fixed, trench ad- vancing, and trench retreating. Retreat of trench may lead to back-arc extension. The Pacific plate ...There are three cases of variation of trench location possible to occur during subduction: trench fixed, trench ad- vancing, and trench retreating. Retreat of trench may lead to back-arc extension. The Pacific plate subducts at low angle beneath the Eurasia plate, tomographic results indicate that the subducted Pacific slab does not penetrate the 670 km discontinuity, instead, it is lying flat above the interface. The flattening occurred about 28 Ma ago. Geo- dynamic computation suggests: when the frontier of the subducted slab reaches the phase boundary of lower and upper mantle, it may be hindered and turn flat lying above the boundary, facilitates the retreat of trench and back-arc extension. Volcanism in northeastern China is likely a product of such retreat of subduction, far field back-arc extension, and melting due to reduce of pressure while mantle upwelling.展开更多
文摘It is dominantly characterized that arc and back\|arc basin occur mutually in arc\|basin systems, Jomda arc and Sinda back\|arc basin located in Qamdo area are typical(Fig.1). Jomda arc covered by Triassic with thickness about 10000m.Marine sediments predominate, and are Characterized by the largely thick turbidity rocks and arc volcanic rocks of calc\|alkali suite which frequent volcanic events raised. Sinda back\|arc basin with a land\|crust basement is filled by the Upper Triassic sedimentary strata of more than 5000m. The active marginal sediments are composed of terrigenous,basinal and volcanic turbidity deposits of bathyal to deep\|sea facies,Characteristic extensive alkali basalts and submarine spout hot water deposits. Based on investigation of the cutcrop pro\|file, isotime grillwork for Triassic sequence stratigraphy has been established. for example Jomda arc basin, including 6 type 1 and 4 type 2 boundaries.10 three\|order sequences are divided, including 6 type 1 and 4 type 2 sequences. These sequences evolves during 37Ma,the estimated average time of a sequences is 3～7Ma,with being generally 1～2Ma,the longest being about 10Ma. type 1 and type 2 sequence boundaries are identified, in Upper Triassic Sinda back\|arc basin two type 1 and one type 2 sequences are divided. Relations have been first concluded among mainly controlled factors of sequence stratigraphies in arc and back\|arc basin systems. First, more sequences product and three\|units of its structures are complete in arc systems of complicated tectonic\|volcanic topographies, for example Jomda arc area of island\|sea framework, because lots of deposits are supplied and accumulations are allowed. Secondly, tectonic control is very clear, type 1 boundaries of SQ1 and SQ7 are clearly unconformity interfaces stressed by tectonism.Thirdly,volcanic rocks is greatly related with sequences, and there are various volcanic rocks in mang sequences,for example Jomda sequence stratigraphies,volcanic rocks of calc alkaline suite occurs in LST which thickness occupying in LST is middle; both tholeiite and calc\|alkaline,alkaline suite (Sinda back\|arc area) in TST, thickness smallest; calc\|alkaline suite in HST, Thickness biggest. It proves that intra\|genetic association between volcanic and relative sea\|level changes, which is gained by the concordance of thick curves of volcanic rock and sea\|level in different systematic traces. When thickness of volcanic rocks growing or progressing, relative sea\|level falls; otherwise, when reducing, it rises. There are larger differences in quantities, structures and types of sequences by comparing sequence stratigraphies of arc, back\|arc with craton area. Those varieties are responses for interactions among tectonic\|volcano, sediment and eustacy. It is pointed out that tectonic and arc volcanic processes are crucial.
基金financially supported by the Chinese National Basic Research 973-Program(No.2014CB440802)Project No.IS-2353 of GIGCAS
文摘The Yamansu belt,an important tectonic component of Eastern Tianshan Mountains,of the Central Asian Orogenic Belt,NW China hosts many Fe-(Cu)deposit.In this study,we present new zircon U-Pb geochronology and geochemical data of the volcanic rocks of Shaquanzi Formation and diorite intrusions in the Yamansu belt.The Shaquanzi Formation comprises mainly basalt,andesite/andesitic tuff,rhyolite and sub-volcanic diabase with local diorite intrusions.The volcanic rocks and diorites contain ca.315-305 Ma and ca.298 Ma zircons respectively.These rocks show calc-alkaline affinity with enrichment in large-ion lithophile elements(LILEs),light rare-earth elements(LREEs),and depletion in high field strength elements(HFSEs)in primitive mantle normalized multi-element diagrams,which resemble typical back-arc basin rocks.They show depleted mantle signature with ε_(Nd)(t)ranging from+3.1 to +5.6 for basalt;+2.1 to+4.7 for andesite;-0.2 to+1.5 for rhyolite and the ε_(Hf)(t)ranges from-0.1 to +13.0 for andesites;+5.8 to +10.7 for andesitic tuffs.We suggest that the Shaquanzi Formation basalt might have originated from a depleted,metasomatized lithospheric mantle source mixed with minor(3-5%)subduction-derived materials,whereas the andesite and rhyolite could be fractional crystallization products of the basaltic magma.The Shaquanzi Formation volcanic rocks could have formed in an intracontinental back-arc basin setting,probably via the southward subduction of the Kangguer Ocean beneath the Middle Tianshan Massif.The Yamansu mineralization belt might have undergone a continental arc to back-arc basin transition during the Late Carboniferous and the intra-continental back-arc basin might have closed in the Early Permian,marked by the emplacement of dioritic magma in the Shaquanzi belt.
基金Financial support for this study was jointly provided by the Hundred Talents Project of Ministry of Land and Resources of China, the Ten-Hundred-Thousand Talent Project of Guangxi (Grant No. 2006218)Guangxi Science Foundation (Grant No.0728089)+1 种基金Institute of Mineral Resources, Chinese Academy of Geological Sciences (Grant No. K0914)China Geological Survey (Grant No. 201111020 and1212010510805)
文摘The Napo-Qinzhou Tectonic Belt （NQTB） lies at the junction of the Yangtze, Cathaysia and Indochina （North Vietnam） Blocks, which is composed of five major lithotectonic subunits： the Qinzhou-Fangcheng Suture Zone （QFSZ）, the Shiwandashan Basin （SB）, the Pingxiang-Nanning Suture Zone （PNSZ）, the Damingshan Block （DB） and the Babu-Lingma Suture Zone （BLSZ）. On the basis of geochemical compositions, the Permian mafic igneous rocks can be divided into three distinct groups： （1） mafic igneous rocks （Group 1） from the Longjing region in the PNSZ and Hurun region in the BLSZ, which are characterized by intermediate Ti, P and Zr with low Ni and Cr contents; （2） mafic igneous rocks （Group 2） from the Naxiao and Chongzuo region in the DB, characterized by low-intermediate Ti, P and Zr with high Ni and Cr concentrations; and （3） mafic igneous rocks （Group 3） from the Siming region in the Jingxi carbonate platform of the northwestern margin of the NQTB, with intermediate-high Ti, P and Zr and low Ni and Cr contents. The Group 1 rocks yield a weighted mean 206 Pb/ 238 U age of 250.5±2.8 Ma and are geochemically similar to basalts occurring in back-arc basin settings. The Group 2 rocks exhibit geochemical features to those basalts in island arcs, whereas the Group 3 rocks show geochemical similarity to that of ocean island basalts. All three groups are characterized by relatively low ε Nd （t） values （-2.61 to ＋1.10） and high initial 87 Sr/ 86 Sr isotopic ratios （0.705309-0.707434）, indicating that they were derived from a subduction-modified lithospheric mantle and experienced assimilation, fractional crystallization, and crustal contamination or mixing during magmatic evolution. Accordingly, we propose the existence of an arc-back arc basin system that developed along the NQTB at the border of SW Guangxi Province （SW China） and northern Vietnam, and it was formed by continued northwestward subduction of the Cathaysian （or Yunkai） Block under the Yangtze Block, and northeastward subduction of the Indochina Block beneath the Yangtze Block during Permian time.
文摘The Qom Formation comprises Oligo-Miocene deposits from a marine succession distributed in the Central Basin of Iran. It is composed of five members designated as A-F. Little previous work exists on the sequence stratigraphy. Based on an integrated study of sequence stratigraphy with outcrop data, wells and regional seismic profiles, the Qom Formation is interpreted as a carbonate succession deposited in a mid.Tertiary back-arc basin. There are two second-order sequences （designated as SS1 and SS2） and five third-order sequences （designated as S1-S5）. Five distinct systems tracts including transgressive, highstand, forced regressive, slope margin and Iowstand have been recognized. The relationship between the sequences and lithologic sub-units has been collated and defined （S1 to S5 individually corresponding to A-C1, C2--C4, D-E, the lower and upper portions of F）; a relative sea level change curve and the sequence stratigraphic framework have been established and described in detail. The coincidence of relative sea level change between that of the determined back-arc basin and the world indicates that the sedimentary cycles of the Qom Formation are mainly controlled by eustatic cycles. The variable combination of the systems tracts and special tectonic-depositional setting causally underpin multiple sequence stratigraphic framework styles seen in the carbonates of the back-arc basin revealing： （1） a continental margin basin that developed some form of barrier, characterized by the development of multiple cycles of carbonate-evaporites; （2） a flat carbonate ramp, which occurred on the southern shelf formed by the lack of clastic supply from nearby magmatic islands plus mixed siliciclastics and carbonates that occurred on the northern shelf due to a sufficient clastics supply from the land; and （3） a forced regressive stratigraphic stacking pattern that occured on the southern shelf and in basin lows due to the uplifting of the southern shelf. Thick and widespread aggradational framework limestone usually occurs in the initial sequences （S1 and S3） of the supersequence, which led to preferential oil reservoir deposition but a lack of source and cap rocks, whereas the retrogradational and progradational framework limestone usually occurs in the later sequences （S2 and S4-S5） of the supersequence, which results in two perfect sets of source, reservoir and cap rock assemblies, so that the limestone in sub-member C2-C4 and the F-Member can be predicted as important objects for oil exploration.
基金the National Natural Science Foundation of China (No.40776032)Key Discipline Program of Chinese Academy of Sciences (No.KZCX2-211-01)National Basic Research Program of China (973 Program,No.207CB411702)
文摘To look for gas hydrate, 22 multi-channel and 3 single-channel seismic lines on the East China Sea （ECS） shelf slope and at the bottom of the Okinawa Trough were examined. It was found that there was indeed bottom simulating reflector （BSR） occurrence, but it is very rare. Besides several BSRs, a gas seepage was also found. As shown by the data, both the BSR and gas seepage are all related with local geological structures, such as mud diapir, anticline, and fault-controlled graben-like structure. However, similar structural ＂anomalies＂ are quite common in the tectonically very active Okinawa Trough region, but very few of them have developed BSR or gas seepage. The article points out that the main reason is probably the low concentration of organic carbon of the sediment in this area. It was speculated that the rare occurrence of gas hydrates in this region is governed by structure-controlled fluid flow. Numerous faults and fractures form a network of high-permeability channels in the sediment and highly fractured igneous basement to allow fluid circulation and ventilation. Fluid flow in this tectonic environment is driven primarily by thermal buoyancy and takes place on a wide range of spatial scales. The fluid flow may play two roles to facilitate hydrate formation： to help gather enough methane into a small area and to modulate the thermal regime.
文摘The evolution of the Mediterranean area since the Oligocene-Lower Miocene has been driven by the convergence of the surrounding plates. This implies that the observed deformation pattern in that region must be the most convenient shortening pattern, i.e. the one controlled by the minimum action principle. To understand why the fulfilment of such condition has required a complex spatio-temporal distribution of major tectonic events, such as uplift, lateral displacement and bending of orogenic belts, consumption of large lithospheric domains and formation of back arc basins, it may be very useful to take into account a basic tectonic concept, which helps to identify the process that can minimize the resistance of tectonic forces. Such concept starts from the fact that the most convenient consumption process is the one that involves low buoyancy oceanic lithosphere (Tethyan domains). However, such process is highly favoured where the oceanic lithosphere is stressed by vertical forces, a situation that develops when orogenic wedges are forced to over thrust and load the oceanic domain to be consumed. This interpretation can provide plausible and coherent explanations for the complex pattern of the observed deformations. In this view, the generation of back arc basins is taken as a side effect of an extrusion process, as suggested by numerical and mechanical experiments.
基金National Natural Science Foundation of China (40234042 and 40174027).
文摘There are three cases of variation of trench location possible to occur during subduction: trench fixed, trench ad- vancing, and trench retreating. Retreat of trench may lead to back-arc extension. The Pacific plate subducts at low angle beneath the Eurasia plate, tomographic results indicate that the subducted Pacific slab does not penetrate the 670 km discontinuity, instead, it is lying flat above the interface. The flattening occurred about 28 Ma ago. Geo- dynamic computation suggests: when the frontier of the subducted slab reaches the phase boundary of lower and upper mantle, it may be hindered and turn flat lying above the boundary, facilitates the retreat of trench and back-arc extension. Volcanism in northeastern China is likely a product of such retreat of subduction, far field back-arc extension, and melting due to reduce of pressure while mantle upwelling.
