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1.
The west Junggar,located in the eastern part of Balkash-Junggar tectonic province,is a major component of the core of the Central Asian metallogenic region.This area is characterized by occurrences of ophiolitic mélanges,such as the Sartohay ophiolitic mélange in the NE and the Tangbale ophiolitic mélange in the west.As a hydrothermal alteration product of serpentinite in the Sartohay ophiolitic mélange,listwaenite lenses are gold-mineralized and crop out on surface in the ophiolitic mélange via weathering of exhumated hanging wall of fault zone.Listwaenite is mainly composed of magnesite,quartz,dolomite,and trace amounts of mariposite,chromian spinel,talc and sulfide.A vertical thermal gradient model for the hydrothermal alteration shows that serpentinite would first be transformed to talc schist,then into listwaenite as the ophiolite slices continued to rise along shear zone,with XCO2,oxygen and sulfur fugacity increase and temperature decrease.Both serpentine and magnetite were progressively destroyed during the transformation from serpentinite to talc schist,andcompletely vanished in listwaenite,while mariposite generated in weakly deformed to mylonitized listwaenite.Concentrations of most trace elements including high field strength elements and metallogenic elements,increasing from undeformed,through weakly deformed,to mylonitized listwaenite,show a positive correlation with deformation degree and content of apatite,rutile,monazite,zircon and sulfide in listwaenite.The shear zone served as pathways for percolation and accumulation of fluid and trace elements during the metasomatism from serpentinite to listwaenite.Compared to undeformed listwaenite,mylonitized listwaenite will be more favorable to be fractured and brecciated due to more intense shearing,which caused strong metasomatic reaction and then induced trace element-bearing mylonitized listwaenite. 相似文献
2.
The Neo-Proterozoic ophiolites occur in the central and southern Eastern Desert along suture zone as dismemberedmassesinvolcano-sedimentary assemblages.The ophiolite component includes ultramafic rocks mainly serpentinites,mafic rocks,minor bodies of trondhjemite,sheeted dykes,metabasalts,and pillow lavas.The Present studies include two ophiolites in Central and southern eastern Desert named Mubarak–El Mayet and Ghadir respectively(Fig.1).The first one named after wadi Mubarak and wadi El Mayet area(55 km north Marsa Alam city)and the second named after Wadi Ghadir(30 km south Marsa Alam city).The dismembered ophiolite components in MubarakEl Mayet mainly composed mainly of serpentinites,ophiolitic metagabbros,sheeted dykes and Pillow lavas.All components occur as thrusted blocks and sheets in metavolcano-sedimentary assemblages(matrix).Gabbros sometimes occur as coarse grained gabbros(appenites)whereas pillows range in size from 30 cm to 1 m(Fig.2a).The second ophiolite sequence expose in Wadi Ghadir and its tributary.It consists of serpentinized peridotites,layered gabbro,massive isotropic gabbro,1fine grained gabbro,sheeted diabase dykes,pillowed basaltic lavas and minor plagiogranites.The serpentinizedperidotites,metapyroxenitesand serpentinites occur as allochthonous dismembered blocks,fragments and sheets in highly sheered metasediments and metavolcanics(mélange)(Fig.2b,c).The massive and layered gabbros occur in the main wadi(Fig.2d,f)and in many places contain some veins and pockets from plagiogranites.The present gabbros intruded by syenogranites from the east.Pillow lavas occur between metasedimentary mélange and ophiolitic gabbros in wadi El Beda as tributary of Wadi Ghadir and sometimes occur as fragments in mélange.The pillows range in size from 40 cm to 1 m(Fig.2f)and are mainly amygdaloidal and porphyritic basalt and spilite.Sheeted dykes cut the gabbros and pillow lavas in the Wadi El Beda and composed mainly from diabase(Fig.2g,h).In the present study,47 samples for major,trace and REE elements from different rock types in Mubarak-El Mayet(18 samples)and Ghadir ophiolite(29 samples)were analyzed.The field work and the geochemical data will discussed in the present work to evaluate the tectonic setting,origin and mantle source for two ophiolite suites. 相似文献
3.
Mesozoic magmatism is widespread in the eastern South China Block and has a close genetic relationship with intensive polymetallic mineralization. However, proper tectonic driver remains elusive to reconcile the broad intracontinental magmatic province. This study presents integrated zircon U-Pb dating, Hf isotopes and whole-rock geochemistry of the Xiwan dioritic porphyry in the NE Jiangxi ophiolitic mélange. Zircon U-Pb dating by SIMS and LA-ICP-MS methods yielded an emplacement age of ～160 Ma for the Xiwan diorite, confirming its inclusion into the Mesozoic magmatic province in SE China, instead of a component of the Neoproterozoic ophiolitic mélange genetically. The dioritic rocks have low Si02(58.08 wt%-59.15 wt%), and high Na_2 O(5.00 wt%-5.21 wt%) and MgO(4.60 wt%-5.24 wt%) contents with low TFeO/MgO ratios(1.02-1.09). They show an adakitic geochemical affinity but exhibit relatively low Sr/Y ratios(24.8-31.1) and high Y contents(14.6-18.3 ppm) compared to the Dexing adakitic porphyries. In addition, the Xiwan diorites have moderately evolved zircon Hf isotopic compositions(ε_(Hf)(t)=-6.1--0.1; T_(DM2)=1597-1219 Ma). These elemental and isotopic signatures suggest that the Xiwan diorite formed through partial melting of a remnant arc lower crust(i.e., early Neoproterozoic mafic arc-related rocks) in response to the underplating of coeval mafic magmas. In conjunction with the temporal-spatial distribution and complex geochemical characteristics of the Mesozoic magmatism, our case study attests to the feasibility of a flat-slab subduction model in developing the broad intracontinental magmatic province in SE China. The flat-slab delamination tends to trigger an asthenospheric upwelling and thus results in extensive partial melting of the overlying lithospheric mantle and lower crustal materials in an extensional setting during the Mesozoic. 相似文献
4.
<正>We report here new geochemical and geochronological data from mafic-ultramafic rock suites in the Ankara Mélange in north-central Turkey,and present a new tectonic model for its origin.Considered as one of most important relics of the Neotethyan realm in the region,the Ankara Mélange occurs between the Sakarya Continent 相似文献
5.
Seamount accretion is one of the most significant accretionary orogenic processes in the Central Asian Orogenic Belt, but there are few paleo-seamounts reported from and debate on the tectonic evolution of the Junggar Ocean still exists. In this study, we present geochronological, mineralogical, geochemical and isotopic data for basalts from the Chagantaolegai ophiolitic mélanges in Junggar. Zircon U-Pb dating on one basalt yielded a weighted mean 206 Pb/238 U age of 469 ± 7 Ma, which suggests that it formed in the Middle Ordovician. All rock samples belong to alkaline basalt and show similar geochemical characteristics, displaying high TiO2(～3 wt%),(La/Yb)N(17.6–19.0), ΣREE(232–289 ppm) and enrichment in Nb and Ta, which implies an ocean island basalt(OIB) affinity. Based upon positive εN d(t)(+4.16 to +4.23), ΔNb(0.20–0.22) and low initial 87 Sr/86 Sr(0.70425 to 0.70452) and Zr/Nb(3.35–3.57), we suggest that the Chagantaolegai OIB samples were likely derived from a fertile mantle source related to plume. The OIB rock assemblage, chert and marble in the southern part of the Chagantaolegai ophiolitic mélange indicates that a Middle Ordovician seamount was accreted to the Boshchekul-Chingiz arc due to the northward subduction of the Junggar-Balkhash Ocean. 相似文献
6.
WU Tairan HE Guoqi ZHANG ChenGeology Department Peking University Beijing 《《地质学报》英文版》1998,72(3):256-263
Two ophiolitic melange belts in the Late Carboniferous formations have been discovered recently in the Alxa region. One is in the Engger Us fault and possesses properties of oceanic crust. The other is in the Badain Jaran fault and shows properties of a back-arc basin. These two faults, together with the Yagan fault, constitute the important boundaries of tectonic units in the Alax region. The four tectonic units delimited by these faults are different in rock assemblages, metamorphism and geochemistry. They reflect the nature of tectonic environments in which they are found. The tectonic units may be traced and correlated to the eastern and western neighbouring areas. The formation and evolution process of the units and their interaction in the Alxa region may be described in terms of the evolution of the Palaeo-Mongolian Ocean and its continental margins. 相似文献
7.
Turbidites from the Shiquanhe–Namco Ophiolite Mélange Zone(SNMZ) record critical information about the tectonic affinity of the SNMZ and the evolutionary history of the Meso-Tethys Ocean in Tibet.This paper reports sedimentologic,sandstone petrographic,zircon U-Pb geochronologic,and clastic rocks geochemical data of newly identified turbidites(Asa Formation) in the Asa Ophiolite Mélange.The youngest ages of detrital zircon from the turbiditic sandstone samples,together with ～115 Ma U-Pb concordant age from the tuff intercalation within the Asa Formation indicate an Early Cretaceous age.The sandstone mineral modal composition data show that the main component is quartz grains and the minor components are sedimentary and volcanic fragments,suggesting that the turbidites were mainly derived from a recycled orogen provenance with a minor addition of volcanic arc materials.The detrital U-Pb zircon ages of turbiditic sandstones yield main age populations of170–120 Ma,300–220 Ma,600–500 Ma,1000–700 Ma,1900–1500 Ma,and ～2500 Ma,similar to the ages of the Qiangtang Terrane(age peak of 600–500 Ma,1000–900 Ma,～1850 Ma and ～2500 Ma) and the accretionary complex in the Bangong–Nujiang Ophiolite Zone(BNMZ) rather than the age of the Central Lhasa Terrane(age peak of ～300 Ma,～550 Ma and ～1150 Ma).The mineral modal compositions,detrital U-Pb zircon ages,and geochemical data of clastic rocks suggest that the Asa Formation is composed of sediments primarily recycled from the Jurassic accretionary complex within the BNMZ with the secondary addition of intermediate-felsic island arc materials from the South Qiangtang Terrane.Based on our new results and previous studies,we infer that the SNMZ represents a part of the Meso-Tethys Suture Zone,rather than a southward tectonic klippe of the BNMZ or an isolated ophiolitic mélange zone within the Lhasa Terrane.The Meso-Tethys Suture Zone records the continuous evolutionary history of the northward subduction,accretion,arc-Lhasa collision,and Lhasa-Qiangtang collision of the Meso-Tethys Ocean from the Early Jurassic to the Early Cretaceous. 相似文献
8.
We undertook zircon U-Pb dating and geochemical analyses of volcanic rocks from the Manitu Formation in the Hongol area,northeastern Inner Mongolia,to determine their age,petrogenesis and sources,which are important for understanding the Late Mesozoic tectonic evolution of the Great Xing'an Range.The volcanic rocks of the Manitu Formation from the Hongol area consist primarily of trachyandesite,based on their chemical compositions.The zircons from two of these trachyandesites are euhedral-subhedral in shape,display clear oscillatory growth zoning and have high Th/U ratios(0.31-1.15),indicating a magmatic origin.The results of LA-ICP-MS zircon U-Pb dating indicate that the volcanic rocks from the Manitu Formation in the Hongol area formed during the early Early Cretaceous with ages of 138.9-140.5 Ma.The volcanic rocks are high in alkali(Na_2O + K_2O = 6.22-8.26 wt%),potassium(K_2O = 2.49-4.58 wt%) and aluminium(Al_2O_3 = 14.27-15.88 wt%),whereas they are low in iron(total Fe_2O_3 = 3.76-6.53 wt%) and titanium(TiO_2 = 1.02-1.61 wt%).These volcanic rocks are obviously enriched in large ion lithophile elements,such as Rb,Ba,Th and U,and light rare earth elements,and are depleted in high field strength elements,such as Nb,Ta and Ti with pronounced negative anomalies.Their Sr-Nd-Pb isotopic compositions show positive ε_(Nd)(t)(+0.16‰ to+1.64‰) and low T_(DM)(t)(694-767 Ma).The geochemical characteristics of these volcanic rocks suggest that they belong to a shoshonitic series and were likely generated from the partial melting of an enriched lithospheric mantle that was metasomatised by fluids released from a subducted slab during the closure of the MongolOkhotsk Ocean.Elemental and isotopic features reveal that fractional crystallization with the removal of ferromagnesian minerals,plagioclase,ilmenite,magnetite and apatite played an important role during the evolution of the magma.These shoshonitic rocks were produced by the partial melting of the enriched lithospheric mantle in an extensional regime,which resulted from the gravitational collapse following the final closure of the Mongol-Okhotsk Ocean in the Middle-Late Jurassic. 相似文献
9.
JING Yan GE Wenchun DONG Yu YANG Hao JI Zheng BI Junhui ZHOU Hongying XING Dehe 《《地质学报》英文版》2022,96(1):81-99
The northern margin of the North China Craton(NCC)contains widespread Permian magmatic rocks,but the origin of these rocks remains controversial.This uncertainty hampers us from better understanding of tectonic framework and evolution of the eastern Paleo-Asian Ocean,particularly with respect to its final-stage subduction and closure time.To address these questions,this study presents petrological,zircon U-Pb geochronological,whole-rock geochemical and in situ zircon Hf isotopic data for these Permian mafic intrusions in the northern margin of the NCC.Precise zircon U-Pb dating results indicate that these mafic intrusions were emplaced in the Middle Permian(ca.260 Ma).Geochemically,the studied mafic intrusions have high MgO and transition metals element contents,with high Mg# values,indicating a mantle origin.These mafic intrusions are characterized by enrichments in large ion lithophile elements(LILEs;e.g.,Rb,Ba,and K)and light rare earth elements(LREEs),and depletions in high field strength elements(HFSEs;e.g.,Nb,Ta,and Ti)and heavy rare earth elements(HREEs),indicating that they were formed in a subduction-related setting.These geochemical features,together with zircon εHf(t)values(-1.1 to+11.2),indicate that their parental magmas were derived from partial melting of heterogeneous mantle wedge metasomatized by subduction-related fluids,with the contributions of slab sediments.The studied mafic intrusions also show wide range of major and trace elements contents,and variable Mg# values,Eu and Sr anomalies,suggesting that their parental magmas had undergone variable degrees of fractional crystallization.Together with the E-W trending Permian continental arc along the northern margin of the NCC,we confirm that the generation of the Middle Permian mafic intrusions was related to southward subduction of the Paleo-Asian oceanic lithosphere beneath the NCC and the Paleo-Asian Ocean had not closed prior to the Middle Permian. 相似文献
10.
Petrology,geochemistry and geochronology of the Zhongcang ophiolite,northern Tibet: implications for the evolution of the Bangong-Nujiang Ocean 总被引：3，自引：0，他引：3
Ophiolites are widespread along the Bangong-Nujiang suture zone, northern Tibet. However, it is still debated on the formation ages and tectonic evolution process of these ophiolites. The Zhongcang ophiolite is a typical ophiolite in the western part of the Bangong-Nujiang suture zone. It is composed of serpentinized peridotite, cumulate and isotropic gabbros, massive and pillow basalts, basaltic volcanic breccia, and minor red chert. Zircon SHRIMP Ue Pb dating for the isotropic gabbro yielded weighted mean age of 163.4 ± 1.8 Ma. Positive zircon ε Hf(t) values(+15.0 to +20.2) and mantle-like σ~(18)O values(5.29 ±0.21)% indicate that the isotropic gabbros were derived from a long-term depleted mantle source. The isotropic gabbros have normal mid-ocean ridge basalt(N-MORB) like immobile element patterns with high Mg O, low TiO_2 and moderate rare earth element(REE) abundances, and negative Nb,Ti, Zr and Hf anomalies. Basalts show typical oceanic island basalt(OIB) geochemical features, and they are similar to those of OIB-type rocks of the Early Cretaceous Zhongcang oceanic plateau within the Bangong-Nujiang Ocean. Together with these data, we suggest that the Zhongcang ophiolite was probably formed by the subduction of the Bangong-Nujiang Ocean during the Middle Jurassic. The subduction of the Bangong-Nujiang Tethyan Ocean could begin in the Earlye Middle Jurassic and continue to the Early Cretaceous, and finally continental collision between the Lhasa and Qiangtang terranes at the west Bangong-Nujiang suture zone probably has taken place later than the Early Cretaceous(ca. 110 Ma). 相似文献
11.
正An Early Paleozoic ophiolitic mélange has recently been documented in the W.Gangma Co area,north-central Tibetan Plateau.It is composed of serpentinite,isotropic and cumulate gabbros,basalt and plagiogranite.Whole- 相似文献
12.
Fahui Xiong Yuanku Meng Jingsui Yang Zhao Liu Xiangzhen Xu Alireza Eslami Ran Zhang 《地学前缘(英文版)》2020,11(1):277-292
The>2000 km Indus-Yarlung Tsangpo suture zone(IYSZ)is composed of the Neo-tethys oceanic remnants,flysch units and related continental rocks,which has been regarded as the boundary between the Eurasian and Indian terranes.Among the ophiolitic complexes,the Purang ophiolite is the biggest massif in the IYSZ,and many studies have been conducted on this ophiolite.However,previous studies have mainly focused on harzburgite,clinopyroxenite and dunite.Field observations show that mafic dykes were emplaced within the Purang ophiolite.However,petrogenetic evolutions of those mafic dykes are poorly understood.In this study,we present new LA-ICP-MS zircon U-Pb dating results,whole-rock geochemistry and Sr-Nd-Hf isotope analyses for microgabbro,gabbro and dolerite dykes from the Purang ophiolite of the southwestern IYSZ,respectively.Three samples yielded zircon U-Pb ages of144.2±2.1 Ma.127.9±2.3 Ma and 126.5±0.42 Ma,suggesting two different phases of magmatic activities distinctly.Whole-rock geochemical results suggest that the gabbro samples show alkaline features marked by enrichments of light rare earth elements(LREE)and large-ion lithophile elements(LILE),as well as Nb-Ta elements,suggesting an oceanic island basalt-like(OIB-like)geochemical affinity.However,the dolerite and microgabbro samples demonstrate sub-alkaline characteristics with normal mid-oceanic ridge basalt-like(N-MORB-like)geochemical features.Three distinct mafic dykes show significant Rb element depletion.The geochemical data and Sr-Nd-Hf isotopic features suggest that the microgabbro and gabbro rocks were derived from a depleted mantle that had been metasomatized by partial melts of sediments and enriched slab-derived fluids.The dolerite was also originated from a depleted mantle marked by significantly depleted Sr-Nd-Hf compositions,which was not influenced by enriched slab-derived fluids and sediments contamination during subsequent evolution.The isotope and geochemical data and tectonic diagrams suggest a tectonic transition from a within-plate to a midoceanic ridge basalt-like(MORB-like)setting during the period from ca.144 Ma to 127 Ma.Combined with regional background and this study,we propose that these mafic dykes were formed in an oceanic back-arc basin setting.Additionally,integrated with previous studies,we suggest that the geodynamic evolution of the southwestern and central parts of the Neo-Tethys oceanic basin is comparable in Early Cretaceous. 相似文献
13.
《地学前缘(英文版)》2020,11(5):1711-1725
The tectonic setting of the northern Alxa region during the Late Paleozoic is highly controversial.The key to resolve this controversy is to recognize the Late Paleozoic magmatic processes in the northern Alxa.In this paper,we present new zircon U-Pb ages,Hf-isotopic compositions and whole-rock geochemical data of four granitoids along the Zhusileng-Hangwula Tectonic Belt in the northern Alxa region that could provide critical information about the tectonic evolution of this region.The zircon U-Pb data could be grouped as two phases:Late Devonian granite and diorite(ca.373-360 Ma),and Late Carboniferous granodiorite(ca.318 Ma).The Late Devonian granites and diorites are metaluminous to slightly peraluminous,with A/CNK and A/NK ratios of 0.90-1.11 and0.95-2.19,respectively.The Late Devonian diorites are characterized by high MgO,Cr and Ni contents and MgO#values,together with variable ε_(Hf)(t) values from-1.0 to+1.3 and old T_(DM2) ages varied from 1283 Ma to 1426 Ma,indicating the primary magma was potentially derived from magma mixing of depleted mantle with Mesoproterozoic continental crust.Even though the Late Devonian granites yielded most positive and minor negative e_(Hf)(t) values between-1.1 to+5.7(three grains are negative) with two-stage model ages(T_(DM2)) of 1003-1438 Ma,they display low MgO,Cr and Ni contents and MgO#values,suggesting that they were mainly derived from juvenile crustal materials,mixed with a small amount of ancient crust.The Late Carboniferous granitoids are metaluminous and medium-K calc-alkaline series,with A/CNK and A/NK ratios ranging from 0.88 to 0.95 and1.75 to 1.90,respectively.These rocks were potentially derived from juvenile crustal materials mixed with depleted mantle,as evidenced by their high ε_(Hf)(t) values(+11.6 to+14.1) and young TDM2 ages(427 Ma to 586 Ma),as well as high Mg#values,and MgO,Ni and Cr contents.Our data,along with available sedimentary evidence and previous researches,indicate that the Late Devonian and Late Carboniferous rocks are arc-related granitoids under the subduction setting.The identification of arc-related granitoids in the northern Alxa region not only reveals the Late Paleozoic magmatic process in response to the subduction of Paleo Asian Ocean,but also provide significant constrains to the tectonic evolution of the Central Asian Orogenic Belt. 相似文献
14.
Geochemical Features of the Two Early Paleozoic Ophiolitic Zones and Volcanic Rocks in the Central —Southern Tianshan Region ,Xinjiang 总被引：2，自引：0，他引：2
This paper deals with the geochemical features of the two Early Paleozoic ophiolite zones in the central-southem Tianshan region and the central Tianshan igneous rock belt between them.Study results suggest that the central Tianshan belt was an Ordovician volcanic arc with an affinity of continental crust, and the Kumux-Hongluhe ophiolitic zone that is located on the southern margin of central Tianshan has a crustal affinity to back-arc marginal sea.The Aqqikkudug-Weiya ophiolitic zone is an accretionary boundary between the Tuha continental block and the central Tianshan volcanic arc during Late Silurian to Devoniann;Ordovician ophi-olitic blocks,Silurian flysch sequence and HP metamorphic rock relics are distributed along the Aqqikkudug-Weiya zone.Geochemically,ophiolitic rocks in the Aqqikkudug-Weiya zone have an affinity to oceanic crust,reflecting a tectonic setting of paleo-trench or subduction zone .The Early Carboniferous red molasses were deposited unconformably on the pre-Carboniferous meta-mrophosed and ductile sheared volcanic and flysch rocks,providing an upper limit age of the central and southern Tianshan belts. 相似文献
15.
This paper presents age and geochemical data of a recently identified Late Paleozoic volcanic sequence in central Jilin Province, with aims to discuss the petrogenesis and to constrain the tectonic evolution of the Central Asian Orogenic Belt in this area. Firstly, the volcanic rocks have zircon U-Pb ages of 290–270 Ma. Secondly, they are characterized by(a) ranging in composition from the low-K tholeiite series to high-K calc-alkaline series;(b) enrichment in light rare earth elements and depletion of heavy rare earth elements, with negative Eu anomalies; and(c) negative Nb, Ta, and Ti anomalies. Finally, the volcanic rocks yield εHf(t) values of +7.1 to +17. These data suggest that the central Jilin volcanic rocks were possibly derived from predominant partial melting of a depleted lithospheric mantle that might have been modified by subducted slab–derived fluids. Combined with previous studies, the Late Paleozoic–Early Mesozoic magmatism in Central Jilin can be divided into two stages:(a) a volcanic arc stage(290–270 Ma) represented by low-K to high–K, tholeiite to calc–alkaline plutons and(b) a syn–collisional stage(260–240 Ma) represented by high-K calc–alkaline I-type granites. Furthermore, the timing and the tectonic setting of the above magmatic rocks show that the arc was probably produced by the northward subduction of the Paleo-Asian Ocean and that the final closure of the Paleo-Asian Ocean occurred prior to the Early Triassic. 相似文献
16.
Although the middle section of the Bangong-Nujiang suture zone has been intensively investigated, its tectonic framework and evolution is still controversy. The Pungco ophiolite has a relative complete ophiolitic complex, which is an ideal specimen for studying this tricky problem. LA-ICP-MS U-Pb dating of zircons from the diabasic rock yielded an age of 159.0±2.1 Ma. This age suggests that the Pungco ophiolite was formed in the Late Jurassic, indicating the development of the Late Jurassic ophiolite in the third ophiolitic subzone. The whole-rock major and trace element compositions of diabasic and basaltic rocks exhibit mixed arc and N-MORB geochemical characteristics. Two diabasic samples have (87Sr/86Sr)i values of 0.7055 and 0.7063 and εNd(t) values of 11.28 and 11.84, respectively. The geochemical signatures and formation age of the Pungco ophiolite suggest that this ophiolite was probably produced in an active continental fore-arc setting. It originated from a N-MORB-like depleted mantle source with the involvement of subducted-slab fluids. Considering the regional geological background, the Pungco ophiolite was likely generated during the southward subduction of the Bangong-Nujiang Tethyan oceanic lithosphere beneath the Lhasa terrane, and belongs to a regional archipelagic arc-basin system together with the other Early Jurassic-Early Cretaceous ophiolites from the northern Tibet Lake district. © 2018, Science Press. All right reserved. 相似文献
17.
Geochemical Characteristics and Geological Significance of Early Permian Baya’ertuhushuo Gabbro in South Great Xing’an Range 总被引：1，自引：0，他引：1
LIU Jianfeng CHI Xiaoguo ZHAO Zhi ZHANG Xingzhou MA Zhihong WANG Tiefu HU Zhaochu 《《地质学报》英文版》2011,85(1):116-129
Field geological investigation and geochemical analysis are carried out on Baya’ertuhushuo Gabbro in South Great Xing’an Range. Field investigation reveals that the gabbro is a magmatic intrusion rather than a component of an ophiolite suite as previously thought. Zircon laser ablation inductively coupled plasma mass spectroscopy (LA-ICP-MS) U-Pb dating indicates the gabbro was formed in 274–275?Ma, just as the widespread volcanic rocks of Dashizhai Formation (P1d), monzogranites and miarolitic alkali-feldspar granites in the study area. The gabbro has SiO2 content between 47.23 wt% and 50.17 wt%, high MgO and FeOT contents of 6.95–11.29 wt% and 7.32–12.24wt%, respectively, and it belongs to low-K tholeiitic series in the SiO2-K2O diagram. The Chondrite-normalized rare earth element (REE) patterns and primitive mantle-normalized spider diagrams of the gabbro are similar to those of Normal Mid-Ocean Ridge Basalt (N-MORB) except for the enrichment of large ion lithophile elements (LILE), such as Rb, Ba and K. In trace element tectonic discriminative diagrams, the samples are mainly plotted in the N-MORB field, and Zircon in?situ Lu-Hf isotopic analysis also indicates the gabbro originated from depleted mantle. Through synthetic studies of the geochemical characteristics and petrogenesis of Baya’ertuhushuo gabbro, volcanic rocks of Dashizhai Formation and granitoids in the area, it is suggested that the early Permian magmatism in the Xilinhot-Xiwuqi area formed in the tectonic setting of asthenosphere upwelling, which was caused by breaking-off of the subducted Paleo-Asian Ocean slab. 相似文献
18.
Located in the northern part of the Xinlin–Xiguitu suture zone,geochemistry and geochronology of the Xinlin ophiolite provide a unique opportunity to determine the the evolution of the eastern Xing’an–Mongolian Orogenic Belt.The Xinlin ophiolite was initially constrained roughly 21.5 km southeast of the Xinlin town by the First Regional Geological Survey Party of Heilongjiang Province.Subsequent work has shown that the mafic and ultramafic rocks in the adjacent Tayuan town was congenetic with the Xinlin ophiolite(Fig.1).Over the past three years we have conducted a series of studies to the Xinlin ophiolite with the aim to better understand its characteristic and tectonic implications.The present work is is to provide our preliminary geochemical data of the mafic rocks of the Xinlin ophiolite and possible"congenetic"mafic rocks in the Tayuan town.The mafic rocks of the Xinlin ophiolite including the gabbro,diabase and metabasalt show flat REE pattern[(La/Yb)N=0.68~1.58]and no Eu anomalies,which are transitional between normal and enriched mid-ocean ridge basalts(N-MORB and E-MORB).They also exhibit flat patterns from Ba to Yb in the trace elements spider diagram,which lie between those of typical E-MORB and N-MORB but closer to the former.The mafic rocks in the Tayuan town consist mainly of hornblende gabbro with alkaline affinity and are characterized by enriched in light rare earth elements and large ion lithophile elements,depleted in heavy rare earthelements and high field strength elements(Fig.2).The obvious differences in the geochemical characteristics indicate that the mafic rocks in the Tayuan town may not be cogenetic with those of the Xinlin ophiolite.This was further corroborated by their different formation time.Our zircon U–Pb dating indicates that the gabbro in the Tayuan town was emplaced during the late Carboniferous(~310 Ma;Fig.3),significantly younger than the recently reported U–Pb ages for the mafic rocks of the Xinlin ophiolite(~510 Ma;Feng,2015).Therefore,the two units appear as independent bodies and their origin and tectonic implication need to be further examined. 相似文献
19.
The Beila ophiolite is located in the middle part of the Bangong-Nujiang suture zone,northern Tibetan plateau.It is a complete ophiolite suite,and plays a key role in understanding the evolution of the Bangong-Nujiang suture zone,as well as the Meso-Tethys Ocean.The Beila ophiolite was composed of peridotite,serpentinite,gabbro,pillow basalt,and minor rodingite.Peridotites comprisemainlymedium–tocoarse–grained serpentinized harzburgites and minor plagioclase-bearing lherzolites and dunites.There are some felsic-ultramafic dykes within the peridotite and they are mainlypegmatoidal pyroxenites,coarse to fine-grained gabbros,and diabases.Gabbros included isotropic and cumulate gabbros,and they commonly contain minor pegmatoidal gabbros veins.Pillow basalts and basaltic andesites overlaid on the margin of the serpentinized peridotites.Rodingite occurs as lenses and/or dykes within the host serpentinized peridotites.Zircon SHRIMP U–Pb dating for two rodingite samples yielded the ages ranging from172 to 164 Ma.Whole-rock geochemical and zircon Hf isotopic data show that the Beila ophiolite shows SSZ-type ophiolite affinity.Finally,we suggest that the Beila ophiolite was generated in an initial subduction process at the middle Jurassic(164–172 Ma). 相似文献
20.
The only occurrence of Lower Triassic silicic volcanic rocks within the South China Block is in the Qinzhou Bay area of Guangxi Province. LA-ICP-MS zircon U-Pb dating reveals that volcanic rocks of the Beisi and Banba formations formed between 248.8 ± 1.6 and 246.5 ± 1.3 Ma, coeval with peraluminous granites of the Qinzhou Bay Granitic Complex. The studied rhyolites and dacites are characterized by high SiO2, K2O, and Al2O3, and low MgO, CaO, and P2O5 contents and are classified as high-K calc-alkaline S-type rocks, with A/CNK = 0.98–1.19. The volcanic rocks are depleted in high ?eld strength elements, e.g., Nb, Ta, Ti, and P, and enriched in large ion lithophile elements, e.g., Rb, K, Sr, and Ba. Although the analyzed volcanic rocks have extremely enriched zircon Hf isotopic compositions (εHf(t) = ?29.1 to ?6.9), source discrimination indicators and high calculated Ti-in-zircon temperatures (798–835°C) reveal that magma derived from enriched lithospheric mantle not only provided a heat source for anatectic melting of the metasedimentary protoliths but was also an endmember component of the S-type silicic magma. The studied early Triassic volcanics are inferred to have formed immediately before closure of the Paleo-Tethys Ocean in this region, as the associated subduction would have generated an extensional setting in which the mantle-derived upwelling and volcanic activity occurred. 相似文献