0 INTRODUCTION Orogenic belts are commonly built by multiple-stage processes involving oceanic subduction and continental collisions that result in the generation of magma with distinct geochemical compositions,as exe...0 INTRODUCTION Orogenic belts are commonly built by multiple-stage processes involving oceanic subduction and continental collisions that result in the generation of magma with distinct geochemical compositions,as exemplified by Central Asian Orogenic Belts(e.g.,Wang et al.,2024;Yin et al.,2024;Xiao et al.,2005)and the Tethyan tectonic domains(e.g.,Chen et al.,2024;Li et al.,2024;Tao et al.,2024a;Gehrels et al.,2011;Yin and Harrison,2000).展开更多
Permian—Triassic granitoids are widely distributed along the Jinshajiang suture belt,eastern Xizang,and are regarded as the result of the tectonic-magmatic activity associated with the evolution of Paleo-Tethys Ocean...Permian—Triassic granitoids are widely distributed along the Jinshajiang suture belt,eastern Xizang,and are regarded as the result of the tectonic-magmatic activity associated with the evolution of Paleo-Tethys Ocean.This paper focuses on the high-K calc-alkaline I-type Rennong(~235 Ma)and Jiaduoling(~232 Ma)granitoid plutons,eastern Xizang,which are enriched in light rare earth elements(LREEs)and large ion lithophile elements(LILEs),but depleted in high field strength elements(HFSEs)with moderate-weak negative Eu anomalies(0.61–0.90).The Rennong granites are characterized by uniform zircon ε_(Hf)(t)values(-7.3 to-3.5)and negative ε_(Nd)(t)values(-7.6 to-5.7),with old two-stage Nd model ages(T_(DM2)=1.51-1.46 Ga)and was likely formed by partial melting of the basement rocks,whereas the Jiaduoling rock samples have variable zircon ε_(Hf)(t)values(-5.7 to+5.5)but negativeεNd(t)values(-7.6 to-7.7)and are proposed to be formed by hybridization of mantle-derived mafic magma,Rennong felsic magma and sediments.Mafic microgranular enclaves(MMEs)in the Jiaduoling granitic rocks,have similar zircon U-Pb ages(~237 Ma)and zircon ε_(Hf)(t)values(-4.4 to+6.3)to the host rocks,indicating that zircons in the MMEs were actually xenocrysts that formed at an early stage in the granitic magma chamber.These results reveal that the break-off of the Jinshajiang oceanic slab beneath Changdu(Qamdo)-Simao Block was in a post-collisional setting,resulted in the upwelling of asthenosphere in the Late Triassic,and then,generated the wide-spread intermediate-felsic magmatism along the Jinshajing belt,including the Rennong and Jiaduoling plutons.展开更多
Basaltic volcanic conglomerates near the Wulgai village in Balochistan occur in the undivided sedimentary rock unit of the Bagh complex which is the mélange zone beneath the Muslim Bagh ophiolite. The presence of...Basaltic volcanic conglomerates near the Wulgai village in Balochistan occur in the undivided sedimentary rock unit of the Bagh complex which is the mélange zone beneath the Muslim Bagh ophiolite. The presence of Middle Triassic grey radiolarian chert within the upper and lower horizon of the conglomerates suggests that the lavas, from which these conglomerates were principally derived, were eroded and re-deposited in the Middle Triassic. The Wulgai conglomerate contains several textural and mineralogical varieties of volcanic rocks, such as porphyritic, glomerophyric, intersertal and vitrophyric basalts. The main minerals identified in these samples are augite, olivine, plagioclase（An35–78） leucite and nosean, with apatite ilmenite, magnetite and hematite occurring as accessory minerals. These rocks are mildly to strongly-alkaline with low Mg~# and low Cr, Ni and Co contents suggesting that their parent magma had undergone considerable fractionation prior to eruption. Trace element-enriched mantle-normalized patterns with marked positive Nb anomalies are consistent with 10%–15% melting of an enriched mantle source in a within-plate tectonic setting. It is proposed that this Middle Triassic intra-plate volcanism may represent mantle plume-derived melts related to the Late Triassic rifting of micro-continental blocks（including Afghan, Iran, Karakorum and Lhasa） from the northern margin of Gondwana.展开更多
基金supported by the National Key Research and Development Project(No.2022YFC2903302)the Second Tibet Plateau Scientific Expedition and Research Program(STEP),(No.2019QZKK0802)+2 种基金the National Natural Science Foundation of China(No.42361144841)the Chinese Academy of Geological Sciences Basal Research Fund(No.JKYZD202402)the Scientific Research Fund Project of BGRIMM Technology Group(No.JTKY202427822)。
文摘0 INTRODUCTION Orogenic belts are commonly built by multiple-stage processes involving oceanic subduction and continental collisions that result in the generation of magma with distinct geochemical compositions,as exemplified by Central Asian Orogenic Belts(e.g.,Wang et al.,2024;Yin et al.,2024;Xiao et al.,2005)and the Tethyan tectonic domains(e.g.,Chen et al.,2024;Li et al.,2024;Tao et al.,2024a;Gehrels et al.,2011;Yin and Harrison,2000).
基金supported by the National Natural Science Foundation of China(Nos.42072069,41403023)China Geological Survey(No.1212011121270)the Natural Science Foundation of Hainan Province(Nos.521QN274 and 421CXTD441).
文摘Permian—Triassic granitoids are widely distributed along the Jinshajiang suture belt,eastern Xizang,and are regarded as the result of the tectonic-magmatic activity associated with the evolution of Paleo-Tethys Ocean.This paper focuses on the high-K calc-alkaline I-type Rennong(~235 Ma)and Jiaduoling(~232 Ma)granitoid plutons,eastern Xizang,which are enriched in light rare earth elements(LREEs)and large ion lithophile elements(LILEs),but depleted in high field strength elements(HFSEs)with moderate-weak negative Eu anomalies(0.61–0.90).The Rennong granites are characterized by uniform zircon ε_(Hf)(t)values(-7.3 to-3.5)and negative ε_(Nd)(t)values(-7.6 to-5.7),with old two-stage Nd model ages(T_(DM2)=1.51-1.46 Ga)and was likely formed by partial melting of the basement rocks,whereas the Jiaduoling rock samples have variable zircon ε_(Hf)(t)values(-5.7 to+5.5)but negativeεNd(t)values(-7.6 to-7.7)and are proposed to be formed by hybridization of mantle-derived mafic magma,Rennong felsic magma and sediments.Mafic microgranular enclaves(MMEs)in the Jiaduoling granitic rocks,have similar zircon U-Pb ages(~237 Ma)and zircon ε_(Hf)(t)values(-4.4 to+6.3)to the host rocks,indicating that zircons in the MMEs were actually xenocrysts that formed at an early stage in the granitic magma chamber.These results reveal that the break-off of the Jinshajiang oceanic slab beneath Changdu(Qamdo)-Simao Block was in a post-collisional setting,resulted in the upwelling of asthenosphere in the Late Triassic,and then,generated the wide-spread intermediate-felsic magmatism along the Jinshajing belt,including the Rennong and Jiaduoling plutons.
文摘Basaltic volcanic conglomerates near the Wulgai village in Balochistan occur in the undivided sedimentary rock unit of the Bagh complex which is the mélange zone beneath the Muslim Bagh ophiolite. The presence of Middle Triassic grey radiolarian chert within the upper and lower horizon of the conglomerates suggests that the lavas, from which these conglomerates were principally derived, were eroded and re-deposited in the Middle Triassic. The Wulgai conglomerate contains several textural and mineralogical varieties of volcanic rocks, such as porphyritic, glomerophyric, intersertal and vitrophyric basalts. The main minerals identified in these samples are augite, olivine, plagioclase（An35–78） leucite and nosean, with apatite ilmenite, magnetite and hematite occurring as accessory minerals. These rocks are mildly to strongly-alkaline with low Mg~# and low Cr, Ni and Co contents suggesting that their parent magma had undergone considerable fractionation prior to eruption. Trace element-enriched mantle-normalized patterns with marked positive Nb anomalies are consistent with 10%–15% melting of an enriched mantle source in a within-plate tectonic setting. It is proposed that this Middle Triassic intra-plate volcanism may represent mantle plume-derived melts related to the Late Triassic rifting of micro-continental blocks（including Afghan, Iran, Karakorum and Lhasa） from the northern margin of Gondwana.
