Objective The Late Cretaceous Xiuwacu ore-bearing porphyry is located in the Geza area of southern Yidun arc, SW China. In this area, the rock mass is mainly composed of three lithofacies： biotite granite porphyry, ...Objective The Late Cretaceous Xiuwacu ore-bearing porphyry is located in the Geza area of southern Yidun arc, SW China. In this area, the rock mass is mainly composed of three lithofacies： biotite granite porphyry, monzonitic granite and light alkali feldspar granite. As a part of the Yidun arc, the Geza arc has common structure and temporal- spatial evolution with the ~idun arc, which has experienced three stages of oceanic crust subduction, collision orogeny and intracontinent convergence stages. The molybdenite ores in the area are mainly hosted in monzonitic granite-porphyry and structural fracture zone, and the ore bodies are strictly controlled by faults. In recent years, great geological prospecting results have been achieved in Xiuwacu, and the deposit has reached a medium scale. However, there are few researches on the metallogenic porphyry. Based on the previous research, we determined the rock-forming and ore-forming age of the porphyry, and found that there were two stages of magmatism intrusion in Xiuwacu： Indosinian and Yanshanian. We also discussed the geochemical characteristics and source area of the rocks in the area.展开更多
Objective The Yingyangguan Group is widely exposed in the southwestern segment of boundary belt between Yangtze and Cathaysian blocks and is mainly composed of a suit of lower-grade metamorphic marine volcanoclastic-...Objective The Yingyangguan Group is widely exposed in the southwestern segment of boundary belt between Yangtze and Cathaysian blocks and is mainly composed of a suit of lower-grade metamorphic marine volcanoclastic- sedimentary rocks （Zhou Hanwen et al., 2002）. Its forming age and petrogenesis are critical for better understanding the orogenic process and relationship of the Yangtze and Cathaysian blocks since the Neoproterozoic. However, few zircon U-Pb ages of samples from the Yingyangguan Group have been reported, which are much debated, such as the metamorphic spilite （819±11 Ma）, keratophyre （415.1±2.1 Ma） and ignimbrite （821.3±3.9 Ma） （Tian Yang et al., 2015 and references in）. In this study, we focus on the new discovered Early Yanshannian monzogranite and its mafic enclaves from the Yingyangguan Group, and conducted zircon U-Pb dating and in-situ Hf isotopic analyses to constrain their petrogenesis.展开更多
A large area of Late Paleozoic intrusions occursalong the Kalamaili fault in North Xinjiang,which is divided into I-type and A-type granite(Liu et al.,2013),and are the ideal objects for revealing the geological evolu...A large area of Late Paleozoic intrusions occursalong the Kalamaili fault in North Xinjiang,which is divided into I-type and A-type granite(Liu et al.,2013),and are the ideal objects for revealing the geological evolution of this region.However,the study of the granodioritic pluton in East Junggar is particularly weak.展开更多
This study describes a previously unidentified Neoproterozoic mafic dyke emplaced in the northern flank of the Langshan Tectonic Belt. This dyke intruded into the micaquartz schist of the Zhaertaishan Group, and yield...This study describes a previously unidentified Neoproterozoic mafic dyke emplaced in the northern flank of the Langshan Tectonic Belt. This dyke intruded into the micaquartz schist of the Zhaertaishan Group, and yielded an age of 908 ± 8 Ma. The youngest U-Pb ages of micaquartz schist from the Zhaertaishan Group in the Langshan area were 1118 ± 33 Ma,1187 ± 3 Ma and 1189 ± 39 Ma,suggesting that the depositional age of the protolith of the schist was between 908 ± 8 Ma and 1118 ± 33 Ma. In addition, 436 U-Pb age data and 155 Lu-Hf isotopic data from six samples in the Langshan Tectonic Belt and one Permian greywacke from the Wuhai area show distinct differences between the northern and southern flanks of the Main Langshan area. The U-Pb ages of the northern flank are primarily Meso-Neoproterozoic; similar ages have not been identified in the southern flank to date.Moreover, two-stage Hf model ages of the northern flank feature three age peaks at ～900 Ma,～1700 Ma and ～2600 Ma; this differs from Hf model ages of the southern flank, which feature one strong age peak at ～2700 Ma. These results suggest that the northern and southern flanks of the Main Langshan area have different geochronologic characteristics and should be divided further. Based on the U-Pb ages and Hf model ages, the northern and southern flanks of the Main Langshan area are named the North and South Langshan Tectonic Belts. Comparison of the U-Pb age and two-stage Hf model age distributions from the North Langshan Tectonic Belt, South Langshan Tectonic Belt, Alxa Block and the North China Craton(NCC) reveal that the North Langshan Tectonic Belt is similar to the Alxa Block and that the South Langshan Tectonic Belt is similar to the NCC. In addition, the zircon U-Pb age of 860 ±7 Ma commonly observed in the Alxa Block was detected in the Permian greywacke from the Wuhai area of the NCC, which suggests that the amalgamation of the North and South Langshan Tectonic belts(i.e.,the amalgamation of the Alxa Block and the NCC), occurred between Devonian and late Permian.展开更多
The Chinese Altai in northwestern Xinjiang has numerous outcrops of granitoids which provide critical information on accretionary orogenic processes and crustal growth of the Central Asian Orogenic Belt.Zircon U-Pb ag...The Chinese Altai in northwestern Xinjiang has numerous outcrops of granitoids which provide critical information on accretionary orogenic processes and crustal growth of the Central Asian Orogenic Belt.Zircon U-Pb ages, Hf-isotopic compositions and whole-rock geochemistry of monzogranite and granodiorites in the Qinghe County are employed to elucidate Paleozoic tectonics of the Chinese Altai. Granodiorites have crystallization ages of 424.6 ± 3.1 Ma(MSWD = 0.23) and 404.0 ± 3.4 Ma(MSWD = 0.18);monzogranite was emplaced in the early Permian with a crystallization age of 293.7 ± 4.6 Ma(MSWD = 1.06). Both granodiorites and monzogranite are I-type granites with A/CNK ratios of 0.92 -0.97 and 1.03 -1.06, respectively. They also show similar geochemical features of high HREE and Y contents, low Sr contents and Sr/Y ratios, as well as enrichment of Cs, Rb, Th and U, and depletion of Nb, Ta, P and Ti.These geochemical features indicate that the monzogranite and granodiorites were formed in an arc setting related to subduction. The gneissic monzogranites display high SiO_2 and K_2 O contents, and belong to the high-K calc-alkaline series. In the chondrite normalized REE distribution pattern, the monzogranite samples exhibit enrichment of LREE with strong negative Eu anomalies(σE u =0.44 -0.53), zircon εHf(t) values from +7.24 to +12.63 and two-stage Hf model ages of 463 -740 Ma. This suggests that the monzogranite was generated from the mixing of pelitic and mantle material. The granodiorite samples are calc-alkaline granites with lower contents of Si O_2 and Na_2 O + K_2 O, higher contents of TiO_2, Fe_2O_3~t, MgO and CaO compared to the monzogranite samples. They also show enrichment of LREE and moderate negative Eu anomalies(σE u= 0.54 =0.81), as well as slightly higher differentiation of LREE than that of HREE. The425 Ma granodiorite has zircon εHf(t) values from -0.51 to +1.98 and two-stage Hf model ages of 1133 -1240 Ma, whereas the 404 Ma granodiorite displays those of +2.52 to +7.50 and 816 -1071 Ma.Geochemistry and zircon Hf isotopic compositions indicate that granodiorites were formed by partial melting of juvenile lower crust. Together with regional geology and previous data, the geochemical and geochronological data of the monzogranite and granodiorites from this study suggest long-lived subduction and accretion along the Altai Orogen during ca. 425 -294 Ma.展开更多
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...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 variableεHf(t)values from-1.0 to+1.3 and old TDM2 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 eHf(t)values between-1.1 to+5.7(three grains are negative)with two-stage model ages(TDM2)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 highεHf(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.展开更多
The cratonization history of the North China Craton(NCC)and the nature of tectonothermal events are still highly controversial.Tonalite-trondhjemite-granodiorite(TTG)gneisses,as the dominant lithological assemblages i...The cratonization history of the North China Craton(NCC)and the nature of tectonothermal events are still highly controversial.Tonalite-trondhjemite-granodiorite(TTG)gneisses,as the dominant lithological assemblages in Archean metamorphic terranes,can provide significant clues to the magmatic and metamorphic evolution of Precambrian crust.This study presents zircon laser-ablation inductively-coupled-plasma mass spectrometry U–Pb ages,trace-element,and in-situ LA-MC-ICPMS zircon Hf isotope data for the TTG gneisses from the Bengbu-Wuhe area on the southeastern margin of the NCC.Cathodoluminescence images and trace elements indicated that magmatic zircons display the characteristics of euhedral-subhedral crystals with oscillatory growth zoning structures,high RREE contents,marked Ce positive anomalies,and Pr–Eu negative anomalies.The metamorphic zircons display the spherical-oval crystals with distinct core-rim structures,high and homogeneous luminescent intensity,lower RREE,Nb,Ta,Hf contents,relative flat REE patterns,weak Ce positive anomalies,and Pr-Eu negative anomalies.The Ti–in–zircon geothermometer data indicate that the crystallization temperature of the TTG gneiss ranged from 754 to 868℃.Zircon U–Pb ages indicate that the TTG gneisses formed at 2.79–2.77 Ga and 2.50 Ga and underwent metamorphism at 2.57–2.52 Ga.The Hf isotopic data indicate that the magmatic zircons exhibit high,positive eHf(t)values close to those of the coeval depleted mantle,whereas the metamorphic zircons exhibit negative or nil eHf(t)values.This implies that the TTG gneisses were derived from the partial melting of the~2.9–2.6 Ga juvenile crustal sources mixed with~3.0–2.8 Ga ancient crustal materials.Combined with the regional tectonic evolution,we propose that the metamorphic basement at the southeastern margin of the NCC underwent episodic crustal growth at~2.7 and~2.5 Ga and subsequently underwent crustal reworking or re-melting of the ancient crust during the Neoarchean.The Neoarchean TTG gneisses might have been derived from the partial melting of lower crustal materials related to plate subduction.展开更多
The Truong Son metallogenic belt in central Laos and Vietnam is an important Fe-Cu-Sn-Au polymetallic ore district. The Pha Lek Fe deposit is closely related to Late Carboniferous– Early Permian I-type granitic magma...The Truong Son metallogenic belt in central Laos and Vietnam is an important Fe-Cu-Sn-Au polymetallic ore district. The Pha Lek Fe deposit is closely related to Late Carboniferous– Early Permian I-type granitic magmatism, and contains >50 Mt @ 45% to 50% of Fe ore. Ore minerals occur mainly as magnetite and hematite in the skarn alteration zone between a granitic pluton and metamorphosed Middle–Upper Devonian carbonates. The granitic pluton comprises granodiorite and granite, with zircon U-Pb dating indicating synchronous emplacement at 288.2±1.3 and 284.9±1.2 Ma, respectively. Zircons from these granitoids have ε_(Hf)(t) values of 2.9–11.2 and relatively young TDM2 ages(<1.0 Ga), indicating an origin by partial melting of depleted mafic crust or magma mixing. Previous studies have shown that these granitoids have high Y, Yb, and K_2O contents, and low Sr and Na_2O contents, which are interpreted as the melting of mafic continental crust. Pyrite of the main mineralization stage yields an ^(187)Re/^(188)Os-^(187)Os/^(188)Os isochron age of 287±17 Ma, indicating that mineralization is associated with Pha Lek granitic magmatism. A Late Carboniferous–Early Permian subduction-related skarn-type Fe mineralization model is proposed for the Pha Lek deposit. More evidence is needed to verify a hypothesis of volcanic overprinting during Late Triassic post-collisional extension.展开更多
The Wuliangshan Group occurs to the east of the Lancang giant igneous zone in SW Yunnan, and is mainly composed of low-grade metamorphosed sedimentary rocks. The group has been considered as the syn-orogenic product o...The Wuliangshan Group occurs to the east of the Lancang giant igneous zone in SW Yunnan, and is mainly composed of low-grade metamorphosed sedimentary rocks. The group has been considered as the syn-orogenic product of the Baoshan with Simao-Indochina blocks. However, its depositional time and provenance remain to be poorly constrained. This paper presents zircon U-Pb dating and Lu-Hf-isotopic data for five representative sandstone samples from the Wuliangshan Group. The detrital grains yield a major age-peak at ~259 Ma, and four subordinary age-peaks at ~1 859, ~941, ~788, and ~447 Ma, respectively. Our results suggest that the Wuliangshan metasedimentary sequence was deposited after Middle Triassic rather than previously-thought Cambrian. The detrital zircon age spectrum, along with in-situ Lu-Hf isotopic data suggest that the Wuliangshan Group might be a syncollisional sedimentary product related to the collision of Baoshan with Simao-Indochina blocks. It is inferred that the provenance of the Wuliangshan Group is mainly from the Simao/Yangtze blocks to the east rather than the Baoshan Block or Lancang igneous zone to the west.展开更多
ABSTRACT： The widespread Neoproterozoic magmatism along the Yangtze block carries critical in- formation for understanding the Neoproterozoic evolution of the Yangtze block. In the northwestern margin of the Yangtze ...ABSTRACT： The widespread Neoproterozoic magmatism along the Yangtze block carries critical in- formation for understanding the Neoproterozoic evolution of the Yangtze block. In the northwestern margin of the Yangtze block, the Hannan （汉南） intrusive complex includes the Wudumen （五堵门）, Erliba （二里坝） and Zushidian （祖师殿） granitoids. Using LA-ICP-MS U-Pb zircon dating method, the Wudumen and Erliba granitoids yielded magma crystallization ages of 785±4 and 778±3 Ma, respectively. Samples from these three granitoids show variable SiO2 contents ranging from 58.8% to 72.6%. They are characterized by enrichment of Al2O3（14.97%-17.87%）, Na2O（3.80%-5.33%） and Sr （504ppm-741 ppm）, and depletion of Y （〈19 ppm） and HREE （e.g., Yb〈1.6 ppm）, resulting in high Sr/Y （29-161） and （La/Yb）N （7.3-27.8） ratios. The geochemical features of the granitoids are comparable with those of adakite. The granitoids have zircon εHdt） values of ＋3.65 to ＋10.05, whole-rock εNd（t） values of -0.09 to ＋2.98 and whole-rock initial ^87Sr/^86Sr ratios of 0.7034-0.7039, indicating that their magma was derived from a juvenile crustal source. Together with geochemical and Hf-Sr-Nd isotopic compositions, it is suggested that the granitoids formed in island-arc setting and originated from partial melting of a subducted oceanic slab. The results support a model that the Yangtze block was surrounded by ocean and arc magmatism in its northern and northwestern margins in Neoproterozoic.展开更多
基金financially supported by the National Natural Science Foundation of China(grant No.41502076)the Science Research Fund of Yunnan Provincial Education Department(grant No.2015Y066)+1 种基金the Provincial People Training Program of Kunming University of Science and Technology(grant No.KKSY201421042)the Project of China Geological Survey(grant No.12120114013701)
文摘Objective The Late Cretaceous Xiuwacu ore-bearing porphyry is located in the Geza area of southern Yidun arc, SW China. In this area, the rock mass is mainly composed of three lithofacies： biotite granite porphyry, monzonitic granite and light alkali feldspar granite. As a part of the Yidun arc, the Geza arc has common structure and temporal- spatial evolution with the ~idun arc, which has experienced three stages of oceanic crust subduction, collision orogeny and intracontinent convergence stages. The molybdenite ores in the area are mainly hosted in monzonitic granite-porphyry and structural fracture zone, and the ore bodies are strictly controlled by faults. In recent years, great geological prospecting results have been achieved in Xiuwacu, and the deposit has reached a medium scale. However, there are few researches on the metallogenic porphyry. Based on the previous research, we determined the rock-forming and ore-forming age of the porphyry, and found that there were two stages of magmatism intrusion in Xiuwacu： Indosinian and Yanshanian. We also discussed the geochemical characteristics and source area of the rocks in the area.
基金financially supported by the China Geological Survey(grants No.12120113063200 and DD20160035-1)
文摘Objective The Yingyangguan Group is widely exposed in the southwestern segment of boundary belt between Yangtze and Cathaysian blocks and is mainly composed of a suit of lower-grade metamorphic marine volcanoclastic- sedimentary rocks （Zhou Hanwen et al., 2002）. Its forming age and petrogenesis are critical for better understanding the orogenic process and relationship of the Yangtze and Cathaysian blocks since the Neoproterozoic. However, few zircon U-Pb ages of samples from the Yingyangguan Group have been reported, which are much debated, such as the metamorphic spilite （819±11 Ma）, keratophyre （415.1±2.1 Ma） and ignimbrite （821.3±3.9 Ma） （Tian Yang et al., 2015 and references in）. In this study, we focus on the new discovered Early Yanshannian monzogranite and its mafic enclaves from the Yingyangguan Group, and conducted zircon U-Pb dating and in-situ Hf isotopic analyses to constrain their petrogenesis.
基金supported financially by the NSFC projects(Grant Nos.U1403291,41830216,and 41802074)projects of the China Geological Survey(Grant Nos.DD20160024,DD20160123,and DD20160345)IGCP 662.
文摘A large area of Late Paleozoic intrusions occursalong the Kalamaili fault in North Xinjiang,which is divided into I-type and A-type granite(Liu et al.,2013),and are the ideal objects for revealing the geological evolution of this region.However,the study of the granodioritic pluton in East Junggar is particularly weak.
基金supported by the National Natural Science Foundation of China (Grant No. 41473015)a research grant from the Institute of Crustal Dynamics, CEA (ZDJ2014-02+2 种基金 ZDJ2017-05)the Tutor Foundation of the China University of Geosciences (Beijing) (Grant No. 53200859400)the China Geological Survey Projects (Grant Nos. 12120114041401 and 12120113015700)
文摘This study describes a previously unidentified Neoproterozoic mafic dyke emplaced in the northern flank of the Langshan Tectonic Belt. This dyke intruded into the micaquartz schist of the Zhaertaishan Group, and yielded an age of 908 ± 8 Ma. The youngest U-Pb ages of micaquartz schist from the Zhaertaishan Group in the Langshan area were 1118 ± 33 Ma,1187 ± 3 Ma and 1189 ± 39 Ma,suggesting that the depositional age of the protolith of the schist was between 908 ± 8 Ma and 1118 ± 33 Ma. In addition, 436 U-Pb age data and 155 Lu-Hf isotopic data from six samples in the Langshan Tectonic Belt and one Permian greywacke from the Wuhai area show distinct differences between the northern and southern flanks of the Main Langshan area. The U-Pb ages of the northern flank are primarily Meso-Neoproterozoic; similar ages have not been identified in the southern flank to date.Moreover, two-stage Hf model ages of the northern flank feature three age peaks at ～900 Ma,～1700 Ma and ～2600 Ma; this differs from Hf model ages of the southern flank, which feature one strong age peak at ～2700 Ma. These results suggest that the northern and southern flanks of the Main Langshan area have different geochronologic characteristics and should be divided further. Based on the U-Pb ages and Hf model ages, the northern and southern flanks of the Main Langshan area are named the North and South Langshan Tectonic Belts. Comparison of the U-Pb age and two-stage Hf model age distributions from the North Langshan Tectonic Belt, South Langshan Tectonic Belt, Alxa Block and the North China Craton(NCC) reveal that the North Langshan Tectonic Belt is similar to the Alxa Block and that the South Langshan Tectonic Belt is similar to the NCC. In addition, the zircon U-Pb age of 860 ±7 Ma commonly observed in the Alxa Block was detected in the Permian greywacke from the Wuhai area of the NCC, which suggests that the amalgamation of the North and South Langshan Tectonic belts(i.e.,the amalgamation of the Alxa Block and the NCC), occurred between Devonian and late Permian.
基金Financial support for this study was jointly provided by the National Natural Science Foundation of China (Grant Nos. 41421002, 41225008, 41702231)Program for Changjiang Scholars and Innovative Research Team in University (Grant No. IRT1281)MOST Special Fund from the State Key Laboratory of Continental Dynamics, Northwest University, China
文摘The Chinese Altai in northwestern Xinjiang has numerous outcrops of granitoids which provide critical information on accretionary orogenic processes and crustal growth of the Central Asian Orogenic Belt.Zircon U-Pb ages, Hf-isotopic compositions and whole-rock geochemistry of monzogranite and granodiorites in the Qinghe County are employed to elucidate Paleozoic tectonics of the Chinese Altai. Granodiorites have crystallization ages of 424.6 ± 3.1 Ma(MSWD = 0.23) and 404.0 ± 3.4 Ma(MSWD = 0.18);monzogranite was emplaced in the early Permian with a crystallization age of 293.7 ± 4.6 Ma(MSWD = 1.06). Both granodiorites and monzogranite are I-type granites with A/CNK ratios of 0.92 -0.97 and 1.03 -1.06, respectively. They also show similar geochemical features of high HREE and Y contents, low Sr contents and Sr/Y ratios, as well as enrichment of Cs, Rb, Th and U, and depletion of Nb, Ta, P and Ti.These geochemical features indicate that the monzogranite and granodiorites were formed in an arc setting related to subduction. The gneissic monzogranites display high SiO_2 and K_2 O contents, and belong to the high-K calc-alkaline series. In the chondrite normalized REE distribution pattern, the monzogranite samples exhibit enrichment of LREE with strong negative Eu anomalies(σE u =0.44 -0.53), zircon εHf(t) values from +7.24 to +12.63 and two-stage Hf model ages of 463 -740 Ma. This suggests that the monzogranite was generated from the mixing of pelitic and mantle material. The granodiorite samples are calc-alkaline granites with lower contents of Si O_2 and Na_2 O + K_2 O, higher contents of TiO_2, Fe_2O_3~t, MgO and CaO compared to the monzogranite samples. They also show enrichment of LREE and moderate negative Eu anomalies(σE u= 0.54 =0.81), as well as slightly higher differentiation of LREE than that of HREE. The425 Ma granodiorite has zircon εHf(t) values from -0.51 to +1.98 and two-stage Hf model ages of 1133 -1240 Ma, whereas the 404 Ma granodiorite displays those of +2.52 to +7.50 and 816 -1071 Ma.Geochemistry and zircon Hf isotopic compositions indicate that granodiorites were formed by partial melting of juvenile lower crust. Together with regional geology and previous data, the geochemical and geochronological data of the monzogranite and granodiorites from this study suggest long-lived subduction and accretion along the Altai Orogen during ca. 425 -294 Ma.
基金granted by the National Natural Science Foundation of China(Grant Nos.41802119 and 41330315)the Special Projects of China Geological Survey(Grant No.121201011000161111)Doctor’s Fund of Xi’an University of Science and Technology(Grant No.6310117052)。
文摘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 variableεHf(t)values from-1.0 to+1.3 and old TDM2 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 eHf(t)values between-1.1 to+5.7(three grains are negative)with two-stage model ages(TDM2)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 highεHf(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.
基金supported by the National Natural Science Foundation of China(Nos.41303041 and41763005)Open Fund(Nos.Z1909,Z1912,RGET1804,15LCD08)of the State Key Laboratory of Nuclear Resources and Environment+1 种基金Fundamental Science on Radioactive Geology and Exploration Technology LaboratoryState Key Laboratory of Continental Dynamics。
文摘The cratonization history of the North China Craton(NCC)and the nature of tectonothermal events are still highly controversial.Tonalite-trondhjemite-granodiorite(TTG)gneisses,as the dominant lithological assemblages in Archean metamorphic terranes,can provide significant clues to the magmatic and metamorphic evolution of Precambrian crust.This study presents zircon laser-ablation inductively-coupled-plasma mass spectrometry U–Pb ages,trace-element,and in-situ LA-MC-ICPMS zircon Hf isotope data for the TTG gneisses from the Bengbu-Wuhe area on the southeastern margin of the NCC.Cathodoluminescence images and trace elements indicated that magmatic zircons display the characteristics of euhedral-subhedral crystals with oscillatory growth zoning structures,high RREE contents,marked Ce positive anomalies,and Pr–Eu negative anomalies.The metamorphic zircons display the spherical-oval crystals with distinct core-rim structures,high and homogeneous luminescent intensity,lower RREE,Nb,Ta,Hf contents,relative flat REE patterns,weak Ce positive anomalies,and Pr-Eu negative anomalies.The Ti–in–zircon geothermometer data indicate that the crystallization temperature of the TTG gneiss ranged from 754 to 868℃.Zircon U–Pb ages indicate that the TTG gneisses formed at 2.79–2.77 Ga and 2.50 Ga and underwent metamorphism at 2.57–2.52 Ga.The Hf isotopic data indicate that the magmatic zircons exhibit high,positive eHf(t)values close to those of the coeval depleted mantle,whereas the metamorphic zircons exhibit negative or nil eHf(t)values.This implies that the TTG gneisses were derived from the partial melting of the~2.9–2.6 Ga juvenile crustal sources mixed with~3.0–2.8 Ga ancient crustal materials.Combined with the regional tectonic evolution,we propose that the metamorphic basement at the southeastern margin of the NCC underwent episodic crustal growth at~2.7 and~2.5 Ga and subsequently underwent crustal reworking or re-melting of the ancient crust during the Neoarchean.The Neoarchean TTG gneisses might have been derived from the partial melting of lower crustal materials related to plate subduction.
基金supported financially by the National Natural Science Foundation of China (Nos. 41402074 and 41502074)Applied Fundamental Research Funding of Sichuan Province, China (No. 2015JY0055)the National Geological Survey Foundation of China (No. 121201010000150013)
文摘The Truong Son metallogenic belt in central Laos and Vietnam is an important Fe-Cu-Sn-Au polymetallic ore district. The Pha Lek Fe deposit is closely related to Late Carboniferous– Early Permian I-type granitic magmatism, and contains >50 Mt @ 45% to 50% of Fe ore. Ore minerals occur mainly as magnetite and hematite in the skarn alteration zone between a granitic pluton and metamorphosed Middle–Upper Devonian carbonates. The granitic pluton comprises granodiorite and granite, with zircon U-Pb dating indicating synchronous emplacement at 288.2±1.3 and 284.9±1.2 Ma, respectively. Zircons from these granitoids have ε_(Hf)(t) values of 2.9–11.2 and relatively young TDM2 ages(<1.0 Ga), indicating an origin by partial melting of depleted mafic crust or magma mixing. Previous studies have shown that these granitoids have high Y, Yb, and K_2O contents, and low Sr and Na_2O contents, which are interpreted as the melting of mafic continental crust. Pyrite of the main mineralization stage yields an ^(187)Re/^(188)Os-^(187)Os/^(188)Os isochron age of 287±17 Ma, indicating that mineralization is associated with Pha Lek granitic magmatism. A Late Carboniferous–Early Permian subduction-related skarn-type Fe mineralization model is proposed for the Pha Lek deposit. More evidence is needed to verify a hypothesis of volcanic overprinting during Late Triassic post-collisional extension.
基金supported by the National Natural Science Foundationof China(No.41190073)the National Basic Research Program of China(No.2014CB440901)the Fundamental Research Funds for the Central Universities to SYSU
文摘The Wuliangshan Group occurs to the east of the Lancang giant igneous zone in SW Yunnan, and is mainly composed of low-grade metamorphosed sedimentary rocks. The group has been considered as the syn-orogenic product of the Baoshan with Simao-Indochina blocks. However, its depositional time and provenance remain to be poorly constrained. This paper presents zircon U-Pb dating and Lu-Hf-isotopic data for five representative sandstone samples from the Wuliangshan Group. The detrital grains yield a major age-peak at ~259 Ma, and four subordinary age-peaks at ~1 859, ~941, ~788, and ~447 Ma, respectively. Our results suggest that the Wuliangshan metasedimentary sequence was deposited after Middle Triassic rather than previously-thought Cambrian. The detrital zircon age spectrum, along with in-situ Lu-Hf isotopic data suggest that the Wuliangshan Group might be a syncollisional sedimentary product related to the collision of Baoshan with Simao-Indochina blocks. It is inferred that the provenance of the Wuliangshan Group is mainly from the Simao/Yangtze blocks to the east rather than the Baoshan Block or Lancang igneous zone to the west.
基金supported by the National Natural Science Foundation of China (Nos. 40773019 and 40821061)the Ministry of Education of China and the State Administration of Foreign Expert Affairs of China (No. B07039)
文摘ABSTRACT： The widespread Neoproterozoic magmatism along the Yangtze block carries critical in- formation for understanding the Neoproterozoic evolution of the Yangtze block. In the northwestern margin of the Yangtze block, the Hannan （汉南） intrusive complex includes the Wudumen （五堵门）, Erliba （二里坝） and Zushidian （祖师殿） granitoids. Using LA-ICP-MS U-Pb zircon dating method, the Wudumen and Erliba granitoids yielded magma crystallization ages of 785±4 and 778±3 Ma, respectively. Samples from these three granitoids show variable SiO2 contents ranging from 58.8% to 72.6%. They are characterized by enrichment of Al2O3（14.97%-17.87%）, Na2O（3.80%-5.33%） and Sr （504ppm-741 ppm）, and depletion of Y （〈19 ppm） and HREE （e.g., Yb〈1.6 ppm）, resulting in high Sr/Y （29-161） and （La/Yb）N （7.3-27.8） ratios. The geochemical features of the granitoids are comparable with those of adakite. The granitoids have zircon εHdt） values of ＋3.65 to ＋10.05, whole-rock εNd（t） values of -0.09 to ＋2.98 and whole-rock initial ^87Sr/^86Sr ratios of 0.7034-0.7039, indicating that their magma was derived from a juvenile crustal source. Together with geochemical and Hf-Sr-Nd isotopic compositions, it is suggested that the granitoids formed in island-arc setting and originated from partial melting of a subducted oceanic slab. The results support a model that the Yangtze block was surrounded by ocean and arc magmatism in its northern and northwestern margins in Neoproterozoic.
