Geodynamic mechanism responsible for the generation of Silurian granitoids and the tectonic evolution of the Qilian orogenic belt remains controversial. In this study, we report the results of zircon U–Pb age, and sy...Geodynamic mechanism responsible for the generation of Silurian granitoids and the tectonic evolution of the Qilian orogenic belt remains controversial. In this study, we report the results of zircon U–Pb age, and systematic whole-rock geochemical data for the Haoquangou and Liujiaxia granitoids within the North Qilian orogenic belt and the Qilian Block, respectively, to constrain their petrogenesis, and the Silurian tectonic evolution of the Qilian orogenic belt. Zircon U–Pb ages indicate that the Haoquangou and Liujiaxia intrusions were emplaced at423 ± 3 Ma and 432 ± 4 Ma, respectively. The Haoquangou granodiorites are calc-alkaline, while the Liujiaxia granites belong to the high-K calc-alkaline series.Both are peraluminous in composition and have relatively depleted Nd isotopic [ε_(Nd)(t) =(-3.9 – + 0.6)] characteristics compared with regional basement rocks, implying their derivation from a juvenile lower crust. They show adakitic geochemical characteristics and were generated by partial melting of thickened lower continental crust. Postcollisional extensional regime related to lithospheric delamination was the most likely geodynamic mechanism for the generation of the Haoquangou granodiorite, while the Liujiaxia granites were generated in a compressive setting during continental collision between the Qaidam and Qilian blocks.展开更多
Changshagou adakite, an outcrop in the middle segment of the South Altyn Tagh ultra-high pressure metamorphism （UHPM） terrane, contains medium-K cal-alkaline and weakly peraluminous compositions （SiO2 = 66.79% to 6...Changshagou adakite, an outcrop in the middle segment of the South Altyn Tagh ultra-high pressure metamorphism （UHPM） terrane, contains medium-K cal-alkaline and weakly peraluminous compositions （SiO2 = 66.79% to 68.65%, Al2O3 = 17.48% to 18.31%, K20 ＋ Na20 = 6.32% to 6.88%, K2O/Na2O = 0.25 to 0.33, A/CNK = 1.01 to 1.06）. This outcrop is also enriched with large ion lithophile elements but with depleted high-field strength elements （HFSE） showing clearly negative Nb, Ta, and Ti anomalies. REE distribution patterns show a positive anomaly of Eu （6Eu = 1.15 to 1.31） and weakly enriched with LREE compared with HREE （LREE/HREE = 1.02 to 4.20）. Experimental results and several characteristics, including relatively low Nb/Ta ratios （6.03 to 8.45） and high Sr, Sr/Y, （La/Yb）N and low Y and Yb, which indicate the presence of residual garnet and the absence of plagioclase in the source region, show that adakite may form at a pressure ranging from 1.2 GPa to 1.5 GPa and at a temperature of approximately 900~C. Low Cr, Ni, and Mg# values, trace element patterns, and SiO2- Mg# and SiO2-MgO diagrams indicate that rocks are formed by the partial melting of a thickened lower continental crust. LA-ICP-MS in situ U-Pb dating yields two group ages： 503.1±1.7 Ma （core） and 453.1±3.0 Ma （rim）. The Th/U ratios of the core and the rim are 0.11 to 0.40 and 0.03 to 0.07, respectively. Considering the zircon CL image characteristics, Th/U ratios, and previous studies on regional UHPM rocks, adakite formed at 503.1 ± 1.7 Ma and underwent a tectothermal event as a result of the break-off of the Altyn deep subducted continental crust at 453.1 ± 3.0 Ma.展开更多
In this paper, we report new whole-rock geochemical and zircon U–Pb data for monzogranites in the NE Xing'an block. These data constrained the petrogenesis of C type(high Sr/Y) adakitic rocks and showed the spati...In this paper, we report new whole-rock geochemical and zircon U–Pb data for monzogranites in the NE Xing'an block. These data constrained the petrogenesis of C type(high Sr/Y) adakitic rocks and showed the spatial extent of the influence of the Mongol-Okhostsk ocean tectonic regime and the collision between the Jiamusi Massif and Songliao Terrane. New zircon laser-ablation inductivity coupled plasma mass spectrometry(LA-ICP-MS) U–Pb data indicated that the monzogranites in the studied area were emplaced in the Early Jurassic(~180 Ma). These rocks were characterized by unusally high SiO_2(C67.49), and Sr(461–759 ppm), but strikingly low Y(4.63–8.06 ppm) and HREE(P HREE = 3.83–6.49 ppm, Yb = 0.5–0.77 ppm)contents, with therefore high Sr/Y(67.2–119) and(La/Yb)N(29.7–41.5) ratios, showing the geochemical characteristics of C type adakitic granite. The data displayed negligible Eu anomalies(Eu/Eu~ = 0.77–1.08), LREE-enriched and pronounced negative Nb and Ta anomalies. The C-typeadakites in the studied area were most likely derived from the partial melting of a thickened lower continental curst. The magma source is most likely dominated by amphibolites and garnet amphibolites. In combination with previously-reported data from igneous rocks from the Mesozoic in NE China, we conclude that the Xing'an block was influenced by the Mongol-Okhotsk subduction tectonic system, and experiences compressive settings from the amalgamation of the Jiamusi block in the east of the CAOB.展开更多
The Liuyuan area,which is located on the southern margin of the Beishan orogenic belt,develops abundant Early Paleozic granitoids.SHRIMP zircon U-Pb dating yielded a weighted mean 206Pb/238U age of 421±8 Ma for t...The Liuyuan area,which is located on the southern margin of the Beishan orogenic belt,develops abundant Early Paleozic granitoids.SHRIMP zircon U-Pb dating yielded a weighted mean 206Pb/238U age of 421±8 Ma for the Liuyuan granodiorite(Zhao Zehui et al.,2007),implying its Late Silurian intrusion.Geochemical compositions showed that the Liuyuan granodiorite is characterized by high SiO2(65.01%-67.31%),A12O3(17.17%-18.05%) and Na2O(Na2O/K2O=1.67-1.87) but low Mg# contents calculated as 100×Mg2+/(Mg2++∑Fe2+) from 28.77 to 31.15,as well as being enriched in Sr(472×10-6-517×10-6) but depleted in Yb(1.2×10-6-1.42×10-6) and Y(12.8×10-6-14×10-6).The REEs are characterized by right-inclined patterns with LREE enrichment,HREE depletion and slightly negative Eu anomalies(Eu/Eu*=0.91-0.97).Major and trace elements indicate that the granodiorite is an adakite.The Nb/Ta values of the granodiorite vary from 10.80 to 18.01 and Nb/U from 6.32 to 10.09,both lying between the values of the crust and the mantle.The rock has low εNd(t) values(-2.5--0.8) and high ISr(0.706321-0.706495).Geochemical and Sr-Nd isotopic compositions indicate that the Liuyuan granodiorite is possibly derived from partial melting of thickening lower crust,related to mantle underplating.The Yb-Ta and Y+Nb-Rb discriminant diagrams imply the Liuyuan granodiorite intruded in a local extensional tectonic setting during late collision.Combined with previous studies on geochronology,geochemistry and tectonic setting of granitoids,we interprete that the constraint of this adakite in the Liuyuan area indicates that the tectonic setting may have transformed from collision to extension during the Early Devonian.展开更多
The early Paleozoic Terskey Suture zone,located in the southern part of the Northern Tien Shan domain in Kyrgyzstan,comprises tectonic slivers of dismembered ophiolites and associated primitive volcanics and deepmarin...The early Paleozoic Terskey Suture zone,located in the southern part of the Northern Tien Shan domain in Kyrgyzstan,comprises tectonic slivers of dismembered ophiolites and associated primitive volcanics and deepmarine sediments.In the Lake Songkul area,early-middle Cambrian pillow basalts are crosscut by the Songkultau intrusion of coarse-grained gneissose quartz diorites and tonalites with geochemical characteristics typical for high-SiO2 adakites(SiO2>56 wt.%,Al2O3>15 wt.%,Na2 O>3.5 wt.%and high Sr/Y and La/Yb ratios).The Songkultau granitoids have positive initialεNd(+3.8 to+6.4)andεHf(+12.3 to+13.5)values indicating derivation from sources with MORB-like isotopic signature.Volcanic formations,surrounding the Songkultau intrusion,have geochemical affinities varying from ocean floor to island arc series.This rock assemblage is interpreted as a relic of an early-middle Cambrian primitive arc where the adakite-like granitoids were derived from partial melting of young and hot subducted oceanic crust.An age of 505 Ma,obtained for the Songkultau intrusion,shows that hot subduction under the Northern Tien Shan continued until middle Cambrian.The primitive arc complexes were obducted onto the Northern Tien Shan domain,where the Andean type continental magmatic arc developed in Cambrian and Ordovician.Formation of the Andean type arc was accompanied by uplift,erosion and deposition of coarse clastic sediments.A depositional age of ca.470 Ma,obtained for the gravellites in the Lake Songkul area,is in agreement with the timing of deposition for lower Ordovician conglomerates elsewhere in the Northern Tien Shan,and corresponds to the main phase of the Andean type magmatism.The Songkultau adakites in association with surrounding ocean floor and island arc formations constitute a relic of a primitive Cambrian arc and represent a juvenile domain of substantial size identified so far within the predominantly crustal-derived terranes of Tien Shan.On a regional scale this primitive arc can be compared with juvenile Cambrian arcs of Kazakhstan,Gorny Altai and Mongolia.展开更多
Mesozoic intermediate-felsic magmatic rocks in the eastern North China Craton commonly show geochemical similarity to adakites.However,the lack of direct constraints from partial melting experiments at high pressures ...Mesozoic intermediate-felsic magmatic rocks in the eastern North China Craton commonly show geochemical similarity to adakites.However,the lack of direct constraints from partial melting experiments at high pressures and temperatures fuels a debate over the origin of these rocks.In this work,we performed partial melting experiments at 1.5 GPa and 800–950℃on amphibolite samples collected from the vicinity of the Mesozoic potassium-rich adakitic rocks in the Zhangjiakou area,northern margin of the North China Craton.The experimental melts range from granitic to granodioritic compositions,with SiO_(2)=56.4–72.6 wt.%,Al_(2)O_(3)=16.1–19.3 wt.%,FeO^(*)=2.4–9.6 wt.%,MgO=0.3–2.0 wt.%,CaO=0.6–3.8 wt.%,Na_(2)O=4.7–5.3 wt.%,and K_(2)O=2.6–3.9 wt.%,which are in the ranges of the surrounding Mesozoic potassium-rich adakitic rocks,except for the higher Al_(2)O_(3)contents and the data point at 1.5 GPa and 800℃.Trace element compositions of the melts measured by LA-ICP-MS are rich in Sr(849–1067 ppm)and light rare earth elements(LREEs)and poor in Y(<10.4 ppm)and Yb(<0.88 ppm),and have high Sr/Y(102–221)and(La/Yb)n(27–41)ratios and strongly fractionated rare earth element(REE)patterns,whereas no obvious negative Eu anomalies are observed.The geochemical characteristics show overall similarity to the Mesozoic potassium-rich adakitic rocks in the area,especially adakites with low Mg#,again except for the data point at 1.5 GPa and 800℃.The results suggest that partial melting of amphibolite can produce potassium-rich adakitic rocks with low Mg#in the eastern North China Craton under the experimental conditions of 1.5 GPa and 850–950℃.The experimental restites consist of hornblende(Hbl)+plagioclase(Pl)+garnet(Grt)±clinopyroxene(Cpx),a mineral assemblage significantly different from that of the nearby Hannuoba mafic granulite xenoliths which consist of Cpx+orthopyroxene(Opx)+Pl±Grt.Chemically,the experimental restites contain higher Al_(2)O_(3)but lower MgO and CaO than the Hannuoba mafic granulite xenoliths.We therefore argue that the Hannuoba mafic granulite xenoliths cannot represent the direct products of partial melting of the experimental amphibolite.展开更多
On the basis of the geological and geochemical studies, including chemical analysis of bulk rocks, rare-earth and trace element studies, fluid inclusion, and S and O isotopic analyses, the authors described the geolog...On the basis of the geological and geochemical studies, including chemical analysis of bulk rocks, rare-earth and trace element studies, fluid inclusion, and S and O isotopic analyses, the authors described the geological background of the deposit in detail and presented significant proofs for the conditions of formation of the Shaxi porphyry copper-gold deposit. Compared with other large and supper-large porphyry copper deposits in China and the adjacent Cu-Au mineralized areas, the ore-forming processes and conditions were analyzed; and the possibility of forming large porphyry copper deposits in the Shaxi area was discussed. The present study indicated that the ore-forming fluid and material were mainly of magmatic origin, while meteoric water played a certain role in the ore-forming processes. Interactions between subducting and overriding plates provided a major driving force for the formation of igneous rocks and the deposition of metal elements in East China since Jurassic. Based on the geo- chemical data of the Shaxi intrusive, it is found that the copper (gold) mineralization is closely related to the genesis of adakite-like intrusive in the Shaxi area. This adakite-like intrusive was formed in the subduction environment as a result of the subduction of the West Pacific plate toward the East China continent, where there is a great potentiality to form a large porphyry copper deposit.展开更多
基金funded by Gansu Provincial Natural Science Foundation (Grant Numbers 21JR7RA503 and22JR5RA819)the Fundamental Research Funds for the Central Universities (Grant lzujbky-2021-ct07)+1 种基金the Key Talent Project of Gansu Province (2022-Yangzhenxi)the National Second Expedition to the Tibetan Plateau (2019QZKK0704)。
文摘Geodynamic mechanism responsible for the generation of Silurian granitoids and the tectonic evolution of the Qilian orogenic belt remains controversial. In this study, we report the results of zircon U–Pb age, and systematic whole-rock geochemical data for the Haoquangou and Liujiaxia granitoids within the North Qilian orogenic belt and the Qilian Block, respectively, to constrain their petrogenesis, and the Silurian tectonic evolution of the Qilian orogenic belt. Zircon U–Pb ages indicate that the Haoquangou and Liujiaxia intrusions were emplaced at423 ± 3 Ma and 432 ± 4 Ma, respectively. The Haoquangou granodiorites are calc-alkaline, while the Liujiaxia granites belong to the high-K calc-alkaline series.Both are peraluminous in composition and have relatively depleted Nd isotopic [ε_(Nd)(t) =(-3.9 – + 0.6)] characteristics compared with regional basement rocks, implying their derivation from a juvenile lower crust. They show adakitic geochemical characteristics and were generated by partial melting of thickened lower continental crust. Postcollisional extensional regime related to lithospheric delamination was the most likely geodynamic mechanism for the generation of the Haoquangou granodiorite, while the Liujiaxia granites were generated in a compressive setting during continental collision between the Qaidam and Qilian blocks.
基金supported by funds from the Chinese Ministry of Science and Technology (Grant No. 2009CB825003)the State Key Laboratory of Continental Dynamics, Northwest Universitythe National Natural Science Foundation of China (Grant Nos. 40972128 and 40902022)
文摘Changshagou adakite, an outcrop in the middle segment of the South Altyn Tagh ultra-high pressure metamorphism （UHPM） terrane, contains medium-K cal-alkaline and weakly peraluminous compositions （SiO2 = 66.79% to 68.65%, Al2O3 = 17.48% to 18.31%, K20 ＋ Na20 = 6.32% to 6.88%, K2O/Na2O = 0.25 to 0.33, A/CNK = 1.01 to 1.06）. This outcrop is also enriched with large ion lithophile elements but with depleted high-field strength elements （HFSE） showing clearly negative Nb, Ta, and Ti anomalies. REE distribution patterns show a positive anomaly of Eu （6Eu = 1.15 to 1.31） and weakly enriched with LREE compared with HREE （LREE/HREE = 1.02 to 4.20）. Experimental results and several characteristics, including relatively low Nb/Ta ratios （6.03 to 8.45） and high Sr, Sr/Y, （La/Yb）N and low Y and Yb, which indicate the presence of residual garnet and the absence of plagioclase in the source region, show that adakite may form at a pressure ranging from 1.2 GPa to 1.5 GPa and at a temperature of approximately 900~C. Low Cr, Ni, and Mg# values, trace element patterns, and SiO2- Mg# and SiO2-MgO diagrams indicate that rocks are formed by the partial melting of a thickened lower continental crust. LA-ICP-MS in situ U-Pb dating yields two group ages： 503.1±1.7 Ma （core） and 453.1±3.0 Ma （rim）. The Th/U ratios of the core and the rim are 0.11 to 0.40 and 0.03 to 0.07, respectively. Considering the zircon CL image characteristics, Th/U ratios, and previous studies on regional UHPM rocks, adakite formed at 503.1 ± 1.7 Ma and underwent a tectothermal event as a result of the break-off of the Altyn deep subducted continental crust at 453.1 ± 3.0 Ma.
基金supported by the regional geology and mineralization research program of Heilongjiang province (HLJKD201417)
文摘In this paper, we report new whole-rock geochemical and zircon U–Pb data for monzogranites in the NE Xing'an block. These data constrained the petrogenesis of C type(high Sr/Y) adakitic rocks and showed the spatial extent of the influence of the Mongol-Okhostsk ocean tectonic regime and the collision between the Jiamusi Massif and Songliao Terrane. New zircon laser-ablation inductivity coupled plasma mass spectrometry(LA-ICP-MS) U–Pb data indicated that the monzogranites in the studied area were emplaced in the Early Jurassic(~180 Ma). These rocks were characterized by unusally high SiO_2(C67.49), and Sr(461–759 ppm), but strikingly low Y(4.63–8.06 ppm) and HREE(P HREE = 3.83–6.49 ppm, Yb = 0.5–0.77 ppm)contents, with therefore high Sr/Y(67.2–119) and(La/Yb)N(29.7–41.5) ratios, showing the geochemical characteristics of C type adakitic granite. The data displayed negligible Eu anomalies(Eu/Eu~ = 0.77–1.08), LREE-enriched and pronounced negative Nb and Ta anomalies. The C-typeadakites in the studied area were most likely derived from the partial melting of a thickened lower continental curst. The magma source is most likely dominated by amphibolites and garnet amphibolites. In combination with previously-reported data from igneous rocks from the Mesozoic in NE China, we conclude that the Xing'an block was influenced by the Mongol-Okhotsk subduction tectonic system, and experiences compressive settings from the amalgamation of the Jiamusi block in the east of the CAOB.
基金partially funded by the National Science Foundation of China
the Major State Basic Research Program of the PeoplesRepublic of China( No.G19990 43 2 0 2)
基金supported by the Program for Changjiang Schoolars and Innovative Research Team in University (IRT0755)
文摘The Liuyuan area,which is located on the southern margin of the Beishan orogenic belt,develops abundant Early Paleozic granitoids.SHRIMP zircon U-Pb dating yielded a weighted mean 206Pb/238U age of 421±8 Ma for the Liuyuan granodiorite(Zhao Zehui et al.,2007),implying its Late Silurian intrusion.Geochemical compositions showed that the Liuyuan granodiorite is characterized by high SiO2(65.01%-67.31%),A12O3(17.17%-18.05%) and Na2O(Na2O/K2O=1.67-1.87) but low Mg# contents calculated as 100×Mg2+/(Mg2++∑Fe2+) from 28.77 to 31.15,as well as being enriched in Sr(472×10-6-517×10-6) but depleted in Yb(1.2×10-6-1.42×10-6) and Y(12.8×10-6-14×10-6).The REEs are characterized by right-inclined patterns with LREE enrichment,HREE depletion and slightly negative Eu anomalies(Eu/Eu*=0.91-0.97).Major and trace elements indicate that the granodiorite is an adakite.The Nb/Ta values of the granodiorite vary from 10.80 to 18.01 and Nb/U from 6.32 to 10.09,both lying between the values of the crust and the mantle.The rock has low εNd(t) values(-2.5--0.8) and high ISr(0.706321-0.706495).Geochemical and Sr-Nd isotopic compositions indicate that the Liuyuan granodiorite is possibly derived from partial melting of thickening lower crust,related to mantle underplating.The Yb-Ta and Y+Nb-Rb discriminant diagrams imply the Liuyuan granodiorite intruded in a local extensional tectonic setting during late collision.Combined with previous studies on geochronology,geochemistry and tectonic setting of granitoids,we interprete that the constraint of this adakite in the Liuyuan area indicates that the tectonic setting may have transformed from collision to extension during the Early Devonian.
基金supported by the Ministry of Education and Science of the Russian Federation(Project No 14.Y26.31.0018-I.S.,D.K.)。
文摘The early Paleozoic Terskey Suture zone,located in the southern part of the Northern Tien Shan domain in Kyrgyzstan,comprises tectonic slivers of dismembered ophiolites and associated primitive volcanics and deepmarine sediments.In the Lake Songkul area,early-middle Cambrian pillow basalts are crosscut by the Songkultau intrusion of coarse-grained gneissose quartz diorites and tonalites with geochemical characteristics typical for high-SiO2 adakites(SiO2>56 wt.%,Al2O3>15 wt.%,Na2 O>3.5 wt.%and high Sr/Y and La/Yb ratios).The Songkultau granitoids have positive initialεNd(+3.8 to+6.4)andεHf(+12.3 to+13.5)values indicating derivation from sources with MORB-like isotopic signature.Volcanic formations,surrounding the Songkultau intrusion,have geochemical affinities varying from ocean floor to island arc series.This rock assemblage is interpreted as a relic of an early-middle Cambrian primitive arc where the adakite-like granitoids were derived from partial melting of young and hot subducted oceanic crust.An age of 505 Ma,obtained for the Songkultau intrusion,shows that hot subduction under the Northern Tien Shan continued until middle Cambrian.The primitive arc complexes were obducted onto the Northern Tien Shan domain,where the Andean type continental magmatic arc developed in Cambrian and Ordovician.Formation of the Andean type arc was accompanied by uplift,erosion and deposition of coarse clastic sediments.A depositional age of ca.470 Ma,obtained for the gravellites in the Lake Songkul area,is in agreement with the timing of deposition for lower Ordovician conglomerates elsewhere in the Northern Tien Shan,and corresponds to the main phase of the Andean type magmatism.The Songkultau adakites in association with surrounding ocean floor and island arc formations constitute a relic of a primitive Cambrian arc and represent a juvenile domain of substantial size identified so far within the predominantly crustal-derived terranes of Tien Shan.On a regional scale this primitive arc can be compared with juvenile Cambrian arcs of Kazakhstan,Gorny Altai and Mongolia.
基金the National Natural Science Foundation of China(Grant Nos.41772043 and 41802043)the Chinese Academy of Sciences“Light of West China”Program(Dawei Fan,2017 and Jingui Xu,2019)+1 种基金the Youth Innovation Promotion Association CAS(Dawei Fan,2018434)the Innovation and Entrepreneurship Funding of High-Level Overseas Talents of Guizhou Province(Dawei Fan,[2019]10).
文摘Mesozoic intermediate-felsic magmatic rocks in the eastern North China Craton commonly show geochemical similarity to adakites.However,the lack of direct constraints from partial melting experiments at high pressures and temperatures fuels a debate over the origin of these rocks.In this work,we performed partial melting experiments at 1.5 GPa and 800–950℃on amphibolite samples collected from the vicinity of the Mesozoic potassium-rich adakitic rocks in the Zhangjiakou area,northern margin of the North China Craton.The experimental melts range from granitic to granodioritic compositions,with SiO_(2)=56.4–72.6 wt.%,Al_(2)O_(3)=16.1–19.3 wt.%,FeO^(*)=2.4–9.6 wt.%,MgO=0.3–2.0 wt.%,CaO=0.6–3.8 wt.%,Na_(2)O=4.7–5.3 wt.%,and K_(2)O=2.6–3.9 wt.%,which are in the ranges of the surrounding Mesozoic potassium-rich adakitic rocks,except for the higher Al_(2)O_(3)contents and the data point at 1.5 GPa and 800℃.Trace element compositions of the melts measured by LA-ICP-MS are rich in Sr(849–1067 ppm)and light rare earth elements(LREEs)and poor in Y(<10.4 ppm)and Yb(<0.88 ppm),and have high Sr/Y(102–221)and(La/Yb)n(27–41)ratios and strongly fractionated rare earth element(REE)patterns,whereas no obvious negative Eu anomalies are observed.The geochemical characteristics show overall similarity to the Mesozoic potassium-rich adakitic rocks in the area,especially adakites with low Mg#,again except for the data point at 1.5 GPa and 800℃.The results suggest that partial melting of amphibolite can produce potassium-rich adakitic rocks with low Mg#in the eastern North China Craton under the experimental conditions of 1.5 GPa and 850–950℃.The experimental restites consist of hornblende(Hbl)+plagioclase(Pl)+garnet(Grt)±clinopyroxene(Cpx),a mineral assemblage significantly different from that of the nearby Hannuoba mafic granulite xenoliths which consist of Cpx+orthopyroxene(Opx)+Pl±Grt.Chemically,the experimental restites contain higher Al_(2)O_(3)but lower MgO and CaO than the Hannuoba mafic granulite xenoliths.We therefore argue that the Hannuoba mafic granulite xenoliths cannot represent the direct products of partial melting of the experimental amphibolite.
基金supported by the Knowledge Innovation Project of the Chinese Academy of Sciences (Grant No. KZCX1-YW-15)the National Natural Science Foundation of China (Grant No. 90814008)parts of experimental work is supported from the Opening Funding of State Key Laboratory of Geological Processes and Mineral Resources,China University of Geosciences (GPMR0506)
文摘On the basis of the geological and geochemical studies, including chemical analysis of bulk rocks, rare-earth and trace element studies, fluid inclusion, and S and O isotopic analyses, the authors described the geological background of the deposit in detail and presented significant proofs for the conditions of formation of the Shaxi porphyry copper-gold deposit. Compared with other large and supper-large porphyry copper deposits in China and the adjacent Cu-Au mineralized areas, the ore-forming processes and conditions were analyzed; and the possibility of forming large porphyry copper deposits in the Shaxi area was discussed. The present study indicated that the ore-forming fluid and material were mainly of magmatic origin, while meteoric water played a certain role in the ore-forming processes. Interactions between subducting and overriding plates provided a major driving force for the formation of igneous rocks and the deposition of metal elements in East China since Jurassic. Based on the geo- chemical data of the Shaxi intrusive, it is found that the copper (gold) mineralization is closely related to the genesis of adakite-like intrusive in the Shaxi area. This adakite-like intrusive was formed in the subduction environment as a result of the subduction of the West Pacific plate toward the East China continent, where there is a great potentiality to form a large porphyry copper deposit.
