Objective Previous studies on adakitic rocks with high Sr/Y and La/Yb ratios have established that such rocks may form in a variety of tectonic settings through different petrogenetic processes including: (1) parti...Objective Previous studies on adakitic rocks with high Sr/Y and La/Yb ratios have established that such rocks may form in a variety of tectonic settings through different petrogenetic processes including: (1) partial melting of subducted young (〈25 Ma), hot and hydrated oceanic slab; (2) partial melting of thickened lower crust; (3) assimilation and fractional crystallization processes involving basaltic magma; (4) partial melting of delaminated lower crust; and (5) partial melting of hydrous garnet peridotite. The various origins for adakites provide important constraints on crustal growth and evolution throughout the Earth's history.展开更多
The Nadingcuo high-K calc-alkaline rocks mainly composed of trachyte and trachyandesite are the largest outcrop area of volcanic rocks in southern Qiangtang terrane in the Tibetan plateau. However,their exact source a...The Nadingcuo high-K calc-alkaline rocks mainly composed of trachyte and trachyandesite are the largest outcrop area of volcanic rocks in southern Qiangtang terrane in the Tibetan plateau. However,their exact source and peterogenesis are still debated.^(40)Ar-^(39)Ar and LAM-ICPMS zircon U-Pb isotopic dating confirm that these rocks erupted in Eocene.In addition,the Nadingcuo volcanic rocks are characterized by high Sr/Y content ratios,similar with the adakite derived from partial melting of oceanic crust.They can be further classified as high Mg~#(Mg~#=48-57) and low Mg~# (Mg~#=33-42) subtypes.The Nadingcuo adakitic rocks have relatively low(^(87)Sr/^(86)Sr)_i and highε_(Nd)(t), showing a trend of similarity to the Dongcuo ophiolite present in the Bangong-Nujiang oceanic crust. Simple modeling indicates that the Nadingcuo adakitic rocks are a mix resulting from the basalt of Bangong-Nujiang Ocean with 10%-20%crustal material of Lhasa terrane.On these bases we suggest that the low Mg~# Nadingcuo adakitic rocks are the product of partial melting of remnant oceanic crust with small sediment,and the high Mg~# rocks are the result of reaction between rising melt of remnant oceanic crust with subducted sediment and mantle wedge.Therefore,the origin of Nadingcuo adakitic rocks may be related to intracontinental subduction triggered by collision of India-Asia during Cenozoic.展开更多
The Nagercoil block is the southernmost crustal segment of the Southern Granulite Terrane(SGT)in India and is mainly composed of charnockitic rocks and felsic gneisses(charnockite suite).In this study,we present petro...The Nagercoil block is the southernmost crustal segment of the Southern Granulite Terrane(SGT)in India and is mainly composed of charnockitic rocks and felsic gneisses(charnockite suite).In this study,we present petrologic,geochemical,zircon U-Pb,REE,and Hf isotopic studies on the charnockites and leucogneiss from the Nagercoil block.Based on field investigations and petrologic studies,the charnockites can be divided into garnet-bearing and garnet-absent anhydrous granulite facies rocks with orthopyroxene.The charnockites and leucogneiss show transition from adakites to non-adakitic magmatic rocks,with enrichment in LREEs(light rare earth elements)and LILEs(large ion lithophile elements),and depletion in HREEs(heavy rare earth elements)and HFSEs(high field strength elements).Some of the charnockites and the leucogneiss show typical HSA(high silica adakite)characters,(high SiO_(2),Al_(2)O_(3),Ba-Sr,La/Yb,and Sr/Y).The HSA is considered to have formed from the interaction of slab derived melts and peridotitic mantle wedge.The high Ba-Sr features were possibly inherited from subducted oceanic crust melting under high thermal gradient during Precambrian.The magmas were underplated and subjected to fractional crystallization.Zircon grains from the charnockite and leucogneiss show zoned magmatic cores surrounded by structureless metamorphic rims.Magmatic zircon grains from the charnockites show ages ranging from 1983±8.8 Ma to 2046±14 Ma,and the metamorphic domains show an age range of 502±14 Ma to 547±8.7 Ma.Zircon from the leucogneiss yielded magmatic and metamorphic ages of 1860±20 Ma and 575.6±8.8 Ma.Both charnockites and leucogneiss show two prominent age peaks at 1987 Ma and 568 Ma.The REE data of the zircon grains show LREE depletion and HREE enrichment,with the metamorphic grains showing more depletion in HREE.Zircon Hf isotopic data of the magmatic cores of zircon grains from the charnockite yieldedε_(Hf)(t)values from-1.17 to 0.46 with T_(DM)and T_(DM)~C and age peaks at 2392 Ma and 2638 Ma,suggesting Neoarchean to Paleoproterozoic juvenile sources.We suggest that the high Ba-Sr adakitic charnockite suite from the Nagercoil block formed in a Paleoproterozoic magmatic arc setting during the assembly of the Columbia supercontinent,and underwent high-grade metamorphism associated with the amalgamation of the Gondwana supercontinent during the late Neoproterozoic-Cambrian.Our study provides new insights into the vestiges of Columbia fragments within the Gondwana assembly with two distinct cycles of crustal evolution.展开更多
The study of Late Cretaceous magmatic rocks, developed as a result of magmatism and related porphyry mineralization in the northern Lhasa block, is of significance for understanding the associated tectonic setting and...The study of Late Cretaceous magmatic rocks, developed as a result of magmatism and related porphyry mineralization in the northern Lhasa block, is of significance for understanding the associated tectonic setting and mineralization. This paper reports zircon chronology, zircon Hf isotope data, wholerock Sr–Nd isotope data, and geochemistry data of Balazha porphyry ores in the northern Lhasa block. Geochemical features show that Balazha ore-bearing porphyries in the northern Lhasa block belong to high-Mg# adakitic rocks with a formation age of ~90 Ma; this is consistent with the Late Cretaceous magmatic activity that occurred at around 90 Ma in the region. The age of adakitic rocks is similar to the molybdenite Re–Os model age of the ore-bearing porphyries in the northern Lhasa block, indicating that the diagenesis and mineralization of both occurred during the same magmatism event in the Late Cretaceous. The Hf and Sr–Nd isotope data indicate that these magmatic rocks are the product of crust–mantle mixing. Differing proportions of materials involved in such an event form different types of medium-acid rocks, including ore-bearing porphyries. Based on regional studies, it has been proposed that Late Cretaceous magmatism and porphyry mineralization in the northern Lhasa block occurred during collision between the Lhasa and Qiangtang blocks.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
this work focuses on one of the critical points of Earth's history when the Solar System passed through the most distant point of its galactic orbit. During this event, Earth may have suffered from maximum extension,...this work focuses on one of the critical points of Earth's history when the Solar System passed through the most distant point of its galactic orbit. During this event, Earth may have suffered from maximum extension, associated with its relative proximity to the Sun at that time, followed by long-term contraction related to its later distancing. This paper is based on generalized data on the Cretaceous evolution of the Earth as a whole and of East Asia in particular. The evidence suggests that major geological processes at this time may be interpreted as transitional changes in the state of Earth. A liquid nature of its core may have reacted to the gravitational and electromagnetic transformations. When the cosmic changes took place at 135-120 Ma, more turbulent flows in the outer core would have favoured the rise of voluminous magmatic plumes and associated fluid flows. These would substantially transform the mantle, crust, hydrosphere, biosphere and atmosphere. In particular, plume-related melting of overlying subducting slabs and lower continental crust could have initiated numerous adakitic melts that formed the East Asian Adakitic Province. These and associated juvenile events produced numerous metallic ore, coal, gas and oil deposits. The Cretaceous is one of the most significant resource-producing periods.展开更多
The petrogenesis and geodynamic setting of the Late Jurassic Baita porphyry quartz monzodiorite in Xingcheng-Liaoxi area provide information for understanding the Mesozoic tectonic evolution of the northeastern North ...The petrogenesis and geodynamic setting of the Late Jurassic Baita porphyry quartz monzodiorite in Xingcheng-Liaoxi area provide information for understanding the Mesozoic tectonic evolution of the northeastern North China Craton.In this paper,geochronological,whole-rock geochemical,and in-situ zircon Hf isotopic analyses of Baita porphyry quartz monzodiorite were investigated to constrain the crystallization age and petrogenesis.Zircons exhibit typical oscillatory zoning in cathodoluminescence images and show relatively high Th/U ratios(0.78-1.62),and U-Pb analyses indicate that these rocks were crystallized during the Late Jurassic(159±1 Ma).Geochemically,they are characterized by high contents of SiO 2(65.21wt%-65.31wt%),Al 2O 3(16.29wt%-16.31wt%),Sr(521×10^(-6)-539×10^(-6)),and Sr/Y ratio(45.1-47.8)but low Y(10.9×10^(-6)-12.0×10^(-6)),with obvious adakitic geochemical affinities.These above-mentioned findings,combined with their negativeε_(Hf)(t)values(-21.7 to-20.2),corresponding two-stage model age(T_( DM2))of 2579-2484 Ma,as well as low MgO(1.38wt%-1.39wt%),Cr(18.5×10^(-6)-19.5×10^(-6))and Ni(9.45×10^(-6)-9.46×10^(-6))values,indicate that Baita porphyry quartz monzodiorite may be generated by partial melting of the Neoarchean-Paleoproterozoic thickened basaltic lower crust.Based on the results from this study and pre-vious regional studies,it is concluded that Baita porphyry quartz monzodiorite was spatially related to the westward subduction of the Paleo-Pacific plate.展开更多
The metallogenetic porphyry bodies in the Nongping Au-Cu deposit, in the eastern Yanbian area, mainly include porphyritic granodiorite and biotite granodiorite porphyry. They are featured with high silicon and enrichm...The metallogenetic porphyry bodies in the Nongping Au-Cu deposit, in the eastern Yanbian area, mainly include porphyritic granodiorite and biotite granodiorite porphyry. They are featured with high silicon and enrichment in sodium, and classified into sodic rocks of low-K tholeiitic basalt series. Except slightly low Sr content, the rock basically has the geochemical characteristics of the adakite: relatively high A12O3 content, relatively low MgO content, depletion in Y and Yb; relative enrichment in large ion lithophile elements (LILEs) and light rare-earth elements (LREEs), relatively low content of high field strength elements (HFSEs); positive Eu anomaly or weak negative Eu anomaly. In situ zircon dating technology LA-MC-ICP-MS was used to conduct single-grain zircon dating of biotite granodiorite porphyry, and the results show that the age of metallogenetic porphyry body is 100.04±0.88 Ma, indicating that the porphyry bodies were emplaced in the late Cretaceous period. According to the regional tectonic setting and the comparison with the same kind of deposits, we think that the metallogenetic porphyry bodies in the Nongping Au-Cu deposit have a close genetic connection with the subduction of the Pacific plate in the late Yanshanian period. The adakitic magma generated from partial melting of the subducting plate has high formation temperature, high oxygen fugacity, and volatile constituents' enrichment, so it is helpful for enrichment of metallogenetic elements and plays an important role in the formation of porphyry Au-Cu deposits in this region.展开更多
Orthopyroxene-bearing granodiorite(sometimes referred to as‘charnockite’)with an adakitic affinity is a rare type of granitoid.It is generally accepted that the stabilization of orthopyroxene in igneous charnockites...Orthopyroxene-bearing granodiorite(sometimes referred to as‘charnockite’)with an adakitic affinity is a rare type of granitoid.It is generally accepted that the stabilization of orthopyroxene in igneous charnockites essentially requires low aH_(2)O and/or high temperatures in a closed system.However,orthopyroxene can be an antecryst in a trans-crustal magmatic system.In this regard,orthopyroxenebearing granitoids are somewhat analogous to pseudo-charnockites,where the orthopyroxene stems from a mafic reservoir.On the other hand,the source compositions of continental adakites can vary,which is often ignored in the interpretation of their contribution to the adakitic geochemical signature.In this study,we have investigated a rare orthopyroxene-bearing felsic pluton from the Zhuyuan area of West Qinling,Central China.The Zhuyuan pluton was emplaced in the Middle–Late Triassic(222–217 Ma)and is mainly composed of metaluminous to weakly peraluminous granodiorites belonging to the high-K calc-alkaline series.Moreover,they are characterized by high Mg#values(49.7–60.9)and Sr contents(471–697 ppm),low Y(12.2–15.4 ppm)and Yb(1.03–1.24 ppm)contents,high Sr/Y(33.2–46.2)and(La/Yb)_(N)(15.3–21.4)ratios,and weakly negative Eu anomalies(Eu/Eu^(*)=0.78–0.89).The Zhuyuan adakitic granodiorites exhibit fairly limited Sr–Nd–Pb isotopic ratios and variable zircon initial Hf isotopes,indicating a major contribution from the Neoproterozoic basement of the Qinling Orogenic Belt.There is no evidence of any formation through high-pressure magmatic processes,and we propose that the adakitic signature of the Zhuyuan pluton could have been inherited from its source rocks(i.e.,from the Neoproterozoic basement).The orthopyroxenes in the Zhuyuan granodiorites display poikilitic textures with high MgO,NiO and Cr_(2)O_(3) contents,indicating that they have an antecrystic origin.Studies of regional tectonic evolution have shown that the Zhuyuan granodiorites formed during the tearing stage of the A’nimaque–Mianlue oceanic subduction slab.Therefore,this study emphasizes the effect of source inheritance on the formation of pseudo-charnockite with an adakitic signature.展开更多
Eocene intermediate to felsic subvolcanic rocks of the Torud-Ahmad Abad magmatic belt(TAMB),in the northern part of the Central Iran zone,are exposed between the Torud and Ahmad Abad regions in South-Southeast Shahroo...Eocene intermediate to felsic subvolcanic rocks of the Torud-Ahmad Abad magmatic belt(TAMB),in the northern part of the Central Iran zone,are exposed between the Torud and Ahmad Abad regions in South-Southeast Shahrood.These igneous rocks include hypabyssal dacite,trachyte,andesite,trachy-andesite,and basaltic andesite;they are mainly composed of phenocrysts and microcrystalline groundmass of pyroxene,amphibole,and plagioclase,with minor biotite and titanomagnetite;they form domal structures(plugs and stocks),dikes,and sills that intruded into Neoproterozoic to cogenetic Eocene volcano-sedimentary sequences.Based on isotopic analysis of these intermediate to acidic rocks,initial ratios of^(143)Nd/^(144)Nd range from 0.512775 to 0.512893 and initial ratios of^(87)Sr/^(86)Sr range from 0.703746 to 0.705314,with quite positiveε_(Nd(i))values of+3.69 to+6.00.They are enriched in light rare earth elements and large ion lithophile elements and depleted in heavy rare earth elements and high-field strength elements,the SiO_(2) content is(52-62)wt.%,and Na_(2)O content>3 wt.%,Al_(2)O_(3) content>16 wt.%,Yb<1.8 ppm,and Y<18 ppm.These geological,geochemical,and Sr and Nd isotopic data are consistent with adakitic signatures originating by partial melting of the subducted Neo-Tethys oceanic slab(Sabzevar branch)and lithospheric suprasubduction zone mantle.The mantle signatures typifying the rapidly emplaced adakitic rocks(slab(high-silica adakite)and suprasubduction zone(low-silica adakite)melts)together with their locally voluminous extent are evidences that support a locally extensional geodynamic setting;and the evidence is consistent with an evolution to local transpression in the Late Eocene in this convergent margin are environment to rifting(basalts to adakites)towards submarine conditions in the Neogene.展开更多
It is difficult to date a brittle fault because of the absence of effective dating methods.Recently,calcite U-Pb dating has drawn the attention of many researchers and has been successfully applied to constrain the ag...It is difficult to date a brittle fault because of the absence of effective dating methods.Recently,calcite U-Pb dating has drawn the attention of many researchers and has been successfully applied to constrain the age of brittle deformation.The South China Block(SCB)has experienced multiphase deformations characterized by widespread brittle faults and folds,which has led to significant debate on the Mesozoic dynamic mechanism and deformational phases.A syn-faulting calcite vein that occurred in the Permian limestones of the Ningzhen Mountain region was analyzed using U-Pb dating and geochemistry techniques in this paper.The U-Pb dating results display multiphase activities with two mixed ages of 109.9±5.8 Ma(MSWD=46,n=231)and 117.2±2.4 Ma(MSWD=3.6,n=150).The age of 117.2±2.4 Ma likely represents the timing of the brittle faults.Trace elements and rare earth elements data indicate that these fault-related calcites are mainly derived from host limestones and unrelated to Cretaceous magmatic activity.These faults formed in a tectonic reactive period and dormant time of the adakitic magma in the Lower Yangtze region.展开更多
基金financially supported by the National Nature Science Foundation of China(grant No. 41202037)
文摘Objective Previous studies on adakitic rocks with high Sr/Y and La/Yb ratios have established that such rocks may form in a variety of tectonic settings through different petrogenetic processes including: (1) partial melting of subducted young (〈25 Ma), hot and hydrated oceanic slab; (2) partial melting of thickened lower crust; (3) assimilation and fractional crystallization processes involving basaltic magma; (4) partial melting of delaminated lower crust; and (5) partial melting of hydrous garnet peridotite. The various origins for adakites provide important constraints on crustal growth and evolution throughout the Earth's history.
基金supported by the following projects:National Basic Research Program of China (2009CB421004,2009CB421003)Natural Science Foundation of China(41073033,40872055,and 40930316)+1 种基金Chinese Academy of Sciences(KZCX2-YW-Q04)China Geological Survey(1212010818098)
文摘The Nadingcuo high-K calc-alkaline rocks mainly composed of trachyte and trachyandesite are the largest outcrop area of volcanic rocks in southern Qiangtang terrane in the Tibetan plateau. However,their exact source and peterogenesis are still debated.^(40)Ar-^(39)Ar and LAM-ICPMS zircon U-Pb isotopic dating confirm that these rocks erupted in Eocene.In addition,the Nadingcuo volcanic rocks are characterized by high Sr/Y content ratios,similar with the adakite derived from partial melting of oceanic crust.They can be further classified as high Mg~#(Mg~#=48-57) and low Mg~# (Mg~#=33-42) subtypes.The Nadingcuo adakitic rocks have relatively low(^(87)Sr/^(86)Sr)_i and highε_(Nd)(t), showing a trend of similarity to the Dongcuo ophiolite present in the Bangong-Nujiang oceanic crust. Simple modeling indicates that the Nadingcuo adakitic rocks are a mix resulting from the basalt of Bangong-Nujiang Ocean with 10%-20%crustal material of Lhasa terrane.On these bases we suggest that the low Mg~# Nadingcuo adakitic rocks are the product of partial melting of remnant oceanic crust with small sediment,and the high Mg~# rocks are the result of reaction between rising melt of remnant oceanic crust with subducted sediment and mantle wedge.Therefore,the origin of Nadingcuo adakitic rocks may be related to intracontinental subduction triggered by collision of India-Asia during Cenozoic.
基金funded by Foreign Expert grants to M.Santosh from the China University of Geosciences Beijing,Chinapartially supported by NRF 2017R1A6A1A07015374 and NRF 2019R1A2C1002211supervised by the Ministry of Science and ICT,Korea to Sanghoon Kwonfunded the Fundamental Research Fund of Central Universities(Grant 2652019210)through CUGB,China。
文摘The Nagercoil block is the southernmost crustal segment of the Southern Granulite Terrane(SGT)in India and is mainly composed of charnockitic rocks and felsic gneisses(charnockite suite).In this study,we present petrologic,geochemical,zircon U-Pb,REE,and Hf isotopic studies on the charnockites and leucogneiss from the Nagercoil block.Based on field investigations and petrologic studies,the charnockites can be divided into garnet-bearing and garnet-absent anhydrous granulite facies rocks with orthopyroxene.The charnockites and leucogneiss show transition from adakites to non-adakitic magmatic rocks,with enrichment in LREEs(light rare earth elements)and LILEs(large ion lithophile elements),and depletion in HREEs(heavy rare earth elements)and HFSEs(high field strength elements).Some of the charnockites and the leucogneiss show typical HSA(high silica adakite)characters,(high SiO_(2),Al_(2)O_(3),Ba-Sr,La/Yb,and Sr/Y).The HSA is considered to have formed from the interaction of slab derived melts and peridotitic mantle wedge.The high Ba-Sr features were possibly inherited from subducted oceanic crust melting under high thermal gradient during Precambrian.The magmas were underplated and subjected to fractional crystallization.Zircon grains from the charnockite and leucogneiss show zoned magmatic cores surrounded by structureless metamorphic rims.Magmatic zircon grains from the charnockites show ages ranging from 1983±8.8 Ma to 2046±14 Ma,and the metamorphic domains show an age range of 502±14 Ma to 547±8.7 Ma.Zircon from the leucogneiss yielded magmatic and metamorphic ages of 1860±20 Ma and 575.6±8.8 Ma.Both charnockites and leucogneiss show two prominent age peaks at 1987 Ma and 568 Ma.The REE data of the zircon grains show LREE depletion and HREE enrichment,with the metamorphic grains showing more depletion in HREE.Zircon Hf isotopic data of the magmatic cores of zircon grains from the charnockite yieldedε_(Hf)(t)values from-1.17 to 0.46 with T_(DM)and T_(DM)~C and age peaks at 2392 Ma and 2638 Ma,suggesting Neoarchean to Paleoproterozoic juvenile sources.We suggest that the high Ba-Sr adakitic charnockite suite from the Nagercoil block formed in a Paleoproterozoic magmatic arc setting during the assembly of the Columbia supercontinent,and underwent high-grade metamorphism associated with the amalgamation of the Gondwana supercontinent during the late Neoproterozoic-Cambrian.Our study provides new insights into the vestiges of Columbia fragments within the Gondwana assembly with two distinct cycles of crustal evolution.
基金financially supported by the National Key R&D Program of China(No.2016YFC0600404)the National Natural Science Foundation of China(Nos.41272091,41673040,41773026,and 41772200)fund for the geological survey from the Ministry of natural resources of PRC(Nos.DD20160016 and DD20160017)
文摘The study of Late Cretaceous magmatic rocks, developed as a result of magmatism and related porphyry mineralization in the northern Lhasa block, is of significance for understanding the associated tectonic setting and mineralization. This paper reports zircon chronology, zircon Hf isotope data, wholerock Sr–Nd isotope data, and geochemistry data of Balazha porphyry ores in the northern Lhasa block. Geochemical features show that Balazha ore-bearing porphyries in the northern Lhasa block belong to high-Mg# adakitic rocks with a formation age of ~90 Ma; this is consistent with the Late Cretaceous magmatic activity that occurred at around 90 Ma in the region. The age of adakitic rocks is similar to the molybdenite Re–Os model age of the ore-bearing porphyries in the northern Lhasa block, indicating that the diagenesis and mineralization of both occurred during the same magmatism event in the Late Cretaceous. The Hf and Sr–Nd isotope data indicate that these magmatic rocks are the product of crust–mantle mixing. Differing proportions of materials involved in such an event form different types of medium-acid rocks, including ore-bearing porphyries. Based on regional studies, it has been proposed that Late Cretaceous magmatism and porphyry mineralization in the northern Lhasa block occurred during collision between the Lhasa and Qiangtang blocks.
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 National Natural Science Foundation of China(No.41420104001)the ‘111’ Project(No.B17042)
文摘this work focuses on one of the critical points of Earth's history when the Solar System passed through the most distant point of its galactic orbit. During this event, Earth may have suffered from maximum extension, associated with its relative proximity to the Sun at that time, followed by long-term contraction related to its later distancing. This paper is based on generalized data on the Cretaceous evolution of the Earth as a whole and of East Asia in particular. The evidence suggests that major geological processes at this time may be interpreted as transitional changes in the state of Earth. A liquid nature of its core may have reacted to the gravitational and electromagnetic transformations. When the cosmic changes took place at 135-120 Ma, more turbulent flows in the outer core would have favoured the rise of voluminous magmatic plumes and associated fluid flows. These would substantially transform the mantle, crust, hydrosphere, biosphere and atmosphere. In particular, plume-related melting of overlying subducting slabs and lower continental crust could have initiated numerous adakitic melts that formed the East Asian Adakitic Province. These and associated juvenile events produced numerous metallic ore, coal, gas and oil deposits. The Cretaceous is one of the most significant resource-producing periods.
基金Supported by National Natural Science foundations of China(Nos.42072063,41722204).
文摘The petrogenesis and geodynamic setting of the Late Jurassic Baita porphyry quartz monzodiorite in Xingcheng-Liaoxi area provide information for understanding the Mesozoic tectonic evolution of the northeastern North China Craton.In this paper,geochronological,whole-rock geochemical,and in-situ zircon Hf isotopic analyses of Baita porphyry quartz monzodiorite were investigated to constrain the crystallization age and petrogenesis.Zircons exhibit typical oscillatory zoning in cathodoluminescence images and show relatively high Th/U ratios(0.78-1.62),and U-Pb analyses indicate that these rocks were crystallized during the Late Jurassic(159±1 Ma).Geochemically,they are characterized by high contents of SiO 2(65.21wt%-65.31wt%),Al 2O 3(16.29wt%-16.31wt%),Sr(521×10^(-6)-539×10^(-6)),and Sr/Y ratio(45.1-47.8)but low Y(10.9×10^(-6)-12.0×10^(-6)),with obvious adakitic geochemical affinities.These above-mentioned findings,combined with their negativeε_(Hf)(t)values(-21.7 to-20.2),corresponding two-stage model age(T_( DM2))of 2579-2484 Ma,as well as low MgO(1.38wt%-1.39wt%),Cr(18.5×10^(-6)-19.5×10^(-6))and Ni(9.45×10^(-6)-9.46×10^(-6))values,indicate that Baita porphyry quartz monzodiorite may be generated by partial melting of the Neoarchean-Paleoproterozoic thickened basaltic lower crust.Based on the results from this study and pre-vious regional studies,it is concluded that Baita porphyry quartz monzodiorite was spatially related to the westward subduction of the Paleo-Pacific plate.
基金financially supported by the China Geological Survey (No.1212011085485)Basic Research Foundation of Jilin University (No. 200903025 and 201004001)
文摘The metallogenetic porphyry bodies in the Nongping Au-Cu deposit, in the eastern Yanbian area, mainly include porphyritic granodiorite and biotite granodiorite porphyry. They are featured with high silicon and enrichment in sodium, and classified into sodic rocks of low-K tholeiitic basalt series. Except slightly low Sr content, the rock basically has the geochemical characteristics of the adakite: relatively high A12O3 content, relatively low MgO content, depletion in Y and Yb; relative enrichment in large ion lithophile elements (LILEs) and light rare-earth elements (LREEs), relatively low content of high field strength elements (HFSEs); positive Eu anomaly or weak negative Eu anomaly. In situ zircon dating technology LA-MC-ICP-MS was used to conduct single-grain zircon dating of biotite granodiorite porphyry, and the results show that the age of metallogenetic porphyry body is 100.04±0.88 Ma, indicating that the porphyry bodies were emplaced in the late Cretaceous period. According to the regional tectonic setting and the comparison with the same kind of deposits, we think that the metallogenetic porphyry bodies in the Nongping Au-Cu deposit have a close genetic connection with the subduction of the Pacific plate in the late Yanshanian period. The adakitic magma generated from partial melting of the subducting plate has high formation temperature, high oxygen fugacity, and volatile constituents' enrichment, so it is helpful for enrichment of metallogenetic elements and plays an important role in the formation of porphyry Au-Cu deposits in this region.
基金funded by the State Key Program of National Natural Science of China(Grant No.41730426)the National Natural Science Foundation of China(Grant Nos.41872066 and 41702069)+1 种基金the Fundamental Research Funds for the Central Universities of China(Grant No.2652018121)the Open Research Funds for GPMR(Grant No.GPMR201509).
文摘Orthopyroxene-bearing granodiorite(sometimes referred to as‘charnockite’)with an adakitic affinity is a rare type of granitoid.It is generally accepted that the stabilization of orthopyroxene in igneous charnockites essentially requires low aH_(2)O and/or high temperatures in a closed system.However,orthopyroxene can be an antecryst in a trans-crustal magmatic system.In this regard,orthopyroxenebearing granitoids are somewhat analogous to pseudo-charnockites,where the orthopyroxene stems from a mafic reservoir.On the other hand,the source compositions of continental adakites can vary,which is often ignored in the interpretation of their contribution to the adakitic geochemical signature.In this study,we have investigated a rare orthopyroxene-bearing felsic pluton from the Zhuyuan area of West Qinling,Central China.The Zhuyuan pluton was emplaced in the Middle–Late Triassic(222–217 Ma)and is mainly composed of metaluminous to weakly peraluminous granodiorites belonging to the high-K calc-alkaline series.Moreover,they are characterized by high Mg#values(49.7–60.9)and Sr contents(471–697 ppm),low Y(12.2–15.4 ppm)and Yb(1.03–1.24 ppm)contents,high Sr/Y(33.2–46.2)and(La/Yb)_(N)(15.3–21.4)ratios,and weakly negative Eu anomalies(Eu/Eu^(*)=0.78–0.89).The Zhuyuan adakitic granodiorites exhibit fairly limited Sr–Nd–Pb isotopic ratios and variable zircon initial Hf isotopes,indicating a major contribution from the Neoproterozoic basement of the Qinling Orogenic Belt.There is no evidence of any formation through high-pressure magmatic processes,and we propose that the adakitic signature of the Zhuyuan pluton could have been inherited from its source rocks(i.e.,from the Neoproterozoic basement).The orthopyroxenes in the Zhuyuan granodiorites display poikilitic textures with high MgO,NiO and Cr_(2)O_(3) contents,indicating that they have an antecrystic origin.Studies of regional tectonic evolution have shown that the Zhuyuan granodiorites formed during the tearing stage of the A’nimaque–Mianlue oceanic subduction slab.Therefore,this study emphasizes the effect of source inheritance on the formation of pseudo-charnockite with an adakitic signature.
基金supported by the NSERC Discovery to David R.Lentz。
文摘Eocene intermediate to felsic subvolcanic rocks of the Torud-Ahmad Abad magmatic belt(TAMB),in the northern part of the Central Iran zone,are exposed between the Torud and Ahmad Abad regions in South-Southeast Shahrood.These igneous rocks include hypabyssal dacite,trachyte,andesite,trachy-andesite,and basaltic andesite;they are mainly composed of phenocrysts and microcrystalline groundmass of pyroxene,amphibole,and plagioclase,with minor biotite and titanomagnetite;they form domal structures(plugs and stocks),dikes,and sills that intruded into Neoproterozoic to cogenetic Eocene volcano-sedimentary sequences.Based on isotopic analysis of these intermediate to acidic rocks,initial ratios of^(143)Nd/^(144)Nd range from 0.512775 to 0.512893 and initial ratios of^(87)Sr/^(86)Sr range from 0.703746 to 0.705314,with quite positiveε_(Nd(i))values of+3.69 to+6.00.They are enriched in light rare earth elements and large ion lithophile elements and depleted in heavy rare earth elements and high-field strength elements,the SiO_(2) content is(52-62)wt.%,and Na_(2)O content>3 wt.%,Al_(2)O_(3) content>16 wt.%,Yb<1.8 ppm,and Y<18 ppm.These geological,geochemical,and Sr and Nd isotopic data are consistent with adakitic signatures originating by partial melting of the subducted Neo-Tethys oceanic slab(Sabzevar branch)and lithospheric suprasubduction zone mantle.The mantle signatures typifying the rapidly emplaced adakitic rocks(slab(high-silica adakite)and suprasubduction zone(low-silica adakite)melts)together with their locally voluminous extent are evidences that support a locally extensional geodynamic setting;and the evidence is consistent with an evolution to local transpression in the Late Eocene in this convergent margin are environment to rifting(basalts to adakites)towards submarine conditions in the Neogene.
基金financially supported by the Natural Science Foundation of China(No.41872074)the Fundamental Research Funds of the Central UniversitiesChina(No.2013B200202021)。
文摘It is difficult to date a brittle fault because of the absence of effective dating methods.Recently,calcite U-Pb dating has drawn the attention of many researchers and has been successfully applied to constrain the age of brittle deformation.The South China Block(SCB)has experienced multiphase deformations characterized by widespread brittle faults and folds,which has led to significant debate on the Mesozoic dynamic mechanism and deformational phases.A syn-faulting calcite vein that occurred in the Permian limestones of the Ningzhen Mountain region was analyzed using U-Pb dating and geochemistry techniques in this paper.The U-Pb dating results display multiphase activities with two mixed ages of 109.9±5.8 Ma(MSWD=46,n=231)and 117.2±2.4 Ma(MSWD=3.6,n=150).The age of 117.2±2.4 Ma likely represents the timing of the brittle faults.Trace elements and rare earth elements data indicate that these fault-related calcites are mainly derived from host limestones and unrelated to Cretaceous magmatic activity.These faults formed in a tectonic reactive period and dormant time of the adakitic magma in the Lower Yangtze region.