Kimberlite,which is the primary host rock for diamonds,originates from the deepest sources of all the mantle-derived magmas(Giuliani et al.,2023;Foley et al.,2019).This feature provides a vital perspective to explore ...Kimberlite,which is the primary host rock for diamonds,originates from the deepest sources of all the mantle-derived magmas(Giuliani et al.,2023;Foley et al.,2019).This feature provides a vital perspective to explore Earth's internal structure and evolution.The first primary diamond deposit discovered in China was the East No.1 kimberlite pluton(D1)in Maping(26°56′08″N,108°17′07″E),located on the southeastern margin of the Yangtze Craton(Figure 1).展开更多
High-precision data on U and Th contents and Th/U ratios of zircon obtained using secondary ion mass spectrometry analysis have been collected from the literature. Zircon in the granitic rocks has median values of 350...High-precision data on U and Th contents and Th/U ratios of zircon obtained using secondary ion mass spectrometry analysis have been collected from the literature. Zircon in the granitic rocks has median values of 350 ppm U, 140 ppm Th, and Th/U=0.52; the recommended zircon-melt partition coefficients are 81 for Du and 8.2 for DTh. In zircon from mafic and intermediate rocks, the median values are 270 ppm U, 170 ppm Th, and Th/U=0.81, and the recommended zirconmelt partition coefficients are 169 for Du and 59 for DTh. The U and Th contents and Th/U ratios of magmatic zircon are low when zircon crystallizes in equilibrium with the melt. Increasing magma temperature should promote higher Th contents relative to U contents, resulting in higher Th/U ratios for zircon in mafic to intermediate rocks than in granitic rocks. However, when zircon crystallizes in disequilibrium with the melt, U and Th are more easily able to enter the zircon lattice, and their contents and Th/U ratios depend mainly on the degree of disequilibrium. The behavior of U and Th in magmatic zircon can be used as a geochemical indicator to determine the origins and crystallization environments of magmatic zircon.展开更多
A growing body of evidence shows that volcanism near the Permian-Triassic boundary（PTB） may be crucial in triggering the Permian–Triassic（P–Tr） mass extinction. Thus, the ash beds near the PTB in South China may...A growing body of evidence shows that volcanism near the Permian-Triassic boundary（PTB） may be crucial in triggering the Permian–Triassic（P–Tr） mass extinction. Thus, the ash beds near the PTB in South China may carry information on this event. Three volcanic ash layers, altered to clay, outcropped in the PTB beds in Zunyi Section, Guizhou Province, Southwest China. The U-Pb ages, trace elements, and Hf-isotope compositions of zircon grains from these three ash beds were analyzed using LA-ICPMS and LA-MC-ICPMS. The zircons are mainly magmatic in origin（241-279 Ma） except for two inherited/xenocrystic zircons（939 and 2 325 Ma）. The ages of these magmatic zircons indicate three episodes of magmatism which occurred around the MiddleLate Permian boundary（-261.5 Ma, MLPB）, the Wuchiapingian-Changhsingian boundary（-254.5 Ma, WCB）, and the PTB（-250.5 Ma）, respectively. The first two episodes of magmatism near the MLPB and WCB may be attributed to magmatic inheritance or re-deposition. All magmatic zircons share similar trace-element and Hf-isotope compositions. They have Y, Hf, Th and U contents and Nb/Ta ratios are typical of zircons from silicic calc-alkaline magmas. These zircons also exhibit enriched Hf-isotope compositions with _（εHf）（t） values of-11.4 to ＋0.2, which suggests that the three magmatic episodes involved melting of the continental crust. The more enriched Hf-isotope composition （_（εHf）（t）=-11.4--4.8） of Bed ZY13（-250.5 Ma） implies more input of ancient crustal material in the magma. Integration of the Hf-isotope and trace-element compositions of magmatic zircons suggest that these three episodes of magmatism may take place along the convergent continent margin in or near southwestern South China as a result of the closure of the Palaeo-Tethys Ocean.展开更多
We discuss two array-based tomography methods, ambient noise tomography （ANT） and two-plane- wave earthquake tomography （TPWT）, which are capable of taking advantage of emerging large-scale broadband seismic array...We discuss two array-based tomography methods, ambient noise tomography （ANT） and two-plane- wave earthquake tomography （TPWT）, which are capable of taking advantage of emerging large-scale broadband seismic arrays to generate high resolution phase velocity maps, but in complementary period band： ANT at 8-40 s and TPWT at 25-100 s period. Combining these two methods generates surface wave dispersion maps from 8 to 100 s periods, which can be used to construct a 3D vs model from the surface to -200 km depth. As an illustration, we apply the two methods to the USArray/Transportable Array. We process seismic noise data from over 1 500 stations obtained from 2005 through 2009 to produce Rayleigh wave phase velocity maps from 8 to 40 s period, and also perform TPWT using -450 teleseismic earthquakes to obtain phase velocity maps between 25 and 100 s period. Combining dispersion maps from ANT and TPWT, we construct a 3D vs model from the surface to a depth of 160 km in the western and central USA. These surface wave tomography methods can also be applied to other rapidly growing seismic networks such as those in China.展开更多
In order to distinguish the primary microstructures developed under mantle conditions from the secondary phenomena after xenolith entrainment in the host magma, this study intends to discuss the genesis of spongy, sie...In order to distinguish the primary microstructures developed under mantle conditions from the secondary phenomena after xenolith entrainment in the host magma, this study intends to discuss the genesis of spongy, sieve-textured, and reaction rims on mineral grains of mantle xenoliths in the Cenozoic basalts from the western North China craton. The spongy rims on primary clinopyroxene show neither obvious compositional zoning nor preferential development towards the host basalt and probably suggest an origin via partial melting within the lithospheric mantle or pressure release as the xenoliths were carried upwards. The sieve-textured rims on primary spinel show clear chemical zoning with increasing Cr# and decreasing AI towards the host basalt. They are interpreted as the result of partial melting due to heating of the host basaltic magma and decreasing pressure during ascent proc- ess. Post-entrainment reaction mainly generated secondary minerals at contacts between the host ba- saltic melt and xenoliths. The secondary clinopyroxene in reaction rims develops on primary clinopy- roxene and has higher Ti, Ca, and Fe contents and lower Mg# and Si contents than primary one, while the secondary spinel on primary Cr-AI spinel is titanomagnetite. The secondary olivine and clinopy- roxene in the reaction rims on primary orthopyroxene are enriched in Fe, Al, and Ti. The occurrence of reaction rims in mantle xenoliths reflects disequilibrium processes after xenolith entrainment in the basaltic melt. The spongy rims on primary clinopyroxene may not be related to the interaction with thehost basaltic melt, while the sieve-textured rims on primary spinel and reactions rims on primary clinopyroxene, spinel, and orthopyroxene may result from post-entrainment reaction between the host basaltic melt and xenolith minerals.展开更多
The Nianzha gold deposit, located in the central section of the Indus-Yarlung Tsangpo suture （IYS） zone in southern Tibet, is a large gold deposit （Au reserves of 25 tons with average grade of 3.08 g/t） controlled...The Nianzha gold deposit, located in the central section of the Indus-Yarlung Tsangpo suture （IYS） zone in southern Tibet, is a large gold deposit （Au reserves of 25 tons with average grade of 3.08 g/t） controlled by a E-W striking fault that developed during the main stage of Indo-Asian collision （-65-41 Ma）. The main orebody is 1760 m long and 5.15 m thick, and occurs in a fracture zone bordered by Cretaceous diorite in the hanging wall to the north and the Renbu tectonic melange in the footwall to the south. High-grade mineralization occurs in a fracture zone between diorite and ultramafic rock in the Renbu tectonic melange. The wall-rock alteration is characterized by silicification in the fracture zone, serpentinization and the formation of talc and magnesite in the uitramafic unit, and chloritization and the formation of epidote and calcite in diorite. Quartz veins associated with Au mineralization can be divided into three stages. Fluid inclusion data indicate that the deposit formed from H20-NaCl-organic gas fluids that homogenize at temperatures of 203℃-347℃ and have salinities of 0.35wt%-17.17wt% NaCI equivalent. The quartz veins yield δ18Ofluid values of 0.15‰-10.45‰, low δDv-SMow values （-173%o to -96%o）, and the δ13C values of-17.6‰ to -4.7‰, indicating the ore-forming fluids were a mix of metamorphic and sedimentary orogenic fluids with the addition of some meteoric and mantle-derived fluids. The pyrite within the diorite has δ34SV-CDT values of -2.9‰-1.9‰（average -1.1‰）, 206pb/204pb values of 18.47- 18.64, 207pb/204pb values of 15.64-15.74, and 208pb/204pb values of 38.71-39.27, all of which are indicative of the derivation of S and other ore-forming elements from deep in the mantle. The presence of the Nianzha, Bangbu, and Mayum gold deposits within the IYS zone indicates that this area is highly prospective for large orogenic gold deposits. We identified three types of mineralization within the IYS, namely Bangbu-type accretionary, Mayum-type microcontinent, and Nianzha-type ophiolite-associated orogenic Au deposits. The three types formed at different depths in an aeeretionary orogenic tectonic setting. The Bangbu type was formed at the deepest level and the Nianzha type at the shallowest.展开更多
The compositions of the whole rocks and trace elements of minerals in peridotites can reflect the characteristics of the lithospheric mantle. The nature and evolution of the Cenozoic lithospheric mantle beneath Hannuo...The compositions of the whole rocks and trace elements of minerals in peridotites can reflect the characteristics of the lithospheric mantle. The nature and evolution of the Cenozoic lithospheric mantle beneath Hannuoba （汉诺坝）, located on the north edge of the intra-North China orogenic belt, are discussed based on the in-situ LAM-ICPMS detected trace element compositions of clinopyroxenes in the Hannuoba peridotitic xenoliths combined with detailed petrography and geochemistry studies. The Hannuoba lithospheric mantle was formed by different partial meltings of the primitive mantle. Most of the samples reflect the partial melting degree of lower than 5% with a few samples of 15%-20%. Major element compositions of the whole rocks and geochemical compositions of clinopyroxenes reveal the coexistence of both fertile and depleted mantle underneath the Hannuoba region during the Cenozoic. This was probably caused by the asthenospheric mantle replacing the aged craton mantle through erosion, intermingling and modification. Our conclusion is further supported by the existence of both carbonatitic magmatic material and silicate melt/ fluid metasomatism as magnified by the trace elements of the clinopyroxencs from the Hannuoba lithospherJc mantle.展开更多
Morphological and chemical studies on zircon grains from gabbro and granite of the Pingtan magmatic complex, Fujian Province, eastern China, show that there are three stages of zircon growth. The early stage of zircon...Morphological and chemical studies on zircon grains from gabbro and granite of the Pingtan magmatic complex, Fujian Province, eastern China, show that there are three stages of zircon growth. The early stage of zircon growth is characterized by colorlessness, high transparence and birefringence, low and dispersive Ipr and Ipy, weak and homogeneous BSE brightness, lower Hf content and depletion of U, Th and Y; the middle stage is characterized by abruptly increasing lpy, progressively strong and sectoral-zoning BSE brightness, higher Hf content and enrichment of U, Th and Y with Th/U 〉 1; the late stage of growth is characterized by brownish color, poor transparence, low birefringence, highest Ipr and Ipy, middle and oscillatorily-zoning BSE brightness, highest contents of Hf, U and Y with Th/U 〈 1. The stages are considered to be formed in a deep magma chamber, ascent passage and emplacement site, respectively. Due to the more or less long residual time of the magma chamber, the difference in age between the early and late stages of zircon might be great enough to be distinguished, which can be attributed to tectonic constraint for the magnlatism.展开更多
基金supported by the National Natural Science Foundation of China(Nos.41963006,42363006)the Geological Research Project of the Bureau of Geology and Mineral Exploration and Development of Guizhou Province(Nos.QDKKH[2020]26,QDKKH[2024]6,QDKKH[2023]1)。
文摘Kimberlite,which is the primary host rock for diamonds,originates from the deepest sources of all the mantle-derived magmas(Giuliani et al.,2023;Foley et al.,2019).This feature provides a vital perspective to explore Earth's internal structure and evolution.The first primary diamond deposit discovered in China was the East No.1 kimberlite pluton(D1)in Maping(26°56′08″N,108°17′07″E),located on the southeastern margin of the Yangtze Craton(Figure 1).
基金supported by the National Natural Science Foundation of China(Grant No. 40972058)the research grants(2008-Ⅰ-02 and 2008-Ⅱ-08)from the State Key Laboratory for Mineral Deposit Research,Nanjing University
文摘High-precision data on U and Th contents and Th/U ratios of zircon obtained using secondary ion mass spectrometry analysis have been collected from the literature. Zircon in the granitic rocks has median values of 350 ppm U, 140 ppm Th, and Th/U=0.52; the recommended zircon-melt partition coefficients are 81 for Du and 8.2 for DTh. In zircon from mafic and intermediate rocks, the median values are 270 ppm U, 170 ppm Th, and Th/U=0.81, and the recommended zirconmelt partition coefficients are 169 for Du and 59 for DTh. The U and Th contents and Th/U ratios of magmatic zircon are low when zircon crystallizes in equilibrium with the melt. Increasing magma temperature should promote higher Th contents relative to U contents, resulting in higher Th/U ratios for zircon in mafic to intermediate rocks than in granitic rocks. However, when zircon crystallizes in disequilibrium with the melt, U and Th are more easily able to enter the zircon lattice, and their contents and Th/U ratios depend mainly on the degree of disequilibrium. The behavior of U and Th in magmatic zircon can be used as a geochemical indicator to determine the origins and crystallization environments of magmatic zircon.
基金supported by an aid grant from Chengdu Center, China Geological Survey (No. 12120113049100-1)the National Natural Science Foundations (Nos. 40572068, 40839903 and 41272044)+1 种基金the "111" Program (No. B08030)an aid grant (No. GBL11206) from the State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences (Wuhan), China
文摘A growing body of evidence shows that volcanism near the Permian-Triassic boundary（PTB） may be crucial in triggering the Permian–Triassic（P–Tr） mass extinction. Thus, the ash beds near the PTB in South China may carry information on this event. Three volcanic ash layers, altered to clay, outcropped in the PTB beds in Zunyi Section, Guizhou Province, Southwest China. The U-Pb ages, trace elements, and Hf-isotope compositions of zircon grains from these three ash beds were analyzed using LA-ICPMS and LA-MC-ICPMS. The zircons are mainly magmatic in origin（241-279 Ma） except for two inherited/xenocrystic zircons（939 and 2 325 Ma）. The ages of these magmatic zircons indicate three episodes of magmatism which occurred around the MiddleLate Permian boundary（-261.5 Ma, MLPB）, the Wuchiapingian-Changhsingian boundary（-254.5 Ma, WCB）, and the PTB（-250.5 Ma）, respectively. The first two episodes of magmatism near the MLPB and WCB may be attributed to magmatic inheritance or re-deposition. All magmatic zircons share similar trace-element and Hf-isotope compositions. They have Y, Hf, Th and U contents and Nb/Ta ratios are typical of zircons from silicic calc-alkaline magmas. These zircons also exhibit enriched Hf-isotope compositions with _（εHf）（t） values of-11.4 to ＋0.2, which suggests that the three magmatic episodes involved melting of the continental crust. The more enriched Hf-isotope composition （_（εHf）（t）=-11.4--4.8） of Bed ZY13（-250.5 Ma） implies more input of ancient crustal material in the magma. Integration of the Hf-isotope and trace-element compositions of magmatic zircons suggest that these three episodes of magmatism may take place along the convergent continent margin in or near southwestern South China as a result of the closure of the Palaeo-Tethys Ocean.
基金supported by the US National Science Foundation(EAR-0323309)supported by NSF under grants EAR-0711526 and EAR-0844097supported by Macquarie University CORES start-up grant to Y. Yang
文摘We discuss two array-based tomography methods, ambient noise tomography （ANT） and two-plane- wave earthquake tomography （TPWT）, which are capable of taking advantage of emerging large-scale broadband seismic arrays to generate high resolution phase velocity maps, but in complementary period band： ANT at 8-40 s and TPWT at 25-100 s period. Combining these two methods generates surface wave dispersion maps from 8 to 100 s periods, which can be used to construct a 3D vs model from the surface to -200 km depth. As an illustration, we apply the two methods to the USArray/Transportable Array. We process seismic noise data from over 1 500 stations obtained from 2005 through 2009 to produce Rayleigh wave phase velocity maps from 8 to 40 s period, and also perform TPWT using -450 teleseismic earthquakes to obtain phase velocity maps between 25 and 100 s period. Combining dispersion maps from ANT and TPWT, we construct a 3D vs model from the surface to a depth of 160 km in the western and central USA. These surface wave tomography methods can also be applied to other rapidly growing seismic networks such as those in China.
基金supported by GEMOC and the Department of Earth and Planetary Sciences,Macquarie University,Australia
文摘In order to distinguish the primary microstructures developed under mantle conditions from the secondary phenomena after xenolith entrainment in the host magma, this study intends to discuss the genesis of spongy, sieve-textured, and reaction rims on mineral grains of mantle xenoliths in the Cenozoic basalts from the western North China craton. The spongy rims on primary clinopyroxene show neither obvious compositional zoning nor preferential development towards the host basalt and probably suggest an origin via partial melting within the lithospheric mantle or pressure release as the xenoliths were carried upwards. The sieve-textured rims on primary spinel show clear chemical zoning with increasing Cr# and decreasing AI towards the host basalt. They are interpreted as the result of partial melting due to heating of the host basaltic magma and decreasing pressure during ascent proc- ess. Post-entrainment reaction mainly generated secondary minerals at contacts between the host ba- saltic melt and xenoliths. The secondary clinopyroxene in reaction rims develops on primary clinopy- roxene and has higher Ti, Ca, and Fe contents and lower Mg# and Si contents than primary one, while the secondary spinel on primary Cr-AI spinel is titanomagnetite. The secondary olivine and clinopy- roxene in the reaction rims on primary orthopyroxene are enriched in Fe, Al, and Ti. The occurrence of reaction rims in mantle xenoliths reflects disequilibrium processes after xenolith entrainment in the basaltic melt. The spongy rims on primary clinopyroxene may not be related to the interaction with thehost basaltic melt, while the sieve-textured rims on primary spinel and reactions rims on primary clinopyroxene, spinel, and orthopyroxene may result from post-entrainment reaction between the host basaltic melt and xenolith minerals.
基金provided by the National Key Research and Development Program of China "Deep Structure and Ore-forming Process of Main Mineralization System in Tibetan Orogen"(2016YFC0600300)the National Basic Research Program of China (2011CB403104)+1 种基金the China Geological Survey (12120113037901)the National Natural Science Foundation of China(41320104004) and(41503040)
文摘The Nianzha gold deposit, located in the central section of the Indus-Yarlung Tsangpo suture （IYS） zone in southern Tibet, is a large gold deposit （Au reserves of 25 tons with average grade of 3.08 g/t） controlled by a E-W striking fault that developed during the main stage of Indo-Asian collision （-65-41 Ma）. The main orebody is 1760 m long and 5.15 m thick, and occurs in a fracture zone bordered by Cretaceous diorite in the hanging wall to the north and the Renbu tectonic melange in the footwall to the south. High-grade mineralization occurs in a fracture zone between diorite and ultramafic rock in the Renbu tectonic melange. The wall-rock alteration is characterized by silicification in the fracture zone, serpentinization and the formation of talc and magnesite in the uitramafic unit, and chloritization and the formation of epidote and calcite in diorite. Quartz veins associated with Au mineralization can be divided into three stages. Fluid inclusion data indicate that the deposit formed from H20-NaCl-organic gas fluids that homogenize at temperatures of 203℃-347℃ and have salinities of 0.35wt%-17.17wt% NaCI equivalent. The quartz veins yield δ18Ofluid values of 0.15‰-10.45‰, low δDv-SMow values （-173%o to -96%o）, and the δ13C values of-17.6‰ to -4.7‰, indicating the ore-forming fluids were a mix of metamorphic and sedimentary orogenic fluids with the addition of some meteoric and mantle-derived fluids. The pyrite within the diorite has δ34SV-CDT values of -2.9‰-1.9‰（average -1.1‰）, 206pb/204pb values of 18.47- 18.64, 207pb/204pb values of 15.64-15.74, and 208pb/204pb values of 38.71-39.27, all of which are indicative of the derivation of S and other ore-forming elements from deep in the mantle. The presence of the Nianzha, Bangbu, and Mayum gold deposits within the IYS zone indicates that this area is highly prospective for large orogenic gold deposits. We identified three types of mineralization within the IYS, namely Bangbu-type accretionary, Mayum-type microcontinent, and Nianzha-type ophiolite-associated orogenic Au deposits. The three types formed at different depths in an aeeretionary orogenic tectonic setting. The Bangbu type was formed at the deepest level and the Nianzha type at the shallowest.
基金This paper is supported by the Research Foundation for OutstandingYoung Teachers , China University of Geosciences ( Wuhan )(CUGQNL0510)the National Natural Science Foundation of China(No .40425002) .
文摘The compositions of the whole rocks and trace elements of minerals in peridotites can reflect the characteristics of the lithospheric mantle. The nature and evolution of the Cenozoic lithospheric mantle beneath Hannuoba （汉诺坝）, located on the north edge of the intra-North China orogenic belt, are discussed based on the in-situ LAM-ICPMS detected trace element compositions of clinopyroxenes in the Hannuoba peridotitic xenoliths combined with detailed petrography and geochemistry studies. The Hannuoba lithospheric mantle was formed by different partial meltings of the primitive mantle. Most of the samples reflect the partial melting degree of lower than 5% with a few samples of 15%-20%. Major element compositions of the whole rocks and geochemical compositions of clinopyroxenes reveal the coexistence of both fertile and depleted mantle underneath the Hannuoba region during the Cenozoic. This was probably caused by the asthenospheric mantle replacing the aged craton mantle through erosion, intermingling and modification. Our conclusion is further supported by the existence of both carbonatitic magmatic material and silicate melt/ fluid metasomatism as magnified by the trace elements of the clinopyroxencs from the Hannuoba lithospherJc mantle.
基金This work is supported by the National Natural Science Foundation of China （No. 40572038）.
文摘Morphological and chemical studies on zircon grains from gabbro and granite of the Pingtan magmatic complex, Fujian Province, eastern China, show that there are three stages of zircon growth. The early stage of zircon growth is characterized by colorlessness, high transparence and birefringence, low and dispersive Ipr and Ipy, weak and homogeneous BSE brightness, lower Hf content and depletion of U, Th and Y; the middle stage is characterized by abruptly increasing lpy, progressively strong and sectoral-zoning BSE brightness, higher Hf content and enrichment of U, Th and Y with Th/U 〉 1; the late stage of growth is characterized by brownish color, poor transparence, low birefringence, highest Ipr and Ipy, middle and oscillatorily-zoning BSE brightness, highest contents of Hf, U and Y with Th/U 〈 1. The stages are considered to be formed in a deep magma chamber, ascent passage and emplacement site, respectively. Due to the more or less long residual time of the magma chamber, the difference in age between the early and late stages of zircon might be great enough to be distinguished, which can be attributed to tectonic constraint for the magnlatism.
