Five nearly E-W-trending alkali-rich igneous rock belts are distributed from north to south in northern Xinjiang, and they are composed mainly of riebeckite, K-feldspar granite and high-K and medium-K calc-alkaline vo...Five nearly E-W-trending alkali-rich igneous rock belts are distributed from north to south in northern Xinjiang, and they are composed mainly of riebeckite, K-feldspar granite and high-K and medium-K calc-alkaline volcanic rocks and shoshonite. They were mainly emplaced or erupted between the Carboniferous and Permian. The compositions of Sr, Nd, Pb, and O isotopes imply that their principal resource materials are derived from the upper mantle or juvenile crust, indicating obvious continental growth in the Phanerozoic. The trace element association implies that their tectonic settings are within plate and volcanic arc for alkali-rich granites, and post-collisional are, late oceanic are and continental are for alkali-rich volcanic rocks. An archipelago model was suggested for the tectonic evolution in northern Xinjiang. It can be named the central-Asia-type orogeny, which is different from the so called circum-Pacific ocean-continent-type tectonics or the Alpine-Himalayan continent-continent-collisional orogeny.展开更多
Western Yunnan is the well-known polymetallic province in China. It is characterized by copper-gold mineralization related to Cenozoic alkali-rich porphyry. This paper analyzes the silicon isotope data obtained from f...Western Yunnan is the well-known polymetallic province in China. It is characterized by copper-gold mineralization related to Cenozoic alkali-rich porphyry. This paper analyzes the silicon isotope data obtained from four typical alkali-rich porphyry deposits based on the dynamic fractionation principle of silicon isotope. The study shows that the ore materials should originate mainly from alkali-rich magmas, together with silicon-rich mineralizing fluids. The process of mineralization was completed by auto-metasomatism, i.e. silicon-rich mineralizing fluids (including alkali-rich porphyry and wall-rock strata) replaced and altered the country rocks and contaminated with crustal rocks during the crystallization of alkali-rich magmas. Such a process is essentially the continuance of the metasomatism of mantle fluids in crust's mineralization. This provides important evidence of silicon isotopic geochemistry for better understanding the mineralization of the Cenozoic alkali-rich porphyry polymetallic deposits展开更多
Large-scale Cenozoic magmatic rocks from the interplay between the Indian and Eurasian plate are exposed in the Yulong porphyry copper belt in the northern Jinshajiang-Ailaoshan domain.Alkali-rich magmas along the Yul...Large-scale Cenozoic magmatic rocks from the interplay between the Indian and Eurasian plate are exposed in the Yulong porphyry copper belt in the northern Jinshajiang-Ailaoshan domain.Alkali-rich magmas along the Yulong porphyry copper belt can reveal the tectono-magmatic processes in the Sanjiang region.In this study,we present new zircon U-Pb-Hf isotopes and whole rock geochemistry of Cenozoic granitoids from the Zhalaga area in the northern Yulong porphyry copper belt.The Zircon U-Pb dating results show that the Zhalaga granitic porphyry crystallized at ca.42-38 Ma.These porphyry deposits are depleted in Nb,Ta,Sr,and Ti enriched in alkaline and rare earth elements(REEs),and exhibit high zircon saturation temperatures,that strongly indicate A-type affinity.These data and the generally positiveεHf(t)values(2.0-4.5)suggest the magmas originated from a hybrid of partial melting of subduction-modified lithospheric mantle,possibly triggered by upwelling of the asthenospheric mantle.Geochronological and geochemical data of the current and previous studies distinguish three magmatic phases during the Cenozoic in the Jinshajiang-Ailaoshan region:(1)ca.62-48 Ma;(2)ca.44-30 Ma;and(3)ca.28-16 Ma.The strong collision between the Indian and Eurasian plates produced relatively fast convergence rates during the first episode(ca.62-48 Ma),whereas the subsequent right-lateral strike-slip faulting in the Jinshajiang fault zone initiated at ca.43 Ma is associated with the relatively low India-Eurasia convergence rates during ca.44-30 Ma.These significantly impacted the nature and spatial distribution of the magmatism and the large-scale metallogeny during the Cenozoic in the Sanjiang region.We suggest that the Zhalaga alkali-rich magmas occurred in a transition period from involving soft to hard collisional settings.This remarkable example demonstrates that alkali-rich magmas with A-type affinity are also generated in an orogenic tectonic setting.展开更多
Ultramafic hypoxenoliths found in the alkali-rich porphyry in the Liuhe Village, Heqing, Yunnan, China, are of great significance in understanding the origin and evolution of the porphyry. This paper discusses the min...Ultramafic hypoxenoliths found in the alkali-rich porphyry in the Liuhe Village, Heqing, Yunnan, China, are of great significance in understanding the origin and evolution of the porphyry. This paper discusses the mineralogical features of the hypoxenoliths. It shows that the xenoliths are characterized by the upper mantle rocks modified to certain extent by the enriched mantle fluid metasomatism in the mantle environment, with the enriched mantle property of low-degree partial melting. This constitutes the important mineralogical evidence for the petrogenesis and mineralization of alkali-rich porphyry.展开更多
Alkali-rich intrusive rocks in western Yunnan were derived from an enriched lithospheric mantle (EMⅡ) source. The data available indicated they are alkali-rich (K-2ONa-2O>8wt%) and shoshonitic. Although formed in ...Alkali-rich intrusive rocks in western Yunnan were derived from an enriched lithospheric mantle (EMⅡ) source. The data available indicated they are alkali-rich (K-2ONa-2O>8wt%) and shoshonitic. Although formed in a within-plate environment they exhibit signatures of arc magmatic rocks, such as high amounts of LILE and LREE relative to the HFSE and HREE, and thus high Ba/Nb, Ba/Zr, Sr/Y, La/Yb ratios as well as mimic chondrite-normalized REE and primitive mantle-normalized trace element patterns of subducted sediments, and they fall in the collision- or arc-related tectonic setting field on all discrimination diagrams. This might suggest the enrichment be related to the substantial extent of sediment contamination by the Mesozoic Tethyan subduction processes.展开更多
The age of alkali rich porphyries in the western margin of Yangtze Platform is 30—50 Ma; the minerals mainly are orthoclase, quartz, plagioclase; the chemical composition is alkali rich [(K 2O+Na 2O)>8%],high ...The age of alkali rich porphyries in the western margin of Yangtze Platform is 30—50 Ma; the minerals mainly are orthoclase, quartz, plagioclase; the chemical composition is alkali rich [(K 2O+Na 2O)>8%],high potash[(K 2O+Na 2O)=5.09%-8.30%]; the content of REE is relatively low, LREE is concentrated, without anomaly of europium; the average initial ratio of 87 Sr/ 86 Sr is 0.7073; the value of δ 34 S similar to that of the meteoritic sulfur; the ratio of Pb isotope corresponds to that of upper mantle; metallogenic types belong to Cu, Mo, Au, Ag, Pb, Zn polymetal mineralization and rare, rare earth metal mineralization.展开更多
The newly discovered three alkali\|rich intrusive rock belts in the Mt. Kunlun Mt. Altun region of southern Xinjiang are the Lapeiquan\|Yitunbulak alkali\|rich intrusive rock belt, the Gez\|Taxkorgan alkali\|rich intr...The newly discovered three alkali\|rich intrusive rock belts in the Mt. Kunlun Mt. Altun region of southern Xinjiang are the Lapeiquan\|Yitunbulak alkali\|rich intrusive rock belt, the Gez\|Taxkorgan alkali\|rich intrusive rock belt and the Beilisai\|Abulash alkali\|rich intrusive rock belt. The former two belts were formed during the Yanshanian period, and the third one was formed during the Himalayan period, which is the youngest alkali\|rich intrusive rock belt in China. The discovery of the alkali\|rich intrusive rock belts is of great significance in shedding light on the history of tectono\|magmatic activities in this region.展开更多
Minerals of spinel- and garnet-facies mantle xenoliths entrained in Cenozoicbasalts from eastern China (North China, Northeastern China and Southeastern China coastal area)contains lots of melt inclusions. Studies on ...Minerals of spinel- and garnet-facies mantle xenoliths entrained in Cenozoicbasalts from eastern China (North China, Northeastern China and Southeastern China coastal area)contains lots of melt inclusions. Studies on these melt inclusions show that the glass inclusionsare rich in SiO_2 (60%—68%) and alkalis (K_2O+Na_2O = 5%—11%, especially for K_2O) as well asvolatiles such as H_2O and CO_2 (2%—7%), which belong to dacites and andesites of the high-K calcicalkali series rocks with few shoshonites. High Al and Ca diopside in melt inclusion is the productof melt crystallization at high temperature and pressure, rather than the product ofdevitrification. Results show that these K-rich (in general K_2O 】 3%) intermediate-acidic silicatemelt inclusions have characteristics of continent without a genetical link to host basalts and theirphenocrystic minerals. Thus, these trapped melt inclusions represent melts of Mesozoic lithosphericmantle-crust interaction and imply that the continental lithospheric mantle beneath eastern Chinahad undergone fragmentation and recreation processes during the Mesozoic and Cenozoic periods. Thisresult undoubtly provides important implication for the evolution of sub-continental lithospherebeneath eastern China. We propose that these Si- and alkalis-rich melts should be responsible forthe mantle chemical heterogeneity underneath eastern China.展开更多
The alkali-rich igneous rocks in China occur as fifteen linear distributed belts of each extending several hundreds to several thousands kilometers in length. These include most types of alkali-rich igneous rock categ...The alkali-rich igneous rocks in China occur as fifteen linear distributed belts of each extending several hundreds to several thousands kilometers in length. These include most types of alkali-rich igneous rock categories discovered worldwide. The related Au, Cu large and superlarge deposits or metallogenic focus-areas include Dongping, Guilaizhuang, Yulong, ete. Direct and in-direct genetic links have been found between alkali-rich igneous rocks and Au, Cu mineralization. The petrogenesis and metallogenesis of the alkali-rich igneous rocks are mainly controlled by (1) mantle enrichment, (2) strong interaction between mantle and crust, (3) lower contens of s黮f黵, high for and high contents of volatiles, (4) the significant turn of regional tectonic framework from compress to extension and (5) the strong change of regional lithosphere structure.展开更多
SANJING region (the region of three rivers, i.e. Jinsha-Lanchang-Nujiang rivers) is a very active Cenozoicinterplate deformation area on the east margin of Qinghai-Xizang Plateau, where the alkali-rich porphyrybodies ...SANJING region (the region of three rivers, i.e. Jinsha-Lanchang-Nujiang rivers) is a very active Cenozoicinterplate deformation area on the east margin of Qinghai-Xizang Plateau, where the alkali-rich porphyrybodies occur extensively and the porphyry-related polymetallic mineral resources are produced. Manystudies on the petrology and geochemistry of the alkali-rich porphyry have been carried out and thegenerally accepted conclusion is that the petrogenesis material source has something to do with the enriched source in the mantle. The integrated interactive factors of the mineralization related to the alkalirich porphyry consist in the favourable combination of the mantle fluid metasomatism, which is derivedfrom the deep processes, and the conducting and controlling roles of the large-scale deep faults. Alongwith the changes in physical and chemical conditions caused by the diffusion of the ore-forming展开更多
Based on studies on more than 40 alkali-rich intrusions in China, rocks of this family are divided into three groups (alkali granite, syenite and nepheline syenite) and their petrological and petrochemical characters ...Based on studies on more than 40 alkali-rich intrusions in China, rocks of this family are divided into three groups (alkali granite, syenite and nepheline syenite) and their petrological and petrochemical characters are discussed. These alkali-rich rocks can be assigned to 6 rock assemblages characterized by different petrogenesis. Alkali-rich rocks are distributed in linear pattern controlled by deep fault. Genetically, they are characterized by a deep source and emplacement at small depth. Their petrochemistry depends to a great extent on the degree of contamination by the lower crust. The alkali granite is the most, and the miaskite nepheline syenite the least, contaminated.展开更多
Alkali-rich dykes of the Late Permian in Ulungur （乌伦古） area are representative prod- ucts of granitic magmatism in the evolution of the Paleozoic orogenic belt in the East Junggar （准噶尔）, North Xinjiang （新...Alkali-rich dykes of the Late Permian in Ulungur （乌伦古） area are representative prod- ucts of granitic magmatism in the evolution of the Paleozoic orogenic belt in the East Junggar （准噶尔）, North Xinjiang （新疆）. We selected two representative samples for geochemical analysis （major and trace elements）, and twenty-two zircon grains for zircon dating. Isoplot （ver3.0） was used to calculate isotopic age and make concordia diagrams. This study shows that the trachy porphyry dykes, featuring low concentration of A1203, CaO, MgO and high alkali contents, are metaluminous alkaline rock and belong to A-type granitoids. The dykes have low concentration of the REE and incompatible elements, and the REE patterns show clear negative Eu anomalies （6Eu=0.74-0.58）, enriched LREE （LREE/HREE〉4, （La/Yb）N=5.97-4.63） and undifferentiated HREEs. Similar normalized REE and in- compatible element patterns are also showed in the dykes from Yemaquan （野马泉） and granites from Ulungur, suggesting that they are possibly originated from the same source and formed in the same tectonic environment, but the trachy porphyry dykes are more evolved. The age of the trachy porphyry dykes is 255.3 - 2.4 Ma, which is probably the crystallization time of the trachy porphyry. The dykes formed in late-orogenic phase of post-collision process or within-plate environment, which suggested that the trachy porphyry dykes possibly crystallized in the transition period during which the tectonic setting changed from post-collision to with- in-plate environment. So we consider that the age when the post-collision ended and the crustal cratonization begun in the East Junggar is 255 Ma, Late Permian.展开更多
The alkali-rich intrusive rocks in the Qinghai-Xizang Plateau can be divided into two series in terms of dark-colored rock-forming minerals, petrochemical composition and trace elements: i ) sodic alkaline series rock...The alkali-rich intrusive rocks in the Qinghai-Xizang Plateau can be divided into two series in terms of dark-colored rock-forming minerals, petrochemical composition and trace elements: i ) sodic alkaline series rocks consisting of alkaline rocks and alkali granite which contain dark-colored minerals, such as aegirine augite, aegirine and riebeckite, and being petrochemically enriched in alkali and sodium but low in Ca, Sr and Ba; ii ) potassic alkaline series rocks consisting of alkaline rocks and alkali granite which contain non-alkaline dark-colored minerals (diopside, edenite), and being petrochemically enriched in alkali, K and Ca with high abundances of Sr and Ba.展开更多
A suite of alkali-rich porphyry with 26. 5–37. 6Ma occur along the Jinsha River suture zone in west Yunnan. They are characterized by LREE-rich distribution patterns and no Eu anomaly. These porphyries have formed in...A suite of alkali-rich porphyry with 26. 5–37. 6Ma occur along the Jinsha River suture zone in west Yunnan. They are characterized by LREE-rich distribution patterns and no Eu anomaly. These porphyries have formed in post-collisional environment; (87Sr/8bSr) of porphyries, amphibolite xenolithes and associated basalts are 0.707 3, 0.706 5-0.707 l and0.705 8-0.706 5, ENd(T) are -3.4-6.3, -2.1-7.4 and -3.3 respectively. Pb isotope compositions of these rocks also show a little difference. The evidence shows that the porphyry could be derived from partial melting of the “crust-mantle mixed layer”. The relation between Cenozoic magmatism and intraplate deformation since Paleogene has been discussed.展开更多
基金Thanks are due to the financial support from the National 305 Project of Xinjiang(859020601,859020607,959160302)the National ClimbingProgram of China(A-30,95-Y-25).
文摘Five nearly E-W-trending alkali-rich igneous rock belts are distributed from north to south in northern Xinjiang, and they are composed mainly of riebeckite, K-feldspar granite and high-K and medium-K calc-alkaline volcanic rocks and shoshonite. They were mainly emplaced or erupted between the Carboniferous and Permian. The compositions of Sr, Nd, Pb, and O isotopes imply that their principal resource materials are derived from the upper mantle or juvenile crust, indicating obvious continental growth in the Phanerozoic. The trace element association implies that their tectonic settings are within plate and volcanic arc for alkali-rich granites, and post-collisional are, late oceanic are and continental are for alkali-rich volcanic rocks. An archipelago model was suggested for the tectonic evolution in northern Xinjiang. It can be named the central-Asia-type orogeny, which is different from the so called circum-Pacific ocean-continent-type tectonics or the Alpine-Himalayan continent-continent-collisional orogeny.
文摘Western Yunnan is the well-known polymetallic province in China. It is characterized by copper-gold mineralization related to Cenozoic alkali-rich porphyry. This paper analyzes the silicon isotope data obtained from four typical alkali-rich porphyry deposits based on the dynamic fractionation principle of silicon isotope. The study shows that the ore materials should originate mainly from alkali-rich magmas, together with silicon-rich mineralizing fluids. The process of mineralization was completed by auto-metasomatism, i.e. silicon-rich mineralizing fluids (including alkali-rich porphyry and wall-rock strata) replaced and altered the country rocks and contaminated with crustal rocks during the crystallization of alkali-rich magmas. Such a process is essentially the continuance of the metasomatism of mantle fluids in crust's mineralization. This provides important evidence of silicon isotopic geochemistry for better understanding the mineralization of the Cenozoic alkali-rich porphyry polymetallic deposits
基金supported by the National Natural Science Foundation of China(No.41776056)Natural Science Foundation of Guangdong Province(Nos.2017A030310395,2018B030311030)China Postdoctoral Science Foundation(grant No.2020M672671)。
文摘Large-scale Cenozoic magmatic rocks from the interplay between the Indian and Eurasian plate are exposed in the Yulong porphyry copper belt in the northern Jinshajiang-Ailaoshan domain.Alkali-rich magmas along the Yulong porphyry copper belt can reveal the tectono-magmatic processes in the Sanjiang region.In this study,we present new zircon U-Pb-Hf isotopes and whole rock geochemistry of Cenozoic granitoids from the Zhalaga area in the northern Yulong porphyry copper belt.The Zircon U-Pb dating results show that the Zhalaga granitic porphyry crystallized at ca.42-38 Ma.These porphyry deposits are depleted in Nb,Ta,Sr,and Ti enriched in alkaline and rare earth elements(REEs),and exhibit high zircon saturation temperatures,that strongly indicate A-type affinity.These data and the generally positiveεHf(t)values(2.0-4.5)suggest the magmas originated from a hybrid of partial melting of subduction-modified lithospheric mantle,possibly triggered by upwelling of the asthenospheric mantle.Geochronological and geochemical data of the current and previous studies distinguish three magmatic phases during the Cenozoic in the Jinshajiang-Ailaoshan region:(1)ca.62-48 Ma;(2)ca.44-30 Ma;and(3)ca.28-16 Ma.The strong collision between the Indian and Eurasian plates produced relatively fast convergence rates during the first episode(ca.62-48 Ma),whereas the subsequent right-lateral strike-slip faulting in the Jinshajiang fault zone initiated at ca.43 Ma is associated with the relatively low India-Eurasia convergence rates during ca.44-30 Ma.These significantly impacted the nature and spatial distribution of the magmatism and the large-scale metallogeny during the Cenozoic in the Sanjiang region.We suggest that the Zhalaga alkali-rich magmas occurred in a transition period from involving soft to hard collisional settings.This remarkable example demonstrates that alkali-rich magmas with A-type affinity are also generated in an orogenic tectonic setting.
文摘Ultramafic hypoxenoliths found in the alkali-rich porphyry in the Liuhe Village, Heqing, Yunnan, China, are of great significance in understanding the origin and evolution of the porphyry. This paper discusses the mineralogical features of the hypoxenoliths. It shows that the xenoliths are characterized by the upper mantle rocks modified to certain extent by the enriched mantle fluid metasomatism in the mantle environment, with the enriched mantle property of low-degree partial melting. This constitutes the important mineralogical evidence for the petrogenesis and mineralization of alkali-rich porphyry.
文摘Alkali-rich intrusive rocks in western Yunnan were derived from an enriched lithospheric mantle (EMⅡ) source. The data available indicated they are alkali-rich (K-2ONa-2O>8wt%) and shoshonitic. Although formed in a within-plate environment they exhibit signatures of arc magmatic rocks, such as high amounts of LILE and LREE relative to the HFSE and HREE, and thus high Ba/Nb, Ba/Zr, Sr/Y, La/Yb ratios as well as mimic chondrite-normalized REE and primitive mantle-normalized trace element patterns of subducted sediments, and they fall in the collision- or arc-related tectonic setting field on all discrimination diagrams. This might suggest the enrichment be related to the substantial extent of sediment contamination by the Mesozoic Tethyan subduction processes.
文摘The age of alkali rich porphyries in the western margin of Yangtze Platform is 30—50 Ma; the minerals mainly are orthoclase, quartz, plagioclase; the chemical composition is alkali rich [(K 2O+Na 2O)>8%],high potash[(K 2O+Na 2O)=5.09%-8.30%]; the content of REE is relatively low, LREE is concentrated, without anomaly of europium; the average initial ratio of 87 Sr/ 86 Sr is 0.7073; the value of δ 34 S similar to that of the meteoritic sulfur; the ratio of Pb isotope corresponds to that of upper mantle; metallogenic types belong to Cu, Mo, Au, Ag, Pb, Zn polymetal mineralization and rare, rare earth metal mineralization.
文摘The newly discovered three alkali\|rich intrusive rock belts in the Mt. Kunlun Mt. Altun region of southern Xinjiang are the Lapeiquan\|Yitunbulak alkali\|rich intrusive rock belt, the Gez\|Taxkorgan alkali\|rich intrusive rock belt and the Beilisai\|Abulash alkali\|rich intrusive rock belt. The former two belts were formed during the Yanshanian period, and the third one was formed during the Himalayan period, which is the youngest alkali\|rich intrusive rock belt in China. The discovery of the alkali\|rich intrusive rock belts is of great significance in shedding light on the history of tectono\|magmatic activities in this region.
基金supported by the National Natural Science Foundation of China(Grant No.40372044).
文摘Minerals of spinel- and garnet-facies mantle xenoliths entrained in Cenozoicbasalts from eastern China (North China, Northeastern China and Southeastern China coastal area)contains lots of melt inclusions. Studies on these melt inclusions show that the glass inclusionsare rich in SiO_2 (60%—68%) and alkalis (K_2O+Na_2O = 5%—11%, especially for K_2O) as well asvolatiles such as H_2O and CO_2 (2%—7%), which belong to dacites and andesites of the high-K calcicalkali series rocks with few shoshonites. High Al and Ca diopside in melt inclusion is the productof melt crystallization at high temperature and pressure, rather than the product ofdevitrification. Results show that these K-rich (in general K_2O 】 3%) intermediate-acidic silicatemelt inclusions have characteristics of continent without a genetical link to host basalts and theirphenocrystic minerals. Thus, these trapped melt inclusions represent melts of Mesozoic lithosphericmantle-crust interaction and imply that the continental lithospheric mantle beneath eastern Chinahad undergone fragmentation and recreation processes during the Mesozoic and Cenozoic periods. Thisresult undoubtly provides important implication for the evolution of sub-continental lithospherebeneath eastern China. We propose that these Si- and alkalis-rich melts should be responsible forthe mantle chemical heterogeneity underneath eastern China.
文摘The alkali-rich igneous rocks in China occur as fifteen linear distributed belts of each extending several hundreds to several thousands kilometers in length. These include most types of alkali-rich igneous rock categories discovered worldwide. The related Au, Cu large and superlarge deposits or metallogenic focus-areas include Dongping, Guilaizhuang, Yulong, ete. Direct and in-direct genetic links have been found between alkali-rich igneous rocks and Au, Cu mineralization. The petrogenesis and metallogenesis of the alkali-rich igneous rocks are mainly controlled by (1) mantle enrichment, (2) strong interaction between mantle and crust, (3) lower contens of s黮f黵, high for and high contents of volatiles, (4) the significant turn of regional tectonic framework from compress to extension and (5) the strong change of regional lithosphere structure.
文摘SANJING region (the region of three rivers, i.e. Jinsha-Lanchang-Nujiang rivers) is a very active Cenozoicinterplate deformation area on the east margin of Qinghai-Xizang Plateau, where the alkali-rich porphyrybodies occur extensively and the porphyry-related polymetallic mineral resources are produced. Manystudies on the petrology and geochemistry of the alkali-rich porphyry have been carried out and thegenerally accepted conclusion is that the petrogenesis material source has something to do with the enriched source in the mantle. The integrated interactive factors of the mineralization related to the alkalirich porphyry consist in the favourable combination of the mantle fluid metasomatism, which is derivedfrom the deep processes, and the conducting and controlling roles of the large-scale deep faults. Alongwith the changes in physical and chemical conditions caused by the diffusion of the ore-forming
基金Project supported by the Foundation of the Director of Chinese Academy of Sciences.
文摘Based on studies on more than 40 alkali-rich intrusions in China, rocks of this family are divided into three groups (alkali granite, syenite and nepheline syenite) and their petrological and petrochemical characters are discussed. These alkali-rich rocks can be assigned to 6 rock assemblages characterized by different petrogenesis. Alkali-rich rocks are distributed in linear pattern controlled by deep fault. Genetically, they are characterized by a deep source and emplacement at small depth. Their petrochemistry depends to a great extent on the degree of contamination by the lower crust. The alkali granite is the most, and the miaskite nepheline syenite the least, contaminated.
基金supported by the Major State Basic Research Program of China (No. 2007CB411304)the Crisis Mine Project of China National Geological Survey (No. 200699105)
文摘Alkali-rich dykes of the Late Permian in Ulungur （乌伦古） area are representative prod- ucts of granitic magmatism in the evolution of the Paleozoic orogenic belt in the East Junggar （准噶尔）, North Xinjiang （新疆）. We selected two representative samples for geochemical analysis （major and trace elements）, and twenty-two zircon grains for zircon dating. Isoplot （ver3.0） was used to calculate isotopic age and make concordia diagrams. This study shows that the trachy porphyry dykes, featuring low concentration of A1203, CaO, MgO and high alkali contents, are metaluminous alkaline rock and belong to A-type granitoids. The dykes have low concentration of the REE and incompatible elements, and the REE patterns show clear negative Eu anomalies （6Eu=0.74-0.58）, enriched LREE （LREE/HREE〉4, （La/Yb）N=5.97-4.63） and undifferentiated HREEs. Similar normalized REE and in- compatible element patterns are also showed in the dykes from Yemaquan （野马泉） and granites from Ulungur, suggesting that they are possibly originated from the same source and formed in the same tectonic environment, but the trachy porphyry dykes are more evolved. The age of the trachy porphyry dykes is 255.3 - 2.4 Ma, which is probably the crystallization time of the trachy porphyry. The dykes formed in late-orogenic phase of post-collision process or within-plate environment, which suggested that the trachy porphyry dykes possibly crystallized in the transition period during which the tectonic setting changed from post-collision to with- in-plate environment. So we consider that the age when the post-collision ended and the crustal cratonization begun in the East Junggar is 255 Ma, Late Permian.
文摘The alkali-rich intrusive rocks in the Qinghai-Xizang Plateau can be divided into two series in terms of dark-colored rock-forming minerals, petrochemical composition and trace elements: i ) sodic alkaline series rocks consisting of alkaline rocks and alkali granite which contain dark-colored minerals, such as aegirine augite, aegirine and riebeckite, and being petrochemically enriched in alkali and sodium but low in Ca, Sr and Ba; ii ) potassic alkaline series rocks consisting of alkaline rocks and alkali granite which contain non-alkaline dark-colored minerals (diopside, edenite), and being petrochemically enriched in alkali, K and Ca with high abundances of Sr and Ba.
文摘A suite of alkali-rich porphyry with 26. 5–37. 6Ma occur along the Jinsha River suture zone in west Yunnan. They are characterized by LREE-rich distribution patterns and no Eu anomaly. These porphyries have formed in post-collisional environment; (87Sr/8bSr) of porphyries, amphibolite xenolithes and associated basalts are 0.707 3, 0.706 5-0.707 l and0.705 8-0.706 5, ENd(T) are -3.4-6.3, -2.1-7.4 and -3.3 respectively. Pb isotope compositions of these rocks also show a little difference. The evidence shows that the porphyry could be derived from partial melting of the “crust-mantle mixed layer”. The relation between Cenozoic magmatism and intraplate deformation since Paleogene has been discussed.
