The mafic enclaves from Paleoproterozoic domain are considered to be the results of large-scale crust-mantle interaction and magma mixing. In this paper, petrography, mineralogy and geochemistry were jointly used to d...The mafic enclaves from Paleoproterozoic domain are considered to be the results of large-scale crust-mantle interaction and magma mixing. In this paper, petrography, mineralogy and geochemistry were jointly used to determine the origin of the mafic enclaves and their relationship with the host granitoids of the Kan granite-gneiss complex. This study also provides new information on crust-mantle interactions. The mafic enclaves of the Kan vary in shape and size and have intermediate chemical compositions. The diagrams used show a number of similarities in the major elements (and often in the trace elements) between the mafic enclaves and the host granitoids. Geochemical show that the Kan rock are metaluminous, enriched in silica, medium to high-K calc-alkaline I-type granite. The similarities reflect a mixing of basic and acid magma. Mafic enclaves have a typical magmatic structure, which is characterized by magma mixing. The genesis of these rocks is associated with the context of subduction. They result from the mixing of a mafic magma originating from the mantle and linked to subduction, and a granitic magma (type I granite) that arises from the partial melting of the crust.展开更多
Many igneous rocks distribute in Gejiu tin polymetallic ore-field at Yunnan province, rocks including basalt, gabbro, mafic microgranular enclaves, granites （porphyritic granite and equigranular granite） and akaline...Many igneous rocks distribute in Gejiu tin polymetallic ore-field at Yunnan province, rocks including basalt, gabbro, mafic microgranular enclaves, granites （porphyritic granite and equigranular granite） and akaline rocks. The ages of the granites and akaline rocks which are considered to have genetic connecting with the mineralization have been comfirmed, but the gabbro- mafic microgranular enclaves-granite assemblage＇s ages are still unknown. By means of LA-ICP-MS zircon U-Pb dating, the data of Shenxianshui equigranular granite, the mafic microgranular enclave in Jiasha area, the host rock of the mafic microgranular enclaves and the Jiasha gabbro are around ~80 Ma. Besides the above mentioned data, a group of new ages at ~30 Ma were discovered in this study, which is from gabbro and mafic microgranular enclaves. Based on the previous data and the new data gained this time, we suggest the major geochronology framework of the magmatism and mineralization events in Gejiu area is ~80 Ma, which is consistent with the Late Cretaceous magmatism and mineralization events in the whole southeast Yunnan and west Guangxi area and they were suggested to belong to the same geotectonic setting in late Yenshannian. And the new ages of the ~30 Ma obtained in this study is considered to represent a responding to the complicate tectonic evolution history of the Tibetan orogenic events in Cenozoic.展开更多
The petrology, geochronology and geochemistry of the mafic enclaves in the Mid-Late Triassic Jiefangyingzi pluton from Chifeng area, southern Inner Mongolia, in China are studied to reveal their petrogenetic relations...The petrology, geochronology and geochemistry of the mafic enclaves in the Mid-Late Triassic Jiefangyingzi pluton from Chifeng area, southern Inner Mongolia, in China are studied to reveal their petrogenetic relationship with the host pluton. Furthermore, the coeval magmatic assemblage and its petrogenesis on the northern margin of the North China craton(NCC) are studied synthetically to elucidate their tectonic setting and the implications for the destruction of the NCC. Zircon U-Pb dating reveals that the mafic enclaves formed at 230.4 ± 2.2 Ma, which is similar to the age of the host pluton. The most basic mafic enclaves belong to weak alkaline rocks, and they display rare earth element(REE) and trace element normalized patterns and trace element compositions similar to those of ocean island basalt(OIB). In addition, they have positive εNd(t) values(+3.84 to +4.94) similar to those of the Cenozoic basalts on the northern margin of the NCC. All of these geochemical characteristics suggest that the basic mafic rocks originated from the asthenosphere. Petrological and geochemical studies suggest that the Jiefangyingzi pluton and the intermediate mafic enclaves were formed by the mixing of the asthenosphere-derived and crust-derived magmas in different degrees. The Mid-Late Triassic magmatic rocks on the northern margin of the NCC could be classified into three assemblages according to their geochemical compositions: alkaline series, weak alkaline–sub-alkaline series and sub-alkaline series rocks. Petrogenetic analyses suggest that the upwelling of the asthenosphere played an important role in the formation of these Mid-Late Triassic magmatic rocks. Basing on an analysis of regional geological data, we suggest that the northern margin of the NCC underwent destruction due to the upwelling of the asthenosphere during the Mid-Late Triassic, which was induced by the delamination of the root of the collisional orogeny between Sino-Korean and Siberian paleoplates in Late Permian.展开更多
Plagioclase phenocrysts from mafic enclaves and plagioclase from its host granite possess a pat-tem of complex zonation. A plagioclase phenocryst can generally be divided into three parts : an oscillatory, locally pat...Plagioclase phenocrysts from mafic enclaves and plagioclase from its host granite possess a pat-tem of complex zonation. A plagioclase phenocryst can generally be divided into three parts : an oscillatory, locally patchy zoned core (An47-19), a ring with dusty, more calcic plagioclase (An64-20) and a normally zoned rim composed of sodic plagioclase (An22-3. 3). Majordiscontinuities in zoning coincide with resorption suffeces that are overgrown by the more calcic plagioclase. The cores of large plagioclase phenocrysts from mafic enclaves and host granite show similar zoning patterns and similar compositions, indicating their crystallization under the same conditions . Steep normal zoning of the rims of plagioclases both from host granite and mafic enclaves illustrates a drastic decrease in An content which is considered to have resulted from the continuous differentiation of hybrid magma and efficient heat loss because of the upward emplacement of the residual magma. Wide rims of plagioclases from the host granite against thc discrete rims of plagioclases from mafic enclaves indicate that differentiation and cooling lasted much longer in the host granite than in the mafic enclaves.展开更多
The Late Cretaceous Uckapth Granitoid including mafic microgranular enclaves intruded into metapelitic and metabasic rocks, and overlain unconformably by Neogene ignimbrites in the Ni^de area of Turkey. It is mostly g...The Late Cretaceous Uckapth Granitoid including mafic microgranular enclaves intruded into metapelitic and metabasic rocks, and overlain unconformably by Neogene ignimbrites in the Ni^de area of Turkey. It is mostly granite and minor granodiorite in composition, whereas its enclaves are dominantly gabbro with a few diorites in composition. The Uckapdl Granitoid is composed mainly of quartz, K-feldspar, plagioclase, biotite, muscovite and minor amphibole while its enclaves contain mostly plagioclase, amphibole, minor pyroxene and biotite. The Uckapth Granitoid has calcalkaline and peraluminous （AJCNK= 1.0-1.3） geochemical characteristics. It is characterized by high LILE/HFSE and LREE/HREE ratios （（La/Lu）N 3-33）, and has negative Ba, Ta, Nb and Eu anomalies, resembling those of comsion granitoids. The {）fkaplh Granitoid has relatively high STSr/S6Sr0） ratios （0.711189--0.716061） and low eNd（t） values （-5.13 to -7.13）, confirming crustal melting. In contrast, the enclaves are tholeiitic and metaluminous, and slightly enriched in LILEs （K, Rb） and Th, and have negative Ta, Nb and Ti anomalies; propose that they were derived from a subduction-modified mantle source. Based on mineral and whole rock chemistry data, the Uckapth granitoid is H-（hybrid） type, post-collision granitoid developed by mixing/mingllng processes between crustal melts and mantle-derived mafic magmas.展开更多
The Wulong pluton was emplaced in the metamorphic complex of the Mesoproterozoic Foping Group, South Qinling. A few mafic enclaves which are rounded in shape with sharp boundaries with the host granites in the souther...The Wulong pluton was emplaced in the metamorphic complex of the Mesoproterozoic Foping Group, South Qinling. A few mafic enclaves which are rounded in shape with sharp boundaries with the host granites in the southern part of the pluton. Based on petrography, geochemistry and chronology data, it is indicated that the Wulong pluton shows some adakitic affinities with depletion in HREE (Yb=0.33–0.96 μg/g, Y=4.77–11.2 μg/g); enrichment in Sr (643–1115 μg/g) and Ba (775–1386 μg/g), high Sr/Y ratios (57.3–160) and Y/Yb ratios (11.0–14.3), and slightly negative Eu anomaly (δEu=0.70–0.83). These patterns suggest a feldspar-poor and garnet±amohibole-rich fractionation mineral assemblage. The mafic enclaves have high concentrations of Mg (MgO=4.15%–8.13%), Cr (14.8–371 μg/g), and Ni (20.0–224 μg/g), and high Nb/Ta ratios (15.42–21.9). It seems that the underplating mantle magma was responsible for the generation of the mafic magma. Companied with the results of investigations for the Qinling Orogenic Belt, it was found that partial melting of the thickened lower crust, which was triggered by the underplated mantle-derived magmas, had generated the felsic magma. The Wulong pluton provided evidence for a mixing and mingling process of two kinds of mamma. Its formation probably represents the oceanic slab breakoff during the late orogenic stage in the Qinling area.展开更多
In this contribution,detailed field descriptions together with petrographic and bulk-rock major,trace and rare earth elements(REE)data are used to constrain the origin and geodynamic setting of the mafic magmatic encl...In this contribution,detailed field descriptions together with petrographic and bulk-rock major,trace and rare earth elements(REE)data are used to constrain the origin and geodynamic setting of the mafic magmatic enclaves(MMEs)recently discovered within the Pan-African Ngaoundal pluton,Adamawa area,central Cameroon.The investigated MMEs are dark-colored with chilled margins,and display medium to coarse-grain igneous textures.The mineral assemblage is either dominated by K-feldspar and carbonate(group Ⅰ),or by amphibole and plagioclase(group Ⅱ),though the overall mineral phases made of amphibole,plagioclase,K-feldspar,and biotite are similar to that of their host syenite but in different proportions.The MMEs in Ngaoundal area are foid-gabbro in composition with SiO_(2) contents ranging between 41.52% and 43.74% and are contiguous with their host granitoids of intermediate composition(SiO_(2)=57.52% to 58.98%).The host granitoid rocks are metaluminous,and belong to the shoshonitic series.Petrographic and geochemical data have revealed that the Ngaoundal MMEs derived from rapid cooling of hot injected lithospheric mantle-derived magma within cooler host granitoids magma and were emplaced in the intraplate geodynamic setting.展开更多
Recent eruption of Unzen Volcano in 1991-1995 caught attention of scientists all over the world because of disastrous character of previous one in 1792. Intrusion of andesitic magma to the chamber with rhyolitic magma...Recent eruption of Unzen Volcano in 1991-1995 caught attention of scientists all over the world because of disastrous character of previous one in 1792. Intrusion of andesitic magma to the chamber with rhyolitic magma is proposed to be a trigger for these eruptions. T-P-X parameters of two end-member magmas have been estimated several times, but usually estimations are based on phenocrysts assemblages. New results of this research are based on mafic enclaves and groundmass. These results are significant for magma mixing and mingling theory.展开更多
We report the zircon Hf-O isotopic data for mafic enclaves from the Taihang Yanshanian intermediate to felsic plutons, and use them, along with the petrological, whole-rock chemical and Nd-Sr isotopic data, to reveal ...We report the zircon Hf-O isotopic data for mafic enclaves from the Taihang Yanshanian intermediate to felsic plutons, and use them, along with the petrological, whole-rock chemical and Nd-Sr isotopic data, to reveal the petrogenesis of mafic enclaves. Mafic enclaves show magmatic textures and are finer-grained than host rocks. In places they are highly elongated due to stretching within the partially crystallized, convective felsic magma, but show no solid-state deformation. These data suggest that mafic enclaves and host rocks were co-existing, but compositionally distinct magmas. The mafic enclaves contain abundant hydrous minerals such as hornblende and biotite, with pyroxene relict being surrounded by hornblende reaction rim. Plagioclase xenocrysts from mafic enclaves show a complicated compositional and textural disequilibrium. Comparison between mafic enclaves and the immediate host rocks suggests that the two rock units are compositionally correlated. The εNd values of mafic enclaves are generally higher than the host rocks, though the Sr isotopic ratios of the two rock units are indistinguishable. Zircons from a single enclave sample show a significant variation in Hf isotopic compositions, with εHf = -10―-22, suggesting an origin through magma mixing between mafic and felsic magmas. This is supported by the relatively large variation of zircon O isotopic ratios (δ 18O = 5.5‰- 7.8‰) of the mafic enclaves. The petrogenesis of mafic enclaves could be described as below. Evolved basaltic magma (via fractionation of olivine and pyroxene) first mixed with crustally derived granitic melts in depths, forming a hybrid magma; then the hybrid magma broke up into discrete lumps upon entering the above felsic magma. Subsequently, the enclave-forming magma experienced a double mechanical transfer of plagioclase, and inward chemical transfer of fluid and Na, P, Y, Nb and Pb at the contacts with host felsic magmas.展开更多
文摘The mafic enclaves from Paleoproterozoic domain are considered to be the results of large-scale crust-mantle interaction and magma mixing. In this paper, petrography, mineralogy and geochemistry were jointly used to determine the origin of the mafic enclaves and their relationship with the host granitoids of the Kan granite-gneiss complex. This study also provides new information on crust-mantle interactions. The mafic enclaves of the Kan vary in shape and size and have intermediate chemical compositions. The diagrams used show a number of similarities in the major elements (and often in the trace elements) between the mafic enclaves and the host granitoids. Geochemical show that the Kan rock are metaluminous, enriched in silica, medium to high-K calc-alkaline I-type granite. The similarities reflect a mixing of basic and acid magma. Mafic enclaves have a typical magmatic structure, which is characterized by magma mixing. The genesis of these rocks is associated with the context of subduction. They result from the mixing of a mafic magma originating from the mantle and linked to subduction, and a granitic magma (type I granite) that arises from the partial melting of the crust.
基金supported by the National Science Foundation of China(40930419)Special Research Funding for the Public Benefits Sponsored by MLR (200911007–12)+2 种基金Research Program of Yunnan Tin Group (2010–04A)Geological Investigation Program by CGS (1212011120994)the Fundamental Research Funds for the Central Universities(2–9–2010–21)
文摘Many igneous rocks distribute in Gejiu tin polymetallic ore-field at Yunnan province, rocks including basalt, gabbro, mafic microgranular enclaves, granites （porphyritic granite and equigranular granite） and akaline rocks. The ages of the granites and akaline rocks which are considered to have genetic connecting with the mineralization have been comfirmed, but the gabbro- mafic microgranular enclaves-granite assemblage＇s ages are still unknown. By means of LA-ICP-MS zircon U-Pb dating, the data of Shenxianshui equigranular granite, the mafic microgranular enclave in Jiasha area, the host rock of the mafic microgranular enclaves and the Jiasha gabbro are around ~80 Ma. Besides the above mentioned data, a group of new ages at ~30 Ma were discovered in this study, which is from gabbro and mafic microgranular enclaves. Based on the previous data and the new data gained this time, we suggest the major geochronology framework of the magmatism and mineralization events in Gejiu area is ~80 Ma, which is consistent with the Late Cretaceous magmatism and mineralization events in the whole southeast Yunnan and west Guangxi area and they were suggested to belong to the same geotectonic setting in late Yenshannian. And the new ages of the ~30 Ma obtained in this study is considered to represent a responding to the complicate tectonic evolution history of the Tibetan orogenic events in Cenozoic.
基金funded by the National Key Research and Development Program of China from the Ministry of Science and Technology of China(Grant No.2017YFC0601301)National Natural Science Foundation of China(Grant No.41472055)the China Geological Survey(Grant No.DD20160201-01)。
文摘The petrology, geochronology and geochemistry of the mafic enclaves in the Mid-Late Triassic Jiefangyingzi pluton from Chifeng area, southern Inner Mongolia, in China are studied to reveal their petrogenetic relationship with the host pluton. Furthermore, the coeval magmatic assemblage and its petrogenesis on the northern margin of the North China craton(NCC) are studied synthetically to elucidate their tectonic setting and the implications for the destruction of the NCC. Zircon U-Pb dating reveals that the mafic enclaves formed at 230.4 ± 2.2 Ma, which is similar to the age of the host pluton. The most basic mafic enclaves belong to weak alkaline rocks, and they display rare earth element(REE) and trace element normalized patterns and trace element compositions similar to those of ocean island basalt(OIB). In addition, they have positive εNd(t) values(+3.84 to +4.94) similar to those of the Cenozoic basalts on the northern margin of the NCC. All of these geochemical characteristics suggest that the basic mafic rocks originated from the asthenosphere. Petrological and geochemical studies suggest that the Jiefangyingzi pluton and the intermediate mafic enclaves were formed by the mixing of the asthenosphere-derived and crust-derived magmas in different degrees. The Mid-Late Triassic magmatic rocks on the northern margin of the NCC could be classified into three assemblages according to their geochemical compositions: alkaline series, weak alkaline–sub-alkaline series and sub-alkaline series rocks. Petrogenetic analyses suggest that the upwelling of the asthenosphere played an important role in the formation of these Mid-Late Triassic magmatic rocks. Basing on an analysis of regional geological data, we suggest that the northern margin of the NCC underwent destruction due to the upwelling of the asthenosphere during the Mid-Late Triassic, which was induced by the delamination of the root of the collisional orogeny between Sino-Korean and Siberian paleoplates in Late Permian.
文摘Plagioclase phenocrysts from mafic enclaves and plagioclase from its host granite possess a pat-tem of complex zonation. A plagioclase phenocryst can generally be divided into three parts : an oscillatory, locally patchy zoned core (An47-19), a ring with dusty, more calcic plagioclase (An64-20) and a normally zoned rim composed of sodic plagioclase (An22-3. 3). Majordiscontinuities in zoning coincide with resorption suffeces that are overgrown by the more calcic plagioclase. The cores of large plagioclase phenocrysts from mafic enclaves and host granite show similar zoning patterns and similar compositions, indicating their crystallization under the same conditions . Steep normal zoning of the rims of plagioclases both from host granite and mafic enclaves illustrates a drastic decrease in An content which is considered to have resulted from the continuous differentiation of hybrid magma and efficient heat loss because of the upward emplacement of the residual magma. Wide rims of plagioclases from the host granite against thc discrete rims of plagioclases from mafic enclaves indicate that differentiation and cooling lasted much longer in the host granite than in the mafic enclaves.
基金financially supported by the Seluk University Scientific Research Projects Coordination (Project No: 2004/37)
文摘The Late Cretaceous Uckapth Granitoid including mafic microgranular enclaves intruded into metapelitic and metabasic rocks, and overlain unconformably by Neogene ignimbrites in the Ni^de area of Turkey. It is mostly granite and minor granodiorite in composition, whereas its enclaves are dominantly gabbro with a few diorites in composition. The Uckapdl Granitoid is composed mainly of quartz, K-feldspar, plagioclase, biotite, muscovite and minor amphibole while its enclaves contain mostly plagioclase, amphibole, minor pyroxene and biotite. The Uckapth Granitoid has calcalkaline and peraluminous （AJCNK= 1.0-1.3） geochemical characteristics. It is characterized by high LILE/HFSE and LREE/HREE ratios （（La/Lu）N 3-33）, and has negative Ba, Ta, Nb and Eu anomalies, resembling those of comsion granitoids. The {）fkaplh Granitoid has relatively high STSr/S6Sr0） ratios （0.711189--0.716061） and low eNd（t） values （-5.13 to -7.13）, confirming crustal melting. In contrast, the enclaves are tholeiitic and metaluminous, and slightly enriched in LILEs （K, Rb） and Th, and have negative Ta, Nb and Ti anomalies; propose that they were derived from a subduction-modified mantle source. Based on mineral and whole rock chemistry data, the Uckapth granitoid is H-（hybrid） type, post-collision granitoid developed by mixing/mingllng processes between crustal melts and mantle-derived mafic magmas.
基金supported by the National Natural Science Foundation of China (No 40234041)
文摘The Wulong pluton was emplaced in the metamorphic complex of the Mesoproterozoic Foping Group, South Qinling. A few mafic enclaves which are rounded in shape with sharp boundaries with the host granites in the southern part of the pluton. Based on petrography, geochemistry and chronology data, it is indicated that the Wulong pluton shows some adakitic affinities with depletion in HREE (Yb=0.33–0.96 μg/g, Y=4.77–11.2 μg/g); enrichment in Sr (643–1115 μg/g) and Ba (775–1386 μg/g), high Sr/Y ratios (57.3–160) and Y/Yb ratios (11.0–14.3), and slightly negative Eu anomaly (δEu=0.70–0.83). These patterns suggest a feldspar-poor and garnet±amohibole-rich fractionation mineral assemblage. The mafic enclaves have high concentrations of Mg (MgO=4.15%–8.13%), Cr (14.8–371 μg/g), and Ni (20.0–224 μg/g), and high Nb/Ta ratios (15.42–21.9). It seems that the underplating mantle magma was responsible for the generation of the mafic magma. Companied with the results of investigations for the Qinling Orogenic Belt, it was found that partial melting of the thickened lower crust, which was triggered by the underplated mantle-derived magmas, had generated the felsic magma. The Wulong pluton provided evidence for a mixing and mingling process of two kinds of mamma. Its formation probably represents the oceanic slab breakoff during the late orogenic stage in the Qinling area.
文摘In this contribution,detailed field descriptions together with petrographic and bulk-rock major,trace and rare earth elements(REE)data are used to constrain the origin and geodynamic setting of the mafic magmatic enclaves(MMEs)recently discovered within the Pan-African Ngaoundal pluton,Adamawa area,central Cameroon.The investigated MMEs are dark-colored with chilled margins,and display medium to coarse-grain igneous textures.The mineral assemblage is either dominated by K-feldspar and carbonate(group Ⅰ),or by amphibole and plagioclase(group Ⅱ),though the overall mineral phases made of amphibole,plagioclase,K-feldspar,and biotite are similar to that of their host syenite but in different proportions.The MMEs in Ngaoundal area are foid-gabbro in composition with SiO_(2) contents ranging between 41.52% and 43.74% and are contiguous with their host granitoids of intermediate composition(SiO_(2)=57.52% to 58.98%).The host granitoid rocks are metaluminous,and belong to the shoshonitic series.Petrographic and geochemical data have revealed that the Ngaoundal MMEs derived from rapid cooling of hot injected lithospheric mantle-derived magma within cooler host granitoids magma and were emplaced in the intraplate geodynamic setting.
文摘Recent eruption of Unzen Volcano in 1991-1995 caught attention of scientists all over the world because of disastrous character of previous one in 1792. Intrusion of andesitic magma to the chamber with rhyolitic magma is proposed to be a trigger for these eruptions. T-P-X parameters of two end-member magmas have been estimated several times, but usually estimations are based on phenocrysts assemblages. New results of this research are based on mafic enclaves and groundmass. These results are significant for magma mixing and mingling theory.
基金Supported by National Natural Science Foundation of China (Grant Nos. 40625005 and 40821002)National Basic Research Program of China (Grant No. 2006CB403501)
文摘We report the zircon Hf-O isotopic data for mafic enclaves from the Taihang Yanshanian intermediate to felsic plutons, and use them, along with the petrological, whole-rock chemical and Nd-Sr isotopic data, to reveal the petrogenesis of mafic enclaves. Mafic enclaves show magmatic textures and are finer-grained than host rocks. In places they are highly elongated due to stretching within the partially crystallized, convective felsic magma, but show no solid-state deformation. These data suggest that mafic enclaves and host rocks were co-existing, but compositionally distinct magmas. The mafic enclaves contain abundant hydrous minerals such as hornblende and biotite, with pyroxene relict being surrounded by hornblende reaction rim. Plagioclase xenocrysts from mafic enclaves show a complicated compositional and textural disequilibrium. Comparison between mafic enclaves and the immediate host rocks suggests that the two rock units are compositionally correlated. The εNd values of mafic enclaves are generally higher than the host rocks, though the Sr isotopic ratios of the two rock units are indistinguishable. Zircons from a single enclave sample show a significant variation in Hf isotopic compositions, with εHf = -10―-22, suggesting an origin through magma mixing between mafic and felsic magmas. This is supported by the relatively large variation of zircon O isotopic ratios (δ 18O = 5.5‰- 7.8‰) of the mafic enclaves. The petrogenesis of mafic enclaves could be described as below. Evolved basaltic magma (via fractionation of olivine and pyroxene) first mixed with crustally derived granitic melts in depths, forming a hybrid magma; then the hybrid magma broke up into discrete lumps upon entering the above felsic magma. Subsequently, the enclave-forming magma experienced a double mechanical transfer of plagioclase, and inward chemical transfer of fluid and Na, P, Y, Nb and Pb at the contacts with host felsic magmas.
