Mafic-ultramafic magmatic provinces are termed Large Igneous Provinces （LIPs） if they are large （〉10^5 km^3）, are emplaced in a short duration （ca. 〈 5 myr） （or consist of short duration pulses）, and have in...Mafic-ultramafic magmatic provinces are termed Large Igneous Provinces （LIPs） if they are large （〉10^5 km^3）, are emplaced in a short duration （ca. 〈 5 myr） （or consist of short duration pulses）, and have intraplate characteristics （i.e. are not associated with normal plate boundary processes）. This category includes the classic continental flood basalts, oceanic plateaus, bimodal-rift （passive margin） related packages, but also those events, mainly of Phanerozoic-Proterozoic age, where the plumbing system of dykes, sills and layered intrusions has been exposed by erosion. In the Archean, LIPs may be represented by the greenstone belts of the tholeiite-komatiite association. Felsic magmatism is associated with many LIPs and indeed may be dominant in some cases. LIPs are associated with continental breakup, climatic change, extinction events, and major ore deposits especially of the Ni-Cu-PGE type. Continental LIPs occur on average every 20-30 myr since 2.6 Ga; the Archean record is too poorly preserved for generalizations. LIPs occur both as isolated single events （e.g., 2055 Ma Bushveld event）, as approximately coeval but widely separated events （e.g., 65 Ma Deccan and 62 Ma NAIP）, and as regional clusters associated with supercontinent breakup （e.g., the 830-750 Ma events associated with the breakup of the proposed supercontinent Rodinia）. The LIP record represents a key tool for constraining Proterozoic paleocontinental reconstructions.展开更多
Mafic-uitramafic complexes are widespread in Hongqiling in central Jiulin Province, NE China. The Hongqiling complex comprises pyroxenite, olivine websterite, lberzolite, gabbro and leucogabbro. Based on the latest ge...Mafic-uitramafic complexes are widespread in Hongqiling in central Jiulin Province, NE China. The Hongqiling complex comprises pyroxenite, olivine websterite, lberzolite, gabbro and leucogabbro. Based on the latest geochronological results, these intrusions yield a zircon U-Pb age of about 216 Ma, implying that they emplaced in the late Triassic period and that the mafic-uitramafic complexes are post-orogenic in origin. These ages are coeval with the emplacement of A-type granites in the area, but slightly younger than syn-orogenic granitic magmatism. The composition of the parent magma during the equilibration of the accumulated olivine crystallizing is basaltic with high MgO, and it comes from depleted or juvenile lithospheric mantle, according to the results of trace elements and Sr-Nd isotopes. Amount of crustal material contaminated the magmatic source, implying that the mafic-uitramafic rocks originate from the mixing product of crust- and mantle-derived magma. Therefore, the magmatic source was contaminated by an amount of crustal material, and the subsequent crystal fractionation resulted in the Cu-Ni mineralization. Dynamic analyses indicate that, after the collision of the North China Craton and Jiamusi Massif, the lithospheric delamination during post-orogeny resulted in the upwelling of asthenosphere and the intruding of the mass and underplating of the mantle-derived magma, which led to the formation of the primary mafic-uitramafic magma due to the mantle-derived magma and partial melting of the lower crust. This result suggests that the mafic-uitramafic complexes belong to a typically important magmatic suite that evolved during post-orogenic processes, and they were exposed as maficultramafic dyke swarms that existed in the post-orogenic extension environment. It also implies that the orogenic process finished ultimately in this regional geological setting. The widespread occurrence of mafic-uitramafic complexes in the Xing＇an-Mongolia Orogenic Belt in NE China and in the Altay-Tianshan-Junggar O展开更多
The SHRIMP zircon U-Pb dating was carried out and yielded 287±5 Ma (MSWD = 0.34) and 274±3 Ma (MSWD = 1.35) for the Kalatongke No. 1 and Huangshan- dong Cu-Ni-bearing mafic-ultramafic complexes. These ages a...The SHRIMP zircon U-Pb dating was carried out and yielded 287±5 Ma (MSWD = 0.34) and 274±3 Ma (MSWD = 1.35) for the Kalatongke No. 1 and Huangshan- dong Cu-Ni-bearing mafic-ultramafic complexes. These ages are much more precise than pre-existing rock-mineral Rb-Sr, Sm-Nd and Re-Os isochron ages for the two complexes and constrain the timing of not only the complexes but also the magmatic Cu-Ni sulfide deposits more reliably. It is neces- sary to carefully reevaluate the previous chronological data for the complexes. The Cu-Ni-bearing mafic-ultramafic com- plexes have the ages similar to those of postcollisional A-type granites in the same area, implying that they could be related to the delamination of lithospheric mantle and upwelling and partial melting of asthenospheric mantle in postcollisional setting. Therefore, the Cu-Ni-bearing mafic-ultramafic com- plexes are a direct indicator of vertical growth of the conti- nental crustal in the Central Asian Orogenic Belt.展开更多
The Wudangshan, Yaolinghe volcanic-sedimentary sequences and doleritic-gabbroic sills comprise the largest exposed Precambrian basement in South Qinling. Zircons separated from 5 volcanic-pyroclas- tic samples of the ...The Wudangshan, Yaolinghe volcanic-sedimentary sequences and doleritic-gabbroic sills comprise the largest exposed Precambrian basement in South Qinling. Zircons separated from 5 volcanic-pyroclas- tic samples of the Wudangshan Group, 2 volcanic samples of the Yaolinghe Group and one sample for the mafic sills were used for U-Pb dating by laser ablation-inductively coupled plasma mass spec- trometry (LA-ICPMS). The results reveal that the Wudangshan volcanic sequence was formed at (755±3) Ma (a weighted mean from the 5 samples, MSWD=0.47), whereas the Yaolinghe volcanic suite and the mafic sill were crystallized at (685±5) (2 samples, MSWD=0.36) and (679±3) Ma (MSWD=1.6), respectively, which are equal to each other within analysis errors. These ages are markedly younger than those previously documented for the rocks. The newly obtained ages for the Wudangshan and Yaolinghe Groups are identical to those of the bottom Liantuo and slightly older than those of the Nantuo Forma- tions, respectively, lower strata of the Nanhua (middle to late Neoproterozoic) stratotype section in eastern Three Gorges, Yangtze craton. A range of inherited magmatic zircons was recognized with ages of 830 to 780 Ma, which are typical of Neoprotzrozoic magmatisms recorded along the margins and interior of the Yangtze craton. Thus, there is Neoproterozoic basement comprising 830―780 Ma igne- ous suites in South Qinling; the inherited zircons were detrital sediments derived from the northern margin of the Yangtze craton. Accordingly, it is suggested that the South Qinling is a segment of the Yangtze craton before the Qinling Orogeny.展开更多
Huge diabase occurs within the Pro- terozoic strata in the southern margin of the North China Block, geographically in the northern parts of Anhui and Jiangsu provinces, where no strata younger than Neoproterozoic hav...Huge diabase occurs within the Pro- terozoic strata in the southern margin of the North China Block, geographically in the northern parts of Anhui and Jiangsu provinces, where no strata younger than Neoproterozoic have been found. Zir- cons from the diabase show three different structures from cathodoluminesecence imaging, but they are all of magmatic origin. SHRIMP U-Pb dating yields a range of 206Pb/238U ages from 2600 to 124 Ma, but two geological events can clearly be identified from both concordant and discordant ages. One gives two weighted mean 207Pb/206Pb ages of 976 ± 24 and 1038 ± 26 Ma which are interpreted as timing of dia- base crystallization, and the other has a weighted mean 207Pb/206Pb age of 2523 ± 52 Ma that repre- sents formation time of inherited zircon from the old crust. The dating results indicate that the mafic magmatic event occurred in a transition period from the latest Mesoproterozoic to the earliest Neopro- terozoic, consistent with global subduction of Grenvill ocean crust to result in the assembly of superconti- nent Rodinia. Therefore, the North China Block needs to be taken into account when reconstructing the position of China continents within the framework of Rodinia supercontinent.展开更多
More than twenty mafic-ultramafic complexes. which host several medium-or large-sized Cu-Ni deposits, occur along the Huangshan-Jingerquan (HJ ) belt in EastXinjiang. Rock types in these complexes are predominated by ...More than twenty mafic-ultramafic complexes. which host several medium-or large-sized Cu-Ni deposits, occur along the Huangshan-Jingerquan (HJ ) belt in EastXinjiang. Rock types in these complexes are predominated by peridotite, pyroxene peri-dotite, olivine pyroxenite, gabbronorite, orthopyroxene gabbro, troctolite, gabbro anddiorite. The ultramafic rocks are relatively Fe-euriched and are characterised by an as-semblage of olivine + orthopyroxene + clinopyroxene + hornblend ±plagioclase withoutobvious metamorphic textures. Chemically these complexes are relatively Fe-enrichedand show a tholeiitic trend of evolution. The complexes in this belt are intruded underthe extensional environment in a Mid-Carboniferous back-arc basin. They call be consid-ered as a new type of mafic-ultramafic complexes in orogenic belts, as designated by thename of the East-Xinjiang-type complexes.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
文摘Mafic-ultramafic magmatic provinces are termed Large Igneous Provinces （LIPs） if they are large （〉10^5 km^3）, are emplaced in a short duration （ca. 〈 5 myr） （or consist of short duration pulses）, and have intraplate characteristics （i.e. are not associated with normal plate boundary processes）. This category includes the classic continental flood basalts, oceanic plateaus, bimodal-rift （passive margin） related packages, but also those events, mainly of Phanerozoic-Proterozoic age, where the plumbing system of dykes, sills and layered intrusions has been exposed by erosion. In the Archean, LIPs may be represented by the greenstone belts of the tholeiite-komatiite association. Felsic magmatism is associated with many LIPs and indeed may be dominant in some cases. LIPs are associated with continental breakup, climatic change, extinction events, and major ore deposits especially of the Ni-Cu-PGE type. Continental LIPs occur on average every 20-30 myr since 2.6 Ga; the Archean record is too poorly preserved for generalizations. LIPs occur both as isolated single events （e.g., 2055 Ma Bushveld event）, as approximately coeval but widely separated events （e.g., 65 Ma Deccan and 62 Ma NAIP）, and as regional clusters associated with supercontinent breakup （e.g., the 830-750 Ma events associated with the breakup of the proposed supercontinent Rodinia）. The LIP record represents a key tool for constraining Proterozoic paleocontinental reconstructions.
基金The research was sponsored by the China NaturalScience Foundation under the project numbers of 40234040 and 40133020) .
文摘Mafic-uitramafic complexes are widespread in Hongqiling in central Jiulin Province, NE China. The Hongqiling complex comprises pyroxenite, olivine websterite, lberzolite, gabbro and leucogabbro. Based on the latest geochronological results, these intrusions yield a zircon U-Pb age of about 216 Ma, implying that they emplaced in the late Triassic period and that the mafic-uitramafic complexes are post-orogenic in origin. These ages are coeval with the emplacement of A-type granites in the area, but slightly younger than syn-orogenic granitic magmatism. The composition of the parent magma during the equilibration of the accumulated olivine crystallizing is basaltic with high MgO, and it comes from depleted or juvenile lithospheric mantle, according to the results of trace elements and Sr-Nd isotopes. Amount of crustal material contaminated the magmatic source, implying that the mafic-uitramafic rocks originate from the mixing product of crust- and mantle-derived magma. Therefore, the magmatic source was contaminated by an amount of crustal material, and the subsequent crystal fractionation resulted in the Cu-Ni mineralization. Dynamic analyses indicate that, after the collision of the North China Craton and Jiamusi Massif, the lithospheric delamination during post-orogeny resulted in the upwelling of asthenosphere and the intruding of the mass and underplating of the mantle-derived magma, which led to the formation of the primary mafic-uitramafic magma due to the mantle-derived magma and partial melting of the lower crust. This result suggests that the mafic-uitramafic complexes belong to a typically important magmatic suite that evolved during post-orogenic processes, and they were exposed as maficultramafic dyke swarms that existed in the post-orogenic extension environment. It also implies that the orogenic process finished ultimately in this regional geological setting. The widespread occurrence of mafic-uitramafic complexes in the Xing＇an-Mongolia Orogenic Belt in NE China and in the Altay-Tianshan-Junggar O
文摘The SHRIMP zircon U-Pb dating was carried out and yielded 287±5 Ma (MSWD = 0.34) and 274±3 Ma (MSWD = 1.35) for the Kalatongke No. 1 and Huangshan- dong Cu-Ni-bearing mafic-ultramafic complexes. These ages are much more precise than pre-existing rock-mineral Rb-Sr, Sm-Nd and Re-Os isochron ages for the two complexes and constrain the timing of not only the complexes but also the magmatic Cu-Ni sulfide deposits more reliably. It is neces- sary to carefully reevaluate the previous chronological data for the complexes. The Cu-Ni-bearing mafic-ultramafic com- plexes have the ages similar to those of postcollisional A-type granites in the same area, implying that they could be related to the delamination of lithospheric mantle and upwelling and partial melting of asthenospheric mantle in postcollisional setting. Therefore, the Cu-Ni-bearing mafic-ultramafic com- plexes are a direct indicator of vertical growth of the conti- nental crustal in the Central Asian Orogenic Belt.
基金Supported by the National Natural Science Foundation of China (Grant Nos. 40373015, 40173016, 40472099 and 40521001)Program of Innovative Research Team of China University of Geosciences (Wuhan)
文摘The Wudangshan, Yaolinghe volcanic-sedimentary sequences and doleritic-gabbroic sills comprise the largest exposed Precambrian basement in South Qinling. Zircons separated from 5 volcanic-pyroclas- tic samples of the Wudangshan Group, 2 volcanic samples of the Yaolinghe Group and one sample for the mafic sills were used for U-Pb dating by laser ablation-inductively coupled plasma mass spec- trometry (LA-ICPMS). The results reveal that the Wudangshan volcanic sequence was formed at (755±3) Ma (a weighted mean from the 5 samples, MSWD=0.47), whereas the Yaolinghe volcanic suite and the mafic sill were crystallized at (685±5) (2 samples, MSWD=0.36) and (679±3) Ma (MSWD=1.6), respectively, which are equal to each other within analysis errors. These ages are markedly younger than those previously documented for the rocks. The newly obtained ages for the Wudangshan and Yaolinghe Groups are identical to those of the bottom Liantuo and slightly older than those of the Nantuo Forma- tions, respectively, lower strata of the Nanhua (middle to late Neoproterozoic) stratotype section in eastern Three Gorges, Yangtze craton. A range of inherited magmatic zircons was recognized with ages of 830 to 780 Ma, which are typical of Neoprotzrozoic magmatisms recorded along the margins and interior of the Yangtze craton. Thus, there is Neoproterozoic basement comprising 830―780 Ma igne- ous suites in South Qinling; the inherited zircons were detrital sediments derived from the northern margin of the Yangtze craton. Accordingly, it is suggested that the South Qinling is a segment of the Yangtze craton before the Qinling Orogeny.
文摘Huge diabase occurs within the Pro- terozoic strata in the southern margin of the North China Block, geographically in the northern parts of Anhui and Jiangsu provinces, where no strata younger than Neoproterozoic have been found. Zir- cons from the diabase show three different structures from cathodoluminesecence imaging, but they are all of magmatic origin. SHRIMP U-Pb dating yields a range of 206Pb/238U ages from 2600 to 124 Ma, but two geological events can clearly be identified from both concordant and discordant ages. One gives two weighted mean 207Pb/206Pb ages of 976 ± 24 and 1038 ± 26 Ma which are interpreted as timing of dia- base crystallization, and the other has a weighted mean 207Pb/206Pb age of 2523 ± 52 Ma that repre- sents formation time of inherited zircon from the old crust. The dating results indicate that the mafic magmatic event occurred in a transition period from the latest Mesoproterozoic to the earliest Neopro- terozoic, consistent with global subduction of Grenvill ocean crust to result in the assembly of superconti- nent Rodinia. Therefore, the North China Block needs to be taken into account when reconstructing the position of China continents within the framework of Rodinia supercontinent.
文摘More than twenty mafic-ultramafic complexes. which host several medium-or large-sized Cu-Ni deposits, occur along the Huangshan-Jingerquan (HJ ) belt in EastXinjiang. Rock types in these complexes are predominated by peridotite, pyroxene peri-dotite, olivine pyroxenite, gabbronorite, orthopyroxene gabbro, troctolite, gabbro anddiorite. The ultramafic rocks are relatively Fe-euriched and are characterised by an as-semblage of olivine + orthopyroxene + clinopyroxene + hornblend ±plagioclase withoutobvious metamorphic textures. Chemically these complexes are relatively Fe-enrichedand show a tholeiitic trend of evolution. The complexes in this belt are intruded underthe extensional environment in a Mid-Carboniferous back-arc basin. They call be consid-ered as a new type of mafic-ultramafic complexes in orogenic belts, as designated by thename of the East-Xinjiang-type complexes.
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.
