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Mao Jingwen - One of the best experts on this subject based on the ideXlab platform.
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age and geochemistry of Granites in gejiu area yunnan province sw china constraints on their petrogenesis and tectonic setting
Lithos, 2010Co-Authors: Cheng Yanbo, Mao JingwenAbstract:Gejiu is one of the largest polymetallic tin ore districts in the world. Located at the westernmost end of the South China tungsten–tin province (or Nanling tungsten–tin province), it is a Granite-related (Gejiu Granite) magmatic-hydrothermal system. Nine samples from two phases of Gejiu granitic intrusions have been analyzed by SHRIMP and/or LA-ICPMS zircon U–Pb techniques, yielding ages ranging from 77.4 ± 2.5 Ma to 85.0 ± 0.85 Ma. Whole rock analysis shows that both phases are high-K and alkali-rich Granites and their ACNK values fall mainly into a small range of 1.0–1.1. Moreover, Harker diagrams indicate that Granites experienced strong fractional crystallization during magmatic evolution. Most Granites display relative enrichment in LREE and strong Eu depletion. The whole rock average (eNd(t)) values of the Gejiu Granites vary from − 9.3 to − 6.9, whereas a range of − 8.12 < (eHf(t)) < 1.21 is defined by magmatic zircons. Sr–Nd–Hf isotope data indicate that the Granites have been mainly derived from crustal melts with minor input of mantle component. Two stage Nd and Hf model ages, together with isotopic characteristics, indicate that the Gejiu Granite magmas were possibly derived from partial melting of Mesoproterozoic continental crust, with minor input of mantle-derived melts, followed by extensive fractional crystallization.
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Age and geochemistry of Granites in Gejiu area, Yunnan province, SW China: Constraints on their petrogenesis and tectonic setting
Lithos, 2010Co-Authors: Cheng Yanbo, Mao JingwenAbstract:Gejiu is one of the largest polymetallic tin ore districts in the world. Located at the westernmost end of the South China tungsten–tin province (or Nanling tungsten–tin province), it is a Granite-related (Gejiu Granite) magmatic-hydrothermal system. Nine samples from two phases of Gejiu granitic intrusions have been analyzed by SHRIMP and/or LA-ICPMS zircon U–Pb techniques, yielding ages ranging from 77.4 ± 2.5 Ma to 85.0 ± 0.85 Ma. Whole rock analysis shows that both phases are high-K and alkali-rich Granites and their ACNK values fall mainly into a small range of 1.0–1.1. Moreover, Harker diagrams indicate that Granites experienced strong fractional crystallization during magmatic evolution. Most Granites display relative enrichment in LREE and strong Eu depletion. The whole rock average (εNd(t)) values of the Gejiu Granites vary from − 9.3 to − 6.9, whereas a range of − 8.12 < (εHf(t)) < 1.21 is defined by magmatic zircons. Sr–Nd–Hf isotope data indicate that the Granites have been mainly derived from crustal melts with minor input of mantle component. Two stage Nd and Hf model ages, together with isotopic characteristics, indicate that the Gejiu Granite magmas were possibly derived from partial melting of Mesoproterozoic continental crust, with minor input of mantle-derived melts, followed by extensive fractional crystallization
Cheng Yanbo - One of the best experts on this subject based on the ideXlab platform.
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age and geochemistry of Granites in gejiu area yunnan province sw china constraints on their petrogenesis and tectonic setting
Lithos, 2010Co-Authors: Cheng Yanbo, Mao JingwenAbstract:Gejiu is one of the largest polymetallic tin ore districts in the world. Located at the westernmost end of the South China tungsten–tin province (or Nanling tungsten–tin province), it is a Granite-related (Gejiu Granite) magmatic-hydrothermal system. Nine samples from two phases of Gejiu granitic intrusions have been analyzed by SHRIMP and/or LA-ICPMS zircon U–Pb techniques, yielding ages ranging from 77.4 ± 2.5 Ma to 85.0 ± 0.85 Ma. Whole rock analysis shows that both phases are high-K and alkali-rich Granites and their ACNK values fall mainly into a small range of 1.0–1.1. Moreover, Harker diagrams indicate that Granites experienced strong fractional crystallization during magmatic evolution. Most Granites display relative enrichment in LREE and strong Eu depletion. The whole rock average (eNd(t)) values of the Gejiu Granites vary from − 9.3 to − 6.9, whereas a range of − 8.12 < (eHf(t)) < 1.21 is defined by magmatic zircons. Sr–Nd–Hf isotope data indicate that the Granites have been mainly derived from crustal melts with minor input of mantle component. Two stage Nd and Hf model ages, together with isotopic characteristics, indicate that the Gejiu Granite magmas were possibly derived from partial melting of Mesoproterozoic continental crust, with minor input of mantle-derived melts, followed by extensive fractional crystallization.
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Age and geochemistry of Granites in Gejiu area, Yunnan province, SW China: Constraints on their petrogenesis and tectonic setting
Lithos, 2010Co-Authors: Cheng Yanbo, Mao JingwenAbstract:Gejiu is one of the largest polymetallic tin ore districts in the world. Located at the westernmost end of the South China tungsten–tin province (or Nanling tungsten–tin province), it is a Granite-related (Gejiu Granite) magmatic-hydrothermal system. Nine samples from two phases of Gejiu granitic intrusions have been analyzed by SHRIMP and/or LA-ICPMS zircon U–Pb techniques, yielding ages ranging from 77.4 ± 2.5 Ma to 85.0 ± 0.85 Ma. Whole rock analysis shows that both phases are high-K and alkali-rich Granites and their ACNK values fall mainly into a small range of 1.0–1.1. Moreover, Harker diagrams indicate that Granites experienced strong fractional crystallization during magmatic evolution. Most Granites display relative enrichment in LREE and strong Eu depletion. The whole rock average (εNd(t)) values of the Gejiu Granites vary from − 9.3 to − 6.9, whereas a range of − 8.12 < (εHf(t)) < 1.21 is defined by magmatic zircons. Sr–Nd–Hf isotope data indicate that the Granites have been mainly derived from crustal melts with minor input of mantle component. Two stage Nd and Hf model ages, together with isotopic characteristics, indicate that the Gejiu Granite magmas were possibly derived from partial melting of Mesoproterozoic continental crust, with minor input of mantle-derived melts, followed by extensive fractional crystallization
Roberto Dall’agnol - One of the best experts on this subject based on the ideXlab platform.
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Chemical characteristics of zircon from A-type Granites and comparison to zircon of S-type Granites
Lithos, 2014Co-Authors: Karel Breiter, Claudio Nery Lamarão, Régis Munhoz Krás Borges, Roberto Dall’agnolAbstract:Abstract The trace element content in zircons from A-type Granites and rhyolites was investigated by using back-scattered electron images and electron microprobe analyses. The studied Proterozoic (Wiborg batholith, Finland and Para, Amazonas and Goias states, Brazil) and Variscan (Krusne Hory/Erzgebirge, Czech Republic and Germany) plutons cover a wide range of rocks, from large rapakivi-textured geochemically primitive plutons to small intrusions of F-, Li-, Sn-, Nb-, Ta-, and U-enriched rare-metal Granites. While zircon is one of the first crystallized minerals in less fractionated metaluminous and peraluminous Granites, it is a late-crystallized phase in peralkaline Granites and in evolved Granites that may crystallize during the whole process of magma solidification. The early crystals are included in mica, quartz, and feldspar; the late grains are included in fluorite or cryolite or are interstitial. The zircon in hornblende–biotite and biotite Granites from the non-mineralized plutons is poor in minor and trace elements; the zircon in moderately fractionated Granite varieties is slightly enriched in Hf, Th, U, Y, and HREEs; whereas the zircon in highly fractionated ore-bearing Granites may be strongly enriched in Hf (up to 10 wt.% HfO 2 ), Th (up to 10 wt.% ThO 2 ), U (up to 10 wt.% UO 2 ), Y (up to 12 wt.% Y 2 O 3 ), Sc (up to 3 wt.% Sc 2 O 3 ), Nb (up to 5 wt.% Nb 2 O 5 ), Ta (up to 1 wt.% Ta 2 O 5 ), W (up to 3 wt.% WO 3 ), F (up to 2.5 wt.% F), P (up to 11 wt.% P 2 O 5 ), and As (up to 1 wt.% As 2 O 5 ). Metamictized zircons may also be enriched in Bi, Ca, Fe, and Al. The increase in the Hf content coupled with the decrease in the Zr/Hf value in zircon is one of the most reliable indicators of granitic magma evolution. In the zircon of A-type Granites, the Zr/Hf value decreases from 41–67 (porphyritic Granite) to 16–19 (equigranular Granite) in the Kymi stock, Finland, and from 49–52 (biotite Granite) to 18–36 (leucoGranite) in the Pedra Branca pluton, Brazil. In the in situ strongly fractionated Cinovec cupola (Erzgebirge), the Zr/Hf value decreases from 33–51 in the protolithionite Granite at a depth of 1255 m to 7.5–25 in the zinnwaldite Granite at a depth of 40 m. At the scale of individual crystals, the Zr/Hf value decreases from 86 to 68 from the cores to the rims of the zircons from the Teplice rhyolite and from 64 to 33 in the zircons from the biotite Granite at Krupka, Erzgebirge. The contents of Hf and U in zircon are dependent mainly on the degree of Granite fractionation and the nature and volume of the volatile phases and are independent of the A- or S-character of the parental melt. The zircon Zr/Hf ratios 55 and 25 are proposed to approximately distinguish common, moderately evolved and highly evolved Granites. Zircons from the moderately and highly evolved Granites of A- and S-type can be discriminated on the basis of their HREE content and the U/Th ratios. Nb, Ta, and W are present in zircon from the highly evolved Granites from all studied areas, while high As, Bi, and Sc contents are typical only for the Erzgebirge.
Carl Ehlers - One of the best experts on this subject based on the ideXlab platform.
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Emplacement mechanisms of late-orogenic Granites: structural and geochemical evidence from southern Finland
International Journal of Earth Sciences, 2006Co-Authors: Tom Stålfors, Carl EhlersAbstract:The country rock in southern Finland formed mainly during the Svecofennian orogeny ca. 1.9 Ga ago. The middle and lower crust was partially melted 1.83 Ga ago due to crustal thickening and subsequent extension. During this event, S-type migmatites and Granites were formed along a 100×500 km zone. This Late Svecofennian Granite–Migmatite zone (LSGM zone) is a large crustal segment characterised by roughly E–W trending sub-horizontal migmatites and Granites. Combined ductile E–W shear movements and NNW–SSE compressional movements defined a transpressional tectonic regime during the emplacement. Partial melts that moved through the crust pooled as Granite sheets or froze as migmatites. Major transpressive shear zones border the LSGM zone, which forms a tectonic and metamorphic zone that crosscuts the earlier Svecofennian granitoids. Based on field observations and geochemical data from two sets of outcrops, we show that the great volumes of late-orogenic Granites and migmatites in southern Finland were transported and emplaced as small chemically variable batches, possibly extracted from different protoliths. These melt batches were transported along repeatedly activated channels and collected at some horizontal level in the crust. In the Nagu area, the melt batches were trapped under a roof-layer of amphibolite and the whole complex was synchronously folded into open folds with steep axial surfaces and E–W trending fold axes. The sheets of microcline Granite are, in places, strongly sheared; the microcline phenocrysts are imbricated and subsequent deformation of the microcline phenocrysts indicates syn-tectonic movements of the layers as well as a syn-tectonic mechanism for the late-magmatic fractionation. Depending on the degree of crystallisation of the individual melt batches during shearing at different intensities, the Granites have slightly different appearances. Some sheared zones show a cumulate-like trace element geochemistry, indicating that melt fractions were expelled from the system, producing layers of deformation enhanced fractionated Granites and cumulate layers. Our interpretation is that the Nagu area shows shear-assisted fractionation mechanisms in granitic melts, and that similar processes are responsible for the fractionation trends seen in the sub-horizontal sheeted Granites in Hämeenlinna at higher levels in the crust.
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the late svecofennian Granite migmatite zone of southern finland a belt of transpressive deformation and Granite emplacement
Precambrian Research, 1993Co-Authors: Carl Ehlers, Alf Lindroos, Olavi SelonenAbstract:Abstract The late Svecofennian Granite-migmatite (LSGM) zone in southwestern Finland is a ∼ 100 km wide and 500 km long belt transecting the southern Svecofennides from WSW to ENE. It was formed in an area of thin pillow lavas, volcaniclastic sediments and limestones. The area is interpreted as having been an early basin of crustal extension which was the locus of an inherited zone of weakness in the Proterozoic crust. Early recumbent folding was followed by crustal thickening and intrusions of ∼ 1.89-1.88 Ga old plutonics. The LSGM-zone is characterized by 1.84-1.83 Ga old rhomboidal sheets of late Svecofennian microcline Granite and is bounded by ductile shears. Amongst the two major phases of deformation defined in the LSGM-zone, the earlier one (D1) affected only the supracrustals and the 1.89-1.88 Ga old early plutonics. In contrast, the later phase (D2) also deformed the late Svecofennian migmatites and Granites. D1 represents a complex and long-lasting deformation event which included overturning and thrusting of the Svecofennian strata. D2 comprised ENE-WSW directed drag accompanied by NNW-SSE compression. The Svecofennian crust was thickened further and anatectic microcline Granites intruded along thrusts. The rhomboidal outline of the late Svecofennian Granite sheets indicates a sense of movement in agreement with measured dextral strike-slip in the shears delimiting the LSGM-zone. Imbricated feldspar megacrysts in the Granites indicate thrusting towards the west during the stage of granitic magmatism. The gently dipping early Svecofennian gneisses and the late Granite sheets were folded into upright F2 folds with gently plunging axes. Locally, the F2 axial surfaces were intruded by late Svecofennian Granite mobilisates.
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The late Svecofennian Granite-migmatite zone of southern Finland—a belt of transpressive deformation and Granite emplacement
Precambrian Research, 1993Co-Authors: Carl Ehlers, Alf Lindroos, Olavi SelonenAbstract:Abstract The late Svecofennian Granite-migmatite (LSGM) zone in southwestern Finland is a ∼ 100 km wide and 500 km long belt transecting the southern Svecofennides from WSW to ENE. It was formed in an area of thin pillow lavas, volcaniclastic sediments and limestones. The area is interpreted as having been an early basin of crustal extension which was the locus of an inherited zone of weakness in the Proterozoic crust. Early recumbent folding was followed by crustal thickening and intrusions of ∼ 1.89-1.88 Ga old plutonics. The LSGM-zone is characterized by 1.84-1.83 Ga old rhomboidal sheets of late Svecofennian microcline Granite and is bounded by ductile shears. Amongst the two major phases of deformation defined in the LSGM-zone, the earlier one (D1) affected only the supracrustals and the 1.89-1.88 Ga old early plutonics. In contrast, the later phase (D2) also deformed the late Svecofennian migmatites and Granites. D1 represents a complex and long-lasting deformation event which included overturning and thrusting of the Svecofennian strata. D2 comprised ENE-WSW directed drag accompanied by NNW-SSE compression. The Svecofennian crust was thickened further and anatectic microcline Granites intruded along thrusts. The rhomboidal outline of the late Svecofennian Granite sheets indicates a sense of movement in agreement with measured dextral strike-slip in the shears delimiting the LSGM-zone. Imbricated feldspar megacrysts in the Granites indicate thrusting towards the west during the stage of granitic magmatism. The gently dipping early Svecofennian gneisses and the late Granite sheets were folded into upright F2 folds with gently plunging axes. Locally, the F2 axial surfaces were intruded by late Svecofennian Granite mobilisates.
Karel Breiter - One of the best experts on this subject based on the ideXlab platform.
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Chemical characteristics of zircon from A-type Granites and comparison to zircon of S-type Granites
Lithos, 2014Co-Authors: Karel Breiter, Claudio Nery Lamarão, Régis Munhoz Krás Borges, Roberto Dall’agnolAbstract:Abstract The trace element content in zircons from A-type Granites and rhyolites was investigated by using back-scattered electron images and electron microprobe analyses. The studied Proterozoic (Wiborg batholith, Finland and Para, Amazonas and Goias states, Brazil) and Variscan (Krusne Hory/Erzgebirge, Czech Republic and Germany) plutons cover a wide range of rocks, from large rapakivi-textured geochemically primitive plutons to small intrusions of F-, Li-, Sn-, Nb-, Ta-, and U-enriched rare-metal Granites. While zircon is one of the first crystallized minerals in less fractionated metaluminous and peraluminous Granites, it is a late-crystallized phase in peralkaline Granites and in evolved Granites that may crystallize during the whole process of magma solidification. The early crystals are included in mica, quartz, and feldspar; the late grains are included in fluorite or cryolite or are interstitial. The zircon in hornblende–biotite and biotite Granites from the non-mineralized plutons is poor in minor and trace elements; the zircon in moderately fractionated Granite varieties is slightly enriched in Hf, Th, U, Y, and HREEs; whereas the zircon in highly fractionated ore-bearing Granites may be strongly enriched in Hf (up to 10 wt.% HfO 2 ), Th (up to 10 wt.% ThO 2 ), U (up to 10 wt.% UO 2 ), Y (up to 12 wt.% Y 2 O 3 ), Sc (up to 3 wt.% Sc 2 O 3 ), Nb (up to 5 wt.% Nb 2 O 5 ), Ta (up to 1 wt.% Ta 2 O 5 ), W (up to 3 wt.% WO 3 ), F (up to 2.5 wt.% F), P (up to 11 wt.% P 2 O 5 ), and As (up to 1 wt.% As 2 O 5 ). Metamictized zircons may also be enriched in Bi, Ca, Fe, and Al. The increase in the Hf content coupled with the decrease in the Zr/Hf value in zircon is one of the most reliable indicators of granitic magma evolution. In the zircon of A-type Granites, the Zr/Hf value decreases from 41–67 (porphyritic Granite) to 16–19 (equigranular Granite) in the Kymi stock, Finland, and from 49–52 (biotite Granite) to 18–36 (leucoGranite) in the Pedra Branca pluton, Brazil. In the in situ strongly fractionated Cinovec cupola (Erzgebirge), the Zr/Hf value decreases from 33–51 in the protolithionite Granite at a depth of 1255 m to 7.5–25 in the zinnwaldite Granite at a depth of 40 m. At the scale of individual crystals, the Zr/Hf value decreases from 86 to 68 from the cores to the rims of the zircons from the Teplice rhyolite and from 64 to 33 in the zircons from the biotite Granite at Krupka, Erzgebirge. The contents of Hf and U in zircon are dependent mainly on the degree of Granite fractionation and the nature and volume of the volatile phases and are independent of the A- or S-character of the parental melt. The zircon Zr/Hf ratios 55 and 25 are proposed to approximately distinguish common, moderately evolved and highly evolved Granites. Zircons from the moderately and highly evolved Granites of A- and S-type can be discriminated on the basis of their HREE content and the U/Th ratios. Nb, Ta, and W are present in zircon from the highly evolved Granites from all studied areas, while high As, Bi, and Sc contents are typical only for the Erzgebirge.
