The Experts below are selected from a list of 1491 Experts worldwide ranked by ideXlab platform

Bush, Sarah E. - One of the best experts on this subject based on the ideXlab platform.

E. Hoffer - One of the best experts on this subject based on the ideXlab platform.

  • Fluid-present melting of meta-igneous rocks and the generation of leucogranites — Constraints from garnet major- and trace element data, Lu–Hf whole rock–garnet ages and whole rock Nd–Sr–Hf–O isotope data
    Lithos, 2009
    Co-Authors: C. Jung, S. Jung, O. Nebel, E. Hellebrand, P. Masberg, E. Hoffer
    Abstract:

    Pan-African high-grade metamorphism in the Proterozoic Damara orogen (Namibia) led to formation of garnet-bearing leucosomes in potassic meta-igneous gneisses producing a meta-igneous migmatite. In addition, the migmatite (gneiss (Mesosome) plus leucosome) was intruded by small-scale leucogranitic melts with a high amount of accumulated biotite and garnet. U-Pb zircon ages obtained on the Mesosome and the leucosome indicate late Proterozoic (ca. 850 Ma) concordia upper intercept ages which are interpreted as minimum ages of the precursor rock of the migmatite. U-Pb monazite ages obtained on the leucogranite give a concordant age of 512 +/- 1 Ma and two reversely discordant ages with Pb-207/U-235 ages of 544 +/- 1 and 534 +/- 1 Ma, indicating the growth of monazite before or close to the age of high-grade metamorphism in the Damara orogen. High precision Lu-Hf garnet-whole rock dating gave ages of 492.6 +/- 1.7 Ma for the Mesosome, 497.6 +/- 1.7 Ma for the leucosome and 494.0 +/- 1.7 Ma for the garnet- and biotite-bearing leucogranite indicating that the growth of garnet postdates the growth of monazite during high-grade metamorphism. In addition, it is suggested that melting and intrusion was coeval and occurred probably shortly after the main peak of metamorphism which occurred at c. 512 +/- 1 Ma. P-T estimates obtained by conventional thermobarometry (c. 690-720 degrees C) and accessory mineral dissolution thermometry on the leucogranite (c. 730 degrees C) suggest that partial melting occurred through limited fluid present melting of biotite via the reaction: bt + kfs + pig + qtz + H2O double left right arrow grt + melt. Outcrop evidence (diffuse relationship between the gneiss domain and the leucosomes, similar size of the leucosomes, homogeneous distribution of leucosomes on the sample scale) suggests that minor melt segregation had occurred. Whole rock Sr, Nd, Hf and O isotope data of the Mesosome indicate that it belongs to basement rocks from this area. Geochemical and isotope data obtained on the leucosomes argue for derivation by in-situ melting of the Mesosome. Both, leucosome and leucogranite originated from the same source rock but the leucogranite represents an accumulated melt that was able to segregate and to intrude the gneiss domain. The similar isotope features of the Mesosome, leucosome and leucogranite indicate a direct relationship for the gneiss and the melts. Chemical and mineral data favour a derivation of both types of melt through fluid-present melting of isotopically and chemically comparable biotite + plagioclase + K-feldspar + quartz-bearing gneisses. (C) 2008 Elsevier B.V. All rights reserved

Junming Yao - One of the best experts on this subject based on the ideXlab platform.

  • fluid inclusion geochemistry and ore genesis of the longmendian mo deposit in the east qinling orogen implication for migmatitic hydrothermal mo mineralization
    Ore Geology Reviews, 2014
    Co-Authors: Yanjing Chen, Xiaohua Deng, Junming Yao
    Abstract:

    Abstract The 1.85 Ga Longmendian Mo deposit in East Qinling is the oldest Mo system recognized in China. It is unique for three reasons: (1) quartzofeldspathic orebodies are away from any intrusion or fault, (2) it is closely associated with migmatitic rocks, and (3) it has remarkably high Re content in molybdenite (504 to 1660 ppm). The origin of the deposit is poorly constrained. In the Longmendian deposit, strong Mo mineralization is always associated with hydrothermally altered migmatitic amphibolites. To probe into ore genesis, detailed fluid inclusion studies are carried out on both mineralized migmatitic amphibolites and ore-barren rocks. Four compositional types of fluid inclusions are observed, including CO 2  ± CH 4 (PC-type), CO 2 –H 2 O (C-type), daughter mineral-bearing (S-type) and H 2 O–NaCl (W-type). Quartz in Mesosome and melanosome of mineralized migmatitic amphibolites contains all of the four types of inclusions. Measurements of immiscible inclusion assemblages in the ores constrain the Mo-mineralization temperatures and pressures to be 225–390 °C and 114–265 MPa, respectively. Primary fluid inclusions in barren migmatitic gneisses are dominated by S-type, and minor of C- and PC-types which are identical to those in the leucosome of migmatitic amphibolites. These inclusions yield lower homogenization temperatures than those in the mineralized Mesosome and melanosome of migmatitic amphibolites, suggesting that the ore-causative, injected melts should have higher temperatures and originated from depths. Such features of the ore-forming fluids indicate that the Longmendian deposit was a migmatitic-hydrothermal system caused by high-temperature melt injection. This interpretation can also be supported by the observations below: (1) tourmaline is abundant in melanosome, but absent in Mesosome; (2) the consistent quartzofeldspathic composition of leucosome is independent of Mesosome; (3) leucosome in migmatitic amphibolite crosscuts each other; (4) halite-bearing fluid inclusions are prevalent in studied samples, which is the feature of granitic rocks, instead of the scenarios of in situ migmatites; and (5) the trapping temperatures of fluid inclusions in mineralized migmatitic amphibolite are much lower than those required for partial melting, but higher than those obtained from barren migmatitic rocks.

Yao Jun-ming - One of the best experts on this subject based on the ideXlab platform.

  • Fluid inclusion geochemistry and ore genesis of the Longmendian Mo deposit in the East Qinling Orogen: Implication for migmatitic-hydrothermal Mo-mineralization
    ore geology reviews, 2014
    Co-Authors: Li Nuo, Chen Yan-jing, Deng Xiao-hua, Yao Jun-ming
    Abstract:

    The 1.85 Ga Longmendian Mo deposit in East Qinling is the oldest Mo system recognized in China. It is unique for three reasons: (1) quartzofeldspathic orebodies are away from any intrusion or fault, (2) it is closely associated with migmatitic rocks, and (3) it has remarkably high Re content in molybdenite (504 to 1660 ppm). The origin of the deposit is poorly constrained. In the Longmendian deposit, strong Mo mineralization is always associated with hydrothermally altered migmatitic amphibolites. To probe into ore genesis, detailed fluid inclusion studies are carried out on both mineralized migmatitic amphibolites and ore-barren rocks. Four compositional types of fluid inclusions are observed, including CO2 +/- CH4 (PC-type), CO2-H2O (C-type), daughter mineral-bearing (S-type) and H2O-NaCI (W-type). Quartz in Mesosome and melanosome of mineralized migmatitic amphibolites contains all of the four types of inclusions. Measurements of immiscible inclusion assemblages in the ores constrain the Mo-mineralization temperatures and pressures to be 225-390 degrees C and 114-265 MPa, respectively. Primary fluid inclusions in barren migmatitic gneisses are dominated by S-type, and minor of C- and PC-types which are identical to those in the leucosome of migmatitic amphibolites. These inclusions yield lower homogenization temperatures than those in the mineralized Mesosome and melanosome of migmatitic amphibolites, suggesting that the ore-causative, injected melts should have higher temperatures and originated from depths. Such features of the ore-forming fluids indicate that the Longmendian deposit was a migmatitic-hydrothermal system caused by high-temperature melt injection. This interpretation can also be supported by the observations below: (1) tourmaline is abundant in melanosome, but absent in Mesosome; (2) the consistent quartzofeldspathic composition of leucosome is independent of Mesosome; (3) leucosome in migmatitic amphibolite crosscuts each other; (4) halite-bearing fluid inclusions are prevalent in studied samples, which is the feature of granitic rocks, instead of the scenarios of in situ migmatites; and (5) the trapping temperatures of fluid inclusions in mineralized migmatitic amphibolite are much lower than those required for partial melting, but higher than those obtained from barren migmatitic rocks. (C) 2014 Elsevier B.V. All rights reserved.GeologyMineralogyMining & Mineral ProcessingSCI(E)EI3ARTICLEyjchen@pku.edu.cn520-5316

C. Jung - One of the best experts on this subject based on the ideXlab platform.

  • Fluid-present melting of meta-igneous rocks and the generation of leucogranites — Constraints from garnet major- and trace element data, Lu–Hf whole rock–garnet ages and whole rock Nd–Sr–Hf–O isotope data
    Lithos, 2009
    Co-Authors: C. Jung, S. Jung, O. Nebel, E. Hellebrand, P. Masberg, E. Hoffer
    Abstract:

    Pan-African high-grade metamorphism in the Proterozoic Damara orogen (Namibia) led to formation of garnet-bearing leucosomes in potassic meta-igneous gneisses producing a meta-igneous migmatite. In addition, the migmatite (gneiss (Mesosome) plus leucosome) was intruded by small-scale leucogranitic melts with a high amount of accumulated biotite and garnet. U-Pb zircon ages obtained on the Mesosome and the leucosome indicate late Proterozoic (ca. 850 Ma) concordia upper intercept ages which are interpreted as minimum ages of the precursor rock of the migmatite. U-Pb monazite ages obtained on the leucogranite give a concordant age of 512 +/- 1 Ma and two reversely discordant ages with Pb-207/U-235 ages of 544 +/- 1 and 534 +/- 1 Ma, indicating the growth of monazite before or close to the age of high-grade metamorphism in the Damara orogen. High precision Lu-Hf garnet-whole rock dating gave ages of 492.6 +/- 1.7 Ma for the Mesosome, 497.6 +/- 1.7 Ma for the leucosome and 494.0 +/- 1.7 Ma for the garnet- and biotite-bearing leucogranite indicating that the growth of garnet postdates the growth of monazite during high-grade metamorphism. In addition, it is suggested that melting and intrusion was coeval and occurred probably shortly after the main peak of metamorphism which occurred at c. 512 +/- 1 Ma. P-T estimates obtained by conventional thermobarometry (c. 690-720 degrees C) and accessory mineral dissolution thermometry on the leucogranite (c. 730 degrees C) suggest that partial melting occurred through limited fluid present melting of biotite via the reaction: bt + kfs + pig + qtz + H2O double left right arrow grt + melt. Outcrop evidence (diffuse relationship between the gneiss domain and the leucosomes, similar size of the leucosomes, homogeneous distribution of leucosomes on the sample scale) suggests that minor melt segregation had occurred. Whole rock Sr, Nd, Hf and O isotope data of the Mesosome indicate that it belongs to basement rocks from this area. Geochemical and isotope data obtained on the leucosomes argue for derivation by in-situ melting of the Mesosome. Both, leucosome and leucogranite originated from the same source rock but the leucogranite represents an accumulated melt that was able to segregate and to intrude the gneiss domain. The similar isotope features of the Mesosome, leucosome and leucogranite indicate a direct relationship for the gneiss and the melts. Chemical and mineral data favour a derivation of both types of melt through fluid-present melting of isotopically and chemically comparable biotite + plagioclase + K-feldspar + quartz-bearing gneisses. (C) 2008 Elsevier B.V. All rights reserved