Petrography and Mineral Chemistry of Tourmaline in Molla Taleb Ganitoid, Northeast of Aligudarz (Lorestan Province)
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Abstract:
Molla Taleb pegmatites (northeast of Aligudarz) are located in the western part of the metamorphic-igneous Sanandaj-Sirjan Zone (SSZ). Slates and schists along with siliceous veins and veinlet and black Hornfels, as well as metamorphic sandstones are among the oldest deposits of this area. The most important geological event in this area is the development and intrusion of granitoid masses into schists of the Molla Taleb area during the Middle Jurassic. The rocks of the study area are in the range of gabbro, diorite, granodiorite, and granite. Granites are in the range of type-I granites. Most specimens are calc-alkaline and mainly contain peraluminous. Microprobe electron analysis of tourmalines present in pegmatites, tourmaline- aplite-pegmatite veins, nodular tourmalines, and quartz-tourmaline veins shows that all tourmalines are in the Schorl region and the range of alkaline tourmalines. These tourmalines with FeO / FeO + MgO ratios between 0.6 and 0.8 are in the range of magmatic-hydrothermal tourmalines and more than 0.8 in the magmatic range. Therefore, the studied tourmalines are dependent on granite environments and are formed by a hydrothermal fluid of magmatic origin.Keywords:
Pegmatite
Tourmaline
Hornfels
Diorite
SLATES
Petrogenesis
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Tourmaline
Pegmatite
Leucogranite
Cassiterite
Hornfels
Anatexis
Muscovite
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Pegmatite
Massif
Muscovite
Topaz
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Tourmaline-bearing hydrothermal veins and metamorphic tourmalines occur in the Kamihirose Formation, circum-Hida terrane. The Kamihirose Formation was intruded by the Funatsu granitic rocks and underwent the contact metamorphism. Two types of tourmaline-bearing hydrothermal veins were distinguished: (1) tourmaline vein, which consists mostly of tourmaline with quartz and minor apatite; (2) potassium feldspar vein, which consists mostly of orthoclase with quartz, plagioclase and acicular tourmaline. Metamorphic tourmalines are found in sandstone and tonalite porphyry and tuffaceous sandstone clast of conglomerate. There are three types of sandstones that yield metamorphic tourmalines: black, white and acidic tuffaceous sandstones. In the black sandstone, the metamorphic tourmalines occur in shale fragments and occur as overgrowth on detrital tourmalines, whereas, in the white sandstone, those occur in acidic tuff fragments. In the acidic tuffaceous sandstone, metamorphic tourmalines occur in the tuffaceous matrix. The electron-microprobe analyses of tourmalines revealed the facts as follows ; (1) The tourmalines from the Kamihirose Formation are members of schorl-dravite solid solutions. (2) The tourmalines in the hydrothermal veins probably contain Fe3+, which substitutes for Al. (3) The metamorphic tourmalines have a wide compositional range reflecting various chemical features of host rocks.
Tourmaline
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Abstract An extensive dataset of major- and trace-element and B-isotope composition related to the compositional variation of the tourmalines from the S-type granite and pegmatite from the Upper Bonai and Gangpur Group granitoids, eastern India, is provided. The Gangpur Schist Belt, consisting of the Upper Bonai and Gangpur Group, lies at the eastern end of the Proterozoic Central Indian Tectonic Zone. An attempt to constrain the source of the boron isotope and describe the magmatic–hydrothermal evolution of the granite–pegmatite system is made. The tourmalines record generally low trace-element concentrations, with the exception of some elements such as Zn, Li, Ga, Mn and Ti. The Zn and Li concentration increases from the tourmalines in the granites to the tourmalines in the pegmatite. Trace-element compositions also vary slightly from the core tourmaline to the rim tourmaline. Tourmalines in granites/pegmatites are mostly Fe-rich schorl, and have S-type B-isotopic signature (δ 11 B = −10‰ to −12‰). Their chemistries reflect changing salinities of the granitic melts as well as vapour exsolution during progressive crystallization. This study indicates that the tourmalines in the pegmatites crystallized from evolved flux-element-rich (F, B, Li) melt, probably after the crystallization of granite-forming melt.
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