Microstructure characteristics of the ganet-bearing schist from Nam Co formation, Son La area, Song Ma suture zone, Northwestern Vietnam
Abstract
The garnet-bearing schists of the Nam Co formation have an identical mineral assemblage consisting of garnet, chlorte, albite, quartz and muscovite, together with accessory apatite, zircon, monazite, xenotime, and ilmenite. An aggregate of muscovite and chlorite defines the major foliations (Sn). Both albite and garnet occur as a porphyroblast, ranging in size 0.2÷1 mm and 0.5÷1.2 mm, respectively. Albite porphyroblasts commonly have the curved to sigmoidal inclusion trails defined by graphitic materials (Sn-1). Garnet porphyroblasts in the sample is generally characterized by paucity of inclusions and retrograde corona of bitotite and chlorite. Garnet also occurs as an inclusion within albite porphyroblast. Porphyroblastic garnet shows the compositional zonation typified by a bell-shaped spessartine profile balanced by increasing almandine from core to rim. Whereas, inclusion garnet is homogeneous compositions with rich in almandin and poor in spessatin, pyrop and grossula. All the above microstructures suggest two deformation and metamorphic stages (M1 and M2) that were affected to politic rocks of the Nam Co formation, Song Ma suture zone.References
Azañón, J. M., García-Dueñas, V., Goffé, B., (1998). Exhumation of high-pressure metapelites and coeval crustal extension in the Alpujarride complex (Betic Cordillera). Tectonophysics, 285, 231-252.
Breeding, C. M., Ague, J. J., Brocker, M., (2004). Fluid-metasedimentary rock interactions in subduction-zone mélange: Implications for the chemical composition of arc magmas. Gelogical Society of America, 32, 1041-1044.
Carmona, A. L., Pitra, P., Abati, J., (2013). Blueschist-facies metapelites from the Malpica-Tui Unit (NW Iberian Massif): phase equilibria modelling and H2O and Fe2O3 influence in high-pressure assemblages. Journal of Metamorphic Geology, 31, 263-280.
Chmielowski, R. M. and Bery, R. F., (2012). The Cambrian metamorphic history of Tasmania: The Metapelites. Australian Journal of Earth Sciences: An International Geoscience Journal of the Geological Society of Australia, 59:7, 1007-1019.
Findlay, R. H., Phan, T. T., (1997). The structural setting of the Song Ma region, Vietnam and the Indochina plate boundary problem. Gondwana Research, 1, 11-33.
Hau, B. V., Kim, Y., Thanh, N. X., Hai, T. T., Yi, K., (2018). Neoproterozoic deposition and Triassic metamorphism of metasedimentary rocks in the Nam Co complex, Song Ma Suture Zone, NW Vietnam. Geosciences Journal, 22, 459-568.
Hieu, P. T., Qing, S., Yu, Y., Thanh, N. X., Dung, L.T., Tu, V. L., Siebel, W., Chen, F., (2017). Stages of late Paleozoic to early Mesozoic magmatism in the Song Ma belt, NW Vietnam: evidence from zircon U-Pb geochronology and Hf isotope composition. International Journal of Earth Sciences, 106, 855-874.
Hoa, T. T., Tran, T. A., Ngo, T. P., Pham, T. D., Tran, V. A., Izohk, A. E., Borisenko, A. S., Lan, C. Y., Chung, S. L., Lo, C. H., (2008). Permo-Triassic intermediate-felsic magmatism of the Truong Son belt, Eastern margin of Indochina. Comptes Rendus Geoscience, 340, 112-126.
Kim, T., Kim, Y., Cho, M., Lee, J. I., (2019). P-T evolution and episodic zircon growth in barroisite eclogites of the Lanterman Range, northern Victoria Land, Antarctica. Journal of Metamorphic Geology. Doi: 10.1111/jmg. 12474.
Ko, Z.W., Enami, M., Aoya, M., (2005.) Chloritoid and barroisite-bearing pelitic schists from the eclogite unit in the Besshi district, Sanbagawa metamorphic belt. Lithos, 81, 79-100.
Lepvrier, C., Maluski, H., Vu, V. T., Leyreoup, A., Phan, T. T., Vuong, N. V., (2004). The Early Triassic Indosinian orogeny in Vietnam (Truong Son Belt and Kontum Massif): Implications for the geodynamic evolution of Indochina. Tectonophysics, 393, 87-118.
Lepvrier, C., Maluski, H., Vuong, N. V., Roques, D., Axente, V., Rangin, C., (1997). Indosinian NW-trending shear zones within the Truong Son belt (Vietnam): 40Ar-39Ar Triassic ages and Cretaceous to Cenozoic overprints. Tectonophysics, 283, 105-127.
Lepvrier, C., Vuong, N. V., Maluski, H., Phan, T. T, Tich, V. V., (2008). Indosinian tectonics in Vietnam. Comptes Rendus Geoscience, 340, 94-111.
Liu, J., Tran, M., Tang, Y., Nguyen, Q. L., Tran, T. H., Wu, W., Chen, J., Zhang, Z., Zhao, Z., (2012). Permo-Triassic granitoids in the northern part of the Truong Son belt, NW Vietnam: Geochronology, geochemistry and tectonic implications. Gondwana Research, 22, 628-644.
Maldonado, R., Weber, B., Ortega-Gutiérrez, F., Solari, L. A., (2018). High-pressure metamorphic evolution of eclogite and associated metapelite from the Chuacus complex (Guatemala Suture Zone): constraints from phase equilibria modelling coupled with Lu-Hf and U-Pb geochronology. Journal of Metamorphic Geology, 36, 95-124.
Marschall, H. R., Altherr, R., Kalt, A., Lidwig, T., (2008). Detrital, metamorphic and metasomatic tourmaline in high-pressure metasediments from Syros (Greece): intra-grain boron isotope patterns determined by secondary-ion mass spectrometry. Contributions to Mineralogy and Petrology, 155, 703-717.
Meyre, C., Capitani, C. D., Zack, T., Frey, M., (1999). Petrology of High-pressure metapelites from the Adula Nappe (Central Alps, Switzerland). Journal of Petrology, 40, 199-213.
Nakano, N., Osanai, Y., Minh, N. T., Miyamoto, T., Hayasaka, Y., Owada, M., (2008). Discovery of high-pressure granulite-facies metamorphism in north Vietnam: constrains to the Permo-Triassic Indochinese continental collision tectonics. Comptes Rendus Geoscience, 340, 127-138.
Nakano, N., Osanai, Y., Sajeev, K., Hayasaka, Y., Miyamoto, T., Minh, N. T., Owada, M., Windley, B., (2010). Triassic eclogite from northern Vietnam: inferences and geological significance. Journal of Metamorphic Geology, 28, 59-76.
Potel, S., Ferreiro Mählmann, R., Stern, W., Mullis, J., Frey M., (2006). Very low-grade metamorphic evolution of pelitic rocks under high-pressure/low-temperature conditions, NW New Caledonia. Journal of Petrology, 47, 991-1015.
Skola, S., Mahlen, N. J., Johnson, C. M., Baumgartner, L. P., Lapen, T. J., Beard, B. L., Szilvagyi, E. R., (2015). Evidence for protracted prograde metamorphism followed by rapid exhumation of the Zermatt-Saas Fee ophiolite. Journal of Metamorphic Geology, 33, 711-734.
Smye, A .J., Greenwood, L. V., Holland, T. J. B., (2010): Garnet- chloritoid- kyanite assem-blages: eclogite facies indicators of subduction constraints in orogenic belts. J. Metamorphic Geol., 28, 753-768.
Thanh, N. X., Santosh, M., Tran, T. H., Hieu, P. T., (2016). Subduction initiation of Indochina and South China blocks: insight from the forearc ophiolitic peridotites of the Song Ma Suture Zone in Vietnam. Geological Journal, 51, 421-442.
Thanh, N. X., Tran, T. H., Hoang, N., Lan, V. Q., Kwon, S., Itaya, T., Santosh, M., (2014). Backarc mafic-ultramafic magmatism in Northeastern Vietnam and its regional tectonic significance. Journal of Asian Earth Sciences, 90, 45-60.
Tinkham, D. K., Zuluaga, C. A., Stonwell, H. H., (2001). Metapelite phase equilibria modeling in MnNCKFMASH: the effect of variable Al2O3 and MgO/(MgO+FeO) on mineral stability. Geological Materials Research, 3, 1-42.
Tran, T. H., Zaw, Khin, Halpin, J., Manaka, T., Meffre, S., Lai, C. K., Lee, Y. J., Le, V. H., Dinh, S., (2014). The Tamky-Phuoc Son Shear Zone in Central Vietnam: tectonic and metallogenic implications. Gondwana Research, 26 (1), 144-164.
Tran Van Tri., Vu Khuc (Eds.), (2011). Geology and Earth Resources of Vietnam. Publishing House for Science and Technology (645 pp.).
Vuong, N. V., Hansen, B. T., Wemmer, K., Lepvrier, C., Tich, V. V., Thang, T. T., (2013). U/Pb and Sm/Nd dating on ophiolitic rocks of the Song Ma Suture Zone (northern Vietnam): evidence for upper Paleozoic Paleotethyan lithospheric remnants. Journal of Geodynamics, 69, 140-147.
Zhang, R. Y., Lo, C. H., Chung, S. L., Grove, M., Omori, S., Ilzuka, Y., Liou, J. G., Tri, T. V., (2013). Origin and tectonic implication of ophiolite and eclogite in the Song Ma Suture Zone between the South China and Indochina blocks. Journal of Metamorphic Geology, 31, 49-62
