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Presentation Mode : All
Conference Day : 06/08/2021
Time Slot : PM1 13:30 - 15:30
Sections : SE - Solid Earth Sciences










Solid Earth Sciences | Fri-06 Aug




SE15-A002
Mineralogy and Geochemistry of Cumulus Gabbros from the South Andaman Ophiolite, India.

Ashima SAIKIA#+, Salim AKHTAR, Priyanka NEGI
University of Delhi, India


The Indus‐Yarlung Tsangpo Suture Zone (IYTSZ) marks remnants of the once extensive Tethyan Ocean Mesozoic‐age, which formerly lay between India and Asia. ITYSZ is marked by a line of ophiolite occurrences east of the present-day plate boundary through the Indo‐Burma ranges (IBR) southward toward the Andaman Islands of south-east India. The South Andaman Island with several Mesozoic-age ophiolitic exposures is a part of the Andaman Islands. This study presents petrography, mineral chemistry and geochemistry for the cumulate gabbros of South Andaman Ophiolite, India. The cumulate gabbros can be petrographically clubbed into olivine-bearing and olivine-free gabbros. Textural relationships and mineral chemical data establish the following sequence of crystallisation in the gabbros: olivines (Fo~80) ± Cr- spinels (Cr# 59 - 57), plagioclases (An95−61), clinopyroxenes (Mg# = 89 - 82) and amphiboles. Major oxide and trace element whole-rock geochemistry display hybrid signature of Island Arc Tholeiite (IAT) - Mid Oceanic Ridge Basalt (MORB). Trapped melt fraction calculation based on the Equilibrium Distribution Method of Bédard (1994) suggest that the gabbroic rocks were derived from a source more depleted than the DMM. The measured REE compositions of the clinopyroxenes from the South Andaman Island gabbros conforms to the calculated clinopyroxene REE compositions at TMF 10 – 20 %. Cumulate gabbros of the South Andaman Ophiolite were generated in an oceanic back-arc and oceanic arc setting between the Indian and the Burmese plate in the Neo-Tethyan oceanic domain of the Late Cretaceous age.  

SE15-A001 | Invited
Geochemical Approach to Evaluate Slip Behavior of an Ancient Plate Boundary Fault in the Shimanto Accretionary, Japan

Ayana SHIMAMOTO1#+, Tetsuro HIRONO1, Tsuyoshi ISHIKAWA2
1Osaka University, Japan, 2Kochi Institute for Core Sample Research, Japan Agency for Marine-Earth Science Technology, Japan


Ancient plate boundary faults preserved in onland accretionary complexes have been investigated in order to understand the slip behavior during earthquake that occurred along plate-subduction boundary. In order to elucidate the characteristics and slip behavior of faults, we investigated the mélange unit in the Miyama Unit of the Hidakagawa Formation, Wakayama Peninsula, Japan. The unit is composed of sandstone, mudstone, chert, and altered basalt showing remarkable shear deformations, and some linear faults were developed. We collected samples from the main fault and its surrounding host rocks in the unit, and carried out microstructure observation, thermal background analysis using carbonaceous materials, and major- and trace-element concentration measurements. First, as a result of microstructure observation, we confirmed remarkable comminution in the primary slip zone compared to the surrounding cataclasites and host rocks. Next, as a result of Raman spectroscopic analysis of carbonaceous materials, the maximum temperature experienced host rock is estimated to 200 ℃ while the primary slip zone is 400-900 ℃. Furthermore, based on XRD and chemical analyses, the primary slip zone is found to show the decrease of quartz and the increase of plagioclase clearly compared to the host rock. We carried out model calculation assuming albitization which can be caused by high-temperature fluid-rock interactions. The chemical characteristics of the primary slip zone could be explained by albitization at 300 ℃ or higher. Accordingly, these results indicated that the mineral composition in the fault changed significantly due to interaction with high temperature fluids during or immediately after an earthquake along plate boundary fault.

SE15-A006
Geochronology, Geochemistry and Exploration Implications of Garnet at Jiama Skarn-Porphyry Deposit, Tibet, China

Fengqin RAN1#+, Juxing TANG2, Lejun ZHANG3, Bin LIN2
1Chengdu University of Technology, China, 2Institute of Mineral Resources, China, 3University of Tasmania, Australia


The Jiama skarn-porphyry Cu-Mo deposit is located 70 km east of Lhasa, Tibet, in the eastern part of the central Gangdese belt. Jiama is the largest copper skarn deposit in China and the largest copper producer in Tibet. The Jiama skarn-porphyry polymetallic system is composed of skarn Cu–polymetallic, hornfels Cu–Mo, porphyry Mo ± Cu, and distal Au mineralization. Measured and indicated mineral resources were estimated in 2013 as 1,486 Mt at 0.41% Cu, 0.034% Mo, 0.11 g/t Au, 6.14 g/t Ag, 0.05% Pb, and 0.03% Zn (Ying et al., 2016). Well-developed skarn ore and porphyry ore in the same deposit make Jiama an ideal place to study the transition features and evolution processes from porphyry to skarn. In this study, geological logging and mapping have been conducted on a long cross-section, detailed texture, trace elements, U-Pb isotopes and fluid inclusions studies of garnet from different stages and different alteration zones at Jiama using SEM, EPMA and LA-ICP-MS analytical techniques have also been employed, aims to constrain the evolution processes from porphyry to skarn, and to develop new mineral chemistry exploration tools.

SE15-A003
Cu-Au Skarn Deposits in SE Asia and Their Exploration Potentials

Khin ZAW#+
University of Tasmania, Australia


The mainland SE Asia is made up of at least four crustal terranes or blocks (e.g., Indochina, South China, Shan-Thai (Sinbumasu), and west Myanmar terranes). These terranes rifted from Gondwana in the Paleozoic and amalgamated in SE Asia in the Mesozoic. The Cu-Au skarn deposits are widely distributed in these crustal blocks in mainland SE Asia [1]. They are largely confined to fold belts (e.g., the Phu Kham, Sepon, Phonsavan deposits in the Truong Son Fold Belt of Laos PDR, Phu Tha Fah, Phu Lon, Phuthep-PUT1 and PUT2, French Mine in Loei Fold Belt of Thailand, the Khe Rin, Nui Kem and Ho Ray–Thac Trang deposits in Phuoc Son-Tam Ky Belt of Vietnam, Mengapur deposit in western Malay Peninsula Belt and the Shweminbon deposit in Mogok-Mandalay-Mergui Belt in Myanmar. The skarn Cu-Au deposits are hosted in Carboniferous, Devonian, Permian and Early Triassic sequences of volcaniclastic and siliciclastic rocks, calcareous shale and carbonate rocks. The Cu-Au skarn deposits include both oxidized and reduced types. LA ICP-MS U-Pb zircon and Re-Os dating indicate that most strongly mineralized intrusions are Early to Middle Triassic in age. The productive Cu-Au skarns were emplaced in two subduction-related continental arcs of Early Permian and Late Permian to Early Triassic followed by collision to post-collisional setting. The weakly mineralized Late Triassic skarn systems were probably emplaced in a post-collisional environment. The copper-gold skarn system should be considered as an important exploration target in the fold belts of the SE Asia region.  Keywords: Copper; Cu-Au; Skarn type; SE Asia; Collision References [1] Khin Zaw, Meffre, S., Lai, C., Burrett, C., Santosh, M., Graham, I., Manaka, T., Salam, A., Kamvong, T., Cromie, P., 2014. Tectonics and metallogeny of mainland Southeast Asia — A review and contribution. Gondwana Res. 26, 5-30.

SE15-A004
Advanced Argillic Alteration in Lower Yangtze Metallogenic Belt, East China: Porphyry-related or Magnetite (± Apatite) Deposit Related?

Lejun ZHANG1#+, Taofa ZHOU2, Noel WHITE2, Yu FAN2
1University of Tasmania, Australia, 2Hefei University of Technology, China


Lithocaps are horizontal to subhorizontal blankets of residual quartz (vuggy quartz and massive quartz) and advanced argillic alteration zone of hypogene origin (Sillitoe, 1995), are the shallow environments windows of porphyry-epithermal systems.  More and more scholars raise that whether the lithocaps can form in other magmatic-hydrothermal environments rather than the porphyry- epithermal systems?  To answer this hot topic, Luzong basin in Lower Yangtze metallogenic belt in East China is ideal for a case study. The large size of lithocap distributed in the Luzong basin and spatially associated with magnetite-apatite deposits. Vis-NIR (visible near-infrared) and SWIR (short wavelength infrared) techniques, mineral textures and chemistry, isotopic studies, fluid inclusions, and high-precision geochronology have been used in our studies to build a detailed model for the geology and alteration, explaining the genesis of the lithocap and associated deposits. Based on our data and models we will make innovations on regional metallogenic theory, the formation of lithocap, and formation of magnetite-apatite deposits, and will define specific targets for deep drilling.