FEG-EPMA mapping and Fe-Ti oxide mineral chemistry of Brahmaputra River sediments in Bangladesh: provenance and petrogen
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ORIGINAL PAPER
FEG-EPMA mapping and Fe-Ti oxide mineral chemistry of Brahmaputra River sediments in Bangladesh: provenance and petrogenetic implications A. S. M. Mehedi Hasan 1 & Ismail Hossain 2 & Md. Aminur Rahman 1 & Md. Sazzadur Rahman 2 & Mohammad Nazim Zaman 1 & Pradip Kumar Biswas 1 Received: 10 February 2018 / Accepted: 7 September 2018 # Saudi Society for Geosciences 2018
Abstract The present research deals with the FEG-EPMA mapping and Fe-Ti oxide mineral chemistry of Brahmaputra River sediments in Bangladesh. Major heavy minerals in the sediments consist of garnet (8.5–21.3%), kyanite (5.35–11.9%), monazite (2.3–5.3%), sillimanite (1.8–4.7%), zircon (3.6–9.1%), and a considerable amount of opaques mainly Fe-Ti oxide minerals (23.1–35.4%). The detrital Fe-Ti oxide minerals carry significant clues to the parent rocks or sources. In these contexts, detrital opaques (Fe-Ti oxides) have been analyzed with an electron probe microanalyzer (EPMA). These opaques (Fe-Ti oxide) display six types of textural patterns, dominantly seriate with granular, emulsion, and acicular sandwich structures and trellis type of textural patterns. These textural patterns belong to five intergrowths of Fe-Ti oxide minerals such as (1) ilmenite-hematite, (2) magnetite-ilmenite, (3) hematite-rutile, (4) ilmenite-hematite-rutile, and (5) ilmenite-rutile, where ilmenite-hematite intergrowth is common. Alteration is seen in both exsolved and unexsolved ilmenites. Textural patterns and mineral chemistry of the studied ilmenite minerals provide lines of evidence of low-temperature magmatic inheritance, later modified by diffusional processes. The estimated temperature and oxygen fugacity from the magnetite-ilmenite exsolution range from 547.6 to 558.2 °C and from 10−21.4 to 10−21.7, respectively. The data are also consistent with hematite-ilmenite temperature (between 537 and 540 °C) and oxygen fugacity (10−21.7 to 10−21.9) measurements in Cox’s Bazar beach placers. These temperatures and oxygen fugacities specify Fe-Ti oxide assemblages equilibrated in a T-fO2 field very near to the FMQ buffer curve suggesting a crustal source (magmatic and/or metamorphic), which is modified significantly by metamorphic processes. Keywords Opaque minerals . Ilmenite . Exsolution . Geothermometry . Oxygen fugacity
Introduction River sediments have enormous potentiality for heavy minerals like beach placer in Bangladesh. Major rivers of Bengal Basin carry sheer volume of these detrital river sediments, amounting to 7.35–8.00 × 10 8 tons per year by only Brahmaputra River through Bangladesh to the Bay of
* Ismail Hossain [email protected] 1
Institute of Mining, Mineralogy and Metallurgy (IMMM), Bangladesh Council of Scientific and Industrial Research (BCSIR), Science Laboratory Road, Khanjanpur, Joypurhat 5900, Bangladesh
2
Department of Geology and Mining, University of Rajshahi, Rajshahi 6205, Bangladesh
Bengal (Rahman et al. 2012). The sources of these detrital sediments are continuously draining from the whole catchment area (552,000 km2) of the
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