[HCG23-09] Heavy mineral assemblage of river sands along the Kaligandaki River, central Nepal and its application for Bengal Fan sediments
Keywords:Miocene, Himalaya, Bengal Fan
The assemblage of heavy minerals in Kari Gandaki river tributaries clearly reflected the rock assemblage distributed in the catchment. The tributaries from the catchment area of the Tethys Himalaya zone shed ultra-stable minerals, such as zircon, tourmaline and rutile. The High Himalayan Crystalline zone provided metamorphic minerals, such as amphibole, sillimanite, kyanite, staurolite. The catchment consists of the Main Central Thrust zone (MCT zone) and the Lesser Himalayan zone carried the mica-rich detritus with oxidized iron minerals and amphiboles.
The detrital garnet compositions are also depending to geological units distributed in the catchment area; Tethys Himalaya area derives mainly almandine (Mg<20 mol %) garnets, whereas High Himalaya Crystalline produces Mg-rich (Mg>20 mol %) almandine garnets with specific amount of Ca-rich (Ca>20 mol %) almandine derived from calculous gneiss.
Comparison with Bengal Fan sediments which recovered in IODP Exp. 354, sillimanite and kyanite were found from Early Miocene sediments. The detrital amphiboles dramatically increased from the Middle Miocene (13 Ma), which is suggestive to initial major uplift of High Himalaya Crystalline started from this period. In addition, though Mg-rich garnets are minor components until the Early Miocene time, those are clearly increased from Late Miocene time (9.2 Ma). Several compositional fluctuations were detected in the Middle and Late Miocene sections in Bengal Fan sediments, above described compositional change, which is irreversible in the historical record of detrital garnet chemistry, suggests several stages of major uplift of the Himalaya during Miocene time.