The present study describes results obtained from the chemistry of detrital heavy
minerals i.e. pyroxene, amphibole, biotite, garnet, epidote and Fe-Ti oxides in fluvial
sediments of the northern Brahmaputra River (Bangladesh) with an aim to determine
conditions of their petrogenesis and provenance. The primary and sec-ondary genera
of ferromagnesian minerals occurred in calc-alkaline and peraluminous subduction zone.
In which, the garnets are Fe-rich, indicating mostly almandine component (Alm65-Pyp16-Grs8-Sps6
averagely), occurred in medium to high grade metasedimentary rocks in the Lesser Himalaya
(LH), along the Main Central Thrust (MCT) and the eastern Himalayan syntaxis. Besides,
the fingerprint of omphacite and actinolite owe to ascertain the co-existence of garnet
developed in ultrahigh-pressure (UHP) eclogites that may also be drained from the
Tso Morari massif. Augite to aegirine-augite pyroxenes emphasizes Fe enrichment in
basaltic systems and high to ultrahigh grade metamorphic rocks, which are exposed
in the LH, Shillong Plateau, Mikir Hills, South Tibetan Detachment System (STDS),
eastern Himalayan syntaxis and Tso Morari massif. Geochemistry and thermobarometry
of the primary magmatic amphiboles and biotites manifest the source of granitoid and
granodiorite like bodies, and their windows are exposed in the Bomi-Chayu, Gangdese
arcs and the western Arunachal Himalaya. Again, metamorphosed Fe-Ti oxide minerals
are well-exposed along the NE Lesser Hima-laya, where magmatic derivative of Fe-Ti
oxide minerals were modified through the diffusional processes in low-grade metamorphism
(534-562 degrees C with 10-22.1-10- 21.5 fo2). Integrating the aforementioned discussion
with the thermochronology, it is evident that the eastern Himalayan syntaxis is the
major source of sediment flux, which is carried mostly by the upper Himalayan tributaries
i.e. Yigong, Parlung, Dibang and Lohit. Also, the lower Hi-malayan tributaries i.e.
Subansiri and Manas drain the sequestered derivatives dominantly from the Arunachal
Himalayan. Tso Morari eclogites (NW Himalaya) have also contribution somewhat of dense
minerals to the Tsangpo-Brahmaputra River system. Thus, scrutinizing the fingerprint
of single-grain detrital minerals provides key information regarding the source terrains
and tectonics of the Himalayan sequences.
