Introduction
Brahmaputra River, the peculiar drainage pattern of large Southeast Asian rivers, reflects a complicated tectonic history of crustal deformation in the Himalaya and river re-organization. In general, the Himalayas are divided into three tectono-lithologic domains: the Lower Himalayas, the Higher Himalayas and the Tethys Himalayas (Amano and Taira, 1992); surprisingly this river flows through over these three domains (Fig.1). The mineral assemblages are correlated with these subdivisions of the Himalayas on the basis of the similarity between the inferred geology from mineral assemblages and each provenance-geology. The diversity of detrital mineral assemblages is particularly prominent in modern and ancient siliciclastic sequences of river sediments. The value of the technique lies not only in the number of possible minerals, but also in that many of them have petrogenetic parageneses that positively identify the involvement of particular parent rocks.
Single grain analytical methods have been most successful in constraining provenance compared with bulk methods (Gehrels et al., 1995; Mange and Morton, 2007). This approach is based on the principle of finding a diagnostic and distinct property for individual mineral grains using their physical and geochemical properties …show more content…
Two types of information were obtained. Initially, the bulk heavy mineral sample was mapped using a high resolution Field Emission Gun (FEG) equipped EPMA (JEOL 8500F Hyperprobe). It was done in order to determine the distribution of major and minor mineral phases within the sample, and next, to examine the chemical homogeneity of the ilmenite grains. In FEG-EPMA mapping, the operating conditions were an accelerating voltage of 15 kV, a beam current of 100 nA, a step size of 2 mm (in x and y), and a counting time of 25 minutes per
Brahmaputra River, the peculiar drainage pattern of large Southeast Asian rivers, reflects a complicated tectonic history of crustal deformation in the Himalaya and river re-organization. In general, the Himalayas are divided into three tectono-lithologic domains: the Lower Himalayas, the Higher Himalayas and the Tethys Himalayas (Amano and Taira, 1992); surprisingly this river flows through over these three domains (Fig.1). The mineral assemblages are correlated with these subdivisions of the Himalayas on the basis of the similarity between the inferred geology from mineral assemblages and each provenance-geology. The diversity of detrital mineral assemblages is particularly prominent in modern and ancient siliciclastic sequences of river sediments. The value of the technique lies not only in the number of possible minerals, but also in that many of them have petrogenetic parageneses that positively identify the involvement of particular parent rocks.
Single grain analytical methods have been most successful in constraining provenance compared with bulk methods (Gehrels et al., 1995; Mange and Morton, 2007). This approach is based on the principle of finding a diagnostic and distinct property for individual mineral grains using their physical and geochemical properties …show more content…
Two types of information were obtained. Initially, the bulk heavy mineral sample was mapped using a high resolution Field Emission Gun (FEG) equipped EPMA (JEOL 8500F Hyperprobe). It was done in order to determine the distribution of major and minor mineral phases within the sample, and next, to examine the chemical homogeneity of the ilmenite grains. In FEG-EPMA mapping, the operating conditions were an accelerating voltage of 15 kV, a beam current of 100 nA, a step size of 2 mm (in x and y), and a counting time of 25 minutes per