Chromian spinel-rich black sands from eastern shoreline of Andaman Island, India: Implication for source characteristics

Abstract

Black sands rich in chromian spinel commonly occur in pockets along the eastern shoreline of Andaman Island where various types of peridotites and volcanics belonging to the Andaman ophiolite suite are exposed in close vicinity. The chemistry of these detrital chromian spinels has been extensively used here in identifying the source rocks vis-à-vis deciphering the source characteristics. The composition of the chromian spinels (Cr#: 0.20-0.88, Mg#: 0.26-0.77, Al 2 O 3 : 5.04-48.21 wt.%, TiO 2 : up to 1.39 wt.% and Fe 2+ /Fe 3+ : 1.73-9.12) varies widely signifying multiple sources, of which mantle peridotites and volcanic rocks are relevant in an ophiolitic terrain. The volcanic chromian spinels are relatively fresh, commonly euhedral, sometimes with compositional variations, and contain inclusions in contrast to the mantle peridotitic chromian spinels which are rounded, extensively fractured, and altered. We used a number of geochemical bivariate plots in order to know the provenance protoliths. The volcanic chromian spinels show geochemical characters of MORB, related to spreading centers (either MOR or back-arc) and also boninites/arc-tholeiites, related to active subduction. On the other hand, the peridotitic spinels indicate partially depleted lherzolite and depleted harzburgite source of the ophiolite suite.

Chromite Paleoplacer in the Permian Sediments at the East Edge of the East European Platform: Composition and Potential Sources

“…The noted class of chromspinel grain size (0.15-0.25 mm) is typical of placers [17,51,52]. Grains with this size and a density of ca.…”

“…The Fe 2+ /Fe 3+ ratio is an additional criterion to divide chromspinels into the mantle and volcanic types [45,52]. Thus, chromite of mantle affinity usually has a high Fe 2+ /Fe 3+ ratio, and, vice versa, chromite from volcanic rocks has a low ratio.…”

“…Figure18. Discrimination diagrams for chromspinels of Sabantuy paleoplacer: (a) TiO2 vs. Fe 2+ /Fe3+ showing the compositions of all detrital chromspinels studied, peridotite and volcanic chromspinel fields are taken from[13]; (b) Mg# vs. Cr# for peridotite chromspinels, and fields are taken from[62]; (c) Al2O3 vs. TiO2 for peridotite chromspinels, and fields are taken from[52]; (d) Al2O3 vs. TiO2 for volcanic chromspinels, and fields are taken from[45]. MORB-middle ocean ridge basalts; ARC-island arc magmas; OIB-oceanic island basalt.…”

Chromian Spinels from Kazanian-Stage Placers in the Southern Pre-Urals, Bashkiria, Russia: Morphological and Chemical Features and Evidence for Provenance

“…The most popular among these diagrams are Al 3+ -Cr 3+ -Fe 3+ , Cr#-Mg#, Cr#-Fe#, Al 2 O 3 -TiO 2 , TiO 2 -Fe 2+ /Fe 3+ [60,61]. Analysis of geochemical signatures of detrital chromian spinels using these discrimination diagrams is a critical tool for interpretation of sources for terrigenous sediments [21,[66][67][68].…”