Type, Genesis, and Provenance Implications of Amphiboles in Sediments in the Northwest Indian Ocean over 42,000 Years

Abstract

Five layers of detrital amphiboles in the CJ08-008 sediment core from the northwest Indian Ocean have been found. To analyze their genetic types and provenance, an electron probe microanalysis of 300 amphibole grains from the core was conducted to calculate the numerical and characteristic values of cations in the crystal structure. The results showed that amphiboles with high Si, Ca, and Mg contents and low Na and K contents exhibit a low degree of weathering and that amphiboles mainly comprise tschermakite (46.43~70.69%), followed by magnesiohornblende, in the calcic amphibole subgroup. The types of sources for these amphiboles are mainly different types of metamorphic and magmatic rock. A large proportion of the detrital amphiboles (>60%) are derived from metamorphic rocks, followed by intermediate acid-intrusive rocks. The genetic analysis of amphiboles showed that most of the medium acid-intrusive amphiboles belong to the crust–mantle type, followed by the mantle type. Most of the amphiboles of metamorphic origin are of the low-pressure type. The amphiboles in the CJ08-008 sediment core exhibit characteristics different from those brought by monsoons from surrounding land masses. The variations in the amphiboles indicate different sources, which may have different origins; these origins could include the Carlsberg Ridge, the Owen Fault Zone, or older submarine sediment sequences eroded by turbidity currents.

Keywords

• northwest Indian Ocean
• amphiboles
• source rock
• genetic types
• provenance