GEOCHEMICAL ASSESSMENT OF CRYPTOTEPHRAS FROM IODP CORE U1396C

IODP marine drill core U1396C, collected off the coast of Montserrat, Lesser Antilles in 2012, contains a record of nearly 4.5 million years of eruptive and depositional history. This is a significantly longer record than exists on-land as terrestrial volcanic deposits are frequently eradicated or obscured through weathering processes. In comparison, the bathypelagic zone (~800 m below sea level) experiences nearly constant background deposition (2-5 cm kyr^-1) and minimal erosion. Subsequently, both major and minor volcanic deposits are more readily preserved and may possess higher temporal resolution than terrestrial deposits.

Identifying volcaniclastic deposits in drill cores can be challenging. A combination of magnetic susceptibility, VSWIR spectroscopy, and X-ray fluorescence has been shown to accurately identify volumetrically small volcanic deposits (termed cryptotephra) rapidly and accurately. In a previous study, these techniques were used to identify 29 potential cryptotephras from IODP core U1396C. To study the geochemical evolution of the Lesser Antilles Arc, these cryptotephras were extracted, chemically treated to remove biogenic calcium carbonates, and sifted to remove fines. After filtering, the remaining volcaniclastic material, consisting mainly of glassy pumice and mineral fragments, was embedded in epoxy to create 1” rounds. The University of Tennessee Cameca SX100 electron microprobe was used to determine the chemical composition of the volcanic glasses present. We present the analytical results and discuss them in the context of the evolution of the northern Lesser Antilles arc.