MANTLE MELTING RELATIONSHIPS RECORDED BY ABYSSAL PERIDOTITE TRACE ELEMENT ABUNDANCES

The Godzilla Megamullion is the world’s largest oceanic core complex and is located in the Parece Vela Basin of the Philippine Sea. The area of interest in divided into proximal, medial and distal sections with respect to the backarc basin’s spreading ridge. The distal region (~85-155 km from spreading ridge) experienced high rates of spreading and is associated with depleted abyssal peridotites. The medial region (~55-85 km from spreading ridge) is distinguished by a slower spreading rate and peridotites more fertile than ones found in the distal region. The young proximal region (~0-55 km from spreading ridge) contains plagioclase bearing peridotites and had a slower spreading rate than the medial and distal regions. Samples retrieved have experienced post-exhumation processes such as serpentinization, mylonitization and seafloor alteration. Abyssal peridotite clinopyroxene and orthopyroxene minerals from the Godzilla Megamullion were analyzed for trace element compositions to tell the variable mantle melting relationships between the proximal, medial and distal regions. Clinopyroxenes and orthopyroxenes were analyzed using Laser-Ablation Inductively-Coupled-Plasma Mass-Spectrometer. Findings from the most recently exposed proximal region indicate that chondrite-normalized rare earth element patterns from clinopyroxenes vary between samples from mildly depleted patterns (La/Yb_N > 0.7) to significant light rare earth element depletion (La/Yb_N ≈ 0.006). Other trace element abundance data also support this variable depletion pattern (e.g. Sr/Nd_N ≈ 0.01-0.7, La/Nd_N ≈ 0.01-2.0, Lu/Hf_N >1). Chondrite-normalized orthopyroxene trace element data also show a depletion in light rare earth elements (La/Yb_N < 0.01, Sr/Nd_N < 0.01, La/Nd_N < 0.2) and a relative enrichment of heavy rare earth elements (Lu/Hf_N > 3). Though the trace element abundances vary among samples, the depletion of light rare earth elements shows there was a significant degree of partial melting during backarc extension of the Godzilla Megamullion oceanic core complex.