Date of Award


Document Type

Honors Thesis (Open Access)


Colby College. Geology Dept.


Robert A. Gastaldo

Second Advisor

Valerie S. Reynolds

Third Advisor

Paul S. Hall


The northernmost portion of the Lau basin, South Pacific, features numerous geochemical and geophysical anomalies. These include: (1) a strong latitudinal gradient in the trace element and isotopic (Sr-Nd-Pb) enrichment of basalts erupted along the various back-arc spreading centers (BASCs) within the basin, (2) high 3He/4He (up to 28 times RA, where RA, the ratio in Earth's atmosphere, is 1.4 x 10-6) in basalts erupted along some portions of the BASCs (e.g., Rochambeau Bank), and (3) the presence of trench-parallel shear-wave splitting near the Tonga arc. The occurrence of these anomalies has been attributed to the southward flow of mantle from the nearby Samoan hotspot into the northern Lau basin. Here, I present results from a series of numerical geodynamic experiments undertaken to test the viability of this hypothesis, and constrain both the total extent and the spatial distribution of any incursion of Samoan-plume mantle into the northern Lau basin. The experiments were conducted using the COMSOL Multiphysics Finite Element Modeling package to model mantle flow and melting within a 2-dimensional model domain corresponding to a north-south cross-section through the upper 400 km of the mantle, extending from the Pacific plate north of the Vitiaz lineament through the northern Lau basin. Experiments indicate that if the southward-flowing Samoan-plume mantle is hotter than ambient mantle, it would experience extensive melting due to adiabatic decompression as it moves from beneath the older (>100 Ma), colder, and thicker Pacific lithosphere to the younger (<5 Ma), warmer, and thinner lithosphere of the Lau basin south of the Vitiaz lineament. Experimental predictions of melt production are compared to bathymetric data from the northern Lau basin to constrain both the physical characteristics (e.g., temperature) and spatial distribution of the flow of Samoan-plume mantle into the basin.


Lau basin, mantle, modeling software

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