Deciphering Deep Crustal Structure Based on Gravity and Seismic Modeling of the Western Hawaiian Jurassic-Cretaceous Crust
Friday, 19 December 2014
We conducted gravity forward modeling to investigate and gain insight into the evolution and structure of Jurassic-aged ocean crust that has been intruded and disturbed by numerous Cretaceous age seamounts in the western Pacific Basin. Free-air gravity, reflection and refraction seismic, and bathymetry data were collected during R/V T. G. Thompson cruise TN272 over an 800-km-long transect of Mid Jurassic - Early Cretaceous Pacific ocean crust. The geophysical data are used to model the morphology of the sediment layer, upper and lower crust, and the Moho. Seafloor bathymetry reveals topographic highs, including seamounts and other relief shown by the seismic data, to be associated with volcanic intrusions of various sizes that have disturbed the basement and sediment layers along the transect. We were able to infer the shape of the Moho by constraining the thickness and density of the sediment layer and upper crust with seismic reflection and refraction data, and then adjusting the thickness of the lower crustal layer to satisfy the gravity observations. From our forward modeling, we identify three distinct segments along the survey transect characterized by differences in layer thickness of the sediment and crustal sequences and the depth to Moho. Segment-1 is characterized by volcanic intrusions that cause variations in the thickness and density of the layers of sediments and upper crust with the greatest variation in the thickness of layer 3. The Moho reaches ~20km depth. Segment-2, where no seamounts are present, shows the lack of bathymetric features at the seafloor and only small changes in sediment thickness, the upper crust, and layer 3. Segment-3 also lacks bathymetric features at the seafloor and shows the least change in thickness of the sediments, upper crust, and layer 3 in all the three segments. Our modeling suggests that the Cretaceous volcanic overprint on the Jurassic basement has a strong influence on the overall structure of the underlying sediment, upper and lower crust, and Moho depth at confined regions along our survey line.