HR: 09:20h
AN: V21B-06    [PDF]
TI: Origin of Cross-Grain Gravity Lineations and Intraplate Volcanic Ridges: Constraints and Ideas From the GLIMPSE Experiment
AU: * Forsyth, D W
EM: Donald_Forsyth@brown.edu
AF: Brown University, Dept. of Geological Sciences, Brown University, Providence, RI 02912 United States
AB: Three hypotheses have been advanced in the literature for the origin of cross-grain gravity lineations and associated volcanic ridges in the Pacific: small-scale convective rolls aligned by asthenospheric shear in the direction of absolute plate motion; lithospheric boudinage or cracking by remotely applied stresses; and mini-plumes or hotspots. Inspired by the compositional anomalies and age progression along the Pukapuka ridge, we have suggested a fourth possibility; that the volcanic ridge and seamount chains are associated with rapid transport of volatile-rich, low viscosity mantle in the asthenosphere back toward the East Pacific Rise. The GLIMPSE experiment was designed to provide constraints on these conceptual models by measuring crustal thickness variations, seismic velocity anomalies in the underlying mantle, density anomalies as revealed through bathymetry and gravity, variations in mantle composition and the depth and degree of melting as indicated by major and trace elements and isotopic composition of the melt products, thickness of the brittle lithosphere shown by depth extent of microearthquakes, and age progression of volcanism. The study area west of the East Pacific Rise and just south of the Garrett fracture zone includes the Hotu-Matua volcanic complex, which has recent volcanic activity distributed over a region about 60 km across and 200 km long, and the Sojourn/Brown ridges, which are the largest and most continuous of these intraplate volcanic ridges. A year-long deployment of ocean-bottom seismometers, extensive underway geophysical surveying and dredging and geochemical analysis of basalts indicates that there are distinct differences between the processes of formation of the Hotu/Matua and Sojourn/Brown chains. Our current interpretation is that, rather than the gravity lineations beginning to form in seafloor 4-5 Ma old, they die out as the East Pacific Rise spreading center is approached.
DE: 3000 MARINE GEOLOGY AND GEOPHYSICS
DE: 7200 SEISMOLOGY
DE: 7218 Lithosphere and upper mantle
DE: 7220 Oceanic crust
DE: 8120 Dynamics of lithosphere and mantle--general
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting