Crustal Structure of Rifled and Convergent Margins: The U.S. East Coast and Aleutian Margins.
Abstract
Processes that create and modify continental crust occur at continental margins. We investigate the crustal structure across the U.S. East Coast rifted margin and the convergent margin of Alaska using modem marine seismic techniques. Rifling of the U.S. East Coast margin was characterized by voluminous volcanism. We constrain the landward extent of crustal extension and rift magnetism to within a narrow region beneath the shelf and slope. The crust thinned here by 50-80% and then spreading began. Constraints from seismic imaging show that initial volcanism was accompanied by rapid margin subsidence, suggesting a limited and finite mantle source for the volcanism. We study the evolution of continental crust through terrane accretion and arc magnetism along transects across the Alaska Peninsula, where subduction occurs beneath accreted oceanic arc crust, and across older Bristol Bay crust. The velocity structure of the Peninsular accreted terranes is similar to intraoceanic arc crust and more mafic than continental crust. Accretion has apparently not modified the terranes' composition. The Bristol Bay crust is also composed of accreted oceanic arc terranes but has a continental velocity structure. If this crust was originally more mafic, then both crustal thickening and removal of a mafic component are required to explain its current structure processes consistent with the region's history.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jun 01, 1997
- Accession Number
- ADA342944
Entities
People
- Daniel Lizarralde
Organizations
- Massachusetts Institute of Technology