Development of Detachment Faults at Intermediate Magma Supply

点击翻译按钮获取中文摘要

It is now recognized that long-lived (detachment) faults and the formation of core complexes are common, accounting for ~50% of the extension along 2500 km of the northern Mid-Atlantic Ridge (MAR). Not only do detachment faults allow the architecture of the lower ocean crust and upper mantle to be examined, but they change the way we think about the very composition and structure of ocean crust, fluid flow, and hydrothermal venting and associated ecology. But many critical questions remain: Why does a fault continue to extend, rolling over to form a core complex, while another stops after extending only for a short time? Is detachment fault formation associated with overall and/or local magma budget? Are adjacent detachments linked? The goal of this project is to try to answer these questions. In particular, to 1) constrain the processes controlling the formation, evolution, and linking of mid-segment detachment faults and; 2) examine the relationship between magma supply along the ridge axis and detachment fault formation. the chosed study area near 16.5 degrees N at the MAR presents a dramatic demonstration of a new mid-segment detachment fault near to the axis interrupting the overall development of a longer, older and still active detachment fault whose breakaway is farther off-axis. The PIs plan is to obtain regional multibeam bathymetry and magnetic data to understand the spreading history out to 5 Ma. High-resolution multibeam bathymetry, magnetic, CTD and optical sensor data will be collected from the autonomous underwater vehicle (AUV) Sentry, and photographs from the WHOI Towcam. These data will be used to characterize the detachment faults and their terminations, assessing where they are active and examining how they might link along the axis. The data also will allow assessment of the nature of volcanism at the axis. A dredging program will confirm the inferences made from bathymetric analysis as to the mantle, plutonic or volcanic origin of basement, how crustal architecture varies across the region, and will establish the degree to which the regional magma supply has been constant over detachment fault formation and possible relationships to local magma supply variations. This work will place strong constrains on models for detachment fault formation and its relationship to magma supply.Broader Impacts: The proposed study addresses several issues identified by the community at the AGU Chapman Conference ?Detachments in Oceanic Lithosphere: Deformation,Magmatism, Fluid Flow, and Ecosystems? as critical to move forward our understanding of faulting at slow-spreading mid-ocean ridges. The project has a component of international cooperation through the participation of J. Escartin and his graduate student (IPGP, Paris) and H. Zhou (Tonji University, China). Three MIT/WHOI Joint Program students will receive sea-goingexperience, and two of them will collect data that will contribute to their PhD theses. W. Zhu and two undergraduate students from U. Maryland will participate on the cruise.