HR: 18:15h
AN: V74B-07 INVITED     [Abstracts]
TI: Source Variations Along the EPR Identify Melt flow and Influence Segmentation
AU: * Salters, V J
EM: salters@magnet.fsu.edu
AF: Florida State University, 1800 E Paul Dirac Drive, Tallahassee, FL 32310, United States
AU: Mallick, S J
EM: mallick@magnet.fsu.edu
AF: Florida State University, 1800 E Paul Dirac Drive, Tallahassee, FL 32310, United States
AU: Sachi-Kocher, A
EM: sachi@magnet.fsu.edu
AF: Florida State University, 1800 E Paul Dirac Drive, Tallahassee, FL 32310, United States
AB: Understanding the melting processes and the relation between the source variations and the melting process is crucial in understanding the sub-ridge processes. We have analyzed at high "density" samples from the EPR between 8-18N for trace elements and isotopes. At the EPR we observe a systematic variation in the chemical composition of the basalts related to ridge discontinuities, both at fracture zones and at overlapping spreading centers. The variations in the chemistry are of two types: 1. There is a discontinuity in composition across a fracture zone or overlapper. This discrete jump in composition can be identified in both the trace element ratios as well as the isotopic compositions. 2. The chemical variations in each individual ridge segment indicates two component mixing. However, the two components differ from segment to segment. The first type of variation can be explained by low degrees melts traveling across the ridge continuity. At migrating ridges such as the EPR leading (LE) and trailing edges (TE) of ridge segments have been identified. LEs have thicker crust suggesting a larger accumulation of melt. The low degree melts generated of-axis on the TE of the ridge segment can find a shorter route to the ridge by crossing the transform fault plane. The LE therefore has additional low-degree melts which are missing at the TE. The area on the EPR we covered contains four fracture zones (Siqueros, Clipperton, Orozco and 18N) as well as three overlapping spreading centers. We observe discontinuities in the chemical composition of the basalts at all eight ridge discontinuity. The changes in the trace element ratios like Ce/Yb, Ba/La, Sm/Nd at six of the seven discontinuities are consistent with the LE receiving a larger amount of low degree melt, as predicted by the geophysical model. The Clipperton Fracture zone is the only discontinuity that has chemical variations that are the reverse of what is expected based on the model. Secondly, and perhaps most importantly, the chemical variations within the individual ridge segments are distinct from each other. Each individual segment represents two component mixing, but the components change from segment to segment. The coincidence of chemical discontinuities with ridge discontinuities is consistent for all eight ridge segments and indicates that the segmentation is influenced by the mantle composition. It is hypothesized that changes in mantle source composition, like variations in solidus or mineralogy, can potentially result in changes in the melting regime like depth of melting and melt rate that causes enough stresses to locate the ridge discontinuities at places where the discontinuities n the mantkle composition are the largest.
DE: 1009 Geochemical modeling (3610, 8410)
DE: 1038 Mantle processes (3621)
DE: 3614 Mid-oceanic ridge processes (1032, 8416)
SC: Volcanology, Geochemistry, and Petrology [V]
MN: 2009 Joint Assembly