8 Undergraduate Research Poster Session I (Posters)

Thursday, 4 May 2023
8:00 AM - 12:00 PM
EC 215

HYDRAULIC HEAD DIFFERENTIAL FOR FLUID FLOW VECTORS IN SUBAXIAL MAGMA SYSTEMS OF THE MID-ATLANTIC RIDGE (30°N TO 30°S) SUBJECT TO ROTATIONAL SHEARING

Paper number: 8-13
Program: Theme Sessions
Time: 8:00 AM – 12:00 PM

Authors

Abstract

Fluid flow in a porous medium, as with magma produced by partial melting, is governed by hydraulic head differential, porosity, and viscosity. Calculations of magmatic hydraulic heads were completed using ocean depth, crustal depth approximations, densities, and gravity values. Based on previous studies, the magmatic system was defined as a prismatic region produced by decompression melting under the mid-ocean ridge. Bathymetry-based analysis of the Mid-Atlantic Ridge (MAR) system was conducted for the region within 30° N and S of the Equator to establish pressure gradients. ArcGIS software was used to produce quantitative evidence of differential loading for areas of a 20 km radius at intervals of about 9 km for the non-transform ridge segments. Pressure loading under the MAR in both hemispheres showed an overall gradient toward the Equator where ocean depths were the deepest and geoid gravity values were the lowest. Porosity values of 2%, 4%, and 9% were used for the 50 km depth, 10 km depth, and high porosity melt regions respectively. This analysis showed flow vectors between ridge points with averages of 0.78 cm/yr. at 50 km depths and 4.28 cm/yr. at 10 km depths with even greater velocities in the high porosity areas along the flanks of the melt prism. With horizontal flow established, investigation continued with geometric analyses of the ridge and transform segments. If original fracture patterns for the MAR were N-S for ridge segments and E-W for transform offsets, patterns indicate left-lateral, strike-slip faulting of transforms and primarily clockwise rotation in the N. Hemisphere. Comparatively, the S. Hemisphere exhibits counterclockwise rotation of ridge segments and primarily right-lateral strike-slip faulting up to 30° latitudes. Previous studies have suggested connections between the Coriolis force and observed rotation, but lack evidence for large-scale mantle movement as a driver. This study presents the potential for localized flow under the MAR system that may be subject to the Coriolis force thus producing rotational shearing. Calculated Rossby numbers ranged between 1x10-11 at 30° N or S to 1x10-8 near the Equator suggesting an increased impact of Coriolis shearing with latitude. Therefore, the observed displacement and rotation can be linked back to magma flow influenced by pressure at depth.

Geological Society of America Abstracts with Programs. Vol. 55, No. 3

doi: 10.1130/abs/2023NC-386748

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