Date of Award

Spring 5-2021

Degree Type

Masters Thesis

Degree Name

Master of Science (MS)

School

Biological, Environmental, and Earth Sciences

Committee Chair

Jeremy Deans

Committee Chair School

Biological, Environmental, and Earth Sciences

Committee Member 2

Franklin Heitmuller

Committee Member 2 School

Biological, Environmental, and Earth Sciences

Committee Member 3

Mark Puckett

Committee Member 3 School

Biological, Environmental, and Earth Sciences

Abstract

This thesis aims to re-orient borehole images of layered gabbros sampled beneath Hole GT1 in the Wadi Tayin massif of the Oman ophiolite by the Oman Drilling Project to better constrain models of crustal accretion. The gabbro glacier model proposes that crystallized basalt flows down and away from the crystallization site to form the lower crust while the sheeted sill model proposes that basaltic melt crystallizes at multiple levels in the crust through sills. Hole GT1 provides an unprecedented 400 m, 100% recovery, look at the lower oceanic crust. Cores lose their geographic orientation when drilled, requiring use of the programs like Techlog to match core observations with borehole images oriented relative to north to re-orient the core. Layering is more common throughout the borehole overall but becomes sparse past 250 meters below surface (mbs) whereas magmatic fabrics become more frequent past 300 mbs. Most magmatic fabrics share an average strike of 060 while layering measurements strike close to 355. Both undergo an orientation shift from NE to SW past 300 mbs. The non-systematic distribution of MFs and layering observed below Hole GT1 matches more closely with the sheeted sill model and the idea of melt intruding an upper crystal mush reservoir as a mixing bowl that develops layering and fabrics if enough melt is present for further intrusion. The variance in dip azimuth downhole implies that these features formed through local processes, which supports geochemical evidence that the lower crust forms in an open system through multiple re-intrusions.

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