Supra-subduction and abyssal mantle peridotites of the Coast Range ophiolite,California |
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| Authors: | Sung Hi Choi John W Shervais Samuel B Mukasa |
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| Institution: | (1) Department of Geological Sciences, University of Michigan, Ann Arbor, MI 48109-1005, USA;(2) Present address: Korea Polar Research Institute, Songdo Techno Park 7-50, Incheon, 406-840, South Korea;(3) Department of Geology, Utah State University, Logan, UT 84322-4505, USA |
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| Abstract: | The Coast Range ophiolite (CRO) of California is one of the most extensive tracts of oceanic crust preserved in the North
American Cordillera, but its origin has long remained controversial. We present here new data on mineral compositions in mantle
peridotites that underlie crustal sections of the ophiolite, and show that these are dominantly refractory harzburgites related
to high apparent melting in a supra-subduction zone (SSZ) setting. Abyssal peridotite (characterized by high-Al spinels and
relatively high Ti, Na, Nd, Sm, Lu, and Hf in pyroxene) occurs at one location where it is associated with SSZ mantle peridotite
and volcanic rocks with both oceanic and arc-like geochemistry. SSZ mantle peridotites (characterized by intermediate-Cr/Al
or high-Cr spinels, and by extremely low Ti, Na, Nd, Sm, Lu, and Hf in pyroxenes) are associated with crustal sections containing
arc-related volcanic rocks, including boninites. This convergence between conclusions based on crustal lithologies and their
underlying mantle sections confirms previous proposals that link the CRO to SSZ processes, and seriously undermines hypotheses
that invoke formation of the ophiolite at a mid-ocean ridge spreading center. |
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