The Coast Range Ophiolite (CRO) debate is fraught with complimentarities and indeterminacy - a few examples

Abstract

Because we work primarily with rocks, we perhaps assume that our science is immune to complimentarity and indeterminacy. But these information- based limitations plague tectonic analysis as they do for any branch of science. An educated and unbiased (if possible) observer of the CRO debate (Dickinson et al., 1996) should have little trouble recognizing these limitations in the three views (V1, 2 & 3) expressed. Each view is dependent on missing geology: V1 requires the near total destruction of two opposing subduction complex-forearc systems along a Nevadan suture by subduction and/or erosion. V2 requires an unobservable subduction zone along the axis of the Great Valley. V3 appeals to total removal or burial of screens of older Sierran lithosphere from the outer edge or within the CRO. Each view has a different pre-Cretaceous origin for the source of the Great Valley geophysical anomaly, yet basement cores from the area of the anomaly are primarily Early Cretaceous mafic batholithic rocks. V3 is predicated on forearc magmatism. This view is dismissed in V1 on the basis of forearcs being cold and amagmatic, yet V1 requires a regional belt of Middle Jurassic (pre-Nevadan) plutons to have intruded the remnants of the juxtaposed subduction complexes. V1, 2 & 3 are all dependent on subducted slab-related geochemical tracers within the CRO, and on absolute age relations within the igneous sequences. A global survey of Neogene mafic magma systems reveals large uncertainties in the geochemical tracers, particularly when taking into account hydrothermal alteration and mantle metasomatism. Furthermore, Neogene arc systems show reorganization in magmatic loci and microplates at time scales comparable to typical uncertainties in absolute age determinations.