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The Salinian block in the Salinas Valley region of central California consists of arc granitic and metasedimentary rocks (schist of Sierra de Salinas) sandwiched between coeval high-pressure, low-temperature mélange belts. U-Pb zircon ages of three granitic plutons from this region range from 88 to 82 Ma, and coexisting biotite yielded 40 Ar/ 39 Ar cooling ages of 76-75 Ma. The U-Pb ages from detrital zircons indicate derivation of the protolith of the schist from a 117-81 Ma igneous provenance. Muscovite and biotite 40 Ar/ 39 Ar cooling ages of 72-68 Ma from the nearby schist are distinctly younger than those from the granitic plutons. These data indicate that deposition and metamorphism of the schist occurred after emplacement of adjacent granitic rocks, contradicting the prevailing view that the schist comprises the local framework for the Salinian arc. We propose that the schist of Sierra de Salinas was thrust beneath the Salinian magmatic arc along a Campanian thrust fault that has not been recognized. This hypothesis implies that the Salinian arc originated as a klippe of basement rocks derived from the vicinity of the western Mojave Desert. Thrusting initiated southeastward-migrating Laramide tectonism of a style similar to that which formed the Vincent thrust and the latest Cretaceous and Paleocene Pelona and Orocopia Schists of southern California and southwestern Arizona.

Recent detailed work in key regions along two north-south transects in northern New Mexico highlights continued controversy about Proterozoic tectonic evolution. Ductile deformation features (folds, ductile thrusts, and associated foliations and lineations) are grouped into three deformation generations. D, includes cryptic bedding-parallel foliation and fold nappes. D, involves north-verging, km-scale inclined folds, the main shortening foliation, and D,, structures that further attenuate or reactivate F, folds. D, involves east-west-trending open folds and domes and associated crenulation cleavage. Although others can dominate locally, S , is the dominant regional foliation that could possibly be imaged seismically. Map relationships around ca. 1.65-and ca. 1.42-Ga plutons and porphyroblast-matrix studies of dated minerals show that D, occurred at ca. 1.42. The age of D, is more uncertain and could be 1.65 or 1.42 Ga. Metamorphic studies also indicate multiple metamorphic events, MI-M,, that may relate to the deformational events. New geochronology indicates that most metamorphic minerals grew (or were reset) at ca. 1.47-1.35 Ga. U-Pb dates on metamorphic zircon, monazite, titanite, staurolite, garnet, and tourmaline suggest regional metamorphism to 550-700" C at 1.47-1.42 Ga. Metamorphic aureoles are present around plutons, but the highest grades of metamorphism are in areas with no exposed 1.42-Ga plutons. Metamorphism is interpreted to record a regional mantle-driven thermal event, the latter parts of which correspond to a time of pluton emplacement. 40Ar/39Ar dates record post-1.42-Ga cooling: the highest grade rocks yield the youngest cooling ages, indicating slow cooling and gradual unroofing of the 1.42-Ga thermal profile following 1.42-Ga metamorphism. Our preferred model is that macroscopic geometries (D,-D,) were established by 1.65 Ga, and that regional amphibolite-grade metamorphism and associated D, deformation at 1.47-1.42 Ga produced localized high-strain domains and fabric reactivation at exposed levels. At deeper levels, structures and assemblages may increasingly record 1.42-Ga reactivation.

Two major Proterozoic tectonic events are documented in the Taos Range of northern New Mexico.Regional structures involving the tectonic interleaving of c.