Part 1 of this work (Sedlock, Ortega-Gutiérrez, and Speed) is a synthesis of geoscientific data pertaining to México and northern Central America using the framework of a new division of these regions into tectonostratigraphic terranes. First, we review the morphotectonic provinces and the modern plate tectonic framework of the region. Next, we present data for 17 terranes that, except for North America, are named after indigenous cultures. Terrane descriptions are based on published and unpublished geophysical and geologic data of all types, utilizing a much more extensive data base than that used in previous terrane divisions. Each terrane description includes, if possible, an interpretive geologic and tectonic history focusing on distinctive features; a description of constituent rock units, with extended descriptions of especially significant or controversial units; a schematic tectonostratigraphic column, which in many cases shows geographic variation in the form of a structure section; and a compilation of radiometric data, including dates, system used, errors, and sources. Finally, we discuss the rationale for distinguishing individual terranes and summarize data concerning the orientation, nature, and kinematic history of terrane boundaries. An extended reference list is included.Part 2 of this work (Sedlock, Speed, and Ortega-Gutiérrez) is a speculative model of the Late Precambrian to Cenozoic tectonic evolution of the terranes that comprise México and northern Central America. First, we discuss numerous formal premises on which the model is predicated, including Late Jurassic sinistral slip on the Mojave-Sonora Megashear and Late Cretaceous-Paleogene northward displacement of Baja California. Next, we review constraints imposed by plate motion models on the tectonic evolution of the region. Finally, we present a reconstruction of the tectonic evolution of the region that, while certainly not a unique solution, is an internally consistent solution that is testable in many respects.The following are a few of the salient features of the reconstruction. (1) Grenville basement in eastern and southern México is regarded to be far-traveled with respect to the southern termination of the Grenville belt in North America. (2) The late Paleozoic Ouachitan suture that marks the collision of North America and Gondwana does not and did not extend into central México. (3) The Permo-Triassic continental arc on the western margin of Pangea affected only the far eastern edge and far northwestern corner of México; most of what is now México was a complex assemblage of arcs, continental blocks, and basins in the oceanic region west and south of the Pangean continental arc. (4) Continental México grew most markedly toward its present form during the Late Triassic and Jurassic as terranes were episodically accreted to its southern and western flanks. (5) Mesozoic southward and westward continental growth was accompanied by a southward and westward shift of the locus of arc magmatism. (6) The technically active southern and ...

We synthesize available geologic and geophysical data from southern California and adjoining areas in order to develop a reconstruction of the tectonic evolution of the southern Coast Ranges, western Transverse Ranges, and borderland regions of California since 30 Ma. Premises include specified relative plate motions for times prior to 10.5 Ma and after 3 Ma, a mid‐Tertiary bight in the continental margin of southern California, midcrustal detachment faults under much of California and adjoining regions, rotation of the western Transverse Ranges about an eastern pivot, and specified fault displacement histories. Prior to 18 Ma, about 90% of the tangential component of Pacific‐North America relative motion was accommodated on an offshore dextral fault system near the toe of the continental slope. From 18 Ma to 5.5 Ma, dextral slip was accommodated predominantly on the offshore system but also on a second, inboard system that included the San Andreas fault. Fault‐bounded crustal blocks between the offshore and inboard fault systems underwent translation, rotation, and extension from 18 Ma to 11.5 Ma but not from 11.5 Ma to 5.5 Ma. Since 5.5 Ma, dextral slip has been accommodated predominantly on the inboard fault system; dextral slip ceased on the offshore fault system north of the Transverse Ranges but continues on faults west of or within Baja California. The San Gregorio‐San Simeon‐Hosgri fault system has accommodated less than 5 km of the late Cenozoic dextral slip. The distribution of dextral displacement in the plate boundary zone has been controlled by abrupt jumps of the position of a southern triple junction, and, to a lesser degree, changes in magnitude of Pacific‐North America relative motion. Based on our reconstuction, the tangential component of Pacific‐North America relative motion was ∼ 90mm/yr for the period 10.5 Ma to 5.5 Ma and ∼ 60mm/yr for the period 5.5 Ma to 3 Ma.

No abstract

No abstract

Structural data and field observations from Franciscan-type coherent blueschists in western Baja California, Mexico, are used to test proposed mechanisms for exhumation of these high-pressure, low-temperature (high P/T ) metamorphic rocks. Analysis of specific observations that are predicted by, consistent with, or inconsistent with specific mechanisms supports extension and normal faulting as the dominant mechanism in Baja. Erosion and strike-slip faulting may have been active, but their contributions cannot be documented and are inferred to be minor. Buoyancy forces and ductile flow probably played a negligible role. Extension and exhumation probably occurred in Late Cretaceous and Paleogene time, while subduction continued at the convergent margin west of North America. Blueschists probably were exhumed to shallow crustal levels by 30 Ma, and possibly before a decrease in convergence rate at about 40 Ma. Coherent blueschists lie in the footwalls of major normal fault zones that contain serpentinite-matrix mélange with exotic blocks of greenschist, amphibolite, eclogite, and blueschist. Mélange probably formed before normal slip on the fault zones. Most mélange components are consistent with tectonic thinning of the mantle wedge and adjacent parts of the accretionary prism that once lay structurally higher than the lower-plate blueschists. Many of these findings may be applicable to similar rocks in California, including Franciscan blueschists.