Jurassic to Holocene tectonics, magmatism, and metallogeny of northwesternMexico

The present metallic distribution in northwestern Mexico is the culmination of superposed magmatism, tectonism, erosion, and burial over more than 150 m.y. Detailed palinspastic reconstructions of preextensional configuration s-the first study of its kind for this region-clarify the interplay among t hese features on the present distribution and character of mineralized geol ogic systems. This new synthesis goes beyond previous metallogenic investig ations of northwestern Mexico by separating events into specific timing and structural relationships, and by restoring the geology to its preextension al configuration. Metallogenic factors such as enrichment, preservation, an d erosion play major roles in the present distributions and for the first t ime are related to the overall metallogenic framework of northwestern Mexic o. The analysis concludes that modern metallogenic patterns are the result of the complex superposition and subsequent redistribution of geologic syst ems in a way that is related directly to the regional history, rather than simply metallic belts or interpreted angle of a subducting slab. Three main extensional events in the Oligocene-Holocene have been restored, and the palinspastic distributions have been analyzed. Reconstructions rev eal the following: (1) Mineralization events, igneous centers, and sediment ary sequences are continuous across the Gulf of California and other areas with large amounts of extension. (2) Middle Tertiary gold-silver mineraliza tion in Baja California may be the western part of the Sierra Madre Occiden tal metallogenic province, thus expanding the previously recognized extent of this province's mineralization. (3) Late Cretaceous-early Tertiary porph yry copper deposits and intrusive centers form a narrower belt than previou sly noted and are traceable for over 400 km, with parts of the belt buried beneath the younger Sierra Madre Occidental volcanic fields. (4) Interprete d alignments of older geologic features, including lineaments of ore deposi ts, are displaced in the reconstructions. (5) Sedimentary-rock-hosted gold deposits and low-angle-detachment gold systems are closely related and occu r around core complexes. By using structurally restored time slices, it becomes clear that older dep osit types tend to be those formed at greater depths and more proximal to i ntrusions, whereas younger deposits formed at shallower depths are less ero ded and are more commonly volcanic-rock hosted. These characteristics expre ss themselves in the regional distribution of deposit types. Second, minera lization of widely differing ages is spatially superposed, commonly associa ted with coeval magmatic and tectonic events. The structural and magmatic e vents together with paleodistribution of ore deposits define a new framewor k to interpret the metallogenic history of northwestern Mexico.