ABSTRACT This chapter expands upon a model, first proposed in 1998 by Busby and others, in which Mesozoic oceanic-arc rocks of Baja California formed along the Mexican continental margin above a single east-dipping subduction zone, and were extensional in nature, due to rollback of an old, cold subducting slab (Panthalassa). It expands on that model by roughly tripling the area of the region representing this fringing extensional oceanic-arc system to include the western third of mainland Mexico. This chapter summarizes the geologic, paleomagnetic, and detrital zircon data that tie all of these oceanic-arc rocks to each other and to the Mexican margin, herein termed the Guerrero-Alisitos-Vizcaino superterrane. These data contradict a model that proposes the oceanic-arc rocks formed in unrelated archipelagos some 2000–4000 km west of Pangean North America. Following the termination of Permian–Triassic (280–240 Ma) subduction under continental Mexico, the paleo-Pacific Mexico margin was a passive margin dominated by a huge siliciclastic wedge (Potosí fan) composed of sediments eroded from Gondwanan basement and Permian continental-arc rocks. I propose that a second fan formed further north, termed herein the Antimonio-Barranca fan, composed of sediment eroded from southwest Laurentian sources. Zircons from these two fans were dispersed onto the ocean floor as turbidites, forming a unifying signature in the Guerrero-Alisitos-Vizcaino superterrane. The oldest rocks in the Guerrero-Alisitos-Vizcaino superterrane record subduction initiation in the oceanic realm, producing the 221 Ma Vizcaino ophiolite, which predated the onset of arc magmatism. This ophiolite contains Potosí fan zircons as xenocrysts in its chromitites, which I suggest were deposited on the seafloor before the trench formed and then were subducted eastward. This is consistent with the geophysical interpretation that the Cocos plate (the longest subducted plate on Earth) began subducting eastward under Mexico at 220 Ma. The Early Jurassic to mid-Cretaceous oceanic arc of western Mexico formed above this east-dipping slab, shifting positions with time, and was largely extensional, forming intra-arc basins and spreading centers, including a backarc basin along the continental margin (Arperos basin). Turbidites with ancient Mexican detrital zircons were deposited in many of these basins and recycled along normal fault scarps. By mid-Cretaceous time, the extensional oceanic arc began to evolve into a contractional continental arc, probably due to an increase in convergence rate that was triggered by a global plate reorganization. Contraction expanded eastward (inboard) throughout the Late Cretaceous, along with inboard migration of arc magmatism, suggesting slab shallowing with time.

Abstract: This chapter presents one case history – the transfer of the name and virtues of ‘eagle-stones’ to Andean minerals and terebratulid brachiopods such as Clarkeia antisiensis . Eagle-stones, an ancient remedy of Asian origin, were used in early modern Europe to prevent abortion and as a charm to assist obstetric delivery. In the eighteenth century eagle-stones were the subject of what G. Baronti ( Tra bambini e acque sporche Immersioni nella collezione di amuleti di Giuseppe Bellucci , Morlacchi, Perugia, 2008) calls the process of folklorization of European learned medicine, becoming a ‘superstition’ and a popular remedy of medical lore. Based on secondary bibliography and documents from the Archivo de Indias in Seville, the paper discusses the uses of eagle-stones in Spain and Spanish America in connection to the texts published, written or translated in the Iberian Peninsula (lapidaries, early modern medical books). The last section proposes clues to analyse the expansion of the trade in eagle-stones to Spanish America, to finally survey the references to ‘eagle-stones’ in Latin American popular medicine of the late nineteenth and early twentieth centuries. Eagle-stones are inscribed not only in the longue-durée but also in the intricate networks of commerce.