Dynamic paleogeography of the Jurassic Andean Basin: pattern of transgression and localisation of main straits through the magmatic arc

Abstract

The paleogeographic evolution of the Jurassic Andean retroarc basin is examined at a global scale for the Central Andes. In this paper, it is called for the striking continuity and lasting of the active volcanic arc. Both direct and indirect sedimentologic evidences allow to locate the western border (insular) of the basin and opposite it with the eastern border (cratonic). Emphasis is placed on the volcaniclastic deposits and synsedimentary structures associated with this insular border. It is concluded that the arc magmatic activity has contributed considerably in sediment supply to the basin. Extent and continuity of the arc implies to locate the straits connecting with the Paleopacific. Systematic check of the time of transgressions coupled with sequential facies analysis provides a dynamic outlook of the transgressive process. Sectors with early transgression allow to distinguish two main gulfs of passage through the arc from which waters have progressed lengthwise at the same time northward and southward in a narrow retroarc furrow : the first at latitude of Taltal (25°S), the second at latitude of Curepto (35°S). Both initiated in the upper Triassic and extended during the Hettangian. The evolution as separate basins (Tarapacá and Aconcagua-Neuquén) ended by fusion in middle Pliensbachian giving rise to a continuous elongated basin from Chubut to northern Peru. The remarkable continuity and narrowness of the Andean Basin leaves no doubt about its tectonic control. This stems to its geotectonic setting as a typical retroarc basin adjacent to a very active magmatic arc and explains the extreme mobility of its insular margin characterized by a huge volcanoclastic apron with associated debris flows and turbidites.