U–Pb detrital zircon ages from the Paleozoic Marbella Conglomerate of the Malaguide Complex (Betic Cordilleras, Spain). Implications on Paleotethyan evolution

Abstract

The Marbella Conglomerate (Betic Cordilleras, SW Spain) is a poorly sorted and polymictic rock of vaguely constrained Late Carboniferous age interlayered within a sandy sequence. It contains variable amounts of pebbles of quartzite, gneiss, deformed granitoid, schist, aplite, dacite and other volcanic rocks among others, which makes it a potential target for detrital zircon provenance studies. In order to decipher provenance we combined U–Pb SHRIMP and LA–ICP-MS analyses on zircons obtained from single pebbles of deformed rocks (schist, granitoids) and detrital zircons from the sandy sequence, respectively. The age spectra of the detrital zircons indicates that at least the sedimentation took place soon after the start of the Permian according to the youngest detrital zircon age (≈286Ma), and it involved the denudation of terranes with rocks bearing Paleoproterozoic, Neoproterozoic, Cambro-Ordovician, Devonian and Carboniferous zircon age clusters. In contrast with the Permian age of the detrital zircons from the sandstones, igneous (ca. 532 and 516Ma) and metamorphic (ca. 356Ma) U–Pb SHRIMP Concordia ages were obtained from the pebbles. The different age clusters observed could be correlated to igneous, metamorphic and detrital rocks from an already eroded terrane similar to the Ossa-Morena Zone of the Iberian Variscan Belt. Therefore, we propose that most of the sedimentation of the Marbella Conglomerate took place along the western border of the Paleotethys at the north margin of Gondwana during the dismantling of the Variscan orogenic edifice and/or the Neotethys ocean opening and the birth of the Cimmerian ribbon continent.