OROCLINES OF THE IBERIAN VARISCAN BELT: PALEOCURRENT ANALYSIS, U-PB DETRITAL ZIRCON AGE DATING, AND PALEOGEOGRAPHIC IMPLICATIONS

Palinspastic restoration of the Iberian Variscan belt is complicated by (1) a highly arcuate nature, (2) an unusually great orogenic width (>700 km), (3) widespread exposure of passive margin strata of Gondwanan affinity and (4) the absence of a Paleozoic continental sedimentary source. Paleocurrent and U-Pb detrital zircon age data from shallow water pre-Variscan passive margin strata (the Lower Ordovician Armorican Quartzite) are used to constrain geometry and paleogeography of the orogen. Dominant paleoflow directions consistently oriented at high angles to structural strike illuminate large scale structural deflections and reveal that the Cantabrian Orocline of northwest Iberia is continuous with a second and more southerly bend, the Central Iberian Orocline. Palinspastic restoration of the continental scale s-shaped fold pair to a paleomagnetically constrained Late Variscan (Carboniferous) N-S trend yields a linear orogen >1500 km long containing passive margin strata that display a consistent offshore paleoflow towards a westerly oceanic domain (presumably the Rheic). A common detrital zircon age signature is identified by (1) Neoproterozoic (ca. 800-550 Ma), (2) Stenian-Tonian (ca. 0.9 – 1.1 Ga) and lesser (3) Paleoproterozoic and (4) Archean populations (ca. 1.8-2.2 and 2.8-2.5 Ga, respectively), suggesting uniform distribution of varied detrital input along a coherent margin. The common signature is shared by Cambro-Ordovician clastics from the Saharan Metacraton and peripheral Arabian-Nubian shield but inconsistent with the range of basement ages in northeast Africa and Arabia. Hf-isotope data supports long distance sedimentary transport across a northeast African peneplain from basement terranes exposed far to the south (in modern day coordinates), consistent with the extent and mineralogical maturity of the Armorican Quartzite. A paleogeographic model in which the passive margin strata of an originally linear Iberian Variscan belt formed a portion of the Early Paleozoic East-African Gondwanan margin extending along the northern limits of the then low-lying Saharan Metacraton and Arabian-Nubian Shield satisfies known sedimentary, petrologic and paleontological constraints, but contrasts the paleomagnetically constrained Early Variscan N-S orogenic trend.