Neoproterozoic?Cambrian synsedimentary magmatism in the Central Iberian Zone (Spain): geology, petrology and geodynamic significance

Abstract

Petrographic, geochemical and field studies in low grade metamorphic areas (Ciudad Rodrigo-HurdesSierra de Gata domain, CRHSG, central-western Spain) show that Neoproterozoic-Lowermost Cambrian series in the Central Iberian Zone (CIZ) record two kinds of provenance sources including: (1) detrital material derived from recycled orogens and (2) a Cadomian coeval juvenile contribution that governs their isotopic signature. Evidence of magmatism contemporaneous with Neoproterozoic-Cambrian sedimentation is provided by the presence of coherent, massive volcanic rocks (metabasalts, metaandesites, and metarhyolites), volcaniclastic shales, sandstones, conglomerates and breccias. The appearance of volcanogenic lithic fragments and crystals mixed in different proportions with siliciclastic constituents and also present within calcareous components in the sedimentary succession, reinforces this evidence. Although most of the selected volcanic and volcaniclastic samples appear to show tholeiitic affinity, some of them display calc-alkaline affinity. Different trace element ratios, such as Sm/Nd, Nb/Yb and Ta/Yb, suggest a magmatic evolution in the same tectonic setting. The geochemical results reported here support the existence of an active geodynamic setting as a direct contributor to the synsedimentary and magmatic content of the Neoproterozoic-Lowermost Cambrian successions in the CIZ. In particular, the relatively high Nd (T) values and the high range of f Sm/Nd ratios are consistent with an active margin during the Neoproterozoic-Early Cambrian. The existence of tectonic activity is also confirmed by the presence of synsedimentary deformation and volcanic rocks. All of these traits favour a geodynamic model in which the Iberian Cadomian segment represented in the CIZ would have been part of an active northern margin of Gondwana, with an associated magmatic arc and related basins during Neoproterozoic-Lower Cambrian times. A proposed link between the Ossa Morena and the Central Iberian Zones might account for late Cadomian pull-apart basins developed on both sides of the magmatic arc, sharing the same scenario and involving similar magmatic activity during the Neoproterozoic-Cambrian transition.

Age constraints on Lower Paleozoic convection system: Magmatic events in the NW Iberian Gondwana margin

“…Mantle upwelling would have been accompanied by inland topographic uplift (e.g. Rohrman et al, 2002 ), while the erosion of local exposures of the previous sedimentary sequences would produce an Ordovician unconformity (Fig. 9f).…”

“…1 b), the establishment of a Lower Paleozoic passive continental margin followed Neoproterozoic Andean-type activity (Cadomian cycle) (Rodriguez-Alonso et al, 2004). Extensional activity produced high subsidence rates from the Middle Cambrian to Late Ordovician (von Raumer and Stampfli,20OS ).…”

Sm–Nd isotope geochemistry and tectonic setting of the metasedimentary rocks from the basal allochthonous units of NW Iberia (Variscan suture, Galicia)

“…These elements have very low residence times in oceanic waters, being transferred almost quantitatively to sedimentary rocks. Thus, they provide excellent discriminating factors for determining the provenance and tectonic setting of sedimentary rocks (Bathia, 1983;Bathia and Crook, 1986;Hegde and Chavadi, 2009;Roser andKorsch, 1986, 1988;Taylor and Mclennan, 1 985). The effects of homogenization in sedimentary processes result in a relatively uni form distribution of REE in detrital rocks, whose pattern reflects the REE abundance in the upper crust.…”

Exhuming a cold case: The early granodiorites of the northwest Iberian Variscan belt—A Visean magmatic flare-up?

“…1) includes Neoproterozoic rocks with Gondwanan (North Africa) affinity, which form the basement for late Ediacaran-early Cambrian subduction-related and early Paleozoic passive margin sequences, respectively (e.g., Rodríguez Alonso et al, 2004;Murphy et al, 2008;Fernández-Suárez et al, 2014;Rubio-Ordóñez et al, 2015). In Late Devonian and Carboniferous time, the collision of the passive margin of Gondwana (acting as the lower plate) with Laurussia (upper plate) resulted in the Variscan orogen and ultimately in the amalgamation of Pangea (e.g., Matte, 1986Matte, , 2001Murphy et al, 2009;Kroner and Romer, 2013).…”