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.

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Pressure estimates from rapidly erupted crustal xenoliths constrain the depth of intrusion of the silicic lavas hosting them. This represents an opportunity for tracking magmatic bubble's evolution and quantifying the variation in bubble volume during rapid magma ascent through a volcanic dike just prior to eruption. The petrology, stableisotope geochemistry and X-ray micro-tomography of dacites containing crustal xenoliths, erupted from a Neogene volcano in SE Spain, showed an increase in porosity from ~1.7 to 6.4 % from ~19 to 13 km depth, at nearly constant groundmass and crystal volumes. This result provides additional constraints for experimental and numerical simulations of subvolcanic magma-crust degassing processes in silicic systems, and may allow the characterization of volcanic eruptive styles based on volatile content. Direct observation of bubbles in a natural-silicic volcano-laboratoryCombination of petrology, geochemistry and micro-computed-tomography Bubbles evolution in the magma dike from 19 to 13 km depth Implications for the volatiles influence in the eruptive processes at higher depths than the usually considered for the volcanic vent ABSTRACT 26Pressure estimates from rapidly erupted crustal xenoliths constrain the depth of 27 intrusion of the silicic lavas hosting them. This represents an opportunity for tracking 28 magmatic bubble's evolution and quantifying the variation in bubble volume during 29 rapid magma ascent through a volcanic dike just prior to eruption. The petrology, 30 stable-isotope geochemistry and X-ray micro-tomography of dacites containing 31 crustal xenoliths, erupted from a Neogene volcano in SE Spain, showed an increase 32 in porosity from ~1.7 to 6.4 % from ~19 to 13 km depth, at nearly constant 33 groundmass and crystal volumes. This result provides additional constraints for 34 experimental and numerical simulations of subvolcanic magma-crust degassing 35 processes in silicic systems, and may allow the characterization of volcanic eruptive 36 styles based on volatile content. 37 38

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