Tectonothermal analysis of a major unit of the Cantabrian Zone: the Ponga unit (Variscan belt, NW Spain)

Abstract

The paleothermometric evolution of the Ponga unit at the core of the Cantabrian Zone, the arcuate foreland fold and thrust belt of the Variscan orogen in NW Spain, is analyzed using the conodont Color Alteration Index and the Kübler Index of illite. The results indicate that the distribution of the thermal maturity patterns is independent of the stratigraphy and the structure of the unit. These include the occurrence of dominant diagenetic values and very low-to-low-grade metamorphism in the southern area. The main thermal event is interpreted to be related to hydrothermal fluids ascending through late-Variscan extensional faults. The anomalous high heat flow in the southern sector of the Ponga unit is part of a previously identified large band in the Cantabrian Zone, where the common occurrence of low-grade metamorphic rocks, hydrothermal dolostones, and ore mineralizations is related to an extensional orogenic episode that started near the Carboniferous-Permian boundary, soon after the closure of the Asturian arc.

Strain Partitioning Within Bending Orogens, New Insights From the Variscan Belt (Chiroulet‐Lesponne Domes, Pyrenees)

“…Two typical strain patterns were recognized around this late‐orogenic structure, depending on their position within or at the limbs of the arc. The core of the arc (i.e., the Cantabrian Zone) is characterized by contractional structures, such as arc‐radial folds and steep E‐W striking thrusts (e.g., Bahamonde et al., 2007; Blanco‐Ferrera et al., 2017; García‐López et al., 2018; Merino‐Tomé et al., 2009; Pastor‐Galán et al., 2014; Pérez‐Estaún et al., 1988, Figure 1). To the contrary, the branches of the arc (e.g., Armorican Massif, Central Iberian Zone) exhibit arc‐parallel stretching, accommodated by both lateral wrenching and extension (e.g., Authemayou et al., 2019; Díez Fernández & Pereira, 2017; Gapais et al., 2015; Martínez Catalán et al., 2007).…”