Precursor and ambient rock paleothermometry to assess the thermicity of burial dolomitization in the southern Cantabrian Zone (northern Spain)

Abstract

Paleozoic rocks in the Cantabrian Zone, the Variscan foreland fold-and-thrust belt on the Iberian Peninsula, have been affected by a sequence of diagenetic to epizonal thermal events. Late-to Post-Variscan hot fluid circulation caused large-scale burial dolomitization and ore mineralization, mostly in Cambrian and Lower to Middle Carboniferous carbonate sucessions. The goal of this study is to analyze and compare the temperatures experienced by the carbonate precursor rocks, as well as the underand overlying siliciclastic ambient rocks to gain a better understanding of the thermicity of dolomitization. These temperatures are evaluated based on published paleothermal datasets combined with new data obtained from Rock-Eval pyrolysis and vitrinite reflectance analysis of Carboniferous rocks rich in organic matter. The overall results indicate that reworking of detrital sediments in synorogenic ambient siliciclastics results in an anomalously high thermal maturity recorded by bulk rock techniques such as illite crystallinity and Rock-Eval pyrolysis. In situ VR-derived paleotemperatures recorded by ambient siliciclastic rocks appear to be higher compared to CAI-derived temperatures for carbonate precursor rocks. This variation in thermal maturity is likely related to the analytical techniques used to obtain CAI and VR data and the empirical equations applied to calculate corresponding paleotemperatures. Conodont fragments were not as sensitive compared to vitrinite, and the color alteration process could have suffered from hydrothermal alteration. A secondary cause might be a different response to mechanical deformation between siliciclastic and carbonate units during the Variscan and post-Variscan geodynamic evolution of the study area. Rigid precursor carbonate units experienced fluid circulation mainly along distinct and spaced fractures zones, creating fracture-related dolomite geobodies and ore mineralization. Soft ambient Powered by Editorial Manager® and ProduXion Manager® from Aries Systems Corporation Precursor and ambient rock paleothermometry to assess the thermicity of burial dolomitization in the southern Cantabrian Zone (northern Spain).

A new approach to geobarometry by combining fluid inclusion and clumped isotope thermometry in hydrothermal carbonates

“…As a result, hypersaline marine‐derived brines infiltrated the subsurface along reactivated Variscan fractures in the Bodón Unit, an important thrust unit in the CZ (Figure ; Julivert, ; Gasparrini, Bechstädt, & Boni, ). These brines were modified through water–rock interactions and the resulting hydrothermal fluids dolomitised Palaeozoic limestones through thermal convection (Gasparrini, Bechstädt et al., ; Honlet, Gasparrini, Jäger, Muchez, & Swennen, in press). Inclusions within the dolomite crystals are two‐phase aqueous with consistent liquid to vapour ratios.…”

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

“…The presence of igneous rocks at depth in the southern part of the Ponga unit has been suggested by Tornos and Spiro (2000) and by Valín et al (2016) in the Pisuerga-Carrión unit, where small outcrops of intrusive rocks are common. In the La Sobia-Bodón units, south of the León Fault, the positive temperature anomalies broadly correlate with hydrothermal dolostones and ore mineralizations (Honlet et al 2017).…”

Seismically enhanced hydrothermal plume advection through the process zone of the Compione extensional Fault, Northern Apennines, Italy

“…13), and by supra-hydrostatic fluid pressures that promote fast advection of hot fluids from the basement in a channelized, highly-fractured and narrow deformation zone (Sibson et al, 1988(Sibson et al, , 1996(Sibson et al, , 2000Renard et al, 2000;Gratier et al, 2002;Beaudoin et al, 2011). This result highlights the importance of combining different methodologies to constrain host rock and faultrelated fluid paleotemperatures (Mamadou et al, 2016;Honlet et al, 2017;Laurent et al, 2017;Wustefeld et al, 2017).…”

“…Fluid-rock interactions have been widely studied to better understand fluid migration and accumulation and their effects on compositional, petrophysical and rheological rock modifications during deformation (Nesbitt and Muehlenbachs, 1989;Battles, 1999, Roure et al, 2005;Vilasi et al, 2009;Vandeginste et al, 2012). Textural, geochemical and microthermometric analyses of syntectonic vein cements allow constraint of paleofluid properties, such as their origin, migration pathways, temperature and pressure of crystallization and the local state of stress during deformation (Mullis, 1979(Mullis, , 1987(Mullis, , 1988Carter and Dworkin, 1990;Fisher et al, 1995;Muchez et al, 1995;Milliken et al, 1998;Montomoli et al, 2001;Montomoli, 2002;Clemenzi et al, 2014;Honlet et al, 2017). In particular, when deformation is thick-skinned, regional-scale fault systems with kilometric offsets are characterized by highly-connected fracture networks in their damage zones, which are preferential sites for fluid migration and mixing from the metamorphic basement up to surficial aquifers (Gratier et al, 2002;Beaudoin et al, 2011;Doglioni et al, 2014;Mamadou et al, 2016;Laurent et al, 2017;Wüstefeld et al, 2017).…”