The nature of the interface between basalts and serpentinized mantle in oceanic domains: Insights from a geological section in the Alps

Abstract

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The syn‐rift tectono‐stratigraphic record of rifted margins (Part I): Insights from the Alpine Tethys

“…This domain can be restored back to the northern Adriatic distal margin. It was extensively studied by Dietrich (1969), Manatschal and Nievergelt (1997), Desmurs et al (2001), Desmurs et al (2002), Schaltegger et al (2002), Münetner et al ( 2004), and more recently by Epin et al (2017), Epin et al (2019), , Coltat et al (2020) and Amann et al (2020). The Platta Nappe can be subdivided into two units based on their lithology, namely the Upper-and Lower Platta Units (Desmurs et al, 2002) (Figure 8c).…”

“…The first sediments overlying the detachment surface are tectono‐sedimentary breccias and ophicalcites (see section 3 in Figure 8a; Desmurs et al., 2001; Epin et al., 2019). The latter form in a post‐exhumation stage at low temperature (<100–150°C), except where they are overlain by basalts resulting in higher formation temperatures (see section 2 in Figure 8a; Coltat et al., 2020). The next sedimentary sequence (see Figure 8b sections 2 and 3) is made of red clays and radiolarian cherts that include also hydrothermal cherts and reworked, continent‐derived material.…”

“…BB7 (Figure 3a and Table 1) shows magmatic additions that form simultaneous to mantle exhumation along high‐ and low‐angle faults (for detailed descriptions see Coltat et al., 2020; Epin et al., 2019; Manatschal et al., 2011). The exhumed, subcontinental mantle is infiltrated, that is reacted with rift‐related magma, but did not melt and is not genetically linked with the overlying basalts (Mantle‐type 2 of Picazo et al., 2016).…”

“…The upper part of the radiolarian cherts overlies, and thus post-dates the basalts and tectono-sedimentary breccia in the exhumed mantle domain. The basalts that show a T-MOR composition (Desmurs et al, 2002), also referred to as OCT basalts by Amann et al (2020), have been interpreted to be syn-tectonic based on the observation of basalts thickening into high-angle faults and basalts that are deformed during mantle exhumation (Coltat et al, 2020;Epin et al, 2019) (see also sections 2 and 3 in Figure 8b).…”

“…The entire exhumed mantle domain is characterised by intense hydrothermal fluid activity and precipitation of metalliferous mineralisation (Coltat, Boulvais, et al., 2019; Coltat, Branquet, et al., 2019). Extensional structures found in the lower Platta Unit are characterised by polyphase extensional detachment faults, truncated by late, high‐angle normal faults (Figure 8c; Coltat et al., 2020; Epin et al., 2019). They include serpentinite cataclasites and serpentinite gouges, topped by ophicalcites and overlain by tectono‐sedimentary breccias, which are typical fingerprints of Jurassic detachment faults (Epin et al., 2017).…”