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Ophiolites penniques et sédiments associés dans la région d'Arolla (val d'Hérens, Valais, Suisse)

ContributorsKunz, Pierre
Published inEclogae geologicae Helveticae, vol. 81, no. 1, p. 115-124
Publication date1988

The penninic Nappe du Tsaté, top of the Zone du Combin, is composed of an ophiolitic complex, Middle Jurassic to Upper Cretaceous, which belongs to the Piemont realm. This nappe shows two sequences: essentially ophiolitic series with greenstones (ultrabasic, plutonic and effusive basic rocks) and associated abyssal deposits (equivalent to the Série de Chabrière), and a calcareous-siliceous flysch rich in planktonic foraminifera of Upper Cretaceous age (Série Grise). This nappe has been affected by a greenschist-facies metamorphism and superposed deformations. The original ophiolitic sequences have been strongly altered, ultramafic rocks occur as serpentinites, volcanic sequences are represented mostly by prasinites (albite, chlorite, epidote, actinolite schists), whereas the sediments only show a strong recristallisation. Five stages of deformations can be observed: two early phases, Cretaceous (flow cleavage), two main phases of overthrusting, Eocene-Oligocene (major flow cleavage) and a later phase of backthrusting, Oligocene (fracture cleavage). The ophiolitic complex corresponds to a fragment of the old Piemont oceanic lithosphere. A part of the Upper Cretaceous flysch is the result of the submarine erosion of these ophiolites, at the time of closing of the Ligurian-Piemont ocean. During the Tertiary, the alpine deformations have inversed the original stratigraphy of these sequences.

Citation (ISO format)
KUNZ, Pierre. Ophiolites penniques et sédiments associés dans la région d’Arolla (val d’Hérens, Valais, Suisse). In: Eclogae geologicae Helveticae, 1988, vol. 81, n° 1, p. 115–124. doi: 10.5169/seals-166172
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ISSN of the journal0012-9402

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