Multistage metamorphism and deformation in high-pressure metabasites of the northern Adula Nappe Complex (Central Alps, Switzerland)

2010 ◽  
Vol 46 (1) ◽  
pp. 82-103 ◽  
Author(s):  
Fabio Zulbati
Keyword(s):  
High Pressure ◽  
Central Alps ◽  
Nappe Complex ◽  
Adula Nappe

scholarly journals Petrology of High-Pressure Metapelites from the Adula Nappe (Central Alps, Switzerland)

1999 ◽  
Vol 40 (1) ◽  
pp. 199-213 ◽  
Author(s):  
C. Meyre ◽  
C. De Capitani ◽  
T. Zack ◽  
M. Frey
Keyword(s):  
High Pressure ◽  
Central Alps ◽  
Adula Nappe

How to disclose local equilibrium in subducted metapelites from the Cima Lunga Unit (Central Alps)

2020 ◽  
Author(s):  
Francesca Piccoli ◽  
Pierre Lanari ◽  
Jörg Hermann ◽  
Thomas Pettke
Keyword(s):  
High Pressure ◽  
Early Stage ◽  
Local Equilibrium ◽  
White Mica ◽  
Geochemical Data ◽  
Ultramafic Rocks ◽  
Central Alps ◽  
Large White ◽  
Icp Ms ◽  
Polyphase Inclusions

<p>Subducted metapelites are more prone to re-equilibrate during exhumation than mafic or ultramafic rocks to the point that recognizing high-pressure (HP) relicts is often very challenging. Geologic evidence from the Cima Lunga Unit (Central Alps) show this apparent discrepancy between high to ultra-high pressure metamorphism (28 kbar and 780 °C) recorded in mafic/ultramafic lenses, and Barrovian metamorphism (<10 kbar, 650°C) in the adjacent metapelitic rocks. We collected a white mica – garnet – biotite – plagioclase – kyanite (+ quartz, + zircon, + rutile) bearing metapelite adjacent to the garnet metaperidotite lens that displays an apparently well equilibrated Barrovian mineral assemblage (garnet + plagioclase + biotite), with no macroscopic or microtextural indication of a HP and/or HT metamorphic event (e.g. omphacite crystals; migmatitic texture; polyphase inclusions). Nevertheless, microstructures like atoll-like garnet or large white mica flakes surrounded by biotite and ilmenite replacing rutile suggest incomplete re-equilibration. We investigated garnet and phengite crystals by electron probe and laser ablation-ICP-MS mapping. Major and trace element mapping reveals very complex mineral zoning in both minerals. In particular, high Ti content in phengite and increasing P and Zr contents in pyrope-rich garnet indicate that the studied rock underwent a HP-HT event. This is also supported by Zr in rutile thermometry that indicates temperatures well above the Barrovian metamorphism (T > 700 °C). We combined detailed textural analysis with petrological-geochemical data and thermodynamic modelling to reconstruct the metamorphic evolution of the studied rock. We show that, thank to incomplete re-equilibration, the rock documents an evolution from prograde to UHP-HT peak (27 kbar and 800 °C) to retrograde (Barrovian) conditions (10 kbar and 620 °C). Noteworthy, peak metamorphic conditions of metapelite coincide with peak metamorphic conditions of the garnet metaperidotite. Lastly, geochemical evidence for minor wet melting of the studied metapelite at HP-HT conditions was recognized and is likely linked to the dehydration of chlorite to form garnet peridotite in the adjacent ultramafic body. We propose that metapelites and ultramafic rocks were coupled before subduction or at least in its early stage. This finding opens new scenarios for the geodynamic interpretation of the Cima Lunga unit. We propose that the ultramafic lenses at Cima di Gagnone were parts of the exhumed and serpentinised mantle emplaced at the hyper-extended European continental margin of the Piemont-Ligurian ocean. Slices of the margin were detached and tectonically mixed in the subduction channel. These new constraints call for re-evaluation of the paleogeographic position of the Adula-Cima Lunga nappe.</p>

scholarly journals Structure, geometry and kinematics of the northern Adula nappe (Central Alps)

2014 ◽  
Vol 107 (2-3) ◽  
pp. 135-156 ◽  
Author(s):  
Mattia Cavargna-Sani ◽  
Jean-Luc Epard ◽  
Albrecht Steck
Keyword(s):  
Central Alps ◽  
Structure Geometry ◽  
Adula Nappe ◽  
Geometry And Kinematics

Granulite-facies metamorphism of the Palaeoproterozoic – early Palaeozoic gneiss domains of NE Mozambique, East African Orogen

2016 ◽  
Vol 154 (3) ◽  
pp. 491-515 ◽  
Author(s):  
A. K. ENGVIK ◽  
B. BINGEN
Keyword(s):  
High Pressure ◽  
Granulite Facies ◽  
Crustal Thickening ◽  
Northwestern Part ◽  
Granulite Facies Metamorphism ◽  
Medium Pressure ◽  
Nappe Complex ◽  
High Pressure Granulite ◽  
Facies Metamorphism ◽  
Early Palaeozoic

AbstractGranulite-facies metamorphism recorded in NE Mozambique is attributed to three main tectonothermal events, covering more than 1400 Ma from Palaeoproterozoic – early Palaeozoic time. (1) Usagaran–Ubendian high-grade metamorphism of Palaeoproterozoic age is documented in the Ponta Messuli Complex by Grt-Sil-Crd-bearing metapelites, estimated to pressure (P) 0.75 ± 0.08 GPa and temperature (T) 765 ± 96°C. The post-peak P-T path is characterized by decompression followed by near-isobaric cooling. (2) Irumidian medium- to high-pressure granulite-facies metamorphism is evident in the Unango and Marrupa complexes of late Mesoproterozoic – early Neoproterozoic age. High-pressure granulite-facies is documented by Grt-Cpx-Pl-Rt-bearing mafic granulites in the northwestern part of the Unango Complex, with peak conditions up to P = 1.5 GPa and T = 850°C. Medium-pressure granulite-facies conditions recording P of c. 1.15 GPa and T of 875°C are documented by Grt-Opx-Cpx-Pl assemblage in mafic granulites and charnockitic gneisses of the central part of the Unango Complex. (3) Tectonothermal activity during the Ediacaran–Cambrian Kuunga Orogeny is recorded in the Mesoproterozoic gneiss complexes as amphibolite facies to medium-pressure granulite-facies metamorphism. Granulite facies are documented by Grt-Opx-Cpx-Pl-bearing mafic granulites and charnockitic gneisses, reporting P = 0.99 ± 13 GPa at T = 738 ± 84°C in the Unango Complex and P = 0.92 ± 18 GPa at T = 841 ± 135°C in the Marrupa Complex. This metamorphism is attributed to crustal thickening related to overriding of the Cabo Delgado Nappe Complex, and shorthening along the Lurio Belt during the early Palaeozoic Kuunga Orogeny.

Sign in / Sign up

Export Citation Format

Share Document