Permian detachment faulting and syntectonic magmatism constrained by U-Pb LA-ICP-MS on zircon in the Orobic Anticline, Italy.

Obermüller, G., Pohl, F., Tomaschek, F., Heuser, Alexander , Froitzheim, N., Sciunnach, D. and Schröder, O. (2016) Permian detachment faulting and syntectonic magmatism constrained by U-Pb LA-ICP-MS on zircon in the Orobic Anticline, Italy. [Poster] In: GeoTirol 2016. , 25.-28.10.2016, Innsbruck, Austria .

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Abstract

The Grassi Detachment Fault is an Early Permian, low-angle extensional structure located in the Orobic Anticline. It separates the Variscan Basement in its footwall from the volcanic and sedimentary rocks of the Early Permian Collio Formation in its hanging wall. Its textures indicate a top-to-the-southeast displacement. The footwall basement consist of the Variscan Morbegno Gneiss and two granitoid intrusions, the Val Biandino Quarz Diorite (VBQD) and the Valle Biagio Granite (VBG). The former is syntectonic with respect to the detachment, whereas for the latter, the relation to the detachment is unknown. Volcanic rocks of the Collio Formation in the hanging wall may represent the extrusive part of the magmatic system.
In the study area in the western part of the Orobic anticline, several faults and shear zones are exposed: (1) The top-SE Grassi Detachment Fault. It is truncated by the unconformably overlying, post-rift, Late Permian Verrucano Lombardo towards the NW. This reflects the eroded culmination of a Permian metamorphic core complex. (2) The Sasso Rosso Fault, a steeply NW-dipping, brittle normal in the footwall between VBQD and VBG. It is also sealed by the basal unconformity of the Verrucano Lombardo. (3) Several minor south-directed Alpine thrusts, duplicating the lithostratigraphy, including the detachment. (4) The Biandino Fault, a steeply SE-dipping Alpine backthrust, overprinting the detachment as well as the Alpine forethrusts.
U-Pb zircon geochronology using LA-ICP-MS yielded concordant ages of 293.2 ± 4.9 Ma for the VBQD and 286.0 ± 4.8 Ma for the VBG. These ages coincide with the beginning of the Collio volcanism and with the emplacement of mafic melts in the lower crust of the Ivrea Zone, indicating that the volcanics, granitoids and mafic intrusions belonged to a crustal-scale magmatic system. Since structural relations indicate contemporaneity of VBQD intrusion and extensional detachment faulting, it results that the Early Permian magmatism occurred in a framework of core-complex style extension.

Document Type: Conference or Workshop Item (Poster)
Research affiliation: OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-MG Marine Geosystems
Date Deposited: 26 Sep 2016 12:18
Last Modified: 26 Sep 2016 12:18
URI: https://oceanrep.geomar.de/id/eprint/34028

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