T290 Integrated Approaches to Deciphering Major Crustal Boundaries in Polyphase Orogenic Settings (Posters)

Tuesday, 24 October 2017
9:00 AM - 6:30 PM
Halls 4EF

USING GEOCHEMICAL SIGNATURES IN SEARCH FOR RELICS OF PRE-VARISCAN OCEANIC CRUST: THE LESZCZYNIEC UNIT, NORTHERN BOHEMIAN MASSIF, POLAND

Paper number: T290-5
Program: Technical Sessions
Time: 9:00 AM – 6:30 PM

Authors

Abstract

The medium-pressure Leszczyniec unit is the uppermost thrust sheet of the Karkonosze-Izera nappe complex that is associated with the Saxothuringian suture in the West Sudetes, Bohemian Massif (Mazur & Aleksandrowski, 2001). It is composed of medium-pressure metabasites and trondhjemitic gneisses (Kryza & Mazur, 1995) of the late Cambrian age (Oliver et al., 1993).

The structure of the Karkonosze-Izera nappe stack reveals a continuous subduction and underplating of imbricated thrust sheets, derived from the Saxothuringian lower plate, to the base of the Teplá-Barrandian upper plate (Mazur & Aleksandrowski 2001; Jeřábek et al., 2016). It still remains uncertain whether the Leszczyniec unit is an accreted relic of the Saxothuringian oceanic crust (Mazur & Aleksandrowski, 2001) or part of the Teplá-Barrandian mafic lower crust. The latter option is suggested by a characteristic latest Cambrian suite of felsic rocks associated with metagabbros that, in some parts of the Bohemian Massif, is considered indicative of Cambro-Ordovician continental rifting prior to inception of the Saxothuringian Ocean. We aim at solving this dilemma using geochemical, structural, petrological, and geochronological methods.

Bulk chemistry analyses (including major and trace elements) were carried out using the LA-ICP-MS method on different types of meta-igneous rocks, including the hornblende-bearing Paczyn Gneiss, metagabbros and metadiorites from three localities: Paczyn, Wieściszowice-Raszów and Ogorzelec. Our first results reveal the presence of intra-plate basalts as precursors to the Paczyn gneisses. However, the geochemical signature obtained shows a reminiscence of dacite-andezite island arc, pointing to a complex tectonic setting for the emplacement of the Leszczyniec unit protoliths.

Jeřábek, P., Konopásek, J., & Žáčková, E. (2016). Journal of Structural Geology, 89, 214-229.

Kryza, R., & Mazur, S. (1995). Neues Jahrbuch für Mineralogie – Abhandlungen, 169(2), 157-192.

Mazur, S., & Aleksandrowski, P. (2001). International Journal of Earth Sciences, 90(2), 341-360.

Oliver, G. J. H., Corfu, F., & Krogh, T. E. (1993). Journal of the Geological Society, 150(2), 355-369.

Geological Society of America Abstracts with Programs. Vol. 49, No. 6

doi: 10.1130/abs/2017AM-308596

© Copyright 2017 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.