This file contains data tables of the sensitive high resolution ion microprobe with reversed geometry (SHRIMP-RG) U-Pb zircon dating, and anisotropy of magnetic susceptibility (AMS) analyses.
Abstract This paper summarizes the current knowledge on the nature, kinematics and timing of movement along major tectonic boundaries in the Bohemian Massif and demonstrates how the Variscan plutonism and deformation evolved in space and time. Four main episodes are recognized: (1) Late Devonian–early Carboniferous subduction and continental underthrusting of the Saxothuringian Unit beneath the Teplá–Barrandian Unit resulted in the orogen-perpendicular shortening and growth of an inboard magmatic arc during c. 354–346 Ma; (2) the subduction-driven shortening was replaced by collapse of the Teplá–Barrandian upper crust, exhumation of the high-grade (Moldanubian) core of the orogen at c. 346–337 Ma and by dextral strike-slip along orogen-perpendicular NW–SE shear zones; (3) following closure of a Rhenohercynian Ocean basin, the Brunia microplate was underthrust beneath the eastern flank of the Saxothuringian/Teplá–Barrandian/Moldanubian ‘assemblage’; this process commenced at c. 346 Ma in the NE and ceased at c. 335 Ma in the SW; and (4) late readjustments within the amalgamated Bohemian Massif included crustal exhumation and mainly S-type granite plutonism along the edge of the Brunia indentor at c. 330–327 Ma, and peripheral tectonothermal activity driven by strike-slip faulting and possibly mantle delamination around the consolidated Bohemian Massif's interior until late Carboniferous–earliest Permian times.
Multiple magnetic fabrics, referred to as F1–F5, were revealed through the anisotropy of magnetic susceptibility in an Ocean Plate Stratigraphy (OPS) mélange of the Neoproterozoic–Cambrian Blovice accretionary complex, Bohemian Massif. The fabrics post-date the formation of the mélange and the rotation of basalt blocks within the matrix and are interpreted in terms of a complex structural history of the mélange. Excluding local fabrics, the F1 fabric formed earlier along the mélange belt, recording shortening of the accretionary wedge front, whereas the higher grade F4 fabric pervasively overprinted both blocks and matrix in the SW part of the belt, recording shearing and vertical shortening at deeper structural levels closer to a megathrust surface. The preservation of angular relationships between the F1 and F4 fabrics across different parts of the mélange suggests that the blocks were only strained and not rotated during deformation, exemplifying the notion that the OPS mélanges may be a product of deformation at very shallow levels. The F1–F5 fabrics may be viewed as snapshots in a protracted evolution of OPS, where the earlier fabrics in basalt blocks may record the travel path of an oceanic plate from mid-ocean ridge towards the trench, before being overprinted in the accretionary wedge. Thematic collection: This article is part of the Ophiolites, melanges and blueschists collection available at: https://www.lyellcollection.org/topic/collections/ophiolites-melanges-and-blueschists Supplementary material: Thin-section photomicrographs, anisotropy of magnetic susceptibility data and summary diagrams for magnetic fabric types are available at https://doi.org/10.6084/m9.figshare.c.7008173
Research Article| November 21, 2018 Emplacement dynamics of syn-collapse ring dikes: An example from the Altenberg-Teplice caldera, Bohemian Massif Filip Tomek; Filip Tomek † 1The Czech Academy of Sciences, Institute of Geology, Rozvojová 269, Prague, 16500, Czech Republic2Institute of Geology and Paleontology, Faculty of Science, Charles University, Albertov 6, Prague, 12843, Czech Republic †filip.tomek@gmail.com Search for other works by this author on: GSW Google Scholar Jiří Žák; Jiří Žák 2Institute of Geology and Paleontology, Faculty of Science, Charles University, Albertov 6, Prague, 12843, Czech Republic Search for other works by this author on: GSW Google Scholar Martin Svojtka; Martin Svojtka 1The Czech Academy of Sciences, Institute of Geology, Rozvojová 269, Prague, 16500, Czech Republic Search for other works by this author on: GSW Google Scholar Fritz Finger; Fritz Finger 3Department of Chemistry and Physics of Materials, University of Salzburg, Jakob Haringer Strasse 2A, A-5020, Salzburg, Austria Search for other works by this author on: GSW Google Scholar Michael Waitzinger Michael Waitzinger 3Department of Chemistry and Physics of Materials, University of Salzburg, Jakob Haringer Strasse 2A, A-5020, Salzburg, Austria Search for other works by this author on: GSW Google Scholar GSA Bulletin (2019) 131 (5-6): 997–1016. https://doi.org/10.1130/B35019.1 Article history received: 25 Apr 2018 rev-recd: 18 Jul 2018 accepted: 31 Aug 2018 first online: 21 Nov 2018 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Filip Tomek, Jiří Žák, Martin Svojtka, Fritz Finger, Michael Waitzinger; Emplacement dynamics of syn-collapse ring dikes: An example from the Altenberg-Teplice caldera, Bohemian Massif. GSA Bulletin 2018;; 131 (5-6): 997–1016. doi: https://doi.org/10.1130/B35019.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The late Carboniferous Altenberg-Teplice caldera in the northwestern Bohemian Massif provides an intriguing example of rhyolite eruptions evolving to a trapdoor collapse and coeval ring dike emplacement. Geochemical data suggest that withdrawal of an underlying stratified magma chamber beneath the caldera took place in two steps. Eruptions of the reversely zoned Teplice rhyolite drained the chamber, followed by a trapdoor collapse of the caldera floor and emplacement of voluminous microgranite ring dike system at 312 Ma. The mechanism proposed here is that the subsiding caldera floor increased vertical load on the magma chamber and triggered remobilization of residual, cumulate-like, and otherwise non-eruptible magma mush. The magnetic fabrics (determined using the anisotropy of magnetic susceptibility [AMS]), carried by paramagnetic ferrosilicates and titanomagnetite, indicate that the ring dike magma first flowed upwards via four main feeder domains from which the magma was then distributed laterally. The asymmetric trapdoor collapse generated domains of dilation and contraction along the caldera limit, evidenced by different shapes of fabric ellipsoids and uneven apparent width of the individual ring dike segments. Based on this case example, we develop a general kinematic model for polyphase caldera collapse and ring dike emplacement, invoking a combination of multiple space-making processes: piston and trapdoor collapses together with downsag and faulting of the caldera floor, regional tectonic extension, reactivation of the preexisting structures, and volume changes in the caldera floor due to thermal stresses. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
This supporting information file contains data tables of the sensitive high resolution ion microprobe with reversed geometry (SHRIMP-RG) U-Pb zircon dating and anisotropy ofmagnetic susceptibility (AMS) analyses. We also present igures showing the Summitville Andesite and Chiquito Peak Tuff microstructure, and spatial distribution of AMS parametersin the Alamosa River pluton and its host rocks.
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