Multistage magma emplacement and progressive strain accumulation in the shallow‐level Krkonoše‐Jizera plutonic complex, Bohemian Massif

Abstract

[1] Field relationships combined with new U-Pb zircon geochronology suggest that the shallow-level Krkonoše-Jizera plutonic complex, northern Bohemian Massif, was assembled successively from bottom to top, starting with emplacement of the separately evolved S-type Tanvald granite (317.3 ± 2.1 Ma), followed by at least two voluminous batches of the I-type porphyritic Liberec (319.5 ± 2.3 Ma) and Jizera (320.1 ± 3.0 Ma and 319.3 ± 3.7 Ma) granites. The intrusive sequence was completed by uppermost, minor intrusions of the equigranular Harrachov (315.0 ± 2.7 Ma) and Krkonoše granites. The I-type granites exhibit an unusually complex pattern of superposed feldspar phenocryst and magnetic fabrics as revealed from the anisotropy of magnetic susceptibility (AMS). The outer Liberec granite preserves margin-parallel foliations and lineations, interpreted to record emplacement-related strain captured by cooling from the pluton floor and walls. In contrast, the inner Jizera, Harrachov, and Krkonoše granites were overprinted by synmagmatic strain resulting from dextral movements along regional strike-slip faults cutting the opposite ends of the plutonic complex. Late-stage felsic dikes in the Liberec and Jizera granites reorient from horizontal to vertical (lineation-perpendicular) attitude in response to changing the least principal stress direction, whereas mafic schlieren do not do so, representing only randomly oriented small-scale thermal-mechanical instabilities in the phenocryst framework. In general, this case example challenges the common approach of inferring pluton-wide magma flow from interpolated foliation, lineation, and schlieren patterns. More likely, magmatic fabrics in large plutons record complex temporal succession of superposed strains resulting from diverse processes at multiple scales.

Re-assessment of lithostratigraphy, biostratigraphy, and volcanic activity of the Late Paleozoic Intra-Sudetic, Krkonoše-Piedmont and Mnichovo Hradiště basins (Czech Republic) based on new U-Pb CA-ID-TIMS ages

“…It shows the close spatial relationships of shallow-level plutonic bodies with volcanic or subvolcanic facies. The Křenov ignimbrite/tuff complex (312.39 ± 0.10 Ma) overlaps in age with 312.5 ± 0.3 to 312.2 ± 0.3 Ma ID-TIMS ages (Kryza et al 2014) of S-type granites of the Krkonoše-Jizera Pluton (Žák et al 2013(Žák et al , Kusiak et al 2014, Pluton. SHRIMP U-Pb zircon ages of 312.8 ± 2.8 Ma and 312.4 ± 4 Ma for andesite dykes and lamprophyres cutting older acid volcanic and subvolcanic rocks, suggest that mantle-derived mafic melts are closely spatio-temporaly related to the crustally-derived acid melts.…”

Construction of new houses on a uranium vein outcrop: a case study from the Czech Republic

“…It is built mainly of Proterozoic to Early Palaeozoic Construction of new houses on a uranium vein outcrop: a case study from the Czech Republic metamorphic rocks. The area is penetrated by the large Krkonoše-Jizera (K-J) granite pluton of the Carboniferous age (317-320 Ma) [7]. The south--western part of the K-J pluton is composed of Tanvald alkaline granite, which differs geochemically and also by the content of radioactive elements; it is a real 'uranium granite'.…”

Crystal Mush Flow in Small Concentrically Expanded Pluton (Castle Crags Pluton; Klamath Mountains, CA, USA)

“…Research regarding the structural record emplacement mechanisms and growth of magmatic plutons represents an integral part of the decadelong effort of earth scientists to understand magmatic systems, exchange of matter, and heat in the lithosphere and tectonic evolution of regions including magmatic activity. The mode of emplacement and internal flow dynamics of concentrically zoned granitic plutons has been recently discussed in terms of pulse-like, incremental growth by amalgamation of successive melt batches (Barboni et al, 2013;Leuthold et al, 2012;Stearns & Bartley, 2014;Miller et al, 2011;Žák et al, 2013) rather than emplacement of large volumes of magma at once (Marsh, 1982;Miller & Paterson, 1999;Paterson & Vernon, 1995;Weinberg, 1996;Weinberg & Podladchikov, 1994). Paterson and Vernon (1995) suggested that the fabric pattern in such granitic bodies, also called concentrically expanded plutons (CEPs), do not reflect ballooning in terms of late inflation of a diapirically ascended pluton (Mahon et al, 1988;Marsh, 1982;Ramberg, 1972), but were emplaced as syntectonic nested diapirs.…”