Two types of ultrapotassic plutonic rocks in the Bohemian Massif — Coeval intrusions at different crustal levels

Kotková, Jana; Schaltegger, Urs; Leichmann, Jaromı́r

doi:10.1016/j.lithos.2009.11.016

Cited by 67 publications

(48 citation statements)

References 49 publications

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“…There are several known Viséan intermediate to felsic (SiO 2 55 -70%), high-Mg-K granitoid rocks (diorite, monzonite, syenite and granite; Schaltegger, 1997) that occur in a discontinuous belt parallel to the axis of the Variscan orogen ( Fig. 9A; Finger et al, 1997;Schaltegger, 1997;Kotková et al, 2010;von Raumer et al, 2014). Many of these granitoids, including those of southern Vosges and the Black Forest, were intruded into Viséan volcano-sedimentary sequences at shallow depths (Schaltegger et al, 1996;Schaltegger, 1997Schaltegger, , 2000.…”

Section: Possible Locations Of the Source Volcanoesmentioning

confidence: 99%

Geochemistry and origin of Carboniferous (Mississippian; Viséan) bentonites in the Namur-Dinant Basin, Belgium: evidence for a Variscan volcanic source

Pointon¹,

Chew²,

Delcambre³

et al. 2018

Geol. Belg.

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ABSTRACT. Several thin clay-rich horizons occur interbedded with Mississippian (Viséan) limestones in the Namur-Dinant Basin, southern Belgium. These have been interpreted as diagenetically altered volcanic ash layers (bentonites). Whole-rock geochemical analysis of several bentonites was undertaken to provide insight into their original magmatic composition. Ratios of several trace elements that are considered to be immobile during diagenetic alteration and indicators of petrogenetic processes suggest that most of the bentonites were originally trachyandesitic to trachytic ashes. Furthermore, the coarse grain size of euhedral zircon phenocrysts (up to 400 µm in length) suggests a proximal volcanic source. Zircon U-Pb isotopic ages and wholerock geochemical data from these bentonites were compared with literature data from volcanic and intrusive rocks in adjacent areas, and suggest that the bentonites were sourced from volcanoes within the Variscan orogenic belt.KEYWORDS: altered volcanic ash, cinerite, whole-rock geochemistry, trace element geochemistry, X-ray diffraction analysis.http://dx

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Section: Possible Locations Of the Source Volcanoesmentioning

confidence: 99%

Geochemistry and origin of Carboniferous (Mississippian; Viséan) bentonites in the Namur-Dinant Basin, Belgium: evidence for a Variscan volcanic source

Pointon¹,

Chew²,

Delcambre³

et al. 2018

Geol. Belg.

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“…However, new monazite data suggest that this event may have been more widespread. It marks the end of the main granite-forming event in the Western Carpathians or the very beginning of the extensive granite magmatism in the Bohemian massif corresponding to isothermal decompression of the crust (Janoušek & Gerdes 2003;Janoušek et al 2004Janoušek et al , 2010Kotková et al 2010;Žák et al 2014). An important granite forming event at 340 Ma is also known from the Tauern window (Eastern Alps) following volcanic arc granitoid origin at 374 Ma (Eichorn et al 2000).…”

Section: Syn-collisional Granitementioning

confidence: 99%

Variscan thrusting in I- and S-type granitic rocks of the Tribeč Mountains, Western Carpathians (Slovakia): evidence from mineral compositions and monazite dating

Broska¹,

Petrík²

2015

Geologica Carpathica

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Abstract:The Tribeč granitic core (Tatric Superunit, Western Carpathians, Slovakia) is formed by Devonian/Lower Carboniferous, calc-alkaline I-and S-type granitic rocks and their altered equivalents, which provide a rare opportunity to study the Variscan magmatic, post-magmatic and tectonic evolution. The calculated P-T-X path of I-type granitic rocks, based on Fe-Ti oxides, hornblende, titanite and mica-bearing equilibria, illustrates changes in redox evolution. There is a transition from magmatic stage at T ca. 800-850 °C and moderate oxygen fugacity (FMQ buffer) to an oxidation event at 600 °C between HM and NNO up to the oxidation peak at 480 °C and HM buffer, to the final reduction at ca. 470 °C at ∆NN = 3.3. Thus, the post-magmatic Variscan history recorded in I-type tonalites shows at early stage pronounced oxidation and low temperature shift back to reduction. The S-type granites originated at temperature 700-750 °C at lower water activity and temperature. The P-T conditions of mineral reactions in altered granitoids at Variscan time (both I and S-types) correspond to greenschist facies involving formation of secondary biotite. The Tribeč granite pluton recently shows horizontal and vertical zoning: from the west side toward the east S-type granodiorites replace I-type tonalites and these medium/coarse-grained granitoids are vertically overlain by their altered equivalents in greenschist facies. Along the Tribeč mountain ridge, younger undeformed leucocratic granite dykes in age 342 ±4.4 Ma cut these metasomatically altered granitic rocks and thus post-date the alteration process. The overlaying sheet of the altered granites is in a low-angle superposition on undeformed granitoids and forms "a granite duplex" within Alpine Tatric Superunit, which resulted from a syn-collisional Variscan thrusting event and melt formation ~340 Ma. The process of alteration may have been responsible for shifting the oxidation trend to the observed partial reduction.

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“…A segment of the Gföhl Assemblage, consisting of granulite, migmatitic gneiss, and leucocratic migmatite (Hasalová et al 2008), is located in the Vysočina District, western Moravia, between the 335-342 Ma Třebíč durbachite Pluton on the northwest (Holub et al 1997;Kotková et al 2010;Kusiak et al 2010), Bíteš orthogneiss of the Moravian Zone on the northeast, and Permian sedimen-tary rocks and surficial deposits on the southeast (Fig. 1).…”

Section: Geological Settingmentioning

confidence: 99%

Garnet pyroxenite in the Biskupice peridotite, Bohemian Massif: anatomy of a Variscan high-pressure cumulate

Medaris

Jelínek²,

Beard³

et al. 2013

Jour. Geosci.

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A strongly layered garnet pyroxenite, consisting of cm-scale layers of garnetite, garnet orthopyroxenite, garnet clinopyroxenite, and websterite, occurs in the Biskupice garnet peridotite, which is located in migmatitic gneiss of the Gföhl Assemblage in the Vysočina District, western Moravia. Major-and trace-element compositions and REE patterns of minerals and layers in the pyroxenite are consistent with origin of the layers by HT-HP crystallization and accumulation of variable proportions of garnet, orthopyroxene, and clinopyroxene. The present compositions of the minerals (pyroperich garnet, low-Al, low-Ca enstatite and low-Al, high-Ca diopside) are the result of extensive subsolidus re-equilibration at ~900 ºC and ~37 kbar, during the Variscan (332 Ma) Orogeny. Neodymium and strontium isotopic values (ε

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Two types of ultrapotassic plutonic rocks in the Bohemian Massif — Coeval intrusions at different crustal levels

Cited by 67 publications

References 49 publications

Geochemistry and origin of Carboniferous (Mississippian; Viséan) bentonites in the Namur-Dinant Basin, Belgium: evidence for a Variscan volcanic source

Geochemistry and origin of Carboniferous (Mississippian; Viséan) bentonites in the Namur-Dinant Basin, Belgium: evidence for a Variscan volcanic source

Variscan thrusting in I- and S-type granitic rocks of the Tribeč Mountains, Western Carpathians (Slovakia): evidence from mineral compositions and monazite dating

Garnet pyroxenite in the Biskupice peridotite, Bohemian Massif: anatomy of a Variscan high-pressure cumulate

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