Abstract
Permian biotite leucogranites to granite porphyries and rhyolites form small intrusions in several Alpine tectonic units in the Western Carpathians and the Pannonian region (Slovakia and Hungary). Their A-type signature is inferred from main- and trace-element geochemistry, with high K, Rb, Y, REE, Zr, Th, Nb, Fe/Mg and Ga/Al, low Al, Mg, Ca, P, Sr, V and strong negative Eu-anomaly. This geochemical signature is further supported by the mineralogy comprising local hypersolvus alkali feldspars, annitic biotite and the presence and composition of HFSE accessory minerals. The δ18O values measured for zircon (mean value 8.3 ‰ ± 0.36) may be explained by the melting of igneous material of crustal origin and/or mantle basalts which interacted with low-temperature fluids. The in-situ SHRIMP U–Pb isotope dating of zircon from the granites highlights two different periods of magmatic crystallisation and pluton emplacement: the older 281 ± 3 Ma Cisuralian age in the southern part, Velence Hills in the Pannonian region (Transdanubian Unit) and younger Guadalupian ages in the northern part, the West-Carpathian area: 262 ± 4 Ma (Turčok, Gemeric Unit), 267 ± 2 Ma (Hrončok, Veporic Unit) and 264 ± 3 Ma (Upohlav, granitic pebbles in Cretaceous conglomerates of the Pieniny Klippen Belt). The ~ 280 to 260-Ma interval is simultaneous with post-orogenic or anorogenic, rift-related and mainly alkaline (A-type) magmatism on the broader European scale. Our study documents a close relationship between the Permian continental rifting and the Neotethyan Meliatic oceanic basin opening in the Middle Triassic. The A-type granites originated from the partial melting of the ancient lower crustal quartzo-feldspatic rocks with the possible contribution of meta-basic material from the mantle in an extensional tectonic regime consistent with disintegration of the Pangea supercontinent during the Permian–Triassic period.
Highlights
The A-type granites were originally distinguished by Loiselle and Wones (1979) as a specific group of granitic rocks with peculiar chemistry and geotectonic setting (e.g., Bonin 2007, 2008)
The multi-element lithogeochemistry of pulp samples has been performed by Bureau Veritas (AcmeLabs) in Vancouver, Canada, by X-ray fluorescence (XRF) for major elements, and the trace and rare earth elements (REE) were determined by inductively coupled plasma atomic emission spectrometry (ICP–AES) and inductively coupled plasma mass spectrometry (ICP–MS)
The Western Carpathian A-type granite intrusions (Turčok, Hrončok and Upohlav) were emplaced at 270–260 Ma, and the Pannonian Velence A-type granite was emplaced earlier at ~ 280 Ma. This time gap (10 to 20 Ma) between magmatic solidification of the Transdanubian Central Range (Velence) granite and other West-Carpathian A-type granite occurrences most likely reflects their different palaeo-tectonic position during NW-ward prograding of rifting in the Neotethyan continental margin
Summary
The A-type granites were originally distinguished by Loiselle and Wones (1979) as a specific group of granitic rocks with peculiar chemistry and geotectonic setting (e.g., Bonin 2007, 2008). The A-type granites are subdivided into two groups on the basis of trace element abundances, Y/Nb ratio (Eby 1992). The A 1 group with Y/Nb < 1.2 includes felsic rocks chemically similar to those observed in oceanic islands and continental rifts (ocean island basalts, OIB source). The second A 2 group with Y/Nb > 1.2 is proposed to form by several different mechanisms from an island arc or continental margin basalt to the partially melted continental crust sources (Eby 1992). The occurrences of A-type granites can indicate collided plate suture zones (Balen et al 2020)
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