Universität zu Köln

Przybyla, Thomas, Pfaender, Joerg A., Muenker, Carsten, Kolb, Melanie, Becker, Maike ORCID: 0000-0002-6732-5411 and Hamacher, Uli (2018). High-resolution Ar-40/Ar-39 geochronology of volcanic rocks from the Siebengebirge (Central Germany)-Implications for eruption timescales and petrogenetic evolution of intraplate volcanic fields. Int. J. Earth Sci., 107 (4). S. 1465 - 1485. NEW YORK: SPRINGER. ISSN 1437-3262

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Abstract

A key parameter in understanding mantle dynamics beneath continents is the temporal evolution of intraplate volcanism in response to lithospheric thinning and asthenospheric uplift. To contribute to a better understanding of how intraplate volcanic fields evolve through time, we present a high precision Ar-40/Ar-39 age dataset for volcanic rocks from the Siebengebirge volcanic field (SVF) from central Germany, one of the best studied and compositionally most diverse intraplate volcanic fields of the Cenozoic Central European Volcanic Province (CEVP). Petrological and geochemical investigations suggest that the formation of the different rock types that occur in the SVF can be explained by a combination of assimilation and fractional crystallisation processes, starting from at least two different parental magmas with different levels of silica saturation (alkali basaltic and basanitic), and originating from different mantle sources. These evolved along two differentiation trends to latites and trachytes, and to tephrites and tephriphonolites, respectively. In contrast to their petrogenesis, the temporal evolution of the different SVF suites is poorly constrained. Previous K/Ar ages suggested a time of formation between about 28 and 19 Ma for the mafic rocks, and of about 27 to 24 Ma for the differentiated rocks. Our results confirm at high precision that the differentiated lithologies of both alkaline suites (Ar-40/Ar-39 ages from 25.3 +/- 0.2 Ma to 25.9 +/- 0.3 Ma) erupted contemporaneously within a very short time period of similar to 0.6 Ma, whereas the eruption of mafic rocks (basanites) lasted at least 8 Ma (Ar-40/Ar-39 ages from 22.2 +/- 0.2 Ma to 29.5 +/- 0.3 Ma). This implies that felsic magmatism in the central SVF was likely a single event, possibly triggered by an intense phase of rifting, and that ongoing melting and eruption of mostly undifferentiated mafic lavas dominate the > 8 Ma long magmatic history of this region. Among the mafic lavas, most basanites and tephrites predate the alkali basalts and hawaiites, suggesting an overall temporal evolution towards less SiO2-undersaturated primary melts and increasing degrees of melting over time. The peak in alkali basaltic to hawaiitic magmatism slightly post dates the flare-up of genetically related felsic magmatism, by no more than similar to 1 Ma. This is consistent with a model in which the magmatic plumbing system erupted successively from upper to lower levels, i.e. from more evolved to more primitive compositions. One young age for a basanitic sample suggests that silica saturation decreased again towards the end of volcanic activity. This chronology of volcanic events is in good agreement with previous models, suggesting continuous lithospheric thinning beneath the SVF as a response to an extensional regime and asthenospheric uplift in the northern alpine realm.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Przybyla, Thomas UNSPECIFIED UNSPECIFIED UNSPECIFIED Pfaender, Joerg A. UNSPECIFIED UNSPECIFIED UNSPECIFIED Muenker, Carsten UNSPECIFIED UNSPECIFIED UNSPECIFIED Kolb, Melanie UNSPECIFIED UNSPECIFIED UNSPECIFIED Becker, Maike UNSPECIFIED orcid.org/0000-0002-6732-5411 UNSPECIFIED Hamacher, Uli UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-183383
DOI:	10.1007/s00531-017-1553-y
Journal or Publication Title:	Int. J. Earth Sci.
Volume:	107
Number:	4
Page Range:	S. 1465 - 1485
Date:	2018
Publisher:	SPRINGER
Place of Publication:	NEW YORK
ISSN:	1437-3262
Language:	English
Faculty:	Unspecified
Divisions:	Unspecified
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language LOWER CRUSTAL XENOLITHS; CENOZOIC RIFT SYSTEM; CENTRAL-EUROPE; TRACE-ELEMENT; WEST-GERMANY; ISOTOPIC COMPOSITIONS; CONTINENTAL ALKALINE; MANTLE SOURCES; SW GERMANY; PROVINCE Multiple languages Geosciences, Multidisciplinary Multiple languages
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/18338