K—Ar-Altersbestimmungen an basaltischen Vulkaniten der nördlichen Hessischen Senke und ihr Beitrag zur Diskussion der Magmengenese
[K—Ar age determinations on basaltic volcanics from the northern Hessian Depression and their contribution to thoughts about magma genesis]
Wedepohl, K. H.
published: Aug 1, 1982
ArtNo. ESP154014402002, Price: 29.00 €
Thirty-five samples from the more than 250 larger basaltic necks and flows in the northern Hessian Depression have been dated by the K/Ar method (including 23 new determinations). During Tertiary time the volcanism of this area is one of the youngest in Central Europe. Tholeiitic basalts range in age from 20 to 10 Ma. Alkali olivine basalts represent the most abundant species (≤ 70% of the basaltic coverage). Volcanoes of this magma type had their activity from 15 to 11 Ma before present. Olivine nephelinites, nepheline basanites (and limburgites with comparable composition) are restricted to the NW and SE part of the volcanic zone. Their ages range from 14 to 7 Ma. lt has to be assumed that the different magma species are the product of partial melting of mantle rocks at different depths. Tholeiitic magmas have been formed by 5 to 10 percent melting of depleted lherzolites and harzburgites (comparable to common xenoliths in basalts). According to the abundance of incompatible and volatile elements in alkali olivine basalts and nepheline basalts these rocks must originate from metasomatically altered spinel peridotites. Olivine nephelinities are probably products of the lowest degree of partial melting at the deepest level in spinel bearing mantle rocks. Not a diapiric uprise of peridotites but the influence of tectonic stress on levels of increasing depth in a mantle under abnormal thermal conditions can explain the age sequence of basaltic species.