The Role of Tholeiitic Magmatism in the English Lake District: Evidence from Dykes in Eskdale

Abstract

Mafic dykes occur in close association with, and both cut and are cut by, the Eskdale granite in the south-western Lake District. The dykes range compositionally from magnesian basalt to andesite and are divided into two groups: (1) high-Fe-Ti rocks of tholeiitic affinity forming most of the dykes and (2) a lower-Fe-Ti group, comparable in composition to the lavas of the Borrowdale Volcanic Group. The dykes extend the range of tholeiitic magmatism in the Lakes into late Ordovician, and possibly Silurian times, and indicate that published plate tectonic models partly based on the distribution of magma types are perhaps over-simplified. The Eskdale dykes form one end of a spectrum of Lake District compositions from tholeiitic to calc-alkaline. All the magma types may have shared a common mantle source, their final composition reflecting residence times in the crust or LIL-enriched mantle.

جيوكيمياء القواطع المافية في أجزاء من معقدة سينغابوم الجرانيتية: الأصل الصخري والوضع التكتونى

“…During low-grade metamorphism, Zr is considered as a relatively immobile element (Floyd and Lees 1973;Winchester and Floyd 1977;Macdonald et al 1988). Hence, Zr can be used as a parameter for evaluating the elemental mobility and also to understand the differentiation of magma.…”

Geochemistry of mafic dykes in part of Chotanagpur gneissic complex: Petrogenetic and tectonic implications

“…Figure 3.1 is a series of binary plots where all the major elements are plotted against Zr. During low-grade metamorphism Zr is considered to be relatively immobile (Floyd and Lees, 1973;Winchester and Floyd, 1977;Macdonald et al, 1988). Hence, Zr can be used as a parameter for evaluating the elemental mobility and also to understand the differentiation of magma.…”

Origin of Late Palaeoproterozoic Great Vindhyan basin of North Indian shield: Geochemical evidence from mafic volcanic rocks

“…To assess possible element mobility, various elements are plotted against incompatible element Zr (Figs. 3 and 4) which is considered relatively immobile (Winchester and Floyd, 1977;Macdonald et al, 1988). In Khairmalia volcanics K 2 O, CaO and SiO 2 display large variation over a small range in Zr values (Fig.…”