THE BORROWDALE VOLCANIC AND ASSOCIATED ROCKS OF THE SCAFELL AREA, ENGLISH LAKE DISTRICT

Abstract

Thirty-five square miles of lavas and tufts are folded into what is essentially a broad syncline plunging east-north-east, modified b y subsidiary wrinkles. Faults trending north-west and north or north-north-east form a conspicuous pattern. Cleavage appears to be related to the major folding, but the joint-pattern is obscure. The stratigraphical sequence, from bottom to top, is: aphanitic basaltic andesites and porphyritic pyroxene-andesites; garnetiferous flows and welded tufts of dacitic, rhyodacitic and rhyolitic composition, with local bedded tufts and an andesite flow; bedded andesitic and rhyolitic tufts, with a small rhyolite flow; welded rhyolitic tufts; tuffaceous hornstone. The thickness is 9160 to 10,210 feet. Intrusive rocks are granite; granite-porphyry; garnetiferous biotite-quartz-porphyry ; hybrid (?) “porphyry and porphyrite”, with garnets; dolerite, and other basic rocks. The granite is probably connected to the neighbouring Eskdale granite, to which most of the other intrusions may be genetically related. Secondary alteration in the volcanic rocks is mainly the result of contact metamorphism and metasomatism. The chemical relationships (major and minor elements) of the lavas and welded tufts resemble those of a calc-alkali series.