Show simple item record

dc.contributor.author Bromley, Alan Victor
dc.date.accessioned 2009-11-17T16:58:37Z
dc.date.available 2009-11-17T16:58:37Z
dc.date.issued 1963-05
dc.identifier.citation Bromley, A. V., (1963) 'The Geology of the Blaenau Ffestiniog Area, Merionethshire', Institute of Geography and Earth Sciences (formerly, Geology), Aberystwyth University en
dc.identifier.uri http://hdl.handle.net/2160/3541
dc.description.abstract The stratigraphy and structure of the Cambrian and Ordovician rocks of the Blaenau Ffestiniog area are described briefly. This forms a background to a more intensive study of the four types of intrusive igneous rocks which are emplaced among the sedimentary and igneous rocks of the region. The intrusive rocks are: The Tan-y-Grisiau, Microgranite. Microgranodiorite and Quartz Latite. Dolerite. Multiple Intrusions. (Dolerite-quartz latite). The Tan-y-Grisiau microgranite is intruded into Cambrian rocks and has an extensive metamorphic aureole. Structural evidence indicates that it was emplaced prior to the imposition of the regional cleavage (Caledonian) and faunal evidence from outside the area under consideration shows that its emplacement occurred during post-Harnagian, pre-Longvillian times. The mineral assemblage in the main part of the intrusion (hornblende - biotite - plagioclase - orthoclase - quartz) can be equated, in terms of metamorphic facies, with a relict assemblage discovered in the hornfelses (andalusite- - Ooridrite - biotite - plagioclase - quartz). The north-western part of the microgranite has suffered extensive post-magmatic modification as a result of the operation of volatiles. Its mineral assemblage (chlorite - sericite - calcite - albite - quartz) can be equated with the ubiquitous retrograde assemblage in the hornfelses (chlorite - sericite - epidote - albite quartz). This assemblage is attributed to the presence of the slowly cooling microgranite and to the operation of volatiles derived from it rather than to retrogression brought about later by the imposition of cleavage or folding. The microgranodiorite and the quartz latites are considered to be closely related to the pyroclastic rocks of the Moelwyn Volcanic Series. They were intruded at very shallow depth and in some cases intrusion was continued after the rocks had consolidated. This gave rise to the development of autobreccias which have previously been interpretted as agglomerates. The amount of metamorphism associated with these intrusions is very slight. The dolerites occur both as thin dykes and sills of varying dimensions. They are petrographically identical to the dolerites which are ubiquitous throughout the Cambrian and Ordovician successions in the rest of North Wales. The multiple intrusions are thought to have been formed by rising dolerite magma remelting quartz latite through which it passed. This in turn was intruded into the centre part of certain dolerite sills. Petrographic evidence suggests that acid and basic magmas were held in juxtaposition at high temperatures without any significant mixing taking place. en
dc.language.iso en en
dc.publisher Aberystwyth University en
dc.title The Geology of the Blaenau Ffestiniog Area, Merionethshire en
dc.type Text en
dc.type.publicationtype doctoral thesis en


Files in this item

Aside from theses and in the absence of a specific licence document on an item page, all works in Cadair are accessible under the CC BY-NC-ND Licence. AU theses and dissertations held on Cadair are made available for the purposes of private study and non-commercial research and brief extracts may be reproduced under fair dealing for the purpose of criticism or review. If you have any queries in relation to the re-use of material on Cadair, contact is@aber.ac.uk.

This item appears in the following Collection(s)

Show simple item record

Search Cadair


Advanced Search

Browse

Statistics