[Folda] Master's Lecture in Geology - Moneer Fathel Alnethary, 26 January 14:00 at Askja N-367
Siqi Li
sil10 at hi.is
Tue Jan 23 10:49:05 GMT 2018
Master's Lecture in Geology - Moneer Fathel Alnethary
26. Jan - 14:00 to 16:00 | Location: Askja N-367
Target audiance: Everybody welcome
Comment: Will be held in English
Master's student: Moneer Fathel Alnethary
Title: Petrology of the Hornfels Contact Zone around the Hrossatungur Gabbro in the Eroded Hafnarfjall Central Volcano, W-Iceland
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Faculty: Faculty of Earth Sciences
Advisors: Hjalti Franzson, Chief Geologist at Iceland Geosurvey
Members of the master committe: Guðmundur H. Guðfinnsson, Research Scholar at the Earth Science Institute
Examiner: Bjarni Gautason, Head of Akureyri Branch at Iceland Geosurvey
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Abstract
This study focusses on a hornfels zone on the southern side of the Hrossatungur gabbro, within the Hafnarfjall-Skarðsheiði central volcano, W-Iceland. The intrusion formed by repetitive injections of basaltic cone sheets, which were trapped at a lava-pyroclastite boundary within the Hafnarfjall caldera filling. During contact metamorphism in response to the intrusion emplacement, a hornfels contact zone was created by a recrystallization process of previously hydrothermally altered basalt. This recrystallization, which was studied petrographically and with SEM and EMP, consists mainly of clinopyroxene (salite-augite-ferrosalite-hedenbergite), minor orthopyroxene, plagioclase (labradorite-bytownite-anorthite) and oxides (magnetite-titanomagnetite-ilmenite) and subordinate occurrences of garnet, titanite, amphibole, apatite and sulphides. The recrystallization drives volatiles out of the rock, as is clearly seen by the low values attained from LOI analysis. Chemical analysis (ICP-OES) of the hornfels shows relatively minor elemental changes compared to primary rock compositions, except perhaps overall enrichment of Al2O3, Zn, Ni and Cu, and a depletion of Ba and Sr. This can be explained by the rock recrystallizing to similar mineral compositions as found in the primary basalts. A comparative study of a hornfels zone at a dyke margin at about 1500 m depth in well HE-42 in Hellisheiði high-temperature field shows very comparable results. The main research question was to evaluate water/magma interaction during the intrusion of gabbro magma and its consolidation. The results show that the formation of the hornfels is caused by heat conduction, whereas water/magma interaction is absent.
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