Geological Survey of Finland Bulletin 289 - arkisto.gsf.fi

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Geological Survey of Finland, Bulletin 289 SHEARING AND MULTIPLE INTRU SION IN THE DIABASES OF .ALAND ARCHIPELAGO, SW FINLAND BY eARL EHLE R S and MARY EHLERS WITH 23 FIGURES, 0 E TABLE A D 0 E APPE DIX GEOLOGINEN TUTKIMUSLAITOS ESPOO 1977
Ehlers, C. and Ehlers, M. 1977: Shearing and multiple intrusion in the diabases of Aland arehipelago, SW Finland. Geological Survey 0/ Finland, Bulletin 289, 31 pages, 23 figures , one table and one appendix. A set of narrow diabase dykes runs in a NE·SW direetion out· side the eastern eontaet of the Aland rapakivi massif. Chilled margins between adjaeent dykes, eomposite dykes eonsisting of several intrusion phases, and areal differenees in mineral eomposition show that the dykes were intruded in pulses of slightly different ages . Many dykes exhibit eataclastic right-hand shearing. A eonnection between this shearing and the intrusion of the rapakivi granites is suggested. Chemieally the dykes are rieh in iron. Mineralogieally they eonsist of hornblende and plagioclase with a subophitie texture. It is suggested that the diabases intruded as a very liquid, waterrieh magma whieh rushed into fissures, resultning in rapid quenehing at the eontaets and slower erystallisation, possibly under rising water-pressure, in the central parts of the dykes. The pressure builds up until new fissures are formed and a new intrusion pulse is initiated. It is coneeivable that the diabase dykes are eonneeted to the rapakivi granites but are a li ttle earlier in their intrusion beeause of their lower viscosity. The authors' address Carl Ehlers Mary Ehlers Geologisk-Mineralogiska Institutionen Abo Akademi 20500 Abo 50 ISBN 951-690-071-2 Helsinki 1977. Valtion painatuskeskus
Page 1: Geological Survey of Finland Bullet
Page 6 and 7: INTRODUCTION The diabase dykes in t
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Page 32: Rancken, R. (1953) Über eine arch
Page 37: Appendi x 1, continued Known T rend

Geological Survey of Finland Bulletin 289 - arkisto.gsf.fi

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