|
|||||
|
|
Intrusion and Crystallization of a Spinifex-Textured Komatiite Sill in Dundonald Township, Ontario |
|
| Authors: | ARNDT NICHOLAS T; LESHER C MICHAEL; HOULE MICHEL G; LEWIN ERIC; LACAZE YANNICK |
| Institution: | 1 LGCA, UMR5025 CNRS, UNIVERSITÉ JOSEPH FOURIER, GRENOBLE, FRANCE 2 MINERAL EXPLORATION RESEARCH CENTRE, DEPARTMENT OF EARTH SCIENCES, LAURENTIAN UNIVERSITY, SUDBURY, ONTARIO, CANADA 3 OTTAWA–CARLETON GEOSCIENCES CENTRE, UNIVERSITY OF OTTAWA, OTTAWA, ONTARIO, CANADA 4 PRECAMBRIAN GEOSCIENCE SECTION, ONTARIO GEOLOGICAL SURVEY, SUDBURY, ONTARIO, CANADA |
| Abstract: | Although komatiite has been defined as an ultramafic volcanicrock characterized by spinifex texture, there is a growing recognitionthat similar textures can also form in high-level dykes andsills. Here, we report the results of a petrological and geochemicalinvestigation of a  5 m thick komatiite sill in Dundonald Township,Ontario, Canada. This unit forms part of a series of komatiitesand komatiitic basalts, some of which clearly intruded unconsolidatedsediments. The komatiite sill is differentiated into a spinifex-texturedupper part and an olivine cumulate lower part. Features characteristicof the upper sections of lava flows, such as volcanic brecciaand a thick glassy chilled margin, are absent and, instead,the upper margin of the sill is marked by a layer of relativelylarge (1–5 mm) solid, polyhedral olivine grains that gradesdownwards over a distance of only 2 cm into unusually large,centimetre-sized, skeletal hopper olivine grains. This is underlainby a 1 m thick zone of platy spinifex-textured olivine and coarse,complex, dendritic, spinifex-textured olivine. The texture ofthe olivine cumulate zone in the overlying unit is uniform rightdown to the contact and a lower chilled margin, present at thebase of all lava flows, is absent. The textures in the silland the overlying unit are interpreted to indicate that thesill intruded the olivine cumulate zone of the overlying unit.Thermal modelling suggests that soon after intrusion, a narrowinterval of the overlying cumulate partially melted and thatthe liquid in the upper part of the sill became undercooled.The range of olivine morphologies in the spinifex-textured partof the sill was controlled by nucleation and crystallizationof olivine in these variably undercooled liquids. KEY WORDS: komatiite; intrusion; spinifex texture; olivine |
| Keywords: | : komatiite intrusion spinifex texture olivine |
| 本文献已被 Oxford 等数据库收录！ | |