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Formation of Spinifex Texture in Komatiites: an Experimental Study |
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| Authors: | FAURE FRANCOIS; ARNDT NICHOLAS; LIBOUREL GUY |
| Institution: | 1 CENTRE DE RECHERCHE PÉTROGRAPHIQUE ET GÉOCHIMIQUES CNRS-UPR2300, BP 20, 54501 VANDOEUVRE LES NANCY, FRANCE 2 LABORATOIRE DE GÉODYNAMIQUE DES CHAÎNES ALPINES, UMR 5025, UNIVERSITÉ JOSEPH FOURIER BP 53, 38041 ST MARTIN D'HÈRES, FRANCE 3 COLE NATIONALE SUPÉRIEURE DE GÉOLOGIE-INPL BP 40, 54501 VANDOEUVRE LES NANCY, FRANCE |
| Abstract: | The formation of platy olivine spinifex, the texture that characterizeskomatiite lavas, has long been enigmatic. A major problem isthat the dendritic morphology of the olivine resembles thatof crystals grown in laboratory experiments at high coolingrates (>50°C/h), but at the position where these texturesform, up to several meters below the komatiite flow top, thecooling rate cannot have been greater than 1–5°C/h.We performed experiments that demonstrate that the platy habitof spinifex olivine or pyroxene is a consequence of slow coolingof ultramafic magma in a thermal gradient (7–35°C/cm).The charges were cooled at rates between 2 and 1428°C/hand, even at the low cooling rates, the thermal gradient ledto constrained growth and the development of preferentiallyoriented dendritic crystals with morphologies like those innatural platy spinifex-textured lavas. Under these conditions,olivine starts to crystallize at temperatures well below theequilibrium liquidus temperature (37°C < – T<56°C) depending on the composition of the starting material.When the cooling rate is high, the thermal gradient has a negligibleeffect on the texture and the crystals have a random orientation,like that in the upper parts of komatiite flows. KEY WORDS: komatiite; spinifex; cooling rate; experimental petrology; thermal gradient |
| Keywords: | : komatiite spinifex cooling rate experimental petrology thermal gradient |
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