Cheadle There is a tendency of Ti to be less enriched than other more incompatible elements, resulting in a trend towards higher Ti/REE, Ti/Y, etc. D. R. C. M. Within Si-rich, orthopyroxene-saturated magma, pyroxene crystallization depleted the magma below chromite saturation, giving rise to growth of Cr-poor orthopyroxene, either as newly formed euhedral liquidus phases or as Cr-poor overgrowths on Cr-rich inclusion-bearing cores. J. S. T. Geology and ore petrology of the Akanvaara and Koitelainen mafic layered intrusions and the KeivitsaâSatovaaa layered complex, northern Finland. Added 21 days ago|11/21/2020 11:59:36 AM According to conventional cumulus theory, there was a peritectic relationship between olivine and orthopyroxene in the parent magma, and the granular harzburgites represent mechanical mixtures of a disequilibrium assemblage accumulated through crystal settling or density current flow ( Raedeke & McCallum, 1984 ). W. F. (, Oxford University Press is a department of the University of Oxford. A plausible scenario is one where an olivineâchromite framework grows in situ at a sloping sidewall; the crystallization site is subsequently swamped by contaminated magma with a high silica activity, causing a rapid burst of orthopyroxene growth from supersaturated magma and resulting peritectic dissolution of olivine and chromite, as above. F. M. Thomas (, Meurer 16 b): compatible elements Cr, Co, Mn, Zn and Ni follow one another from minima in the grain core to maxima at the outer edge of the Cr-rich zone; Cr then drops slightly in an outer overgrowth. An alternative hypothesis is that the oikocrysts underwent a two-stage growth history: an early stage of growth of homogeneous Cr-rich cores, requiring access to a supply of Cr-undepleted magma, and a second stage of growth from progressively Cr-depleted magma consistent with in situ growth from migrating intercumulus liquid as indicated in Fig. A further point of significance here is the within-sample correlation observed between Cr and Al from cores to rims of orthopyroxene grains, and particularly the observation that this correlation applies within poikilitic and non-poikilitic grains. 4 g). In igneous rocks poikilitic texture is widely used to determine order of crystallization; if one mineral is enclosed by another … (, McBirney D. T. Wilson Sobolev Olivine may also enclose feldspar laths. Reverse zoning from Cr-poor cores to Cr-rich rims, of comparable magnitude to that seen in the normally zoned grains, is observed in some orthopyroxene-rich cumulates ( Fig. A. 6 ) that in detail show many of the same features as the centimetre-scale mingling noted in point (1). Posted by 9 months ago. M. , 2014 ). poikilitic synonyms, poikilitic pronunciation, poikilitic translation, English dictionary definition of poikilitic. G. This is true of many gabbros, aplites and granites. Hence an explanation for rapid variations in the Cr contents of liquidus pyroxenes is fluctuation in silica activity, related to localized assimilation and incorporation of the siliceous country-rock xenoliths abundantly preserved with the pyroxenitic and gabbroic upper parts of the sills or cycles. We thank Marian Holness, Dick Claeson and Julien Leuthold for constructive reviews and Marjorie Wilson for meticulous editing. Postcumulus overgrowth or modification by percolating intercumulus liquid is a relatively minor process, with the exception of dispersed melt percolation channels giving rise to the metasomatic replacement products that we consider below. A postcumulus origin for the rims could still be a viable hypothesis if there was a voluminous convective flow of recharged intercumulus liquid through a permeable mush ( Kerr & Tait, 1986 ), or a reactive flow generated from magma injections into the crystal mush as proposed for Rum ( Leuthold et al. C. G. Whitehouse This thread is archived. E. J. Definition of poikilitic in the Definitions.net dictionary. 11 : phase map, CrâCaâFe RGB false colour image and Cr linear greyscale image; (d, e) element maps from synchrotron XFM; (f) quantitative element profiles for mol % En and Cr from Tornado XFM, electron microprobe (EMP) and synchrotron XFM maps (Maia). K. J. J. C. G. 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