Evidence of silicate immiscibility within flood basalts from the Central Atlantic Magmatic Province J. G. Shellnutt Department of Earth Sciences, National Taiwan Normal University, 88 Tingzhou Rd., Section 4, Taipei 11677, Taiwan (jgshelln@ntnu.edu.tw) J. Dostal Department of Geology, Saint Mary’s University, Halifax, Nova Scotia, Canada Y. Iizuka Institute of Earth Sciences, Academia Sinica, Taipei, Taiwan [1] The role silicate-liquid immiscibility plays in the formation of macro-scale, bimodal volcanic/plutonic igneous complexes, and Fe-Ti oxide deposits is debated as the rock compositions produced by immiscibility are similar to those produced by other petrological processes. Within the flows of the North Mountain basalt of the Central Atlantic Magmatic Province are centimeter-thick granophyre layers. The granophyre layers are a mixture of mafic (i.e., ilmenite, magnetite, ferroaugite, plagioclase, stilpnomelane, ferrorichterite) and felsic (i.e., sanidine, quartz) minerals and highly siliceous (>75 wt% SiO 2 ) mesostases. Petrological modeling indicates that the siliceous mesostasis 1 sanidine 1 quartz 6 ferrorichterite represents a Si-rich silicate immiscible melt whereas the ferroaugite 1 plagioclase 1 stilpnomelane represent the Fe-rich silicate immiscible liquid. The identification of naturally occurring silicate-liquid immiscibility at scales greater than micron level is an important observation which may be useful in identifying volcanic and plutonic rocks which formed by macro-scale silicate-liquid immiscibility. Components : 9,646 words, 4 figures, 2 tables. Keywords : silicate-liquid immiscibility; fractional crystallization; tholeiitic basalt; Central Atlantic Magmatic Province; Early Jurassic ; Nova Scotia. Index Terms: 8410 Geochemical modeling: Volcanology; 8425 Effusive volcanism: Volcanology; 1009 Geochemical modeling: Geochemistry; 4302 Geological: Natural Hazards; 3630 Experimental mineralogy and petrology: Mineralogy and Petrology; 3610 Geochemical modeling: Mineralogy and Petrology; 3640 Igneous petrology: Mineralogy and Petrol- ogy ; 3641 Extrusive structures and rocks : Mineralogy and Petrology. Received 2 August 2013 ; Revised 1 October 2013 ; Accepted 16 October 2013 ; Published 00 Month 2013. Shellnutt, J. G., J. Dostal, and Y. Iizuka (2013), Evidence of silicate immiscibility within flood basalts from the Central Atlantic Magmatic Province, Geochem. Geophys. Geosyst., 14, doi :10.1002/2013GC004977. 1. Introduction [2] Silicate-liquid immiscibility or ‘‘magma unmix- ing’’ is postulated as a possible process for the devel- opment of cogenetic suites of basic and acidic igneous rocks in ophiolites and continental volcanic- plutonic complexes [Dixon and Rutherford, 1979; Eby, 1980; Ferreira et al ., 1994; Jakobson et al ., V C 2013. American Geophysical Union. All Rights Reserved. 1 Article Volume 14, Number 00 00 Month 2013 doi : 10.1002/2013GC004977 ISSN : 1525-2027