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Igneous rocks
Published in W.S. MacKenzie, A.E. Adams, K.H. Brodie, Rocks and Minerals in Thin Section, 2017
W.S. MacKenzie, A.E. Adams, K.H. Brodie
Lamprophyre is the name for a group of rocks which occur as dykes and have one of the ferromagnesian minerals as phenocrysts, and a groundmass of alkali feldspar, plagioclase or sometimes a feldspathoid. They are considered to have similar origins as kimberlites. The feldspar is commonly badly altered. Primary minerals are commonly altered in these rocks due to their high volatile content.
Petrology and petrogenesis of an intraplate alkaline lamprophyre-phonolite-carbonatite association in the Alpine Dyke Swarm, New Zealand
Published in New Zealand Journal of Geology and Geophysics, 2020
Phonolites and carbonatites have many mineralogical compositional similarities, including the albitic nature of their feldspars, acmitic clinopyroxenes, the presence of Fe-bearing carbonates and Nb-rich rutile. The two magmas are also commonly closely associated in the field, evidence that is compatible with them representing conjugate immiscible magmas (Cooper 1986; Cooper and Paterson 2008). Whether all carbonatites are derived by this mechanism is unclear. Several of the UML are carbonate-rich, and it has been suggested that carbonatite may also be derived directly from these parent magmas by liquid immiscibility (Rock 1986; Tappe et al. 2006, 2009). In the ADS, many lamprophyres have selvedges (Figure 2C), veins and offshoots composed largely of carbonate. Similar features have been described for lamprophyres elsewhere and interpreted by Currie and Ferguson (1970) as due to boiling off, from the ascending lamprophyre magma, of a low viscosity, volatile-rich precursor fluid that effectively opens up the fracture system facilitating intrusion of the associated magma. This process implies immiscibility between lamprophyre magma and a carbonate-rich fluid.