The lamprophyre problem: Return to the roots

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angličtina

The term lamprophyre has been introduced in 1874 by Gümbel for Variscan mafic post-collisional dykes from the Bohemian Massif characterized by phenocrysts of mafic mica embedded in a feldspar groundmass (minette and kersantite type). In analogy to these, Rosenbusch in 1887 added the amphibole-bearing types such as vogesite and camptonite, from which spessartite was subsequently distinguished. Unfortunately, during the 20th century, petrologists enlarged this ill-understood group by incorporating different rocks containing mafic phenocrysts, such as kimberlites, lamproites, nepheline-, leucite- and melilite-bearing rocks. This resulted in a single large supergroup of polygenetic rocks termed the lamprophyre clan. In contrast, recent understanding of lamprophyres provides a sound basis for rejecting such a variable group of polygenetic origin. As true lamprophyres, we can now recognize five original types (endmembers) among which there are continuous transitions: minette, kersantite, vogesite, spessartite and partly camptonite (in the original sense). It is important to note, that not every rock labelled as a true lamprophyre falls into this group. For example a peralkaline minette is not a lamprophyre but very probably corresponds to a lamproite. Since the term camptonite is usually used for an alkaline lamprophyre variety (in fact volatile-rich basalt), I recommend not to use it in context with the true lamprophyres. Lamprophyre varieties containing kaersutitic amphibole can be easily described as titanospessartite or titanovogesite, respectively. Moreover, the last proposed variety fills the gap in the current nomenclature.

lamprophyres, proposed nomenclature, new names, titanospessartite, titanovogesite

KRMÍČEK, L.

2011

1. 8. 2011

Mineralogical Society of Great Britain and Ireland

Spojené království Velké Británie a Severního Irska

978-1-86239-207-6

Goldschmidt Conference Abstracts

1

1

0026-461X

MINERALOGICAL MAGAZINE

75

3

Spojené království Velké Británie a Severního Irska

1241

1241

1