compositional trend
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2021 ◽  
Vol 53 ◽  
pp. 257-270
Author(s):  
Christopher Rieser ◽  
Peter Filzmoser
Keyword(s):  

2007 ◽  
Vol 106 (6) ◽  
pp. 3743-3756 ◽  
Author(s):  
Samik Gupta ◽  
Raja Krishnamurthy ◽  
Amit Biswas ◽  
Anil K. Bhowmick

2001 ◽  
Vol 65 (6) ◽  
pp. 787-795 ◽  
Author(s):  
M. Gaeta ◽  
C. Freda

AbstractA magmatic calcic amphibole (M4Ca≥1.50) characterized by large Sr and F contents (SrO>1 wt.%, F>2.5 wt.%) is described. According to the crystal-chemical formula, the amphibole can be classified as a strontian fluoro-magnesiohastingsite and the presence of Sr cations in the A sites is suggested. The amphibole occurs in the groundmass of ultrapotassic lavas from the Alban Hills Volcanic District (Central Italy). This peculiar chemical composition is due to the lavas' groundmass compositional trend occurring under low silica-activity conditions. We suggest that the occurrence of F amphiboles allows us to consider the Alban Hills Volcanic District magmas to be as rich in F as other ultrapotassic magmas.


1996 ◽  
Vol 60 (403) ◽  
pp. 907-925 ◽  
Author(s):  
Roger H. Mitchell ◽  
Nikolai V. Vladykin

AbstractPyroxene and mica found in plutonic rocks of the Little Murun ultrapotassic pluton exhibit trends of compositional evolution that permit evaluation of the differentiation sequence of the complex. Pyroxene evolves from diopside in kalsilite and phlogopite pyroxenites through aegirine-diopside in shonkinite to aegirine in late stage charoitite and evolved hypabyssal rocks. The compositional trend is unusual in that the hedenbergite content of the pyroxenes never exceeds 15 mol.% and is thus unlike pyroxene compositional trends found in sodic alkaline complexes. Mica is Al- and Ti-poor and ranges in composition from Fe-rich phlogopite through biotite towards tetraferriannite. Compositional trends of mica found in ‘lamproite-like’ hypabyssal rocks are identical to those observed in the micaceous plutonic rocks; hence the former are considered to be representatives of the lamprophyric facies of the magmas which formed the plutonic series.


1977 ◽  
Vol 41 (317) ◽  
pp. 111-119 ◽  
Author(s):  
M. T. Hossain

SummaryChemical, X-ray, and optical analyses of eight Ca-rich pyroxenes and three coexisting Ca-poor pyroxenes from the gabbros of the Marangudzi ring complex, Rhodesia, are presented. Both the series show limited Fe-enrichment. High Ca-content of the clinopyroxenes together with their restricted Fe-enrichment, having a trend from Ca44·8Mg42·6Fe12·6to Ca42·7Mg37·7Fe19·6, could be indicative of an alkaline nature. But the presence of a Ca-poor pyroxene phase with a compositional trend between Ca2·9Mg71·2Fe25·9 and Ca3·1Mg63·0 Fe34·9 onwards in small amounts suggests tholeiitic to calc-alkaline nature. Certain characteristics in the variation in composition of the pyroxenes confirm a transitional nature of the Marangudzi parent magma, originating at a depth comparatively greater than the normal tholeiitic magma, but less deep than alkaline magma, at a fairly high pressure. The Marangudzi pyroxenes are compared with the pyroxenes of the similar world-wide igneous complexes.


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