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Distribution of manganese between coexisting biotite and hornblende in plutonic rocks

Geochimica et Cosmochimica Acta

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Abstract

The distribution of manganese between coexisting biotite and hornblende for 80 mineral pairs from igneous rocks of diverse provenance (including Southern California, Sierra Nevada, Boulder, and Boulder Creek batholiths and the Jemez Mountains volcanics) has been determined by neutron activation analysis. Data on the distribution ratio (Kd = Mnhornblende Mnbiotite) indicate that an equilibrium distribution of Mn is closely approached, though not completely attained, in most samples from plutonic environments. Comparison of Kd values of mineral pairs with bulk chemical composition of host rocks reveals no correlation. Because initial crystallization temperatures vary with rock composition, the lack of correlation of composition with Kd suggests that the equilibrium distribution of Mn between biotite and hornblende reflects exchange at subsolidus temperatures rather than initial crystallization temperatures. The highest Kd values are for volcanic rocks, in which rapid quenching prevents subsolidus redistribution of Mn. For sample pairs from the Southern California and Sierra Nevada batholiths there is a positive correlation of Kd with TiO2 content of biotite. Though the evidence is not compelling, Kd may also correlate with the rate of cooling and/or the presence or absence of sphene in the rock. ?? 1968.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Distribution of manganese between coexisting biotite and hornblende in plutonic rocks
Series title:
Geochimica et Cosmochimica Acta
Volume
32
Issue:
11
Year Published:
1968
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
First page:
1149
Last page:
1163
Number of Pages:
15