An ion and electron microprobe study of amphibole in the Garland Peak Syenite, Red Hill Complex, NH

Conference · Wed Jan 01 04:00:00 EST 1992 · Geological Society of America, Abstracts with Programs; (United States)

OSTI ID:5975313

Dorais, M J ^[1]; Macrae, N D ^[2]

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1. Indiana Univ., Bloomington, IN (United States)
2. Univ. of Western Ontario, London, ON (Canada)

The Garland Peak Syenite (GPS) of the Red Hill complex, NH, consists predominantly of amphibole, oligoclase, perthite, and quartz; amphiboles are zoned from kaersutite cores to hastingsite-hornblende rims. The association of kaersutite with quartz indicates that the GPS magma experienced substantial changes in silica activity during its crystallization history. Camptonites are also associated with the Red Hill complex, and in order to elucidate the camptonite-GPS, and the GPS kaersutite-quartz relationships, amphiboles in these rocks were analyzed by electron and ion microprobe techniques. Kaersutites in the camptonites and GPS are very similar in terms of major and minor elements. REE concentrations in the camptonite's kaersutite are slightly less than the GPS kaersutite; LREE abundances are 100 times chondrites, La/Yb values are 4--5. GPS kaersutitic cores have LREE abundances between 200--300 times chondrites with La/Yb values between 6--8. Compared to the cores, the hastingsite rims are preferentially enriched in REE with LREE between 1,000 and 2,000 times chondrites, La/Yb values range between 16--18, and the patterns have large negative Eu anomalies. Although complicated by the certainty of changing partition coefficients during crystallization, the enrichment in total REE from camptonite--GPS kaersutite--GPS hastingsite is consistent with a differentiation origin of the suite. Rimward depletions in Sr, Eu, V, and Ti concentrations, and the increase in La/Yb values suggest that parental camptonites fractionated amphibole, magnetite, and feldspar to produce silica-oversaturated GPS liquids. The significance of amphibole and magnetite fractionation on camptonite-GPS silica activity is also indicated by bulk-rock, major element modeling.

• OSTI ID: 5975313
• Report Number(s): CONF-921058--
• Conference Information: Journal Name: Geological Society of America, Abstracts with Programs; (United States) Journal Volume: 24:7
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
CHEMICAL ANALYSIS
CHEMISTRY
DEVELOPED COUNTRIES
ELECTRON MICROPROBE ANALYSIS
GEOCHEMISTRY
GEOLOGIC FORMATIONS
ION MICROPROBE ANALYSIS
MICROANALYSIS
MINERALOGY
NEW HAMPSHIRE
NONDESTRUCTIVE ANALYSIS
NORTH AMERICA
USA