Sr and Nd isotopic constraints on the origin of the Laramie Anorthosite Complex, Wyoming

Journal Article · · American Mineralogist; (USA)

OSTI ID:6250184

Geist, D J ^[1]; Frost, C D ^[2]; Kolker, A ^[3]

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1. Hamilton College, Clinton, NY (USA)
2. Univ. of Wyoming, Laramie (USA)
3. State Univ. of New York, Stony Brook (USA)

Anorthosites and gabbros from the Anorthosite Complex (LAC) have Nd and Sr isotopic ratios that are similar to values for undepleted mantle, but variation within the anorthosite-gabbro suite suggests that their isotopic ratios are affected by assimilated country rock. Some of the chemically evolved rocks have isotopic ratios indistinguishable from those of the anorthosites and gabbros, although in general the chemically evolved rocks contain a greater component of crustal material. Each of the chemically evolved satellite intrusions have distinct Sr and Nd isotopic ratios, indicating that each intrusion evolved independently. The isotopic data for the chemically evolved rocks are best explained by assimilation of various amounts of crustal material, followed in some instances by crystal fractionation and further assimilation at the level of emplacement. Isotopic ratios in two oxide-rich rocks are identical to those of the anorthosites, consistent with the hypothesis that they are late-stage fractionates of the anorthosite series.

• OSTI ID: 6250184
• Journal Information: American Mineralogist; (USA), Journal Name: American Mineralogist; (USA) Vol. 75:1-2; ISSN AMMIA; ISSN 0003-004X
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
ALKALINE EARTH ISOTOPES
ANORTHOSITES
CHEMISTRY
CONTINENTAL CRUST
EARTH CRUST
EARTH MANTLE
FEDERAL REGION VIII
FRACTIONATION
GABBROS
GEOCHEMISTRY
GEOLOGIC FORMATIONS
GEOLOGIC HISTORY
GEOLOGIC MODELS
IGNEOUS ROCKS
ISOTOPE RATIO
ISOTOPES
MAGMA
NEODYMIUM ISOTOPES
NORTH AMERICA
ORIGIN
PLUTONIC ROCKS
ROCKS
SEPARATION PROCESSES
STRONTIUM ISOTOPES
USA
WYOMING