Trace-element modeling of the petrogenesis of granophyres and aplites in the Notch Peak granitic stock, Utah

Journal Article · · Am. Mineral.; (United States)

OSTI ID:6913774

Nabelek, P I

The petrogeneses were modeled using published experimental data for mineral/melt, mineral/fluid, and melt/fluid partitioning of alkali, alkaline-earth and rare-earth elements. Calculations suggest that the granophyre formed by 2013% crystallization from an aqueous fluid that exsolved from the magma during emplacement and was trapped beneath the limestones. The observed strong enrichment of Ba and Sr in the granophyre relative to the granite is due to large alkali feldspar/fluid partition coefficients for these elements, while the depletion of large-ion-lithophile elements is due to their small solubility in aqueous fluids. On the other hand, the aplite is depleted in Ba, Sr, and the REEs, while the concentration of Zr, Ta, Hf, Th, and U is about the same as the major lithologic units in the stock. It is not possible to explain the alkaline-earth element and REE concentrations in the aplite by any model that employs mineral/melt partition coefficients for anhydrous melts. However, the composition and the large concentration of the highly charged elements are difficult to explain by direct crystallization from aqueous fluids. It is apparent that the partition coefficients of Ba, Sr, and the REEs between minerals and melt significantly increase when the system becomes saturated with chlorine-rich aqueous fluids. The results of this study have implications for the petrogenesis of pegmatites and other aplites because many have depletion and enrichment characteristics similar to the aplite and granophyre at Notch Peak. It is shown that rocks that are the result of fractionation off anhydrous melts can be distinguished on the basis of their major- and trace-element chemistries from those that crystallized in the presence of aqueous fluids or those that crystallized directly from the fluids.

• Research Organization: Univ. of Missouri, Columbia
• OSTI ID: 6913774
• Journal Information: Am. Mineral.; (United States), Journal Name: Am. Mineral.; (United States) Vol. 71:3-4; ISSN AMMIA
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580300* -- Mineralogy
Petrology
& Rock Mechanics-- (-1989)
ACTINIDES
ALKALINE EARTH METALS
APLITES
BARIUM
CHEMISTRY
CRYSTALLIZATION
ELEMENTS
ENRICHMENT
FEDERAL REGION VIII
GEOCHEMISTRY
GEOLOGIC HISTORY
GRANITES
HAFNIUM
IGNEOUS ROCKS
MAGMA
METALS
NORTH AMERICA
PEGMATITES
PETROGENESIS
PHASE TRANSFORMATIONS
PLUTONIC ROCKS
ROCKS
STRONTIUM
TANTALUM
THORIUM
TRANSITION ELEMENTS
URANIUM
USA
UTAH
ZIRCONIUM