Geochemical evolution of the Maloin Ranch pluton, Laramie Anorthosite Complex, Wyoming: Trace elements and petrogenetic models
- State Univ. of New York, Stony Brook (USA)
The Maloin Ranch pluton is a layered composite intrusion at the southeast margin of the main body of the Laramie Anorthosite. The layering defines a body shaped like a half bowl, which contains ferrodiorite at its base, overlain progressively by fine-grained monzonite and porphyritic monzonite, monzosyenite, and porphyritic granite. The trace element data presented here, together with isotopic data for these rocks (Kolker, 1989) show that each of the members of this composite intrusion has a separate origin. Field, geochemical, and isotopic evidence are consistent with a comagmatic relation between ferrodiorite and anorthositic rocks, either by fractionation or immiscibility. The fine-grained monzonite is not the result of fractionation of ferrodiorite, or mixing of ferrodiorite with a more evolved magma, such as monzosyenite or granite. At intermediate levels in the intrusion, porphyritic monzonite formed by mixing of fine-grained monzonite (or biotite gabbro) and monzosyenite magmas. Textures, REE patterns, and other trace-element data show that the monzosyenite is a feldspar cumulate, with a highly variable proportion of liquid. Trace-element and isotopic characteristics of the Maloin monzosyenite are consistent with derivation from a more evolved deep crustal source or more extensive fractionation, compared to the fine-grained monzonite. REE data suggest that some of the overlying porphyritic granite is a late-stage segregation related to the monzosyenite and not to the overlying Sherman Granite.
- OSTI ID:
- 6033425
- Journal Information:
- American Mineralogist; (USA), Vol. 75:5-6; ISSN 0003-004X
- Country of Publication:
- United States
- Language:
- English
Similar Records
Model for the possible origin of anorthosite-syenite associations like the Laramie anorthosite complex (lac)
Origin and interaction of some alkalic and silicic plutons in the Vermilion Granitic Complex, NE Minnesota