Award Date

1-1-2003

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

First Committee Member

Terry L. Spell

Number of Pages

248

Abstract

Analysis of 40Ar/39Ar age, major/trace element geochemical, and Nd and Sr isotopic data indicates that the Jemez volcanic field, a long-lived continental volcanic center located at the intersection of the Rio Grande rift and Jemez Lineament in northern New Mexico, evolved in a complex two-phase manner. The Jemez volcanic field evolved two ∼3.8 m.y.-long pulses of volcanic activity separated by a ∼2.2 m.y. period of eruptive quiescence. Each eruptive phase is composed of: (1) an initial ∼2 Ma period of intense volcanic activity dominated by basaltic and andesitic compositions that formed by variable amounts of mixing between lithospheric mantle-derived basalt and lower crustal melts; (2) followed by a 0.3 to 0.8 m.y. period of eruptive quiescence; (3) and culminating in the eruption of rhyolite magmas from large, shallow silicic systems that formed by the contamination of lower crustal melts by lithospheric mantle-derived basalt. This two phase model stands in contrast to the conventional view that long-lived continental volcanic centers simply evolve in an initial protracted interval of mafic eruptions that culminate in the formation of a large silicic system. Compositional and eruptive timing trends predicted by models simulating basaltic intrusion into the lower crust (Annen and Sparks, 2002) imply that the Jemez volcanic field's evolution was likely controlled by several factors in addition to the presence or absence of fault conduits as proposed by Gardner (1985) and Gardner and Goff (1984). The basalt intrusion model implies that the thermal effects of modest constant basalt intrusion rates produces a diversity of magma compositions and intervals of eruptive quiescence as seen in the Jemez volcanic field.

Keywords

Basalt; Basalt Intrusion; Effects; Evolution; Field; Intrusion; Jemez; Jemez Volcanic Field; New Mexico; Phase; Volcanic; Volcanism

Controlled Subject

Geology

File Format

pdf

File Size

9.64 MB

Degree Grantor

University of Nevada, Las Vegas

Language

English

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