Date of Award
1991
Degree Type
Dissertation
Degree Name
Doctor of Philosophy
Abstract
The Prairie Creek, Arkansas olivine lamproite intrusion consists of three facies of rock: tuff, breccia and hypabyssal facies of rock; and two suites of cognate xenoliths. Suprasolidus experiments on the hypabyssal rock were undertaken between 10 and 40 kilobars, and 1000 and 1400{dollar}\sp\circ{dollar}C, with three different volatile conditions. A petrogenetic model for the intrusion is proposed based on the integration of phase relations and mineral chemistry.;Clinopyroxene, phlogopite, spinel and titan potassic richterite mineral analyses from the intrusion independently define a single continuous compositional trend. Comparison of the mineral analyses from the intrusion to those from the experiments suggests that the composition of phlogopite and clinopyroxene may be controlled by pressure, and spinel by temperature. In addition, the paragenetic sequence defined by the tuff and breccia facies of rock is similar to that observed in the experiments on the hypabyssal rock, with H{dollar}\sb2{dollar}O and F as additional components.;The data indicate that the crystallization of an olivine lamproite magma, ascending from below the diamond-graphite transition to the surface in a buoyancy-driven magma fracture, can model the petrogenesis of the intrusion. Increased abundance of water, and possibly fluorine, at the top of the magma fracture resulted in the crystallization of olivine followed by phenocrystic phlogopite at depths greater than 30 kilometers. This magma erupted explosively at the surface, and formed the tuff and breccia facies of rock. Below the volatile enriched portion of the magma column, olivine, spinel, perovskite, apatite and clinopyroxene crystallized before poikilitic phlogopite. The poikilitic phlogopite is compositionally different than the phenocrystic phlogopite, and crystallized at depths less than 30 kilometers. The magma in which the poikilitic phlogopite crystallized ascended more slowly, intruded the tuff and breccia facies, and is represented by the hypabyssal facies of rock.;As the hypabyssal facies ascended through the conduit produced by the eruption of the tuff and breccia magma, remnant magma within the conduit was incorporated as cognate xenoliths into the ascending hypabyssal facies at successively lower pressures. These cognate xenoliths host a similar paragenetic sequence and mineral chemistry, with respect to clinopyroxene, phlogopite and amphibole, to that observed in the tuff, breccia and hypabyssal facies of rock.;The paragenetic sequence and mineral compositions of the Prairie Creek intrusion are similar to those in the Kapamba and Western Australia olivine lamproites, described by other authors. Such a correlation is considered to suggest that crystallization within a buoyancy driven magma fracture may be an important petrogenetic process for the genesis of olivine lamproite magmas.
Recommended Citation
Walker, Edward C., "Petrogenesis Of The Prairie Creek, Arkansas, Diamondiferous Olivine Lamproite" (1991). Digitized Theses. 2041.
https://ir.lib.uwo.ca/digitizedtheses/2041