CRYSTAL PREFERRED ORIENTATION IN QUARTZ FROM THE AUREOLE OF THE PRIEST PLUTON: DISTRIBUTION OF MICROFABRICS AND IMPACT ON THERMAL CONDUCTIVITY

Quartz crystal preferred orientation (CPO) data, as well as grain size and aspect ratio measurements, have been measured in a suite of nine quartzites from the thermal aureole of the Priest Pluton, Manzano Mountains (NM). With increasing proximity to the pluton there is a weak, general decrease in grain size until immediately before the pluton contact, where grain size increases. There is no correlation in the length-to-width ratio with distance from pluton or mineral assemblage. CPO data shows variable intensity of deformation: samples collected between 200 and 550 m from the pluton have strong preferred orientation; samples closer to the pluton have weaker to absent CPO. Immediately adjacent to the pluton, samples have strong CPO fabrics. Steady state thermal conductivity measurements perpendicular to foliation range from 5.0 to 8.5 W/(m*K) and values parallel to foliation range from 7.4 to 8.3 W/(m*K). Differences between measurements parallel and perpendicular were expected because of quartz’s thermal anisotropy. However, contrary to expectations, the difference between perpendicular and parallel measurements, as well as the maximum thermal conductivity is greatest in samples with lower CPO intensity. On the other hand, a weak positive correlation between grain size and thermal conductivity for samples with grain sizes <0.02 mm² is noted. The dataset suggests three conclusions: 1) samples >300 m from the contact retain regional deformation fabrics, while those <300 m from the pluton recrystallized during thermal metamorphism; 2) the strong fabric adjacent to the pluton may reflect deformation associated with pluton accommodation; and, 3) quartzite fabrics and their orientation impact thermal conductivity and, together with mica, may contribute to rates of heat transport in metamorphic terranes and partially explain why the width of contact aureoles vary around a pluton.