HR: 0800h
AN: GP21A-0118    [Abstracts]
TI: Paleomagnetic Baked Contact Test of a Permo-Carboniferous Dike Intruding the Ross of Mull Granite, Isle of Mull, NW Scotland
AU: * Lowry, J
EM: joellowry3@hotmail.com
AF: Department of Natural Sciences, New Mexico Highlands University, Las Vegas, NM 87701, United States
AU: Petronis, M S
EM: mspetro@nmhu.edu
AF: Department of Natural Sciences, New Mexico Highlands University, Las Vegas, NM 87701, United States
AU: O'Driscoll, B
EM: brian.odriscoll@ucd.ie
AF: Department of Geology, University College Dublin, Dublin, 4, Ireland
AU: Geissman, J W
EM: jgeiss@unm.edu
AF: Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM 87106, United States
AB: The Caledonian Ross of Mull Granite (ROMG) forms the western-part of the Ross of Mull peninsula, NW Scotland, and consists of three roughly concentric zones that vary in composition from diorite, granodiorite, to granite. The western contact of the ROMG with Iona Group metasedimentary rocks is exposed on the skerries off the east coast of Isle of Iona. The eastern contact and floor of the intrusion is exposed on the west side of Ardalanish Bay on the south coast of the isle. Field relations suggest that magma ascent may have occurred along the Sound of Iona fault with magma flowing laterally away from the structure to the east-southeast. At least two later magmatic pulses of intermediate to mafic composition intrude the ROMG as dikes and dike swarms of late Caledonian (Silurian) to Permo-Carboniferous age. One hundred thirty-two anisotropy of magnetic susceptibility (AMS) and paleomagnetic sites were established across the ROMG in order to test the magma emplacement model. In addition, seventeen mafic dikes were sampled to evaluate post-emplacement deformation of the intrusion and to evaluate the antiquity of the magnetization of the granite. A detailed paleomagnetic baked contact test involving one of the Permo-Carboniferous dikes hosted by ROMG country rock is underway to determine if the characteristic magnetization (ChRM) of the granite is a thermoremanent magnetization acquired at time of cooling or if the ROMG was remagnetized since the emplacement of the dikes. The baked contact test includes 10 paleomagnetic samples from a lamprophyre dike to define its ChRM. The results from the dike are being compared with results from those from 22 samples collected from the ROMG at progressively farther distances from the contact with the dike. The results should provide critical information to evaluate the antiquity of the magnetization of the ROMG and aid in interpreting the paleomagnetic and AMS data. Preliminary hysteresis and susceptibility experiments on the ROMG yield very narrow laboratory Curie point estimates between 558 C to 565 C consistent with a low-Ti oxide phase (magnetite) as a principal magnetic phase. Additional rock magnetic experiments are underway and the results should allow us to fully characterize the magnetic properties of all rock types and define the exact mineralogy and magnetic grain size of the iron oxide phases.
DE: 1518 Magnetic fabrics and anisotropy
DE: 1519 Magnetic mineralogy and petrology
DE: 1540 Rock and mineral magnetism
DE: 1599 General or miscellaneous
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2007 Fall Meeting