GSA Annual Meeting in Phoenix, Arizona, USA - 2019

Paper No. 170-4
Presentation Time: 9:05 AM


MURDOCK, Kathryn J., Exponent, Inc., 1075 Washington Street, Natick, MA 01760 and BROWN, Laurie L., Department of Geosciences, University of Massachusetts, Amherst, 611 North Pleasant Street, Amherst, MA 01003-9297

Abnormally strong localized magnetic signatures were first detected above the crust of Mars by the Mars Global Surveyor (MGS) nearly two decades ago. Questions still remain as to the cause of the magnetic field and dynamo cessation, and how rocks – presumably basaltic – would be able to retain magnetic remanences an order of magnitude larger than most basalts on Earth for almost 4Ga. Without the ability to obtain Martian samples for analysis on Earth, terrestrial analogues based on geochemical and magnetic data need to be investigated. While the presumed age of the basalts poses a problem for terrestrial analogues (few unmetamorphosed or unaltered basalts remain from Archean time), finding a suitable geochemical and magnetic representation is necessary in understanding the geologic history of Mars. NASA and others have studied one particular rock formation, the Saddleback Basalt (20Ma), which is used in part for the Mars Mojave Simulant (MMS) due to its physical similarities to Martian rocks once reduced to regolith, and use it in Martian rover simulations. We propose that additional magnetic studies of the MMS will prove useful in determining Martian geologic, environmental, and magnetic history. Brown and Golombek (1988) collected over 100 samples from 12 sites from the Saddleback Basalt for paleomagnetic analysis. These samples have undergone additional rock magnetic measurements since their original collection. Hysteresis and temperature-susceptibility measurements indicate small PSD-sized magnetite as the main magnetic carrier with possibility of other magnetic minerals, particularly hematite. NRM values for the Saddleback range from 0.12 to 43.20 A/m with an average of 3.70 A/m. Magnetic susceptibility ranges from 1.514 x10-3 to 5.77 x10-2 with an average of 1.286 x10-2. NRM and magnetic susceptibility, while showing average mean values for terrestial basalts, appear to be bimodally distributed. Four sites (30 samples) exhibit high remanences up to an order of magnitude greater than similar units. Magnetic susceptibilities, however, although also bimodal, do not indicate corresponding high values. The results of this study indicate the Saddleback Basalt, with its potential for strong remanence magnetization, could be used as not only a physical analog, but a magnetic Martian analog as well.