Magnetic Properties of Synthetic Gusev Crater Basalts: Implications for Remanence Acquisition and Impact Demagnetization of the Martian Crust
Abstract
Fe-rich and Mg-rich basalts patterned on the Adirondack-class Humphrey basalt outcrop at Gusev Crater, Mars, were synthesized to investigate potential carriers of the Mars crustal magnetic anomalies and examine the modification of crustal anomalies by impact events. Gusev Crater is located at the northern edge of the Noachian Highlands. The crater carries minimal magnetization due to shock demagnetization during the impact, excavation of magnetized crust, or hydrothermal alteration. However, geochemical analyses conducted in Gusev Crater by the Mars Spirit rover's alpha particle x-ray spectrometer provide in-situ information on the composition of Mars' magnetized crust. Humphrey contains 18.7% Fe, but lower Si (45.8%), lower Ti (0.58%) and higher Mg (10.7%) content than Fe-rich SNC meteorites. Samples were prepared in a 1-atm gas mixing furnace under conditions consistent with the Fe2+/Fe3+ ratio of Humphrey, and cooled at 28-320 °C h-1 from the olivine liquidus temperature ( 1285 °C) down to 900 or 300 °C. Experimental samples contain olivine, pyroxene, Cr-spinel, and either plagioclase or glass. Spinel is the liquidus phase, with 1350 °C < liquidus < 1530 °C. The oxides produced are Fe-Mg-Cr-Al-Ti spinels. Olivine is relatively Fe-rich, with phenocryst cores of Fo75 and pervasive chain morphologies of Fo42-61. These run products are more weakly magnetic than Fe-rich basalts patterned on SNC compositions, with magnetic susceptibility, anhysteretic remanent magnetization, and thermoremanent magnetization all 0.5 to 1.5 orders of magnitude weaker than their counterparts with higher Ti and lower Mg. A thermoremanent magnetization was imparted to a subset of samples and subjected to peak shock pressures of approximately 4, 7, and 10 GPa. The intensity of TRM was reduced by an average of 80% after the 4 GPa treatment and by 90% following the 7 and 10 GPa treatments, consistent with single-mineral data and modeling studies that predict that demagnetization of large impact basins on Mars occurred at pressures below 5 GPa. A magnetized crust composed of Gusev basalts would be capable of generating the observed magnetic anomalies only if the magnetized layer is sufficiently thick, on the order of 30-80 km.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFMGP13A..04B
- Keywords:
-
- 1510 Dynamo: theories and simulations;
- GEOMAGNETISM AND PALEOMAGNETISMDE: 1540 Rock and mineral magnetism;
- GEOMAGNETISM AND PALEOMAGNETISMDE: 1595 Planetary magnetism: all frequencies and wavelengths;
- GEOMAGNETISM AND PALEOMAGNETISMDE: 6030 Magnetic fields and magnetism;
- PLANETARY SCIENCES: COMETS AND SMALL BODIES