[meteorite-list] Pyrrhotite and the remanent magnetization of SNC meteorites

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 09:43:31 2004
Message-ID: <200107121638.JAA15112_at_zagami.jpl.nasa.gov>

http://www.elsevier.nl/gej-ng/10/18/23/113/25/25/abstract.html

Earth and Planetary Science Letters, Vol. 190 (1-2) (2001) pp. 1-12
PII: S0012-821X(01)00373-9

Pyrrhotite and the remanent magnetization of SNC meteorites: a changing
perspective on Martian magnetism

Pierre Rochettea * rochette_at_cerege.fr, Jean-Pierre Lorandb, Gérard
Fillionc and Violaine Sautterb a Istituto Nazionale di Geofisica e
Vulcanologia (INGV), Roma, Italy b Muséum National d'Histoire Naturelle (MNHN)
CNRS FR 32 Paris, France c Laboratoire Louis Néel (LLN), CNRS UPR 5051
Grenoble, France

Received 2 February 2001; received in revised form 3 May 2001; accepted 5 May 2001

Abstract

A combined magnetic and mineralogical study of 10 Shergotty-Nakhla-Chassigny
type (SNC) meteorites, including six recent desert finds, provides strong
evidence that, like in ALH84001, the natural remanence (NRM) of basaltic
shergottites (apart from Los Angeles, LA) is carried by pyrrhotite. Low Curie
point titanomagnetite is the major magnetic carrier only in nakhlites,
Chassigny and LA. LA appears to be by far the most magnetic SNC. The dominant
role of pyrrhotite has major implications on the interpretation of Martian
magnetic anomalies and SNC paleomagnetism: in particular pyrrhotite undergoes
magnetic and/or phase transition at room temperature in a pressure range of
1.6-3.6 GPa, much lower than the peak shock pressure experienced by shergottites.
Any impact-related pressure above this value should thus totally reset remanent
magnetism. It is also suggested that the very low thermal stability of remanence
in some SNCs may be due to hexagonal pyrrhotite in metastable
ferrimagnetic state or shock-induced substructures in monoclinic pyrrhotite.

Keywords: Mars; SNC meteorities; magnetic properties; magnetic anomalies; pyrrhotite

*Corresponding author. Present address: CEREGE CNRS UMR 6635, P.O. Box 80,
13545 Aix en Provence Cedex 4, France
Received on Thu 12 Jul 2001 12:38:45 PM PDT