Title: Toward a robust normalized magnetic paleointensity method applied to meteorites

Author(s): Gattacceca J, Rochette P

Source: EARTH AND PLANETARY SCIENCE LETTERS 227 (3-4): 377-393 NOV 15 2004

Document Type: Article

Language: English

Abstract: We propose a new paleointensity method based on normalization by isothermal remanent magnetization derivative vs. alternating field (REM' method). It provides an estimate of the absolute paleointensity with an uncertainty of about a factor two. Contrary to methods using normalization by total isothermal remanent magnetization or anhysteretic magnetization, it is applicable to multicomponent magnetizations. Artificial or natural isothermal remanent magnetizations can be recognized, and relaxation of natural remanent magnetization can be taken into account. It is applicable for magnetizations carried by magnetite, FeNi alloys and pyrrhotite. The REM' method is of particular interest to estimate paleointensities in meteorites, as these materials are often characterized by complex multicomponent magnetization of various origins (impact magnetization, thermoremanence, isothermal remanent magnetization) and metastable magnetic minerals not suitable for Thellier experiments. However, like other paleointensity methods, the REM' method underestimates the true paleointensity for meteorite samples with magnetizations that are heterogeneous on spatial scales below the sampling scale. For L ordinary chondrites, an upper limit of 1 muT is proposed for the paleofield. Tentative paleofield estimates in the 0.05-0.5 muT range are proposed for LL ordinary chondrites, which is much lower than previous results. The first paleofield estimates for Rumuruti chondrites indicate the presence of magnetic fields around 6 muT during the last major impact on their parent body. Aubrites and HED achondrites paleofields of at least 10 muT may suggest the existence of a dynamo field during the cooling of their parent body. Results from Martian meteorites are scattered between 1 and 24 muT and may represent the crustal magnetic field of the planet after dynamo shutdown. Carbonaceous chondrites provide contrasting results, with possible evidence of strong field (mT) processes that clearly require additional studies. (C) 2004 Elsevier B.V All rights reserved.

Author Keywords: meteorites; paleointensity; magnetic field; solar system; dynamo

KeyWords Plus: NATURAL REMANENT MAGNETIZATION; MONOCLINIC PYRRHOTITE FE7S8; ORDINARY CHONDRITES; THERMOREMANENT MAGNETIZATION; SHOCK METAMORPHISM; GEOMAGNETIC-FIELD; ALLENDE METEORITE; MARTIAN METEORITE; STONY METEORITES; SNC METEORITES

Addresses: Gattacceca J (reprint author), Univ Aix Marseille 3, CNRS, CEREGE, BP80, Aix En Provence, F-13545 4 France
Univ Aix Marseille 3, CNRS, CEREGE, Aix En Provence, F-13545 4 France

E-mail Addresses: gattacceca@cerege.fr, rochette@cerege.fr

Publisher: ELSEVIER SCIENCE BV, PO BOX 211, 1000 AE AMSTERDAM, NETHERLANDS

Subject Category: GEOCHEMISTRY & GEOPHYSICS

IDS Number: 871IS