Title: Evolution of the Tharsis region of Mars: insights from magnetic field observations

Author(s): Catherine CL, Phillips RJ

Source: EARTH AND PLANETARY SCIENCE LETTERS 230 (3-4): 241-254 FEB 15 2005

Document Type: Article

Language: English

Abstract: Mars Global surveyor (MGS) observations of crustal magnetic fields over Tharsis provide new constraints on models for the thermal and magmatic evolution of this region. We analyze the distribution of magnetic field anomalies over Tharsis surface units of Noachian, Hesperian and Amazonian age. These data suggest that early Noachian crust underlies the Tharsis province, and formed contemporaneously with the existence of a martian dynamo. This crust either pre-dates the formation of Tharsis, or formed during the earlier phases of Tharsis volcanism. The preservation of strong magnetic field anomalies over some of the earliest Noachian and topographically high units, together with the observation of magnetic field anomalies over Hesperian- and Amazonian-age surface units, indicate that a large fraction of the magnetized crust has remained cool (below the blocking temperature of the magnetic carrier) throughout the construction of Tharsis. Moreover, the distributions of magnetic anomaly amplitudes over Noachian, Hesperian, and Amazonian surface units suggest that the youngest units overlie sites of prolonged intrusion and have undergone a greater extent of thermal demagnetization. The absence of magnetic anomalies around the Tharsis Montes and Olympus Mons argues for strong, localized heating, as would be expected at volcanic centers. We show that end-member models for progressive thermal demagnetization of a Noachian magnetized crustal layer are consistent with the anomaly amplitude distributions. We integrate the magnetic field observations with constraints from tectonics, gravity, and topography, and present a revised scenario for the evolution of the Tharsis region. (C) 2004 Elsevier B.V. All rights reserved.

Author Keywords: Tharsis; Mars; magnetism; volcanism; magmatism

KeyWords Plus: MANTLE CONVECTION; REMANENT MAGNETIZATION; THERMAL EVOLUTION; MARTIAN MANTLE; GRAIN-SIZE; PROVINCE; GRAVITY; MODEL; RIDGE; CRUST

Addresses: Catherine CL (reprint author), Univ Calif San Diego, Scripps Inst Oceanog, Inst Geophys & Planetary Phys, 9500 Gilman Dr, La Jolla, CA 92093 USA
Univ Calif San Diego, Scripps Inst Oceanog, Inst Geophys & Planetary Phys, La Jolla, CA 92093 USA
Washington Univ, Dept Earth & Planetary Sci, St Louis, MO 63130 USA

E-mail Addresses: cljohnson@ucsd.edu, phillips@wustl.edu

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

Subject Category: GEOCHEMISTRY & GEOPHYSICS

IDS Number: 897LG