On the compositional field of self‐reversing titanomaghemite: Constraints from Deep Sea Drilling Project Site 307

Abstract

[1] In 1956, Verhoogen proposed that ionic reordering during low-temperature oxidation of titanomagnetite could result in self-reversal of natural remanent magnetization. Later, in 1966, O'Reilly and Banerjee concluded that (1) the compositional field of self-reversing titanomaghemite was restricted to very high oxidation states and (2) that high oxidation temperature (!250°C) would be required to reach these oxidation levels, which would in turn be inconsistent with stability of the cation-deficient structure of titanomaghemite in nature. However, an example of the process has been reported, in some altered pillow basalt lavas of Late Cretaceous age from Detroit Seamount (Ocean Drilling Program (ODP) sites 883, 1203, and 1204) in the northwestern Pacific Ocean. Here we present new paleomagnetic, rock magnetic and compositional data from mid-ocean ridge tholeiitic basalts of Late Jurassic age collected at Deep Sea Drilling Project (DSDP) Site 307. Although severely oxidized, the DSDP Site 307 basalt samples lack the clear self-reversed magnetizations seen in some samples from Detroit Seamount. These data constrain the compositional field of self-reversing titanomaghemite to extremely high oxidation states (z ! 0.95), consistent with the first conclusion of O'Reilly and Banerjee. The comparison of results from ODP sites 883, 1203, and 1204 on Detroit Seamount and those from the DSDP Site 307 basalts suggests that the presence of self-reversed magnetizations may signify unusually vigorous and sustained fluid flow that resulted in very efficient removal of Fe from titanomaghemite producing the extremely high oxidation states required for self-reversal.Citation: Doubrovine, P. V., and J. A. Tarduno (2005), On the compositional field of self-reversing titanomaghemite:

Palaeomagnetism, rock magnetism and AMS of the Cabo Magmatic Province, NE Brazil, and the opening of South Atlantic

“…It is possible that a secondary magnetization was acquired during a short reversed event within the Cretaceous Normal Superchron or later. A possible explanation for the origin of the reversed component bears on self‐reversal processes as described for highly oxidized MORB basalts (Doubrovine & Tarduno 2004, 2005; Krása & Matzka 2007) but it deserves furtherinvestigation.…”

Origin of apparent magnetic excursions in deep‐sea sediments from Mendeleev‐Alpha Ridge, Arctic Ocean

“…Partial and complete self‐reversals have been reported in oceanic basalts [ Doubrovine and Tarduno , 2004, 2006a], carried by titanomaghemite with N‐type thermomagnetic properties, and were attributed to CRM acquired during the oxidation of titanomagnetite by ionic reordering. Theoretical models of the maghemitization process [ O'Reilly and Banerjee , 1966] and studies on compositions of titanomaghemite with/without self‐reversal observations [ Doubrovine and Tarduno , 2005, 2006a, 2006b] suggest that a limited range of high oxidation states ( z ≥ 0.9) and relatively high Ti contents ( x ≥ 0.6) are required to produce natural self‐reversed components. High temperatures were thought to be required to achieve such high oxidation state [e.g., O'Reilly and Banerjee , 1966]; however, high temperatures may destroy the stability of the cation‐deficient structure of titanomaghemite.…”

Oxidation processes and their effects on the magnetic remanence of Early Cretaceous subaerial basalts from Sierra Chica de Córdoba, Argentina

“…The decrease in susceptibility would be related to the inversion of titanomaghemite to rhombohedral phases during heating (e.g. Doubrovine & Tarduno 2005;Lattard et al 2006). Usually a single cycle of heating is enough to stabilize the oxide assemblage, the second heating cycle being reversible.…”