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

Doubrovine, Pavel V.; Tarduno, J. A.

doi:10.1029/2005jb003865

Cited by 23 publications

(17 citation statements)

References 42 publications

(112 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…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.…”

Section: Discussionmentioning

confidence: 97%

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

Font¹,

Ernesto²,

Silva³

et al. 2009

Geophysical Journal International

View full text Add to dashboard Cite

S U M M A R YReconstruction of the South Atlantic opening has long been a matter of debate and several models have been proposed. One problem in tracing properly the Atlantic history arises from the existence of a long interval without geomagnetic reversals, the Cretaceous Normal Superchron, for which ages are difficult to assign. Palaeomagnetism may help in addressing this issue if high-quality palaeomagnetic poles are available for the two drifting continental blocks, and if precise absolute ages are available. In this work we have investigated the Cabo Magmatic Province, northeastern Brazil, recently dated at 102 ± 1 Ma (zircon fission tracks, Ar 39 /Ar 40 ). All volcanic and plutonic rocks showed stable thermal and AF demagnetization patterns, and exhibit primary magnetic signatures. AMS data also support a primary origin for the magnetic fabric and is interpreted to be contemporaneous of the rock formation. The obtained pole is located at 335.9 • E/87.9 • S (N = 24; A 95 = 2.5; K = 138) and satisfies modern quality criteria, resulting in a reference pole for South America at ∼100 Ma. This new pole also gives an insight to test and discuss the kinematic models currently proposed for the South Atlantic opening during mid-Cretaceous.

show abstract

Section: Discussionmentioning

confidence: 97%

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

Font¹,

Ernesto²,

Silva³

et al. 2009

Geophysical Journal International

View full text Add to dashboard Cite

show abstract

“…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.…”

Section: Discussionmentioning

confidence: 99%

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

Xuan

Channell

2010

Geochem Geophys Geosyst

View full text Add to dashboard Cite

Arctic deep‐sea sediments often record intervals of negative inclination of natural remanence that are tens of centimeters thick, implying magnetic excursions with durations of tens of thousand years that far exceed excursion durations estimated elsewhere, and the lack of tight age control usually provides excessive freedom in the labeling of Arctic excursions. Fortuitous variations in sedimentation rate have been invoked to explain the “amplified” excursions. Alternating field demagnetization of natural remanent magnetization (NRM) of sediment cores 08JPC, 10JPC, 11JPC, and 13JPC recovered by the Healy Oden Trans‐Arctic Expedition in August 2005 (HOTRAX05) to the Mendeleev‐Alpha Ridge yields apparent magnetic “excursions” in sediments deposited in the Brunhes Chron. Thermal demagnetization of the NRM, however, implies multiple magnetization components with negative inclination components usually “unblocked” below ∼350°C. Analysis of isothermal remanent magnetization acquisition curves from magnetic extracts indicates two magnetic coercivity components superimposed on one another. Magnetic experiments conducted under high and low temperatures show features that are characteristic for (titano)magnetite and titanomaghemite. Presence of the two magnetic phases is further confirmed by elemental mapping on a scanning electron microscope equipped for X‐ray energy dispersive spectroscopy (EDS) and by high‐resolution X‐ray diffraction (XRD). It is unlikely that anomalously thick intervals of negative inclination in these Brunhes‐aged sediments are caused by unusual behavior of the magnetic field in the Arctic area. We therefore attribute low and negative NRM inclinations in these cores to partially self‐reversed chemical remanent magnetizations, apparently carried by titanomaghemite and acquired during the oxidation of detrital (titano)magnetite grains. The high Ti contents and high oxidation states indicated by EDS and XRD data provide the conditions required for partial self‐reversal by ionic reordering during diagenetic maghemitization, and this process appears to have affected all HOTRAX05 cores collected from the Mendeleev‐Alpha Ridge.

show abstract

“…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.…”

Section: Thermomagnetic Curvesmentioning

confidence: 98%

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

Geuna

Lagorio

Vizán

2014

View full text Add to dashboard Cite

We carried out magnetic analyses on a sequence of Cretaceous alkaline-transitional subaerial basalts of Córdoba Province, Argentina, which have high-Ti magnetite as the main opaque phase. Three different groups are identified based on the degree of high-temperature oxidation during the lava extrusion, combined with superimposed maghemitization and hematization. In the first group, titanomagnetites are optically homogeneous or exhibit coarse intergrowths with ilmenite. The magnetic susceptibility and its variation with temperature and magnetic field point to Ti-poorer compositions than those indicated by electron microprobe, which is interpreted as due to low-temperature oxidation with subsolvus microexsolution. The second group of basalts suffered moderate high-temperature oxidation, with crowded exsolved ilmenite laths within a Ti-poor magnetite ss host, followed by maghemitization and hematite replacement. The third group shows a strongly advanced degree of low-temperature alteration, with the virtual disappearance of magnetite. Based on magnetic properties and field tests applied to the magnetic remanence, we interpret that maghemitization and hematization must have been responsible for the acquisition of a stable magnetic remanence, in the presence of hydrothermal fluids coeval with volcanism. The most advanced degree of alteration, typical of highly porous amygdaloidal lava flows and volcanic breccias, occurred later, probably due to weathering.

show abstract

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

Cited by 23 publications

References 42 publications

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

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

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

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

Contact Info

Product

Resources

About