Morphology and microstructure of magnetite and ilmenite inclusions in plagioclase from Adirondack anorthositic gneiss

Wenk, Hans‐Rudolf; Chen, Kai; Smith, R. J.

doi:10.2138/am.2011.3760

Cited by 45 publications

(55 citation statements)

References 25 publications

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“…The present study has revealed that exsolved magnetite in oceanic gabbros provide the expected paleointensity, and that FORC analysis is effective to find samples dominated by exsolved magnetite. Exsolved magnetite seems to be common in oceanic gabbros (Davies, 1981), and it has been also reported from continental plutonic and metamorphic rocks (e.g., Selkin et al, 2000;Usui et al, 2006;Wenk et al, 2011). In particular, oceanic gabbros of various geologic ages are preserved on land as ophiolites, and some of them have been successfully investigated for paleointensity (Granot et al, 2007).…”

Section: Cooling Rate Effect On Plutonic Paleointensitymentioning

confidence: 99%

Paleointensity estimates from oceanic gabbros: Effects of hydrothermal alteration and cooling rate

Usui

2013

Earth Planet Sp

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Gabbros recovered by previous ocean drillings were investigated in paleointensity and rock magnetic experiments. The young ages of the samples (ca. 0.78-1.3 Ma) enable a direct comparison between the plutonic paleointensity and volcanic data. Microscopic observations revealed two kinds of magnetite: needle-shaped exsolution in plagioclase and aggregate associated with the hydrothermal alteration of olivine. In Shaw paleointensity experiments, some samples revealed reasonable estimates, while some others showed an anomalously low ratio of natural remanent magnetization (NRM) versus thermoremanent magnetization (TRM). First-order reversal curve (FORC) diagrams indicated that the reasonable NRM/TRM were from non-interacting single domain magnetite exsolved in plagioclase, while the anomalously low NRM/TRM were from secondary magnetite associated with olivine. From the paleointensity results, the mean virtual axial dipole moment (VADM) was calculated to be 8.2 ± 2.1 10 22 Am 2 . Volcanic records in the PINT database for 0.78-1.3 Ma revealed a mean virtual dipole moment (VDM) of 6.3 ± 0.73 10 22 Am 2 . The difference between them is consistent with the theoretical prediction of the cooling rate effect on paleointensity. These results indicate that oceanic gabbros are reliable paleointensity recorders.

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Section: Cooling Rate Effect On Plutonic Paleointensitymentioning

confidence: 99%

Paleointensity estimates from oceanic gabbros: Effects of hydrothermal alteration and cooling rate

Usui

2013

Earth Planet Sp

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“…They both consist of close-packed arrangement of oxygen atoms and stacked cation layers in crystal lattice. The close packing of oxygen atoms plays an important role in determining orientations of the exsolved magnetite (Barbosa and Lagoeiro 2010;Wenk et al 2011). Thus, the close-packed oxygen atom planes and directions in host ilmenite and exsolved magnetite are mainly investigated in this study.…”

Section: Formation Of Magnetite Lamellae In Ilmenitementioning

confidence: 99%

“…Magnetite is considered to control magnetic anomalies of rocks (Frost 1991), magnetite exsolution in ilmenite may thus explain the unusually strong NRM of ilmenite in some metamorphic and igneous rocks Robinson et al 2002Robinson et al , 2004. Several mineralogical and geophysical studies have dealt with Fe-Ti oxide exsolution in silicate minerals such as pyroxene, plagioclase, and olivine (Dobrzhinetskaya et al 1996;Feinberg et al 2004;Fleet et al 1980;Hwang et al 2008;Prior et al 1999;Wenk et al 2011). However, magnetite exsolution in ilmenite is more or less neglected compared with hematite exsolution in ilmenite and magnetite exsolution in silicates.…”

Section: Introductionmentioning

confidence: 99%

Magnetite exsolution in ilmenite from the Fe-Ti oxide gabbro in the Xinjie intrusion (SW China) and sources of unusually strong remnant magnetization

Tan

Wang

et al. 2016

American Mineralogist

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“…According to Davis (1981), magnetite exsolves along one or several of four directions of the plagioclase lattice. Wenk et al (2011) observed that the long axes of magnetite needles are aligned with the plagioclase c-axis. Shape-preferred orientation of the 480 A.R.…”

Section: Introductionmentioning

confidence: 99%

Anisotropy of magnetic susceptibility in alkali feldspar and plagioclase

et al. 2016

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S U M M A R YFeldspars are the most abundant rock-forming minerals in the Earth's crust, but their magnetic properties have not been rigorously studied. This work focuses on the intrinsic magnetic anisotropy of 31 feldspar samples with various chemical compositions. Because feldspar is often twinned or shows exsolution textures, measurements were performed on twinned and exsolved samples as well as single crystals. The anisotropy is controlled by the diamagnetic susceptibility and displays a consistent orientation of principal susceptibility axes; the most negative or minimum susceptibility is parallel to [010], and the maximum (least negative) is close to the crystallographic [001] axis. However, the magnetic anisotropy is weak when compared to other rock-forming minerals, 1.53 × 10 −9 m 3 kg −1 at maximum. Therefore, lower abundance minerals, such as augite, hornblende or biotite, often dominate the bulk paramagnetic anisotropy of a rock. Ferromagnetic anisotropy is not significant in most samples. In the few samples that do show ferromagnetic anisotropy, the principal susceptibility directions of the ferromagnetic subfabric do not display a systematic orientation with respect to the feldspar lattice. These results suggest that palaeointensity estimates of the geomagnetic field made on single crystals of feldspar will not be affected by a systematic orientation of the ferromagnetic inclusions within the feldspar lattice.

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Morphology and microstructure of magnetite and ilmenite inclusions in plagioclase from Adirondack anorthositic gneiss

Cited by 45 publications

References 25 publications

Paleointensity estimates from oceanic gabbros: Effects of hydrothermal alteration and cooling rate

Paleointensity estimates from oceanic gabbros: Effects of hydrothermal alteration and cooling rate

Magnetite exsolution in ilmenite from the Fe-Ti oxide gabbro in the Xinjie intrusion (SW China) and sources of unusually strong remnant magnetization

Anisotropy of magnetic susceptibility in alkali feldspar and plagioclase

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