Subsolidus evolution and alteration of titanomagnetite in ocean ridge basalts from Deep Sea Drilling Project/Ocean Drilling Program Hole 504B9 Leg 83: Implications for the timing of magnetization

Shau, Yen-Hong; Torii, Masayuki; Horng, C. S.; Peacor, Donald R.

doi:10.1029/2000jb900191

Cited by 16 publications

(23 citation statements)

References 44 publications

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“…and/or titanomagnetites present. Very little has been reported so far on the magnetic properties of volcanic and, in particular, of the basaltic rocks below 77 K (Moskowitz et al, 1998;Shau et al, 2000). Nevertheless, even these limited data show a potential of low-temperature magnetometry in characterizing the magnetic mineralogy of basalts.…”

Section: Introductionmentioning

confidence: 99%

Magnetic properties of subaerial basalts at low temperatures

Kosterov

2014

Earth Planet Sp

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Magnetic properties have been measured as a function of temperature from 2 K to room temperature for twentyone samples of subaerial basalts of different origin and age, using an MPMS instrument. In all samples but four, titanomagnetite with a titanium content of less than 5 per cent has been determined as a dominant magnetic mineral carrying NRM from χ(T ) measurements above room temperature and Verwey transition observations. However, the new low-temperature experiments yielded evidence of the presence of another magnetic mineral in all samples. This mineral accounts for up to 70 per cent of saturation magnetization at 2 K and acquires a relatively strong but thermally unstable SIRM at this temperature. Comparison of susceptibility vs. temperature curves measured in low and high DC biasing fields reveals evidence of superparamagnetic behavior, peaks marking the effective blocking temperatures being shifted from <2 K to about 16 K by a 4.8 T DC magnetic field. At the same time, the presence of peaks in the high-field susceptibility curves indicate that the corresponding magnetic phase does not reach saturation, even in the highest field available to us. A possible candidate to account for these properties is a hemoilmenite with 8-10 mole per cent of hematite, originating from high-temperature deuteric oxidation. This is in accordance with the prevailing occurrence of exsolution lamellae within titanomagnetite grains observed in scanning electron microscopy (SEM) images.

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Section: Introductionmentioning

confidence: 99%

Magnetic properties of subaerial basalts at low temperatures

Kosterov

2014

Earth Planet Sp

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“…Let us consider first the magnetic susceptibility data. The χ-T curves show a rather variable shape, but neither of them resembles well-known curves for multidomain Muxworthy, 1999;Skumryev et al, 1999;Kosterov, 2003) or pseudo-single domain (Kosterov, 2003) magnetite. However, these curves can be classified into two groups according to their shape, and, furthermore, these groups overlap significantly with those identified in RT-SIRM cycling experiments (Table 1).…”

Section: Discussionmentioning

confidence: 97%

“…This preference is a consequence of limited applicability of traditional high-temperature magnetic techniques in studies of the magnetic mineralogy of sediments, because of chemical alteration during heating. At the same time, relatively little has been reported on the magnetic properties of volcanic rocks at low temperatures and, moreover, these studies have been so far limited to basalts (Radhakrishnamurty et al, 1981;McElhinny, 1981, 1982;UrrutiaFucugauchi et al, 1984;Thomas, 1993;Shau et al, 2000;Kosterov, 2001;Kontny et al, 2003;Yamamoto, 2006).…”

Section: Introductionmentioning

confidence: 99%

Low-temperature magnetic properties of andesitic rocks from Popocatepetl stratovolcano, Mexico

et al. 2009

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To contribute to the growing database of magnetic properties of rocks and minerals at cryogenic temperatures, we have measured magnetization, low-field susceptibility, and hysteresis loops as a function of temperature between 2 K (10 K for hysteresis) and 300 K for twelve representative samples from a suite of volcanic rocks of predominantly andesitic composition erupted by the Popocatepetl stratovolcano, Mexico. High temperature susceptibility measurements have yielded Curie points (T C ) mostly between 430 and 550• C, two samples additionally containing a magnetic phase with T C of 300-320• C, and one sample-with 140-170• C. Hysteresis measurements at room temperature have revealed invariably the presence of a low-coercivity mineral with coercive force ranging from 10 to 20 mT. This suggests that NRM of Popocatepetl rocks is carried by an intermediate titanomagnetite of composition between approximately TM04 and TM20. Thermal demagnetization of SIRM given at 2 K displays no evidence for the Verwey transition, further showing that samples are essentially magnetite free. At the same time, an inflection between 30-50 K reported previously for intermediate titanomagnetites (Moskowitz et al., EPSL, 157, 141-149, 1998) is seen in all studied Popocatepetl samples except one. As well, below 50 K the coercive force increases sharply with decreasing temperature reaching up to 100 mT at 10 K. On the other hand, examining the behavior of low-field susceptibility at cryogenic temperatures shows that susceptibility signal is dominated by intermediate titanomagnetites only in a part of our samples. In four out of 12 samples, however, susceptibility signal appears to be due to a hemoilmenite phase containing about 20 mole% of hematite. Caution is thus advised when interpreting low-temperature susceptibility data in terms of magnetic mineralogy.

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“…11e, f; large range of Tj). The titanomagnetite of the dike and lava sequences progressively oxidizes with distance from the spreading axis, achieving most of its oxidation after about 30 Ma (Johnson and Pariso 1993;Shau et al 2000;Xu et al 1997;Zhou et al 2000). This may account for the broad range of AMS ellipsoid shapes for dikes.…”

Section: Anisotropy Of Low Field Magnetic Susceptibility (Ams)mentioning

confidence: 94%

“…Consequently, in the dikes and overlying lava, ChRMs blocked in at various times during the post-metamorphic crystallization and secondary metamorphic recrystallization of RBM. Modern ocean-floor studies show that remanence is acquired by at least two separate stages of crystallization remanent magnetization (CRM) some distance from the spreading axis (Shau et al 2000), and certainly post-dating any dike-rotation associated sea-floor grabenfaulting or even with the transform fault. (Thus, the de-tilting of dike remanences is unnecessary, even if it is possible, as discussed later).…”

Section: Ophiolite Chrms: When Were They Blocked In?mentioning

confidence: 99%

Ophiolite Tectonics, Rock Magnetism and Palaeomagnetism, Cyprus

et al. 2009

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Magnetic properties of minerals may be sensitive indicators of provenance. Remanence-bearing minerals (RBM) such as iron-titanium oxides, and matrix-forming minerals such as paramagnetic phyllosilicate or diamagnetic calcite yield different clues to provenance, strain history and tectonics, and are essential supplements for the full interpretation of palaeomagnetic data. Moreover, mineral magnetic properties provide magnetic-petrofabric indicators of tectonic strain, determine the suitability of sites for palaeomagnetism, and permit the restoration of palaeomagnetic vectors in some strained rocks. In the Cretaceous Troodos ophiolite (*88 Ma) magnetic properties are dictated by the relative importance of mafic silicates and largely primary, ophiolite-derived RBM. In its cover of deformed pelagic sedimentary rock, magnetic properties are dictated by the balance of clastic RBM versus matrix calcite and in some cases clay. The two larger Cretaceous ophiolite outcrops (Troodos & Akamas) share a common orientation of their plutonic flow fabrics, determined by magnetic methods. The dike complex shows fabrics indicating plumelike feeders spaced along and perpendicular to the spreading axis, with longevities[0.5 Ma. South of the ophiolite, its Cretaceous-Miocene limestone cover possesses ubiquitous tectonic petrofabrics inferred from anisotropy of magnetic susceptibility (AMS) and anisotropy of anhysteretic remanent susceptibility (AARM). Its foliation and maximum extension dip and plunge gently northward, sub-parallel to a common but previously unreported North-dipping stylolitic cleavage. In well-known localized areas, there are S-vergent thrusts and overturned folds. The S-vergent deformation fabrics are due to Late Miocene (pre-Messinian *8 Ma) deformation. The structures are geometrically consistent with overthrusting of the Cretaceous Troodos-Akamas ophiolite, and its sedimentary cover, onto the underlying Triassic Mamonia terrane. The northern limit of pre-Messinian tectonic fabrics, the TroodosMamonia terrane boundary and the Arakapas-Transform fault form an approximate E-W composite boundary that we term the Troodos Tectonic Front. Miocene deformation remagnetized the ophiolite and its sedimentary cover in many places and also affects the Mamonia terrane to the SW, with which the Troodos terrane docked in the late Cretaceous. Magnetic mineralogy, particularly of the RBM traces the progressive un-roofing of the ophiolite during the deposition of its sedimentary cover. During the submarine exposure and erosion of the ophiolite, the contribution of RBM clasts to the overlying sedimentary cover changed qualitatively and quantitatively. Thus, magnetic mineralogy of the sedimentary rock cover records the progressive denudation of the ophiolite from lavas, down through dikes, to gabbros and deeper mantle rocks. Palaeomagnetic studies previously revealed the anticlockwise rotation of the Troodos terrane and its northwards migration. Characteristic remanent magnetism (ChRM) is most reliable for lavas and dikes although it...

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Subsolidus evolution and alteration of titanomagnetite in ocean ridge basalts from Deep Sea Drilling Project/Ocean Drilling Program Hole 504B9 Leg 83: Implications for the timing of magnetization

Cited by 16 publications

References 44 publications

Magnetic properties of subaerial basalts at low temperatures

Magnetic properties of subaerial basalts at low temperatures

Low-temperature magnetic properties of andesitic rocks from Popocatepetl stratovolcano, Mexico

Ophiolite Tectonics, Rock Magnetism and Palaeomagnetism, Cyprus

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