The effects of serpentinization on density and magnetic susceptibility: a petrophysical model

Toft, Paul B.; Arkani‐Hamed, J.; Haggerty, Stephen E.

doi:10.1016/0031-9201(90)90082-9

Cited by 196 publications

(185 citation statements)

References 51 publications

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“…This is consistent with previous studies of serpentinized oceanic peridotites (e.g., Dunlop and Prévot, 1982; and theoretical arguments (Frost, 1985(Frost, , 1991Toft et al, 1990). Observations made by reflected light microscopy show that the opaque minerals mainly occur within the serpentinized groundmass and along altered fractures within the less altered grains, particularly due to the serpentinization of olivine (Gillis, Mével, Allan, et al, 1993).…”

Section: -supporting

confidence: 90%

“…There is a general inverse relationship between the degree of serpentinization and density within peridotites because serpentine is less dense than its parent mineral, typically olivine and pyroxene (e.g., Toft et al, 1990). A plot of magnetic susceptibility vs. density for the harzburgites shows that susceptibility increases as density decreases (Fig.…”

Section: Magnetization Intensitymentioning

confidence: 99%

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Rock Magnetic Properties, Magnetic Mineralogy, and Paleomagnetism of Peridotites from Site 895, Hess Deep

Kelso¹,

Richter²,

Pariso³

1996

Proceedings of the Ocean Drilling Program, 147 Scientific Results

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Serpentinized oceanic peridotites collected during Ocean Drilling Program Leg 147 at Site 895 in the Hess Deep were studied magnetically to further our understanding of the magnetization of the oceanic lithosphere. The majority of the samples are dunites and harzburgites, with varying degrees of serpentinization. Rock magnetic studies suggest that the dominant magnetic mineral is relatively pure pseudo-single-domain magnetite. Optical observations reveal that the magnetite has a secondary origin related to the serpentinization process. The dunites and the harzburgites have median natural remanent magnetization values of 3.2 and 1.2 A/m and magnetic susceptibility values of 0.053 and 0.023 (S1 volume units), respectively. The NRM is the dominant component of magnetization and has a magnitude similar to values observed for oceanic basalts of Layer 2a. Similarly serpentinized peridotites residing within the oceanic lithosphere are likely contributors to magnetic anomalies. Thermal and alternating-field demagnetizations usually yield a stable remanent magnetization direction that often has an inclination much greater than expected for the time-averaged geomagnetic field (>5°) at Site 895. This disparity suggests that the samples acquired their magnetization and were subsequently reoriented. Hole 895E samples have relatively coherent inclinations (30°) that become shallower in the bottom 30 m of the hole. Inclinations in Hole 895D vary from +60° to -60°, with no systematic trends evident with depth in the hole, suggesting differential vertical rotation of blocks on a scale of a few meters. Experimental evidence suggests that room-temperature magnetic viscosity does not significantly effect the magnetization intensity or direction of these samples.

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Section: -supporting

confidence: 90%

Section: Magnetization Intensitymentioning

confidence: 99%

Rock Magnetic Properties, Magnetic Mineralogy, and Paleomagnetism of Peridotites from Site 895, Hess Deep

Kelso¹,

Richter²,

Pariso³

1996

Proceedings of the Ocean Drilling Program, 147 Scientific Results

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“…It is expected that susceptibility and NRM values should increase as the density decreases because the process of serpentinization increases the amount of magnetite. The range in density for these rocks agrees with other samples from serpentinized ultramafic rocks (Toft et al, 1990;Bonnemains et al, 2016).…”

Section: Densitysupporting

confidence: 86%

Geophysical expression of the Leka Ophiolite, Norway, modeled from integrated gravity, magnetic and petrophysical data

Michels¹,

McEnroe²,

Fichler³

2018

NJG

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The ca. 497 Ma Leka Ophiolite Complex (LOC) comprises oceanic lithosphere that formed near the margin of Laurentia in a suprasubductionzone setting. The LOC was obducted onto Laurentia in the Early Ordovician and later thrust onto Baltica during the Scandian continent-continent collisional orogeny (ca. 430 Ma), and now forms part of the Uppermost Allochthon. The LOC contains superb exposures of partially serpentinized mantle rocks, crustal cumulate layered series and wehrlites, sheeted dykes and pillow basalts, including exposures of the petrologic and geophysical paleo-Moho. 564 specimens were collected and measured for density, magnetic susceptibility and natural remanent magnetization. These form the constraints for three profiles forming a new 2.5D gravity and magnetic model. This is the first study of the LOC that models both gravity and magnetic data, whereas previous models were based on gravity data alone. The Bouguer-corrected anomalies express a distinct high correlating with the topographic highs in the center of the island, as well as an additional high in the southern part of the island, indicating an increasing depth of the LOC southwards. New high-resolution aeromagnetic data were used to characterize the nature of the contacts between the rock units, and the orientation of the major normal fault between the ultramafic units and the gabbro to the east. We suggest that this major fault is serpentinized, which accounts for the distinct magnetic anomaly along the trace of the fault (magnetic anomaly up to 2800 nT). Three model sections that transect the island from east to west were created. These sections indicate that the LOC has a bowl-shaped, synformal structure. Extensive serpentinization was found in samples in the uppermost portion of the LOC. The new models suggest that the deepest extent of the complex is approximately 4 km and that the volume of the LOC is approximately 200 km 3 .

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“…The density of peridotite is linearly related to the degree of serpentinization, lying in the range 2.5- Figures 11 and 7). This model assumes that significant volumes of serpentinized peridotite are not taken above the 500øC stability limit [Toft et al, 1990] when intruded by melt and may not be valid if the thickness of melt intruded is large. The top of the reflective layer in IAM-9 occurs 0.5-1.0 s (1-2 km) below the top of the basement, and this layer may be 0.5s (1 km) thick (Figures 3 and 4).…”

Section: Gravity Modelingmentioning

confidence: 99%

Deep structure of the ocean‐continent transition in the southern Iberia Abyssal Plain from seismic refraction profiles: The IAM‐9 transect at 40°20′N

Dean¹,

Minshull²,

Whitmarsh³

et al. 2000

J. Geophys. Res.

299

488

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The effects of serpentinization on density and magnetic susceptibility: a petrophysical model

Cited by 196 publications

References 51 publications

Rock Magnetic Properties, Magnetic Mineralogy, and Paleomagnetism of Peridotites from Site 895, Hess Deep

Rock Magnetic Properties, Magnetic Mineralogy, and Paleomagnetism of Peridotites from Site 895, Hess Deep

Geophysical expression of the Leka Ophiolite, Norway, modeled from integrated gravity, magnetic and petrophysical data

Deep structure of the ocean‐continent transition in the southern Iberia Abyssal Plain from seismic refraction profiles: The IAM‐9 transect at 40°20′N

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