South Pole Aitken Basin magnetic anomalies: Evidence for the true polar wander of Moon and a lunar dynamo reversal

Jafar Arkani-Hamed; Daniel Boutin

doi:10.1002/2016je005234

Magnetic Anomalies on the Pacific Plate Reveal True Polar Wander

Eos ◽

10.1029/2019eo117729 ◽

2019 ◽

Vol 100 ◽

Author(s):

Aaron Sidder

Keyword(s):

Magnetic Anomalies ◽

Pacific Plate ◽

Standard Approach ◽

Polar Wander ◽

True Polar Wander ◽

The Pacific ◽

New Locations ◽

Paleomagnetic Poles

A new study rebuffs the standard approach to paleomagnetism and offers an updated methodology and new locations of paleomagnetic poles.

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Magnetization in the South Pole-Aitken basin: Implications for the lunar dynamo and true polar wander

Icarus ◽

10.1016/j.icarus.2016.09.038 ◽

2017 ◽

Vol 286 ◽

pp. 153-192 ◽

Cited By ~ 12

Author(s):

Michael Nayak ◽

Doug Hemingway ◽

Ian Garrick-Bethell

Keyword(s):

South Pole ◽

The South ◽

Polar Wander ◽

True Polar Wander

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Skewness Pole from Magnetic Anomaly C21n Implies Rapid Early Eocene True Polar Wander

10.5194/egusphere-egu21-13644 ◽

2021 ◽

Author(s):

Daniel Woodworth ◽

Richard Gordon ◽

Kevin Gaastra

Keyword(s):

Sediment Accumulation ◽

Magnetic Anomalies ◽

Pacific Plate ◽

Spin Axis ◽

Early Eocene ◽

Polar Wander ◽

True Polar Wander ◽

Paleomagnetic Pole ◽

The Pacific ◽

Paleomagnetic Poles

Skewness analysis of marine magnetic anomalies is the most misunderstood methodology in paleomagnetism. Such analysis has several advantages. First, marine magnetic anomalies innately average secular variation. Second, paleomagnetic poles determined by analysis of their skewness are not biased by overprints. Third, skewness analysis can determine high precision paleomagnetic poles. Specifically, skewness analysis of magnetic anomalies recording Late Cretaceous and early to mid-Cenozoic seafloor spreading between the Pacific and Farallon plates, because of their geometry with respect to the paleo-spin axis, results in high-precision paleomagnetic poles. These anomalies in many cases span ~140&#176; of effective remanent inclination over a span of ~40&#176; of latitude, reducing uncertainty by a factor of ~0.3 when mapping from direction space to pole space (Zheng et al. 2018).Paleomagnetic poles have been previously determined from skewness analysis for six Pacific plate anomalies: C32n (74-71 Ma), C31n-C27r (60-63 Ma), C26r (62-59 Ma), C25r (59-58 Ma), C24r (57-54 Ma), C20r (46-43 Ma), and C12r (33-31 Ma). The younger group, C20r and C12r, together with independent paleo-spin axis estimates from the paleo-distribution of sediment accumulation rates from 12-46 Ma, define an approximately stationary paleo-spin axis location relative to the Pacific hotspots but offset from the current spin axis by 3&#176;. The older group, 74-54 Ma, also shows that the Pacific hotspots remained approximately stationary relative to an additional paleo-spin axis location separated by 8&#176; from the 12-46-Ma paleo-spin axis, implying an episode of reorientation of the entire solid earth &#8211; i.e., true polar wander (TPW) &#8211; of ~8&#176; over at most 8 Ma between 54 and 46 Ma, or a rate of TPW of ~1&#176;/Ma or more.To constrain the timing and rate of reorientation, we analyze anomaly C21n (47-46 Ma), the youngest anomaly inside the 54-46-Ma interval. We incorporate 33 total-intensity ship- and 11 vector aero-magnetic track lines and find a well-constrained paleomagnetic pole near 77N, 23E in the fixed-Pacific plate reference frame.Our new paleomagnetic pole is consistent with a prior, more uncertain, 48-Ma paleo-spin axis location from the paleo-distribution of sediment accumulation rates. When reconstructed into the Pacific hotspot reference frame, our new paleomagnetic pole lies close to the younger 46 to 12-Ma TPW stillstand location, indicating that true polar wander was completed by 47 Ma, if not earlier. Thus the ~8&#176; shift occurred in, at most, 6.0 Ma at a rate of at least ~1.3&#176;/Ma, and potentially even faster. The lower bound of ~1.3&#176;/Ma of TPW indicate that Early Eocene TPW is comparable to the rate of present-day TPW (~1.1&#176;/Ma extrapolated from geodetic data (Argus and Gross, 2004)). This new pole bounds the Early Eocene TPW episode between approximately the old and young ends of the Early Eocene Climatic Optimum (EECO; 53.2-49.1 Ma (Westerhold et al. 2018)). Thus, there may be a link between Early Eocene TPW and important climate events, such as the frequency of hyperthermals and the onset of Eocene cooling. In addition, TPW was likely complete before the 47.4-Ma age of the bends in Pacific plate hotspot chains (Gaastra & Gordon, this meeting).

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The paleoinclination of the ancient lunar magnetic field from an Apollo 17 basalt

10.21203/rs.3.rs-311626/v1 ◽

2021 ◽

Author(s):

Claire Nichols ◽

Benjamin Weiss ◽

Brenna Getzin ◽

Harrison Schmitt ◽

Annemarieke Beguin ◽

...

Keyword(s):

Magnetic Field ◽

Lunar Surface ◽

Magnetic Anomalies ◽

Wall Rock ◽

The Moon ◽

Polar Wander ◽

True Polar Wander ◽

Field Geometry ◽

Mare Basalts ◽

Over Time

Abstract Paleomagnetic studies of Apollo samples indicate that the Moon generated a core dynamo lasting for at least 2 billion years. However, the geometry of the lunar magnetic field is still largely unknown because the original orientations of essentially all Apollo samples have not been well-constrained. Determining the direction of the lunar magnetic field over time could elucidate the mechanism by which the lunar dynamo was powered and whether the Moon experienced true polar wander. Here we present measurements of the lunar magnetic field 3.7 billion years (Ga) ago as recorded by Apollo 17 mare basalts 75035 and 75055. These samples formed as part of basalt flows in the Taurus-Littrow valley that make up wall-rock within Camelot crater, now exposed at the rim of the crater. Using apparent layering in the parent boulder for 75055, we inferred its original paleohorizontal orientation on the lunar surface at the time of magnetization. We find that 75035 and 75055 record a mean paleointensity of ~50 µT. Furthermore, 75055 records a paleoinclination of 34 ± 11°. This inclination is consistent with, but does not require, a selenocentric axial dipole field geometry (i.e., a dipole in the center of the Moon and aligned along the spin axis). Additionally, although true polar wander is also not required by our data, true polar wander paths inferred from some independent studies of lunar hydrogen deposits and crustal magnetic anomalies are consistent with our measured paleoinclination.

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