Improved Late Cretaceous and early Cenozoic Paleomagnetic apparent polar wander path for the Pacific plate
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Apparent polar wander
Seamount
Polar wander
Pacific Plate
Magnetostratigraphy
The paleomagnetism of 10 seamounts from the Joban Seamount Chain (northwestern Pacific) were studied using a method that calculates mean magnetization parameters by an inversion of magnetic anomaly and edifice bathymetry. Of the 10 seamounts, eight gave results consistent with other paleomagnetic studies of Pacific seamounts. Joban seamounts appear to have formed at two different mean paleolatitudes, contrary to what would be expected for a single hotspot origin. Furthermore, six of the consistent poles plot along the 129 to 82 Ma portion of the Pacific plate apparent polar wander path (APWP), implying the seamounts formed mainly during the mid‐ to Late Cretaceous. Two other poles, from Iwaki and Hitachi seamounts, are located northwest of the older end of the established Pacific APWP, possibly indicating Early Cretaceous ages. Because Iwaki and Hitachi seamounts are located in the middle of the chain, age does not progress along the chain, arguing against a single‐hotspot origin. Perhaps the chain formed by recurrent volcanism along a line of weakness or by another mechanism. Iwaki and Hitachi seamounts display smaller northward drift compared to the others, consistent with the Pacific plate drifting southward from Late Jurassic or Early Cretaceous to mid‐Cretaceous time.
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Apparent polar wander
Pacific Plate
Polar wander
Hotspot (geology)
Geomagnetic pole
Pillow lava
Magnetostratigraphy
Seamount
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Magnetostratigraphy
Clockwise
Apparent polar wander
Geomagnetic pole
Polar wander
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Abstract We present paleomagnetic data from basaltic pillow and lava flows drilled at four Ocean Drilling Program (ODP) Leg 192 sites through the Early Cretaceous (∼120 Ma) Ontong Java Plateau (OJP). Altogether 270 samples (out of 331) yielded well-defined characteristic remanent magnetization components all of which have negative inclinations, i.e. normal polarity. Dividing data into inclination groups we obtain 5, 7, 14 and 15 independent inclination estimates for the four sites. Statistical analysis suggests that paleosecular variation has been sufficiently sampled and site-mean inclinations therefore represent time-averaged fields. Of particular importance is the finding that all four site-mean inclinations are statistically indistinguishable, strongly supporting indirect seismic observation from the flat-lying sediments blanketing the OJP that the studied basalts have suffered little or no tectonic disturbance since their emplacement. Moreover, the corresponding paleomagnetic paleolatitudes agree excellently with paleomagnetic data from a previous ODP site (Site 807) drilled into the northern portion of the OJP. Two important conclusions can be drawn based on the presented dataset: (i) the Leg 192 combined mean inclination (Inc.=−41.4°, N =41, k =66.0, α 95 =2.6°) is inconsistent with the Early Cretaceous part of the Pacific apparent polar wander path, indicating that previous paleomagnetic poles derived mainly from seamount magnetic anomaly modeling must be used with care; (ii) the Leg 192 paleomagnetic paleolatitude for the central OJP is ∼20° north of the paleogeographic location calculated from Pacific hotspot tracks assuming the hotspots have remained fixed. The difference between paleomagnetic and hotspot calculated paleolatitudes cannot be explained by true polar wander estimates derived from other lithospheric plates and our results are therefore consistent with and extend recent paleomagnetic studies of younger hotspot features in the northern Pacific Ocean that suggest Late Cretaceous to Eocene motion of Pacific hotspots.
Apparent polar wander
Pacific Plate
Polar wander
Seamount
Magnetostratigraphy
Geomagnetic pole
Hotspot (geology)
Pillow lava
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Abstract A magnetostratigraphic study has been performed on the Mae Moh basin, well known for its lignite mining in the Lampang province. Paleomagnetic samples were collected from 66 stratigraphic levels. Rock magnetic investigations indicate the presence of low coercivity minerals. Specimens subjected to progressive thermal (or alternating field) demagnetization procedures show that nearly all of them exhibit a low temperature magnetization component, and a high temperature characteristic component (ChRM), with either positive or negative virtual geomagnetic pole latitudes and opposite polarity, considered as the characteristic Miocene magnetization. The overall mean paleomagnetic direction (incl.=22.2°, decl.=358.3°, κ =15, α 95 =4) documents a counterclockwise vertical axis rotation of about 13°±1.32 with respect to the expected Miocene direction derived from the Eurasian polar wander curve (incl.=42°, decl.=11°). Our paleomagnetic results are not consistent with the previously reported paleomagnetic data. The rotation observed in the Mae Moh basin can be the response to local tectonics. A section sampled for magnetostratigraphy reveals a polarity sequence of nine magnetozones that can reliably be correlated to the geomagnetic polarity time scale. According to biochronological constraints, the magnetostratigraphic results from the mammal-bearing succession correlate with chron C5ABn–C5An2n, between 13.5 and 12.1 Ma. According to the mean sedimentation rate of about 17.5 cm/ka, ages of 12.5 and 12.8 Ma are proposed for the fossiliferous levels (J5 and K1, K2 lignite zones) were the mammal remains were found.
Magnetostratigraphy
Clockwise
Apparent polar wander
Geomagnetic pole
Polar wander
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Abstract We present paleomagnetic data from basaltic pillow and lava flows drilled at four Ocean Drilling Program (ODP) Leg 192 sites through the Early Cretaceous (∼120 Ma) Ontong Java Plateau (OJP). Altogether 270 samples (out of 331) yielded well-defined characteristic remanent magnetization components all of which have negative inclinations, i.e. normal polarity. Dividing data into inclination groups we obtain 5, 7, 14 and 15 independent inclination estimates for the four sites. Statistical analysis suggests that paleosecular variation has been sufficiently sampled and site-mean inclinations therefore represent time-averaged fields. Of particular importance is the finding that all four site-mean inclinations are statistically indistinguishable, strongly supporting indirect seismic observation from the flat-lying sediments blanketing the OJP that the studied basalts have suffered little or no tectonic disturbance since their emplacement. Moreover, the corresponding paleomagnetic paleolatitudes agree excellently with paleomagnetic data from a previous ODP site (Site 807) drilled into the northern portion of the OJP. Two important conclusions can be drawn based on the presented dataset: (i) the Leg 192 combined mean inclination (Inc.=−41.4°, N =41, k =66.0, α 95 =2.6°) is inconsistent with the Early Cretaceous part of the Pacific apparent polar wander path, indicating that previous paleomagnetic poles derived mainly from seamount magnetic anomaly modeling must be used with care; (ii) the Leg 192 paleomagnetic paleolatitude for the central OJP is ∼20° north of the paleogeographic location calculated from Pacific hotspot tracks assuming the hotspots have remained fixed. The difference between paleomagnetic and hotspot calculated paleolatitudes cannot be explained by true polar wander estimates derived from other lithospheric plates and our results are therefore consistent with and extend recent paleomagnetic studies of younger hotspot features in the northern Pacific Ocean that suggest Late Cretaceous to Eocene motion of Pacific hotspots.
Apparent polar wander
Pacific Plate
Polar wander
Geomagnetic pole
Hotspot (geology)
Seamount
Pillow lava
Magnetostratigraphy
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Palaeomagnetic results from mainly Cretaceous rocks in Honduras delineate a distinctive apparent polar wander path (APWP) which is well suited for magnetostratigraphy. The APWP is based on palaeomagnetic data from palaeontologically dated units in the established stratigraphic column and three radiometrically dated intrusions. The ages and stratigraphic positions of sedimentary units whose stratigraphic assignments have been debated, can be inferred by comparing their palaeomagnetic pole postion with the known APWP. The results demonstrate the usefulness of magnetostratigraphy for resolving stratigraphic problems in the absence of fossils or marker beds, and for areas of discontinuous exposures. For regional interpretations, the most important conclusion is that strata in Honduras that have been assigned to the Todos Santos Formation were not deposited on the same tectonic plate as the Todos Santos Formation of Guatemala and southern Mexico. There is no evidence that the Honduran 'Todos Santos' strata are depositionally related to the true Todos Santos Formation. The name 'Todos Santos Formation' should be abandoned in Honduras and for the entire Chortis Block.
Apparent polar wander
Magnetostratigraphy
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