Paleomagnetic paleolatitude of Early Cretaceous Ontong Java Plateau basalts: implications for Pacific apparent and true polar wander
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Keywords:
Apparent polar wander
Pacific Plate
Polar wander
Hotspot (geology)
Geomagnetic pole
Pillow lava
Magnetostratigraphy
Seamount
Paleolatitudes determined from paleomagnetic study of azimuthally unoriented sediment cores recovered by deep sea drilling on the Pacific plate have been previously used in determining reference poles for the Pacific plate apparent polar wander (APW) path. From discordant paleoinclinations and corresponding paleolatitudes determined from these data, some workers have inferred tectonic tilting or large horizontal motion of some deep‐sea drilling sites relative to other parts of the Pacific plate. Here the reliability of these paleolatitudes is evaluated by comparing them with paleolatitudes determined from a Pacific plate reference APW path determined from seamount poles, skewness and amplitudes of magnetic profiles across magnetically lineated seafloor, and paleocolatitudes from azimuthally unoriented basalt cores and from equatorial sediment facies. The reference APW path includes a new determination of the Early Cretaceous pole from several types of paleomagnetic data, which agree well with one another. Sediment paleolatitudes are found to be systematically less southerly than those predicted from the reference APW path, a discrepancy that corresponds to inclinations shallower than expected. Thus most deep‐sea drilling sediment paleomagnetic paleolatitudes are unreliable and should be omitted from the data used in determining reference APW paths. Inclination and paleolatitude discrepancies noted in prior studies may be due not to tectonic causes but to shallowly biased inclinations.
Apparent polar wander
Pacific Plate
Seamount
Seafloor Spreading
North American Plate
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In this paper we show that: (1) The positions of the Cretaceous palaeomagnetic poles (PP) for South America and Africa exhibit elongated distributions that are due to rapid movement of these continents from the south pole. (2) The positions of the Middle—late Jurassic virtual geomagnetic poles for South America exhibit an elongated distribution along the meridians 20–200° E; it is suggested that this is due to a rapid shift of South America in Middle—late Jurassic time. (3) The late early—early late Cretaceous sections of the apparent polar wandering paths for South America and Africa are consistent with South Atlantic seafloor spreading data. On the basis of the comparison of the reliable late Palaeozoic—late Cretaceous PPs for South America and Africa, taking into account the restrictions established by geological, palaeontological and seafloor spreading data, it is suggested that minor movements could have occurred within Western Gondwana in middle—late Jurassic time along a narrow zone which later became the South Atlantic divergent boundary. Four 'hairpins' are defined in the late Palaeozoic—late Cretaceous section of the apparent polar wandering path for South America; the two youngest of these can be correlated with the origin of the South Atlantic Ocean basin and the onset of the Andean Orogeny, respectively. The magnetostratigraphy for the Serra Geral lava flow sequence suggests that some of these flows were poured out rapidly without significant interruption.
Magnetostratigraphy
Apparent polar wander
Polar wander
Geomagnetic pole
Seafloor Spreading
Red beds
Oceanic basin
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Apparent polar wander
Pacific Plate
Polar wander
Hotspot (geology)
Geomagnetic pole
Pillow lava
Magnetostratigraphy
Seamount
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Apparent polar wander
Pacific Plate
Seamount
Hotspot (geology)
Polar wander
Geomagnetic pole
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Seamount
Pacific Plate
Apparent polar wander
North American Plate
Hotspot (geology)
Polar wander
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The paleomagnetism of Cretaceous Pacific seamounts is reexamined. Herein techniques for nonuniform magnetic modeling are applied to determine paleomagnetic pole positions and their associated confidence limits. Modeling techniques are presented for reconstruction of both uniform and nonuniform components of the seamount magnetization. The uniform component yields an estimate of the paleomagnetic pole position, and the nonuniform component accounts for irregularities in the seamount magnetization. A seminorm minimization approach constructs maximally uniform magnetizations and is used to represent seamount interiors. A statistical modeling approach constructs random nonuniform magnetizations and is used to determine the confidence limits associated with each pole position. Mean paleopoles are calculated for groups of seamounts, including their associated error bounds. The mean paleopole for seven reliably dated Upper Cretaceous seamounts is located close to the position predicted by Pacific‐hotspot relative motion. The paleopole for five seamounts with Cretaceous minimum dates is located west of the hotspotpredicted apparent polar wander path and may represent a Lower Cretaceous or Upper Jurassic pole.
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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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Apparent polar wander
Seamount
Polar wander
Pacific Plate
Magnetostratigraphy
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Citations (33)
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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