Center for Geodynamics

Trondheim, Norway

Center for Geodynamics

Trondheim, Norway
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Dupont-Nivet G.,University Utrecht | Dupont-Nivet G.,Peking University | Van Hinsbergen D.J.J.,University of Oslo | Van Hinsbergen D.J.J.,University of Leicester | And 3 more authors.
Tectonics | Year: 2010

Paleomagnetism provides independent paleolatitude constraints on the India-Asia convergence. However, implied Cenozoic latitudinal convergence within Asia (thousands of km) largely exceeds geologic estimates of tectonic shortening (hundreds of km). This discrepancy may result from a notoriously low bias in paleomagnetically determined Cenozoic paleolatitudes in Asia. We provide here new paleomagnetic data from Cenozoic Mongolian volcanic rocks and from Chinese Paleogene sediments corrected from the depositional bias of inclination shallowing. These results combined with similar Asian data sets, confirm that paleolatitudes are still 5-10° lower than predicted by the paleomagnetic Apparent Polar Wander Path (APWP) for Asia between 50 and 20 Ma. Inclination-shallowing being excluded from the selected data sets, we investigate the likeliness of other proposed mechanisms for this discrepancy: (1) more southerly positions of Asia than expected by the APWP (due to APWP inaccuracies rather than Eurasian non-rigidity), or (2) non-dipolar geomagnetic field contributions. Fully explaining this discrepancy by only one of these mechanisms would imply either unrealistically large (>10°) APWP inaccuracies, or unrealistically large octupolar field contributions (up to 16%). A combination of these mechanisms is found more likely to have produced the observed latitudinal discrepancy, but their respective contributions cannot be quantified given the still relatively low amount and poor quality of Cenozoic paleomagnetic data from stable cratons of Asia, India, and Europe. By allowing for reasonable time-dependant non-dipolar contributions and a slight (<5°) APWP bias, the latitudinal discrepancy can be resolved and the excessive amounts of intra-Asian shortening decrease to values in line with tectonic shortening from structural studies. Copyright 2010 by the American Geophysical Union.

Torsvik T.H.,Center for Geodynamics | Torsvik T.H.,University of Oslo | Torsvik T.H.,University of Witwatersrand | Rousse S.,Center for Geodynamics | And 3 more authors.
Geophysical Journal International | Year: 2010

In their comment, Aslanian & Moulin argue that our model of South Atlantic opening is incompatible with several kinematic and geological constraints as recently evaluated in Moulin et al. They also claim that we have not appropriately referenced their work. We strongly disagree and in addressing their points will argue that our model is compatible with the most important constraints that have been assembled by the many scientists who have worked on the South Atlantic and that instead the interpretation by Moulin et al. suffers from serious flaws. © 2010 The Authors Journal compilation © 2010 RAS.

Torsvik T.H.,University of Oslo | Torsvik T.H.,Center for Geodynamics | Torsvik T.H.,University of Witwatersrand | Steinberger B.,University of Oslo | And 5 more authors.
Earth and Planetary Science Letters | Year: 2010

We have developed an improved model of global digital palaeo-plate boundaries and plate motion to describe the distribution and history of plates since the Late Jurassic. From this history we computed net lithospheric rotation (NR) through time confirming the so-called westward drift, but only for the past 30 Myr. The NR has significantly smaller magnitudes (0.13°/My, past 5 My) than for some other plate models; it averages to 0.11 ± 0.03°/My for the past 50 My with a small but systematic increase toward the present. The westward drift, seen only for the past 30 My, is attributed to the increased dominance of a steadily growing and accelerating Pacific plate. NR shows peaks with time but only an Early Tertiary peak of 0.33°/My (when the Indian plate was undergoing the largest known acceleration/deceleration) can be interpreted with some confidence. We find a linear decreasing trend in net rotation over the past 150 My, but attribute this trend to increasing reconstruction uncertainties back in time, as subduction consumed more than half of the oceanic crust since the Jurassic. After removing a linear time-trend, we find a NR average of about 0.12°/My for the past 150 My. © 2009 Elsevier B.V. All rights reserved.

Steinberger B.,Center for Geodynamics | Steinberger B.,Helmholtz Center Potsdam | Steinberger B.,University of Oslo | Torsvik T.H.,Center for Geodynamics | And 2 more authors.
Geochemistry, Geophysics, Geosystems | Year: 2010

Earth's orientation relative to its spin axis is determined by its nonhydrostatic inertia tensor. We show here that the present-day nonhydrostatic inertia tensor can be modeled by combining contributions due to large low shear velocity provinces (LLSVPs) in the lowermost mantle and due to subduction. With the first contribution only, the spin axis would be at ∼67°N, 96°E (north Siberia). The distribution of recent subduction, with largest amounts in the northwest Pacific (beneath East Asia) and the southeast Pacific (beneath South America), adds a secondary contribution which moves the spin axis toward the observed poles. We use plate reconstructions to infer subduction and inertia tensor through time, assuming that the LLSVP contribution has remained constant. Motion of the pole toward Greenland since ∼50 Ma is attributed to increased subduction beneath East Asia and South America and a decrease beneath North America since then. Motion of the pole toward Siberia before that is attributed to large amounts of subduction beneath North America between ∼120 and 50 Ma and decreasing amounts of subduction in East Asia after 60-70 Ma. Greater stability of the spin axis since ∼100 Ma can be attributed to a decrease in the amount of subduction in polar latitudes and an increase in equatorial latitudes. Copyright 2010 by the American Geophysical Union.

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