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Cande, SC, Patriat P.  2015.  The anticorrelated velocities of Africa and India in the Late Cretaceous and early Cenozoic. Geophysical Journal International. 200:227-243.   10.1093/gji/ggu392   AbstractWebsite

We present a revised interpretation of magnetic anomalies and fracture zones on the Southwest Indian Ridge (SWIR; Africa-Antarctica) and the Southeast Indian Ridge (SEIR; Capricorn-Antarctica) and use them to calculate 2-plate finite rotations for anomalies 34 to 20 (84 to 43 Ma). Central Indian Ridge (CIR; Capricorn-Africa) rotations are calculated by summing the SWIR and SEIR rotations. These rotations provide a high-resolution record of changes in the motion of India and Africa at the time of the onset of the Reunion plume head. An analysis of the relative velocities of India, Africa and Antarctica leads to a refinement of previous observations that the speedup of India relative to the mantle was accompanied by a slowdown of Africa. The most rapid slowdown of Africa occurs around Chron 32Ay (71 Ma), the time when India's motion relative to Africa notably starts to accelerate. Using the most recent Geomagnetic Polarity Timescale (GTS12) we show that India's velocity relative to Africa was characterized by an acceleration from roughly 60 to 180 mm yr(-1) between 71 and 66 Ma, a short pulse of superfast motion (similar to 180 mm yr(-1)) between 66 and 63 Ma, an abrupt slowdown to 120 mm yr(-1) between 63 and 62 Ma, and then a long period (63 to 47 Ma) of gradual slowing, but still fast motion (similar to 100 mm yr(-1)), which ends with a rapid slowdown after Chron 21o (47 Ma). Changes in the velocities of Africa and India with respect to the mantle follow a similar pattern. The fastest motion of India relative to the mantle, similar to 220 mm yr(-1), occurs during Chron 29R. The SWIR rotations constrain three significant changes in the migration path of the Africa-Antarctic stage poles: following Chron 33y (73 Ma), following Chron 31y (68 Ma), and following Chron 24o (54 Ma). The change in the migration path of the SWIR stage poles following Chron 33y is coincident with the most rapid slowdown in Africa's motion. The change in the migration path after Chron 31y, although coincident with the most rapid acceleration of India's northward motion, may be related to changes in ridge push forces on the SWIR associated with the onset of extension along the Bain transform fault zone. The initial slowdown in India's motion relative to Africa between 63 and 62 Ma is more abrupt than predictions based on published plume head force models, suggesting it might have been caused by a change in plate boundary forces. The abrupt change in the migration path of the SWIR stage poles after Chron 24o is not associated with major changes in the velocities of either Africa or India and may reflect Atlantic basin plate motion changes associated with the arrival at the Earth's surface of the Iceland plume head. The abruptness of India's slowdown after Chron 21o is consistent with a collision event.

Cande, SC, Patriat P, Dyment J.  2010.  Motion between the Indian, Antarctic and African plates in the early Cenozoic. Geophysical Journal International. 183:127-149.   10.1111/j.1365-246X.2010.04737.x   AbstractWebsite

P>We used a three-plate best-fit algorithm to calculate four sets of Euler rotations for motion between the India (Capricorn), Africa (Somali) and Antarctic plates for 14 time intervals in the early Cenozoic. Each set of rotations had a different combination of data constraints. The first set of rotations used a basic set of magnetic anomaly picks on the Central Indian Ridge (CIR), Southeast Indian Ridge (SEIR) and Southwest Indian Ridge (SWIR) and fracture zone constraints on the CIR and SEIR, but did not incorporate data from the Carlsberg Ridge and did not use fracture zones on the SWIR. The second set added fracture zone constraints from the region of the Bain fracture zone on the SWIR which were dated with synthetic flowlines based on the first data set. The third set of rotations used the basic constraints from the first rotation set and added data from the Carlsberg Ridge. The fourth set of rotations combined both the SWIR fracture zone constraints and the Carlsberg Ridge constraints. Data on the Indian Plate side of the Carlsberg Ridge (Arabian Basin) were rotated to the Capricorn Plate before being included in the constraints. Plate trajectories and spreading rate histories for the CIR and SWIR based on the new rotations document the major early Cenozoic changes in plate motion. On the CIR and SEIR there was a large but gradual slowdown starting around Chron 23o (51.9 Ma) and continuing until Chron 21y (45.3 Ma) followed 2 or 3 Myr later by an abrupt change in spreading azimuth which started around Chron 20o (42.8) Ma and which was completed by Chron 20y (41.5 Ma). No change in spreading rate accompanied the abrupt change in spreading direction. On the SWIR there was a continuous increase in spreading rates between Chrons 23o and 20o and large changes in azimuth around Chrons 24 and 23 and again at Chron 21. Unexpectedly, we found that the two sets of rotations constrained by the Carlsberg Ridge data diverged from the other two sets of rotations prior to anomaly 22o. When compared to rotations for the CIR that are simultaneously constrained by data from all three branches of the Indian Ocean Triple Junction, there is a progressively larger separation of anomalies on the Carlsberg Ridge, with a roughly 25 km misfit for anomaly 23o and increasing to over 100 km for anomaly 26y. These data require that there was previously unrecognized convergence somewhere in the plate circuit linking the Indian, Capricorn and Somali plates prior to Chron 22o. We quantify this motion by summing our new Capricorn-Somalia rotations with previously published rotations for Neogene India-Capricorn motion and for early Cenozoic Somali-India motion based solely on Carlsberg Ridge data. The most likely possibility is that there was motion within the Somalia Plate due to a distinct Seychelles microplate as young as Chron 22o. The sense of the misfit on the Carlsberg Ridge is consistent with roughly 100-150 km of convergence across a boundary passing through the Amirante Trench and extending north to the Carlsberg Ridge axis between anomalies 26y and 22o. Alternatively, there may have been convergence within the Indian Plate, either along the western margin of Indian or east of the CIR in the region of the current Capricorn-Indian diffuse plate boundary. Our work sharpens the dating of the two major Eocene changes in plate motion recognized in the Indian Ocean.

Granot, R, Cande SC, Stock JM, Davey FJ, Clayton RW.  2010.  Postspreading rifting in the Adare Basin, Antarctica: Regional tectonic consequences. Geochemistry Geophysics Geosystems. 11   10.1029/2010gc003105   AbstractWebsite

Extension during the middle Cenozoic (43-26 Ma) in the north end of the West Antarctic rift system (WARS) is well constrained by seafloor magnetic anomalies formed at the extinct Adare spreading axis. Kinematic solutions for this time interval suggest a southward decrease in relative motion between East and West Antarctica. Here we present multichannel seismic reflection and seafloor mapping data acquired within and near the Adare Basin on a recent geophysical cruise. We have traced the ANTOSTRAT seismic stratigraphic framework from the northwest Ross Sea into the Adare Basin, verified and tied to DSDP drill sites 273 and 274. Our results reveal three distinct periods of tectonic activity. An early localized deformational event took place close to the cessation of seafloor spreading in the Adare Basin (similar to 24 Ma). It reactivated a few normal faults and initiated the formation of the Adare Trough. A prominent pulse of rifting in the early Miocene (similar to 17 Ma) resulted in normal faulting that initiated tilted blocks. The overall trend of structures was NE-SW, linking the event with the activity outside the basin. It resulted in major uplift of the Adare Trough and marks the last extensional phase of the Adare Basin. Recent volcanic vents (Pliocene to present day) tend to align with the early Miocene structures and the on-land Hallett volcanic province. This latest phase of tectonic activity also involves near-vertical normal faulting ( still active in places) with negligible horizontal consequences. The early Miocene extensional event found within the Adare Basin does not require a change in the relative motion between East and West Antarctica. However, the lack of subsequent rifting within the Adare Basin coupled with the formation of the Terror Rift and an on-land and subice extension within the WARS require a pronounced change in the kinematics of the rift. These observations indicate that extension increased southward, therefore suggesting that a major change in relative plate motion took place in the middle Miocene. The late Miocene pole of rotation might have been located north of the Adare Basin, with opposite opening sign compared to the Eocene-Oligocene pole.