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Gaina, C, Muller RD, Cande SC.  2000.  Absolute plate motion, mantle flow, and volcanism at the boundary between the Pacific and Indian Ocean mantle domains since 90 Ma. The history and dynamics of global plate motions. ( Richards MA, Gordon RG, Van der Hilst RD, Eds.).:189-210., Washington, D.C.: American Geophysical Union Abstract
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Croon, MB, Cande SC, Stock JM.  2010.  Abyssal hill deflections at Pacific-Antarctic ridge-transform intersections. Geochemistry Geophysics Geosystems. 11   10.1029/2010gc003236   AbstractWebsite

Nearly complete coverage of shipboard multibeam bathymetry data at the right-stepping Menard and Pitman Fracture Zones allowed us to map abyssal hill deviations along their traces. In this study we distinguish between (1) J-shaped curvatures at their origin, where modeling is addressing primary volcanism and faulting following a curved zone, and (2) straight abyssal hills getting bent in anti-J-shaped curvatures, in response to increased coupling across the transform fault, after they were formed. We compared the mapped abyssal hill deflections to a detailed plate motion model for the Pacific-Antarctic Ridge to test how abyssal hill curvature correlates to changes in plate motion direction, which lead to periods of transtension or transpression. This test was based on the number and size of the abyssal hill deflections. The observations show a high abundance of J-shaped abyssal hills during periods of significant clockwise change in plate motion direction, which leads to transtension. The tip of the ridge axis can deflect up to 60 into the transform fault in response to changes in the stress field at ridge-transform intersections. This is observed, in particular, at the Pitman Fracture Zone, where there has been a similar to 15 degrees clockwise rotation of the spreading direction azimuth during the last 9 Myr. In addition, we observed anti-J-shaped curvatures at Menard, Pitman, and Heirtzler Fracture Zones during periods of transpression when increased coupling across an oceanic transform fault is partially accommodated by distributed strike-slip deformation rather than solely by discontinuous displacement at the transform fault. Anti-J-shaped deflections typically develop in seafloor less than 2 Myr old when the oceanic lithosphere is thin.

Herron, EM, Cande SC, Hall BR.  1981.  An Active Spreading Center Collides with a Subduction Zone - a Geophysical Survey of the Chile Margin Triple Junction. Geological Society of America Memoirs. 154:683-701. AbstractWebsite
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Cande, SC.  1978.  Anomalous Behavior of Paleomagnetic Field Inferred from Skewness of Anomalies-33 and Anomalies-34. Earth and Planetary Science Letters. 40:275-286.   10.1016/0012-821x(78)90098-5   AbstractWebsite

Marine magnetic anomalies 33 and 34, corresponding to the first two reversals following the long normal polarity interval in the Cretaceous, are anomalously skewed by 30° to 40° throughout the North and South Atlantic. This phenomenon is most likely related to some aspect of the dipole paleomagnetic field. Specifically the magnetic field at the time of anomalies 33 and 34 appears to be characterized by the following: the dipole field gradually decreases in average intensity between reversals and/or there is an increase in the frequency or duration of undetected short polarity events toward the end of long periods (>106 years) of predominantly one polarity. Such long-period trends in the field are in conflict with the popular model for the generation of the earth's magnetic field that treats reversals as a Poisson process and assumes that the core has no memory greater than about 10^4 years.

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.

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Bougault, H, Cande SC.  1985.  Background, Objectives, and Summary of Principal Results - Deep-Sea Drilling Project Sites-556-564. Initial Reports of the Deep Sea Drilling Project. 82:5-16.   10.2973/dsdp.proc.82.101.1985   AbstractWebsite
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Larson, RL, Pitman III WC, Golovchenko X, Cande SC, Dewey JF, Haxby WF, Labrecque JL.  1985.  The bedrock geology of the world. , New York: W.H. Freeman and Co., Abstract
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Cande, SC, Labreque JL.  1974.  Behavior of Earths Paleomagnetic Field from Small-Scale Marine Magnetic-Anomalies. Nature. 247:26-28.   10.1038/247026a0   AbstractWebsite

Certain areas of the ocean crust exhibit a high resolution recording of the magnetic field history. A recent survey1 of the Gorda-Juan de Fuca Rise area in the North Pacific displays short wavelength (10 to 20 km), low amplitude (40 to 80 gamma) features superimposed upon the larger scale (30 to 200 km, 200 to 800 gamma) magnetic anomaly pattern of Heirtzler et al. 2. Many of these small scale anomalies form lineations which are parallel to the major magnetic lineations of Heirtzler et al. Sequences of small scale anomalies form characteristic patterns within intervals previously thought to be of constant polarity. We have identified two of these patterns that we observed in the North Pacific on profiles from the South Pacific and South-east Indian Oceans. Because of their global distribution, we conclude that the small scale anomalies are due to time variations of the Earth's magnetic field. That is, these features record either short (less than 3 × 10^4 yr) polarity reversals or fluctuations in the intensity of the dipole moment, perhaps with periods greater than 3 × 10^4

Barckhausen, U, Ranero CR, Cande SC, Engels M, Weinrebe W.  2008.  Birth of an intraoceanic spreading center. Geology. 36:767-770.   10.1130/g25056a.1   AbstractWebsite

The Cocos-Nazca spreading center is one of the few examples of the formation of a spreading center by splitting of oceanic lithosphere. It was created when the Farallon plate broke up in the early Miocene following the collision of the Pacific-Farallon spreading center with the North American continent. Much of the ancient Farallon plate corresponding to the area of opening is lost to subduction beneath Central America and South America, but new data from the conjugate area on the Pacific plate allow the first detailed reconstruction of the break-up process. The opening began after chron 7 (25 Ma) at a location of focused crustal extension caused by overlapping spreading centers that had evolved in response to a slight reorientation of a Pacific-Farallon ridge segment. Beginning at chron 6B (22.7 Ma), eastward progressing seafloor spreading started along an axis that most likely migrated toward the region of weak lithosphere created by the Galapagos hotspot. By chron 6 (19.5 Ma), plate splitting from the spreading center to the trench was complete, allowing the fully detached Cocos and Nazca plates to move independently. This kinematic change resulted in a significant ridge jump of the newly established Pacific-Nazca spreading center, a change in plate motion direction of the Nazea plate by 20 degrees clockwise, and a large increase in Pacific-Cocos plate velocity in the middle Miocene.

Mutter, JC, Hegarty KA, Cande SC, Weissel JK.  1985.  Breakup between Australia and Antarctica - a Brief Review in the Light of New Data. Tectonophysics. 114:255-279.   10.1016/0040-1951(85)90016-2   AbstractWebsite

The arguments justifying the revised timing of breakup between Australia and Antarctica (Cande and Mutter, 1982) and the reconstruction of Broken Ridge and Kerguelen Plateau (Mutter and Cande, 1983) are reviewed and considered with respect to new subsidence data. The age of breakup was revised from anomaly 22 time (55 My B.P.) to anomaly 34 time (85 My B.P.). The rough topography of the Diamantina Zone can be attributed to very slow spreading (−5 mm/yr.) beginning between the times of anomaly 34 and anomaly 19. The reconstruction of Broken Ridge and Kerguelen Plateau at anomaly 34 time shows overlap of these two features, but the overlap problem is nearly resolved by anomaly 18 time ( ~ 42 My B.P.). Normal seafloor spreading rates (22 mm/yr.) commenced at anomaly 19 time ( ~ 43 My B.P.). Subsidence patterns calculated from biostratigraphic data from wells drilled along Australia's southern margin are interpreted as more consistent with the revised age of Australia-Antarctic breakup. Subsidence curves systematically show rapid subsidence associated with the rift phase of margin development followed by much slower thermally-controlled subsidence during the drift phase. The timing of the rift-to-drift transition is believed to coincide with the age of breakup ( ~ 60 to 110 My B.P.). In addition, the subsidence curves indicate a west-to-east propagation of breakup along the southern margin. Magnetic anomaly patterns and stratigraphie observations are consistent with this hypothesis.

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Cande, SC, Stock JM, Muller RD, Ishihara T.  2000.  Cenozoic motion between East and West Antarctica. Nature. 404:145-150.   10.1038/35004501   AbstractWebsite

The West Antarctic rift system is the result of late Mesozoic and Cenozoic extension between East and West Antarctica, and represents one of the largest active continental rift systems on Earth. But the timing and magnitude of the plate motions leading to Be development of this rift system remain poorly known, because of a lack of magnetic anomaly and fracture zone constraints on seafloor spreading. Here we report on magnetic data, gravity data and swath bathymetry collected in several areas of the south Tasman Sea and northern Boss Sea. These results enable us to calculate mid-Cenozoic rotation parameters for East and West Antarctica. These rotations show that there was roughly 180 km of separation in the western Ross Sea embayment in Eocene and Oligocene time. This episode of extension provides a tectonic setting for several significant Genozoic tectonic events in the Ross Sea embayment including the uplift of the Transantarctic Mountains and the deposition of large thicknesses of Oligocene sediments. Inclusion of this East-West Antarctic motion in the plate circuit linking the Australia, Antarctic and Pacific plates removes a puzzling gap between the Lord Howe rise and Campbell plateau found in previous early Tertiary reconstructions of the New Zealand region. Determination of this East-West Antarctic motion also resolves a long standing controversy regarding the contribution of deformation in this region to the global plate circuit linking the Pacific to the rest of the world.

Cande, SC, Stock JM.  2004.  Cenozoic reconstructions of the Australia-New Zealand-South Pacific sector of Antarctica. The Cenozoic Southern Ocean : tectonics, sedimentation, and climate change between Australia and Antarctica. ( Exon NF, Kennett JP, Malone MJ, Eds.).:5-18., Washington, DC: American Geophysical Union Abstract
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Tebbens, SF, Cande SC, Kovacs L, Parra JC, Labrecque JL, Vergara H.  1997.  The Chile ridge: A tectonic framework. Journal of Geophysical Research-Solid Earth. 102:12035-12059.   10.1029/96jb02581   AbstractWebsite

A new Chile ridge tectonic framework is developed based on satellite altimetry data, shipboard geophysical data and, primarily, 38,500 km of magnetic data gathered on a joint U.S.-Chilean aeromagnetic survey. Eighteen active transforms with fossil fracture zones (FZs), including two complex systems (the Chile FZ and Valdivia FZ systems), have been mapped between the northern end of the Antarctic-Nazca plate boundary (Chile ridge) at 35 degrees S and the Chile margin triple junction at 47 degrees S. Chile ridge spreading rates from 23 Ma to Present have been determined and show slowdowns in spreading rates that correspond to times of ridge-trench collisions. The Valdivia FZ system, previously mapped as two FZs with an uncharted seismically active region between them, is now recognized to be a multiple-offset FZ system composed of six FZs separated by short ridge segments 22 to 27 km long. At chron 5A (similar to 12 Ma), the Chile ridge propagated from the Valdivia FZ system northward into the Nazca plate through crust formed 5 Myr earlier at the Pacific-Nazca ridge. Evidence for this propagation event includes the Friday and Crusoe troughs, located at discontinuities in the magnetic anomaly sequence and interpreted as pseudofaults. This propagation event led to the formation of the Friday microplate, which resulted in the transferal of crust from the Nazca plate to the Antarctic plate, and in a 500-km northward stepwise migration of the Pacific-Antarctic-Nazca triple junction. Rift propagation, microplate formation, microplate extinction, and stepwise triple junction migration are found to occur during large-scale plate motion changes and plate boundary changes in the southeast Pacific.

Seton, M, Whittaker JM, Wessel P, Muller RD, DeMets C, Merkouriev S, Cande S, Gaina C, Eagles G, Granot R, Stock J, Wright N, Williams SE.  2014.  Community infrastructure and repository for marine magnetic identifications. Geochemistry Geophysics Geosystems. 15:1629-1641.   10.1002/2013gc005176   AbstractWebsite

Magnetic anomaly identifications underpin plate tectonic reconstructions and form the primary data set from which the age of the oceanic lithosphere and seafloor spreading regimes in the ocean basins can be determined. Although these identifications are an invaluable resource, their usefulness to the wider scientific community has been limited due to the lack of a central community infrastructure to organize, host, and update these interpretations. We have developed an open-source, community-driven online infrastructure as a repository for quality-checked magnetic anomaly identifications from all ocean basins. We provide a global sample data set that comprises 96,733 individually picked magnetic anomaly identifications organized by ocean basin and publication reference, and provide accompanying Hellinger-format files, where available. Our infrastructure is designed to facilitate research in plate tectonic reconstructions or research that relies on an assessment of plate reconstructions, for both experts and nonexperts alike. To further enhance the existing repository and strengthen its value, we encourage others in the community to contribute to this effort.

Cande, SC, Kent DV.  1976.  Constraints Imposed by Shape of Marine Magnetic-Anomalies on Magnetic Source. Journal of Geophysical Research. 81:4157-4162.   10.1029/JB081i023p04157   AbstractWebsite

A two-layer source model for marine magnetic anomalies can accommodate several observations made on the shapes of anomalies in the Pacific and southeast Indian oceans. The layers are defined on the basis of cooling history and magnetic properties. The upper layer consists of rapidly cooled basalts, which acquire a strong magnetization near the ridge axis. This layer, with narrow transition zones, can account for the observed short polarity events. The lower layer consists of moderately magnetized, slowly cooled intrusive rocks in the lower oceanic crust. The transition zones in this layer are broad, sloping boundaries reflecting the delayed acquisition of magnetization with depth as, for example, along a sloping Curie point isotherm. The lower layer can account for a skewness discrepancy of 10°–15° in the observed skewness of some anomalies. It is shown that the upper layer has to contribute about three quarters of the total amplitude of magnetic anomalies in order for this model to simulate the observed shape of the anomalies. The model predicts that a deep drill hole located just to the older side of a reversal boundary in the upper part of the oceanic crust should encounter a magnetization polarity reversal within the lower oceanic crust.

Heinemann, J, Stock J, Clayton R, Hafner K, Cande S, Raymond C.  1999.  Constraints on the proposed Marie Byrd Land-Bellingshausen plate boundary from seismic reflection data. Journal of Geophysical Research-Solid Earth. 104:25321-25330.   10.1029/1998jb900079   AbstractWebsite

Single-channel and multichannel marine seismic data off the coast of West Antarctica collected during two Nathaniel B. Palmer cruises (NP92-8 and NP96-2) in the vicinity of 65 degrees S to 71 degrees S, 220 degrees E to 250 degrees E, reveal a NNW trending graben. We interpret this graben to be part of the paleodivergent plate boundary between the Marie Byrd Land and Bellingshausen plates. This graben coincides with a -520 nT magnetic anomaly to the NNW and a -720 nT anomaly to the SSE, as well as a 20 mGal negative gravity anomaly. Seismic profiles subparallel to the graben (22 km/Ma half-spreading rate) reveal greater seafloor roughness to the NE, where seafloor spreading was slower, than to the SW (27 km/Ma half-spreading rate). These data allow the position of the Marie Byrd Land-Bellingshausen plate boundary to be constrained more precisely than has previously been possible, with a trend of N17 degrees W from 68.52 degrees S, 233.65 degrees E to 68.41 degrees S, 233.56 degrees E. The sediment-filled graben has normal separation of sedimentary layers varying from 740 +/- 30 m to 580 +/- 20 m imaged in seafloor of age A33y (74 Ma).

Muller, RD, Cande SC, Stock JM, Keller WR.  2005.  Crustal structure and rift flank uplift of the Adare Trough, Antarctica. Geochemistry Geophysics Geosystems. 6   10.1029/2005gc001027   AbstractWebsite

The Adare Trough, located 100 km northeast of Cape Adare, Antarctica, represents the extinct third arm of a Tertiary spreading ridge between East and West Antarctica. It is characterized by pronounced asymmetric rift flanks elevated up to over 2 km above the trough's basement, accompanied by a large positive mantle Bouguer anomaly. On the basis of recently acquired seismic reflection and ship gravity data, we invert mantle Bouguer anomalies from the Adare Trough and obtain an unexpectedly large oceanic crustal thickness maximum of 9-10.5 km underneath the extinct ridge. A regional positive residual basement depth anomaly between 1 and 2.5 km in amplitude characterizes ocean crust from offshore Victoria Land to the Balleny Islands and north of Iselin Bank. The observations and models indicate that the mid/late Tertiary episode of slow spreading between East and West Antarctica was associated with a mantle thermal anomaly. The increasing crustal thickness toward the extinct ridge indicates that this thermal mantle anomaly may have increased in amplitude through time during the Adare spreading episode. This scenario is supported by a mantle convection model, which indicates the formation and strengthening of a major regional negative upper mantle density anomaly in the southwest Pacific in the last 50 million years. The total amount of post-26 Ma extension associated with Adare Trough normal faulting was about 7.5 km, in anomalously thick oceanic crust with a lithospheric effective elastic thickness (EET) between 3.5 and 5 km. This corresponds to an age between 3 and 5 million years based on a thermal boundary layer model and supports a scenario in which the Adare Trough formed soon after spreading between East and West Antarctica ceased, confined to relatively weak lithosphere with anomalously thick oceanic crust. There is little evidence for major subsequent structural activity in the Adare trough area from the available seismic data, indicating that this part of the West Antarctic Rift system became largely inactive in the early Miocene, with the exception of minor structural reactivation which is visible in the seismic data as offsets up to end of the early Pliocene.

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Selvans, MM, Stock JM, Clayton RW, Cande S, Granot R.  2014.  Deep crustal structure of the Adare and Northern Basins, Ross Sea, Antarctica, from sonobuoy data. Earth and Planetary Science Letters. 405:220-230.   10.1016/j.epsl.2014.08.029   AbstractWebsite

Extension associated with ultraslow seafloor spreading within the Adare Basin, in oceanic crust just north of the continental shelf in the Ross Sea, Antarctica, extended south into the Northern Basin. Magnetic and gravity anomaly data suggest continuity of crustal structure across the continental shelf break that separates the Adare and Northern Basins. We use sonobuoy refraction data and multi-channel seismic (MCS) reflection data collected during research cruise NBP0701, including 71 new sonobuoy records, to provide constraints on crustal structure in the Adare and Northern Basins. Adjacent 1D sonobuoy profiles along several MCS lines reveal deep crustal structure in the vicinity of the continental shelf break, and agree with additional sonobuoy data that document fast crustal velocities (6000-8000 m/s) at shallow depths (1-6 km below sea level) from the Adare Basin to the continental shelf, a structure consistent with that of other ultraslow-spread crust. Our determination of crustal structure in the Northern Basin only extends through sedimentary rock to the basement rock, and so cannot help to distinguish between different hypotheses for formation of the basin. (C) 2014 Elsevier B.V. All rights reserved.

Hill, IA, Cande SC.  1985.  Downhole Logging and Laboratory Physical-Properties Measurements. Initial Reports of the Deep Sea Drilling Project. 82:351-360.   10.2973/dsdp.proc.82.114.1985   AbstractWebsite

During DSDP Leg 82 downhole logging experiments, the very poor hole conditions and technical failures that have affected earlier legs were absent. As a result, Holes 556, 558, and 564 were logged with a full suite of tools. In addition, nearly complete continuously cored sections were obtained at Sites 558 and 563, and these sections have been subjected to laboratory physical property measurements. The resulting data set allows a comparison of logged and laboratorymeasured values and correlation between holes.The sediments encountered in all holes were calcareous oozes and chalks. Despite the lack of distinctive lithologies, changes in density and seismic velocity can be seen in both the laboratory and logged data and identified with sedimentologic features in the cores; the logged curves can be correlated between holes. Within basement rocks the logged curves provide information on the part of the formations not recovered by coring (about 55%) and allow comparisonbetween bulk properties and the sample properties measured in the laboratory. Comparison of the logged data with that from Site 417 shows systematic differences, perhaps related to crustal aging.

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Cande, SC, Herron EM, Hall BR.  1982.  The Early Cenozoic Tectonic History of the Southeast Pacific. Earth and Planetary Science Letters. 57:63-74.   10.1016/0012-821x(82)90173-x   AbstractWebsite

New marine geophysical data collected in the southeast Pacific enable us to define better the early Cenozoic tectonic history of the area and to interpret previously unexplained bathymetric features in terms of plate tectonic processes. We have identified a major re-organization in plate boundaries at anomaly 21 time when a large fragment was broken off the Pacific plate and joined to the Antarctic plate. This interpretation is based on three pieces of evidence: (1) a major ESE-trending feature, the Humboldt Fracture Zone, marks the southern boundary of the Farallon-Antarctic anomalies identified by Weissel et al. [1], (2) a north-south striking trough, the Hudson Trough, which represents the scar left by the Pacific-Antarctic Ridge when it rifted across old Pacific crust, (3) a sequence of north-south striking magnetic lineations south of the Humboldt Fracture Zone and east of the Hudson Trough is correlated to anomalies 27 to 22 and identified with Pacific-Aluk spreading.

Mutter, JC, Cande SC.  1983.  The Early Opening between Broken Ridge and Kerguelen Plateau. Earth and Planetary Science Letters. 65:369-376.   10.1016/0012-821x(83)90174-7   AbstractWebsite

Reconstructions to total closure of the Australia-Antarctic continents causes an unacceptable overlap of Broken Ridge and Kerguelen Plateau. This has been partially resolved in the past by supposing that the northern part of Kerguelen, that is principally involved in the overlap, is younger than the remainder. We have revised the early reconstructions using a newly proposed breakup chronology of Australia and Antarctica which suggests that opening began at least 90 m.y. B.P. at an initially slow rate. This eliminates the overlap problem without invoking major age differences within the Kerguelen Plateau. We also suggest that the northeastern flank of Kerguelen Plateau may be underlain by the “missing” westward continuation of the Diamantina Zone. It may have been isolated on the Antarctic plate by a ridge crest jump at about anomaly 24 time that also formed the Ob Trench.

Cande, SC, Haxby WF.  1991.  Eocene Propagating Rifts in the Southwest Pacific and Their Conjugate Features on the Nazca Plate. Journal of Geophysical Research-Solid Earth. 96:19609-19622.   10.1029/91jb01991   AbstractWebsite

We have mapped a 1200 km long NW-SE trending lineament in Seasat and Geosat radar altimeter data crossing a remote portion of the Southwest Pacific Basin. This lineament runs obliquely both to the fracture zones (FZs) and magnetic lineations between the Austral and Agassiz FZs. By examining shipboard magnetics, gravity, and bathymetric profiles in this region and in the conjugate regions of the Nazca plate, we identify this feature as the site of a series of small ridge jumps, highly asymmetrical spreading and small propagating rifts, during the mid-to-late Eocene (chron C21 to chron C13). Between the Austral and Agassiz FZs there is roughly 250 to 350 km of missing Pacific plate crust, which must have been transferred to the Nazca plate by the propagating rifts and small ridge jumps. On the Nazca plate, the conjugate area to the gravity lineament is now being subducted beneath the Chile Trench. North of the Challenger FZ this area corresponds to a region of undecipherable magnetic anomalies. South of the Challenger FZ, there is evidence for a small 50 km ridge jump offshore of the Chile Trench. This small ridge jump by itself is not sufficient to account for the missing crust on the Pacific plate, and we conclude that there must have been repeated small ridge jumps at the same site. One consequence of these ridge jumps is that crust on the Nazca plate entering the trench is not as old as would be predicted by simply mirror imaging the anomaly pattern on the Pacific plate.

Muller, RD, Gohl K, Cande SC, Goncharov A, Golynsky AV.  2007.  Eocene to Miocene geometry of the West Antarctic Rift System. Australian Journal of Earth Sciences. 54:1033-1045.   10.1080/08120090701615691   AbstractWebsite

Tectonic models for the Late Cretaceous/Tertiary evolution of the West Antarctic Rift System range from hundreds of kilometres of extension to negligible strike-slip displacement and are based on a variety of observations, as well as kinematic and geodynamic models. Most data constraining these models originate from the Ross Sea/Adore Trough area and the Transantarctic Mountains. We use a new Antarctic continental crustal-thinning grid, combined with a revised plate-kinematic model based on East Antarctic-Australia-Pacific-West Antarctic plate circuit closure, to trace the geometry and extensional style of the Eocene-Oligocene West Antarctic Rift from the Ross Sea to the South Shetland Trench. The combined data suggest that from chron 21 (48 Ma) to chron 8 (26 Ma), the West Antarctic Rift System was characterised by extension in the west to dextral strike-slip in the east, where it was connected to the Pacific-Phoenix-East Antarctic triple junction via the Byrd Subglacial Basin and the Bentley Subglacial Trench, interpreted as pullapart basins. Seismic-reflection profiles crossing the De Gerlache Gravity Anomaly, a tectonic scar from a former spreading ridge jump in the Bellingshausen Sea, suggest Late Tertiary reactivation in a dextral strike-slip mode. This is supported by seismic-reflection profiles crossing the De Gerlache Gravity Anomaly in the Bellingshausen Sea, which show incised narrow sediment troughs and vertical faults indicating strike-slip movement along a north-south direction, Using pre-48 Ma plate circuit closure, we test the hypothesis that the Lord Howe Rise was attached to the Pacific Plate during the opening of the Tasman Sea, We show that this plate geometry may be plausible at least between 74 and 48 Ma, but further work especially on Australian-Antarctic relative plate motions is required to test this hypothesis.

Bangs, NL, Cande SC.  1997.  Episodic development of a convergent margin inferred from structures and processes along the southern Chile margin. Tectonics. 16:489-503.   10.1029/97tc00494   AbstractWebsite

Seismic reflection data acquired in the vicinity of Isla Mocha across the southern coast of Chile image structures formed along the continental margin and reveal an episodic history of accretion, nonaccretion, and possibly erosion. Structures formed at the toe of the continental slope suggest frontal accretion of 3/4 to 1 3/4 km of trench fill. Seismic images also reveal that a small accretionary wedge, 20-30 km wide, abuts the truncated continental metamorphic basement that extends seaward from beneath the shelf. The small size of the accretionary wedge on three profiles examined here is not consistent with a long history of accretion with the current deformational style, as current rates of frontal accretion could have accumulated all of the existing accretionary wedge in less than 1-2 m.y. This is a small fraction of convergence history along this margin, and the current accretionary mode has not been consistently maintained in the past. The Isla Mocha region is located between the temperate climate of central Chile and the glacial climate of southern Chile, and climatic conditions in this region have likely fluctuated sufficiently to cause significant variation in trench sediment supply. Accretionary and nonaccretionary or erosional episodes are probably linked to temporal variations in trench sediment thickness, as suggested by observations along the Chile margin. Currently, thick trench sediment correlates with accretion along the southern Chile margin, and thin trench sediment correlates with nonaccretion/tectonic erosion as near the Chile Ridge and from the Juan Fernandez Ridge to northern Chile. The Isla Mocha region also lies 900-1000 km north of the Chile triple junction, and the Chile Ridge lies approximately 2000 km to the west and has not yet collided and affected the margin near Isla Mocha. This part of the precollision zone provides an excellent reference to examine the effects of Chile Ridge collision in the development of the Chile margin. The most apparent effect of subduction of the buoyant, young crust of the Chile Ridge is a shallow trench that is nearly devoid of sediment. Consequently, the triple junction is undergoing nonaccretion or erosion, and the accretionary complex near the triple junction remains smaller than to the north or south because the current phase of rapid accretion elsewhere in the trench has bypassed the triple junction region. The interplay of subduction zone processes, such as trench sedimentation and ridge collision, has resulted in an episodic development of the margin and produced a discontinuous record of convergence history within the accretionary wedge.

Jones, EJW, Cande SC, Spathopoulos F.  1995.  Evolution of a major oceanographic pathway: the equatorial Atlantic. The tectonics, sedimentation, and palaeoceanography of the North Atlantic Region, Geological Society Special Publication. 90( Scrutton RA, Stoker MS, Shimmield GB, Tudhope AW, Eds.).:199-213., LondonTulsa, Okla.: The Geological Society ;AAPG Bookstore Abstract
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