Lawver, L. A., D. D. Blankenship, and L. M. Gahagan, East Antarctica: Onshore-offshore uncertainties for cryosphere evolution, Terra Antartica, 12, 177-186, 2006, #1768
Golonka, J., W. Kissling, L. M. Gahagan, and L. A. Lawver, Biohermy juraskie w globalnych bazach danych - Jurassic biotherms in the global databases, Nafta Gaz. R., 61, 288-293, 2005, #1845
Lawver, L. A., and F. J. Davey, River-like erosion within the Bounty submarine channel, southwest Pacific Ocean, Marine Geol., 216, 101-106, 2005, 1 citation, doi:10.1016/j.margeo.2005.02.005, #1747 
A multibeam bathymetric crossing of Bounty Channel, east of South Island New Zealand fortuitously imaged a large recent slump that partially dammed the channel. Together with a later, adjacent multibeam crossing, these bathymetric data show the average gradient for this section of the channel to be 15 m per km, steeper than the general average for the whole channel (3 m per km). In the immediate vicinity of the slump, there is a negative gradient followed downstream by a maximum gradient of 1450 m/km for a 70 m section of the channel. Typical riverine erosional features are seen in this section of the channel including an over-deepened basin at the bottom of the greatest slope as well as additional major slump features.
Brozena, J. M., V. A. Childers, L. A. Lawver, L. M. Gahagan, R. Forsberg, J.-I. Fileide, and O. Eldholm, New aerogeophysical study of the Eurasia basin and Lomonosov ridge: Implications for basin development, Geology, 31, 825-828, 2003, 45 citations, doi:10.1130/G19528.1, #1643
In 1998 and 1999, new aerogeophysical surveys of the Arctic Ocean's Eurasia Basin produced the first collocated gravity and magnetic measurements over the western half of the basin. These data increase the density and extend the coverage of the U.S. Navy aeromagnetic data from the 1970s. The new data reveal prominent bends in the isochrons that provide solid geometrical constraints for plate reconstructions. Tentative identification of anomaly 25 in the Eurasia Basin links early basin opening to spreading in the Labrador Sea before the locus of spreading in the North Atlantic shifted to the Norwegian-Greenland Sea. With the opening of the Labrador Sea, Greenland began ∼200 km of northward movement relative to North America and eventually collided with Svalbard, Ellesmere Island, and the nascent Eurasia ocean basin. Both gravity and magnetic data sets reconstructed to times prior to chron 13 show a prominent linear anomaly oriented orthogonal to the spreading center and immediately north of the Yermak Plateau and Morris Jesup Rise. This anomaly may mark the locus of shortening and possibly subduction as Greenland collided with the nascent Eurasia Basin and impinged upon the southern Gakkel Ridge. This collision may have contributed to volcanism on the Morris Jesup Rise. By chron 13, Greenland had ended its northward motion and had become fixed to North America, and the plateau north of Greenland had rifted apart to become the Morris Jesup Rise and the Yermak Plateau.
Lawver, L. A., and L. M. Gahagan, Evolution of Cenozoic seaways in the circum-Antarctic region, Palaeogeography, Palaeoclimatology, Palaeoecology, 198, 11-37, 2003, 160 citations, doi:10.1016/S0031-0182(03)00392-4, #1592
A complete circum-Antarctic seaway did not open until both the South Tasman Rise cleared the Oates Land coast of East Antarctica and Drake Passage opened between the southern tip of South America and the northern end of the Antarctic Peninsula. Major plate motions based on dated seafloor spreading anomalies and distinct fracture zone lineations constrain the age of the opening of a seaway between the South Tasman Rise and Antarctica as very close to the Eocene–Oligocene boundary, with an unrestricted opening deeper than 2000 m dating from 32 Ma. Timing of the opening of Drake Passage is more circumstantial because the exact motions of certain micro-continental fragments are not known. The motion of Africa with respect to South America as well as the motion of East Antarctica with respect to Africa are well constrained for the Cenozoic. These major plate motions are used with the reasonable assumption of no Cenozoic motion of the Antarctic Peninsula with respect to East Antarctica to constrain the location of the Antarctic Peninsula with respect to the southern tip of South America for the critical period of late Eocene to late Oligocene. Uncertainty of motion of the South Georgia and South Orkney microcontinents and other possible continental fragments make an exact time for opening of Drake Passage difficult to ascertain. Even so, the early Oligocene position of the Antarctic Peninsula with respect to South America requires a through-going, deep-water seaway to have been open at Drake Passage prior to 28 Ma, even given the unconstrained motion of various high-standing crustal fragments in the Scotia Sea. With reasonable assumptions concerning motion of the crustal fragments in the western and central Scotia Sea, it is likely that Drake Passage or passage through Powell Basin was open to deep water circulation by 31±2 Ma.
Macdonald, D. I. M., I. Gomez-Perez, J. Franzese, L. Spalletti, L. A. Lawver, L. M. Gahagan, I. W. D. Dalziel, C. Thomas, N. Trewin, M. Hole, and D. Paton, Mesozoic break-up of SW Gondwana: Implications for regional hydrocarbon potential of the southern South Atlantic, Marine Petroleum Geol., 20, 287-308, 2003, 35 citations, doi:10.1016/S0264-8172(03)00045-X, #1618
This work provides new palinspastic palaeofacies reconstructions of SW Gondwana incorporating rotation of a Falkland/Malvinas microplate. We discuss the implications of this for the tectonic evolution of the southern South Atlantic and hence for the regional hydrocarbon potential.
Existing Gondwana reconstructions display good fits of major continents but poorly constrained fits of microcontinents. In most continental reconstructions, the Falkland/Malvinas Plateau was assumed to be a rigid fragment of pre-Permian South American crust. However, it has been suggested, on the basis of palaeomagnetic data, that the Falkland/Malvinas Islands were rotated by 180° after 190 Ma. This rotation hypothesis has been successfully tested on the basis of Devonian stratigraphy and palaeontology, Permian stratigraphy and sedimentology and Late Palaeozoic and Early Mesozoic structure, making it unlikely that the plateau behaved as a rigid structure during breakup. We have explored the consequences of accepting this hypothesis for the tectonic evolution of SW Gondwana by compiling new palaeogeographic maps for the Permian–Cretaceous of the southern Atlantic area. To achieve a realistic close fit, we have devised a pre-rift proxy for the ocean–continent boundary for the South Atlantic. In order to produce the best fit, it is necessary to subdivide South America into four plates. The consequences of this are far-reaching. Our work suggests that although sedimentary basins were initiated at different times, three major tectonic phases can be recognised; in regional terms these can be thought of as pre-, syn- and post-rift.
During the pre-rift time (until the Late Triassic), the area was dominated by compressional tectonism and formed part of the Gondwana foreland. The Falkland/Malvinas Islands lay east of Africa, the Falkland/Malvinas Plateau was 33% shorter and Patagonia was displaced east with respect to the rest of South America, in part along the line of the Gastre Fault System. Potential source facies are dominantly post-glacial black shales of Late Permian age deposited in lacustrine or hyposaline marine environments; these rocks would also be an effective regional seal. Sandstones deposited in the Late Permian would be dominantly volcaniclastic with poor reservoir qualities; Triassic sandstones tend to be more mature.
There was significant extension from about 210 Ma (end-Triassic) until the South Atlantic opened at about 130 Ma (Early Cretaceous). In the early syn-rift phase, extension was accompanied by strike-slip faulting and block rotation; later extension was accompanied by extrusion of large volumes of lava. Early opening of the South Atlantic was oblique, which created basins at high angle to the trend of the ocean on the Argentine margin, and resulted in microplate rotation in NE Brazil. Intermittent physical barriers controlled deposition of Upper Jurassic–Cretaceous anoxic sediments during breakup; some of these mudrock units are effective seals with likely regional extent. During crustal reorganisation, clastic sediments changed from a uniform volcaniclastic provenance to local derivation, with variable reservoir quality.
In the late rift and early post-rift phase, continental extension changed from oblique to normal and basins developed parallel to the continental margins of the South Atlantic. This change coincides with the main rifting in the Equatorial basins of Brazil and the early impact of the Santa Helena Plume. It resulted in widespread development of unconformities, the abandonment of the Recôncavo–Tucano–Jatoba rift and the end of NE Brazil plate rotation, which remained attached to South America. There was extensive deposition of evaporites, concentrated in (but not restricted to) the area north of the Rio Grande Rise/Walvis Ridge.
Widespread deposits can be used to define potential regional elements of hydrocarbon systems and to provide a framework for relating more local elements. Our main conclusion is that the regional hydrocarbon potential of the southern South Atlantic has been constrained by the tectonic evolution.
Keller, R. A., M. R. Fisk, J. L. Smellie, J. A. Strelin, and L. A. Lawver, Geochemistry of backarc basin volcanism in Bransfleid Strait, Antarctica: Subducted contributions and along-axis variations, J. Geophys. Res., 107, 2171, 2002, 9 citations, doi:10.1029/2001JB000444, #1653
Bransfield Strait is a Quaternary, ensialic back arc basin at the transition from rifting to spreading. Fresh volcanic rocks occur on numerous submarine features distributed along the rift axis, including a discontinuous neovolcanic ridge similar to the nascent spreading centers seen in some other back arc basins. Smaller edifices near the northeast end of the rift yielded basalts with the most arc-like compositions (e.g., high large-ion lithophile element/high field strength element and 87Sr/86Sr). The most mid-ocean ridge basalt (MORB)-like basalts are from a large, caldera-topped seamount and a 30-km-long axial neovolcanic ridge toward the southwest end of the rift, but these two features also yielded andesite and rhyolite, respectively. The volcanic and geochemical variations are not systematic along axis and do not reflect the unidirectional propagation of rifting suggested by geophysical data. The most depleted basalts have major and trace element characteristics indistinguishable from MORB except for slightly higher Cs and Pb concentrations. Pb isotopic ratios show little variation compared to Sr and Nd isotopic ratios and do not extend to the depleted Pb isotopic ratios found in other back arc basins. Either the depleted mantle beneath Bransfield Strait has higher than normal Pb isotopic ratios or the subducted component beneath Bransfield Strait has such high Pb concentrations that it dominates the Pb isotopic composition of the Bransfield Strait mantle without significantly affecting the Sr and Nd isotopic compositions. Metalliferous sediments and fluids extracted from a subducting slab may have the necessary high concentrations of Pb.
Lawver, L. A., A. Grantz, and L. M. Gahagan, Plate kinematic evolution of the present Arctic region since the Ordovician, in Geology and Tectonic Development of the Bering and Chukchi Shelves and Adjacent Arctic Margins, edited by E. L. Miller, A. W. Grantz, and S. L. Kemperer, Geol. Soc. Amer. Spec. Paper, 360, 333-358, 2002, #1513
Dalziel, I. W. D., and L. A. Lawver, The lithospheric setting of the West Antarctic Ice Sheet, in The West Anarctic Ice Sheet: Behavior and Environment, edited by R. Bindschadler, Amer. Geophys. Un., Washington, D. C., Antarctic Research Ser., 77, 29-44, 2001, #1489
Muszala, S. P., P. L. Stoffa, and L. A. Lawver, An application for removing cultural nose from aeromagnetic data, Geophysics, 66, 213-219, 2001, 2 citations, doi:10:1190/1.1444897, #1515
A high-resolution aeromagnetic survey collected over the North Slope of Alaska by World Geoscience was acquired in response to a need for highly detailed data in an area where traditional geophysical techniques are expensive and prohibitive (McConnell, 1995) (Figure 1). These data were recently released to the University of Texas' Institute for Geophysics and provide a unique opportunity to investigate the problem of cultural noise suppression in aeromagnetic data. The data contain isolated magnetic anomalies that are presumably from the many drill platforms and their accompanying cultural objects such as buildings and pipe repositories (Figure 2). We present a new, automated method to reduce the amplitude of these cultural anomalies without affecting the magnetic signal from the surrounding geology.
Barker, P. F., and L. A. Lawver, Anomalous temperatures in central Scotia Sea sediments - bottom water variation or pore water circulation in old ocean crust, Geophys. Res. Lett., 27, 13-16, 2000, doi:10.1029/1999GL008381, #1495
We report low temperature gradients (from 60% to 12% of geothermal), and extrapolated temperatures offset from modern bottom water temperatures, in sediments from the central Scotia Sea. We examine possible causes, bearing in mind similar anomalous measurements 18 years previously, attributed at the time to instrumental error. Small temperature offsets (±0.1°C) may reflect short‐term bottom temperature variation within eddies of the Antarctic Circumpolar Current. Low sediment temperature gradients may be caused by horizontal advection of cold water within the upper oceanic basaltic layer (documented in younger ocean floor elsewhere), or by northward encroachment of colder bottom waters (from the Antarctic Peninsula shelf or Weddell Sea) for several years prior to measurement.
Dalziel, I. W. D., L. A. Lawver, and J. B. Murphy, Plumes, orogenesis, and supercontinental fragmentation, Earth Planet. Sci. Lett., 178, 1-11, 2000, 67 citations, doi:10.1016/S0012-821X(00)00061-3, #1496
A time–space relationship between large igneous provinces (LIPS), present day hot spots, and the fragmentation of Pangea has been documented over several decades, but the cause of fragmentation has remained elusive. LIPS are regarded either as the result of impingement of a mantle plume on the base of the lithosphere, or as the initial products of adiabatic decompression melting of anomalously hot mantle. Do LIPS therefore constitute evidence of an active role for plumes from the deep mantle in supercontinental fragmentation, or are they merely the first indications of a large-scale but near-surface tectonic process? Two long recognized and enigmatic orogenic events may offer a solution to this geologically important ‘chicken or egg’ conundrum. The reconstructed early Mesozoic Gondwanide fold belt of South America, southern Africa, and Antarctica, could have resulted from ‘plume-modified orogeny’, flattening of a downgoing lithospheric slab due to the buoyancy of a plume rising beneath a continental margin subduction zone. If so, the 180 Ma Karroo and Ferrar LIPS associated with the opening of the ocean basin between East and West Gondwanaland at 165 Ma resulted from impingement of this plume and are unrelated to the thermal insulation of the shallow mantle beneath Gondwanaland. It would then follow that the plume itself played an active, possibly critical, role in the initial breakup of the supercontinent. The Late Paleozoic ‘Ancestral Rockies’ deformation in the southwestern United States could be yet another example of orogeny driven by a plume that initiated the break-up of Pangea approximately 15 Myr earlier in the Central Atlantic region.
Kong, F. C., L. A. Lawver, and T.-Y. Lee, Evolution of the southern Taiwan-Sinzi folded zone and opening of the southern Okinawa trough, J. Asian Earth Sci., 18, 325-341, 2000, 10 citations, doi:10.1016/S1367-9120(99)00062-0, #1494
Recent interpretation of seismic sections and free-air gravity anomalies in offshore northern Taiwan reveals that the southern Taiwan–Sinzi Folded Zone began to form in late Middle Miocene, though it was mainly constructed in the Late Pliocene with strong reverse faulting and folding. Two westward progradational sequences were deposited in the shelf basin with sediments supplied from the southern Taiwan–Sinzi Folded Zone and the southern Ryukyu Arc. These two structures are displaced by several northwest-striking dextral strike–slip faults that were active in the early Quaternary when the clockwise-rotated southern Ryukyu Arc and the folded southern Taiwan–Sinzi Folded Zone were broken. It is believed that recent extension in the southern Okinawa Trough started in the early Quaternary because uplift on the southern Taiwan–Sinzi Folded Zone continued to latest Pliocene–early Quaternary. Paleogene–Miocene sediments of the East China Sea Shelf in the western part of the southern Okinawa Trough Basin are interpreted to indicate that the East China Sea Shelf Basin extended to the east of the southern Taiwan–Sinzi Folded Zone.
Ghidella, M. E., L. A. Lawver, B. J. Sloan, D. H. N. Barker, J. A. Strelin, and R. A. Keller, Extension en la cuenca de Bransfield: consideraciones basadas en batimetrÂa de multibeam, in Actas de las Cuartas Jornadas de Comunicaciones Antarticas, edited by C.A.Rinaldi, Publicación de la Direccion Nacional del Antartico, Argentina, 2, 396-404, 1999, #1453
Lawver, L. A., L. M. Gahagan, and I. W. D. Dalziel, A tight fit-Early Mesozoic Gondwana, a plate reconstruction perspective, Mem. Natl. Inst. Polar Res. Spec. Issue, 53, 214-229, 1999, #1398
Lawver, L. A., and L. M. Gahagan, Opening of Drake Passage and its impact on Cenozoic ocean circulation
, in Tectonic Boundary Conditions for Climate Reconstructions, edited by T. J. Crowley and K. C. Burke, Oxford Monographs Geol. Geophys., 39, 212-223, 1998, 110 citations, #1353
Wiens, D. A., M. E. Wysession, and L. A. Lawver, Recent oceanic interplate earthquake in Balleny Sea was largest ever detected, Eos, Trans. Amer. Geophys. Un., 79, 353-354, 1998, doi:10.1029/98EO00265, #1452
Sloan, B. J., and L. A. Lawver, Larsen Shelf, eastern Antarctic Peninsula continental margin, in Glaciated Continental Margins: An Atlas of Acoustic Images, edited by T. A. Davies, et al, Chapman and Hall, London, UK, 224-227, 1997, #1234
Klepeis, K. A., and L. A. Lawver, Tectonics of the Antarctic-Scotia plate boundary near Elephant and Clarence Islands, West Antarctica, J. Geophys. Res., 101, 20211-20231, 1996, 49 citations, #1239
Over 5000 km of new bathymetric data collected from near the northern Antarctic Peninsula (60°S–63.5°S latitude, 53.5°W–63°W longitude) show the morphology of an irregular segment of the Antarctic-Scotia plate boundary and nearby Shetland microplate. The irregular plate boundary is formed by an oblique intersection (>70°) of the sinistral transpressional Shackleton fracture zone (SFZ) and the sinistral transtensional South Scotia Ridge transform (SSR) near Elephant (EI) and Clarence (CI) Islands. Mapped boundaries of the Shetland microplate include the South Shetland Trench and the volcanic rift axis of Bransfield Strait marginal basin. Bathymetric data, single-channel seismic reflection profiles, and Geosat/ERS 1 free air gravity data show a southeast trending fault zone on the northeast side of a prominent ridge in the SFZ. The fault zone is defined by scarps that affect ocean floor sediments, fault-bounded subbasins, rotated sedimentary layers, angular unconformities, linear gravity trends, and transtensional followed by contractional deformation. Southeast of a termination of the SFZ ridge at the South Shetland Trench, the fault zone subdivides into segments displaying steep scarps (up to 23°) and canyons on the northeast margin of the EI platform. These features become east-west trending nearer to the western SSR. South of the islands, southwest trending extensional or transtensional fault zones disrupt the Bransfield Strait volcanic rift axis. These data suggest that (1) recent (<4 Ma) changes in the configuration of the Antarctic plate near the Antarctic Peninsula caused a segment of the SFZ transform to adjust to a more stable, rectilinear geometry with the SSR transform, and (2) diffuse transtension resulting from current Antarctic-Scotia relative motion is dissecting the Shetland microplate near EI and CI and transferring slivers of the Scotia plate onto the Antarctic plate.
Klinkhammer, G. P., C. S. Chin, C. R. Wilson, and L. A. Lawver, Hydrothermal and hydrographic survesy of the Bransfield Strait: Results from cruise NBP95-07, Antarctic J. of the U. S., Review, 30, 92-94, 1996, #1399
Lawver, L. A., B. J. Sloan, D. H. N. Barker, M. E. Ghidella, R. P. Von Herzen, R. A. Keller, and G. P. Klinkhammer, Distributed, active extension in Bransfield Basin, Antarctic Peninsula: Evidence from multibeam bathymetry, GSA Today, 6 (11), 1-6, 1996, 39 citations, #1235
Lawver, L. A., S. P. Srivastava, K. Fujita, D. Stone, and A. Embry, Penrose Conference report: The tectonic development of the Canada Basin and surrounding basins, GSA Today, 6 (5), 17-18, 1996, #1352
Nagihara, S., J. G. Sclater, J. D. Phillips, E. W. Behrens, T. Lewis, L. A. Lawver, Y. Nakamura, J. Garcia-Abdeslem, and A. E. Maxwell, Heat flow in the western abyssal plain of the Gulf of Mexico: Implications for thermal evolution of the old oceanic lithosphere, J. Geophys. Res., 101, 2895-2913, 1996, 8 citations, #1182
The seafloor depth of an oceanic basin reflects the average temperature of the lithosphere. Thus the western abyssal plain of the Gulf of Mexico, which has technically subsided much (> 1 km) deeper than other basins of comparable ages (late Jurassic), should be underlain by an anomalously cold lithosphere. In order to examine this hypothesis, we made suites of high-accuracy heat flow measurements at 10 sites along a line connecting Deep Sea Drilling Project (DSDP) sites 90 and 91 in the Sigsbee abyssal plain. The new heat flow sites were initially surveyed by 3.5-kHz echo sounding, 4-channel seismic reflection, seismic refraction with eight ocean bottom seismometers, and nine piston cores. We occupied a total of 48 heat flow stations along the seismic survey line (3 to 6 at each site), including 28 where we measured in situ thermal conductivities over the practical depth interval (4 m) of the new multioutrigger bow heat flow probe. We determined the heat flow associated with the lithosphere by correcting the values measured at the seafloor (41 to 45 mW/m2) for (1) the thermal effect of the sedimentation and (2) the additional heat from the radioactive elements within the sediments. The sedimentation history, required for the first, was reconstructed at each heat flow site based on ages and thicknesses of the major seismic stratigraphical sequences, age data from the DSDP cores, 3.5-kHz subbottom reflectors, and correlation of turbidite units found in the piston cores. Radiogenic heat production was measured for 55 sediment samples from four DSDP holes in the gulf, whose age ranged from present to Early Cretaceous (0.83 μW/m3 on the average). This provided the correction for the second. The effects of these two secondary factors approximately cancel one another. The lithospheric heat flow under the abyssal plain thus estimated ranges from 40 to 47 mW/m2. These heat flow values are among the lowest in the Mesozoic ocean basins where highly reliable data (45 to 55 mW/m2) have been reported. Therefore the lithosphere under the gulf seems indeed colder than that under other old ocean basins. However, it is not as cold as expected from the large tectonic subsidence. The inconsistency between the depth and heat flow may imply an anomaly in the regional thermal isostasy.
Cunningham, W. D., I. W. D. Dalziel, T.-Y. Lee, and L. A. Lawver, Southernmost South America-Antarctic Peninsula relative plate motions since 84 Ma: Implications for the tectonic evolution of the Scotia Arc region, J. Geophys. Res., 100, 8257-8266, 1995, 48 citations, #1144
We have attempted to quantify the relative motion history between southernmost South America (SSA) and the Antarctic Peninsula (AP) by calculating and comparing SSA-Africa, AP-Africa and SSA-AP synthetic flow lines for 84–0 Ma. The flow lines were created using published poles of rotation and plate reconstruction software. The results indicate that since 84 Ma, SSA and AP have moved approximately westward relative to a fixed Africa; however, SSA's rate of westerly motion in that reference frame has been significantly more rapid than AP's rate. Approximately 1320 km of east-west, left-lateral strike-slip displacement and 490 km of north-south, divergent displacement have occurred between the southern tip of SSA and the northern tip of AP since 84 Ma. Increased rates of SSA-AP interplate separation and a change in the angle of plate divergence at approximately 55–40 Ma marked the onset of accelerated continental separation that eventually led to seafloor spreading in the western Scotia Sea at 30 Ma and the development of the Scotia Arc. Increased separation rates between SSA and AP at 55–40 Ma may be related to a global Eocene plate reorganization event. The northeast-southwest oriented western Scotia Sea spreading centers appear to have accommodated all of the SSA-AP interplate motion between 30 and 9 Ma. We suggest that prior to 30 Ma and the opening of Drake Passage, components of interplate strike-slip and divergent motion were accommodated by intracontinental deformation that included strike-slip faulting, counterclockwise tectonic rotation, and continental extension in the southernmost Andes. The results indicate that the opening of the Scotia Sea was caused by plate-scale motions as SSA and AP drifted away from Africa at different velocities along different, nonparallel trajectories. Subduction retreat along the South Scotia Ridge and South Sandwich arc and back arc spreading in the Scotia Sea contributed to the width of separation between SSA and AP across Drake Passage. The results place limits on how SSA-AP relative motion has been temporally and spatially partitioned in the Scotia Arc region.
Lawver, L. A., R. A. Keller, M. R. Fisk, and J. A. Strelin, Bransfield Strait, Antarctic Peninsula: Active extension behind a dead arc, in Backarc Basins: Tectonics and Magmatism Volume, edited by B. Taylor, Plenum Press, New York, 315-342, 1995, 49 citations, #1062
Lee, T.-Y., and L. A. Lawver, Cenozoic plate reconstruction of southeast Asia, Tectonophysics, 251, 85-138, 1995, 211 citations, doi:10.1016/0040-1951(95)00023-2 , #1219
The India-Eurasia collision alone set up a series of chain reactions and caused the formation and destruction of sedimentary basins within the domain of the collision belt. Changes in the rate and angle of convergence between the India and Eurasia plates reflect different stages of tectonic development in Southeast Asia. For example, extrusion of the Indochina block induced the consumption of the pre-existing proto-South China Sea along northeastern Kalimantan and led to the eventual opening of the South China Sea along the South China margin. Subsequent motions of the Sino-Burma-Thailand, Malay Peninsula, Sumatra, and Kalimantan blocks have produced a succession of basins stretching from north Sumatra to central Thailand and on to the Natuna area.
We present reconstructions of the Southeast Asia region at 60 Ma, 50 Ma, 40 Ma, 30 Ma, 20 Ma, 15 Ma, 10 Ma, and 5 Ma. It is clear, from the reconstructions, that the impact between Greater India and Southeast Asia took place in the northwestern part of Southeast Asia. The duration for the impact was probably from the Middle Eocene to Early Miocene. This timing is in good agreement with the dating of the main Red River Fault motion (Wu et al., 1989; Schärer et al., 1990). Since the impact between Greater India and Southeast Asia was basically west of the Burma block, there is no reason to assume that the Sumatra, Malay Peninsula, and Kalimantan should extrude to the southeast first along the left-laterally displaced Mae Ping and Three Pagodas fault zones as suggested by Peltzer and Tapponnier (1988). If the opening of the central Thailand basins, the Gulf of Thailand, and the Malay Basin are taken into consideration, a dextral megashear zone is required to compensate the relative motion between Indochina and the Malay Peninsula. This dextral megashear zone might even extend into western Kalimantan and serve as a boundary between the Indochina block and Kalimantan.
Sloan, B. J., L. A. Lawver, and J. B. Anderson, Seismic stratigraphy of the Larsen Basin, eastern Antarctic Peninsula, in Geology and Seismic Stratigraphy of the Antarctic Margin, edited by A. K. Cooper, P. F. Barker, and G. Brancolini, Antarctic Research Series, 68, 59-74, 1995, #1166
Lawver, L. A., and R. D. Muller, Iceland hotspot track, Geology, 22, 311-314, 1994, 126 citations, doi:10.1130/0091-7613(1994)022<0311:IHT>2.3.CO;2, #1015
We use a model of plate motions relative to major hotspots underneath the African, Indian, North American, South American, and Australian plates to compute the track of the Iceland hotspot after 130 Ma. The present-day hotspot is located under eastern Iceland offset about 240 km east of the Reykjanes and Kolbeinsey ridges. At 40 Ma, the Kangerlussuaq region of East Greenland would have been directly above the hotspot. The anomalous postdrift uplift of the East Greenland margin can also be explained by passage of the rifted margin over a hotspot. At 60 Ma, the Umanak Fjord region of the west coast of Greenland was above the hotspot, where picrites and hyaloclastites of nearby Disko Island are dated at ∼64 to 59 Ma. Our reconstruction shows Ellesmere Island above the hotspot between 130 and 100 Ma. Latest Albian to early Cenomanian volcanic rocks on Axel Heiberg Island and northern Ellesmere Island indicate a nearby hotspot at that time. At 130 Ma, our model locates the hotspot near the northern margin of Ellesmere Island, close to the intersection of the Alpha Ridge with the coast. The hotspot would have been located beneath the Arctic Alaska-Chukotka plate when it formed the Mendeleyev Ridge, and as the spreading center migrated over the hotspot, it transferred to the North American plate, where it formed the Alpha Ridge. Our model suggests that the initiation of the Iceland hotspot predates the opening of the North Atlantic by at least 70 m.y. and that the massive early Tertiary volcanism along the North Atlantic plate margins reflects the effect of rifting in the vicinity of existing thinned crust, rather than the arrival of a plume head.
Lawver, L. A., T. Williams, and B. J. Sloan, Seismic stratigraphy and heat flow of Powell Basin, Terra Antartica, 1, 309-310, 1994, #1111
Lawver, L. A., L. M. Gahagan, and A. K. Cooper, Comparison of eastern Ross Sea with Campbell Basin, Terra Antartica, 1, 375-377, 1994, #1112
Lawver, L. A., and L. M. Gahagan, Constraints on timing of extension in the Ross Sea region, Terra Antartica, 1, 545-552, 1994, #1351
Lee, T.-Y., and L. A. Lawver, Cenozoic plate reconstruction of the South China Sea region, Tectonophysics, 235, 149-180, 1994, 55 citations, doi:10.1016/0040-1951(94)90022-1, #870
Reconstructions of the South China Sea region at 60 Ma, 40 Ma, 30 Ma, 20 Ma, 10 Ma and 5 Ma are presented. We have attempted to place the South China Sea Basin in a regional tectonic framework. The tectonic evolution of the major blocks surrounding the South China Sea were analyzed, as well as the relative motions of the Indian and Australian plates. We have tried to correct the tectonic models available in this region. A 3-D graphics terminal was used to derive rotation poles for the different tectonic blocks and our model was then tested to determine its self-consistency. When the model conflicted with previous interpretations the input data were evaluated for alternative explanations.
At least two, and possibly three, stages of extension can be recognized in this region. The earliest one, active in the Late Cretaceous to Eocene, involved NW-SE extension. The second one, active from the Late Eocene to Early Miocene involved north-south extension. The third stage of extension, which probably trended NW-SE, can be dated as post-Oligocene. The first extensional event produced the NE-SW trending proto-South China Sea and a series of sedimentary basins along the South China margin. Following the southeastward extrusion of Indochina, the proto-South China Sea was mostly consumed at the Palawan Trough. Renewed north-south extension in the South China continental margin started the present-day South China Sea spreading in the Oligocene. The southeastward extrusion of Indochina, blocked by Sundaland, resulted in the NW-SE trending opening of the South China Sea Basin in the Early Miocene. Collision of the North Palawan microcontinental block with the West Philippines block stopped the opening of the South China Sea at the end of Early Miocene. Spreading activity switched to the Sulu Sea Basin in the Middle Miocene but collision between the Sulu Ridge and the West Philippines at Mindanao halted the opening of the Sulu Sea at the end of the Middle Miocene. In the Late Miocene, Greater India continued its northward path and seems to have ripped open the Andaman Sea. In the Pliocene, subduction along the northern Manila Trench placed the North Luzon Arc on a collision path with the East Asia continental margin at Taiwan.
Our reconstructions, along with detailed geological and geophysical information, may be used as a predictive tool for basin evolution models and block interactions in this region. The development of the South China Sea Basin, the Gulf of Thailand, the Malay Basin and the central Thailand basins are the result of collision-induced extensional forces. The Sulu, Celebes and Sumatra basins were formed as a consequence of prolonged subduction. The opening of the Pearl River Mouth, West Natuna, South China Sea, Sulu, and possibly Celebes, basins were terminated by various plate collisions. During the course of plate reorganizations major boundary faults have changed their slip senses during different stages of evolution.
Muller, R. D., J.-Y. Royer, and L. A. Lawver, Reply, to comment on "Revised plate motions relative to the hotspots from combined Atlantic and Indian Ocean hotspot tracks", Geology, 22, 277-278, 1994, 4 citations, doi:10.1130/0091-7613(1994)022<0276:RPMRTT>2.3.CO;2, #1056
Sloan, B. J., J. B. Anderson, and L. A. Lawver, Seismic stratigraphy of the Larsen Basin, eastern Antarctic Peninsula, Terra Antartica, 1, 281-282, 1994, #1110
Keller, R. A., J. A. Strelin, L. A. Lawver, and M. R. Fisk, Dredging young volcanic rocks in Bransfield Strait, Antarctic J. of the U. S., Review, 28, 98-100, 1993, #1258
Klepeis, K. A., and L. A. Lawver, Bathymetry of the Bransfield Straight, southeastern Shackleton fracture zone and South Shetland Trench, Antactica, Antarctic J. of the U. S., Review, 28, 103-104, 1993, #1259
Lawver, L. A., and L. M. Gahagan, Subduction zones, magmatism, and the breakup of Pangea, in Flow and Creep in the Solar System: Observations, Modeling and Theory, edited by D. B. Stone and S. K. Runcorn, NATO meeting/NATO ASI ser., 139, Kluwer Academic, 225-247, 1993, #903
Lawver, L. A., I. W. D. Dalziel, and D. T. Sandwell, Antarctic plate: Tectonics from a gravity anomaly and infrared satellite image, GSA Today, 3 (5), 117-122, 1993, #992
Lawver, L. A., R/V Nathaniel B. Palmer NBP93-1 survey of the Antarctic Peninsula and Powell Basin, Antarctic J. of the U. S., Review, 28, 105-106, 1993, #1260
Muller, R. D., J.-Y. Royer, and L. A. Lawver, Revised plane motions relative to the hotspots from combined Atlantic and Indian Ocean hotspot tracks, Geology, 21, 275-278, 1993, 271 citations, doi:10.1130/0091-7613(1993)021<0275:RPMRTT>2.3.CO;2, #931
We use an updated model for global relative plate motions during the past 130 m.y. together with a compilation of bathymetry and recently published radiometric dates of major hotspot tracks to derive a plate-motion model relative to major hotspots in the Atlantic and Indian oceans. Interactive computer graphics were used to find the best fit of dated hotspot tracks on the Australian, Indian, African, and North and South American plates relative to present-day hotspots assumed fixed in the mantle. One set of rotation parameters can be found that satisfies all data constraints back to chron 34 (84 Ma) and supports little motion between the major hotspots in this hemisphere. For times between 130 and 84 Ma, the plate model is based solely on the trails of the Tristan da Cunha and Great Meteor hotspots. This approach results in a location of the Kerguelen hotspot distinct from and south of the Rajmahal Traps for this time interval. Between 115 and 105 Ma, our model locates the hotspot underneath the southern Kerguelen Plateau, which is compatible with an age estimate of this part of the plateau of 115-95 Ma. Our model suggests that the 85°E ridge between lat 10°N and the Afanasiy Nikitin seamounts may have been formed by a hotspot now located underneath the eastern Conrad rise.
Nagihara, S., J. G. Sclater, J. D. Phillips, E. W. Behrens, L. A. Lawver, Y. Nakamura, A. E. Maxwell, T. Lewis, and J. Garcia, Heat flow in the western abyssal plain of the Gulf of Mexico: Implications for thermal evolution of the old oceanic crust, SIO Tech. Rep., Scripps Inst. of Oceanography, 45 pp., 1993, #1305
Sloan, B. J., and L. A. Lawver, R/V Nathaniel B. Palmer NBP93-1 cruise to the Larsen Shelf region of the Antarctic Peninsula, Antarctic J. of the U. S., Review, 28, 107-108, 1993, #1261
Della Vedova, B., G. Pellis, L. A. Lawver, and G. Brancolini, Heat flow and tectonics of the western Ross Sea, Recent Progress in Earth Science, edited by Y. Yoshida, Terra Scientific Publishing Co., 627-637, 1992, #904
Lawver, L. A., L. M. Gahagan, and M. F. Coffin, The development of paleoseaways around Antarctica, in The Antarctic Paleoenvironment: A Perspective on Global Change, edited by J. P. Kennett and D. A. Warnke, Amer. Geophys. Un., Antarctic Res. Series, 56, 7-30, 1992, 205 citations, #902
Lawver, L. A., M. F. Coffin, and L. M. Gahagan, The Mesozoic break-up of Gondwana, in First Indian Ocean Petroleum Seminar, edited by P. S. Plummer, U. N. Dept. of Technical Cooperation for Development, 345-356, 1992, #935
Lee, T.-Y., and L. A. Lawver, Tectonic evolution of the South China Sea region, J. Geol. Soc. China, 35, 353-388, 1992, #825
Nagihara, S., J. G. Sclater, L. M. Beckley, E. W. Behrens, and L. A. Lawver, High heat flow anomalies over salt structures on the Texas continental slope, Gulf of Mexico, Geophys. Res. Lett., 19, 1687-1690, 1992, 11 citations, #910
We made 74 closely spaced (< 2 km apart) heat flow measurements around and over two salt structures on the Texas continental slope, Gulf of Mexico. The values outlined the shape of the heat flow anomalies over both structures. Based on a preceding high resolution seismic survey, we interpreted these structures to be a cylindrical plug and a salt tongue extending from the crest of a wall‐shaped feeder. The heat flow observations clearly reflect differences between the two features and are consistent with the prior structural interpretation. The values over the salt plug are nearly all greater than 70 mW/m². The measurements over the salt tongue have a sharp heat flow peak of 90 mW/m² associated with the presumed feeder and rather uniform values around 60 mW/m² over the remainder. The variation of heat flow over both structures is smooth and shows no apparent scatter. Heat flow values off these features are uniformly low, around 30 mW/m². Thermal effects from bottom water temperature fluctuation, slope sedimentation, diapiric movement of the salt body, and pore fluid migration appear unable to provide a satisfactory explanation for the observations. However, thickness variations of a highly conductive salt body can easily account for the heat flow anomalies. We suggest that modeling of the conductive anomaly should provide substantial constraints on the bottom geometry of the salt.
Sandwell, D. T., L. A. Lawver, I. W. D. Dalziel, W. H. F. Smith, and M. Wiederspahn, Antarctica: Gravity Anomaly and Infrared Satellite Image, (map), Scripps Inst. Oceanography and Inst. for Geophys., Univ. Texas, 1992, #962
Jeffers, J. D., J. B. Anderson, and L. A. Lawver, Evolution of the Bransfield Basin, Antarctic Peninsula, in Antarctic Earth Science, edited by M. R. A. Thompson, J. Thompson, and J. A. Crane, Cambridge Univ., 481-486, 1991, #842
Lawver, L. A., J.-Y. Royer, D. T. Sandwell, and C. R. Scotese, Crustal development: Gondwana break-up - Evolution of the Antarctic continental margins, in Geological Evolution of Antarctica, edited by M. R. A. Thompson, J. A. Crame, and J. Thompson, Cambridge Univ., 533-540, 1991, 57 citations, #742
Lawver, L. A., B. Della Vedova, and R. P. Von Herzen, Heat flow in Jane Basin, northwest Weddell Sea, J. Geophys. Res., 96, 2019-2038, 1991, 11 citations, #766
The Jane Basin is a marginal basin situated immediately to the east of the South Orkney microcontinent in the Northwest section of the Weddell Sea. Thirty-five heat flow measurements made in the Jane Basin ranged in value from 67.5±4.3 to 92.1±3.0 mW/m2. Excluding values that were corrected for tilting or were on the very edge of the basin, the remaining 28 values range between 75.0±8.0 and 84.6±9.1 mW/m2. Magnetostratigraphy on the recovered core from Ocean Drilling Program hole 697, which was drilled in Jane Basin to a depth of 322 m, allowed sedimentation rates to be calculated back to 4.5 Ma. Single-channel seismic reflection data from RSS Shackleton allowed estimations of total sediment thickness for the Jane Basin to be made. We calculate that the measured heat flow is only 86–89% of the actual heat flow as a result of sedimentation. Heat generation in the sediments contributes 1.5–1.9 mW/m2to the total heat flow. The corrected heat flow gives an age for the Jane Basin of between 25 and 32 Ma from age-versus-heat flow comparisons, similar to the age determined from basement depth. The Scotia Sea, located to the north of Jane Basin and the South Orkney microcontinent, has been dated as anomaly 10 (30 Ma) and younger. Our calculated age for the Jane Basin would indicate that it may have been created prior to the initiation of seafloor spreading in the Scotia Sea. Evidence from major plate motions indicate that Antarctica began to rotate clockwise away from South America at about 65 Ma. Such motion may have triggered subduction along the southeast side of Jane Bank and the opening of Jane Basin as a back arc basin. Subduction at Jane Bank ended at anomaly 6A time (22 Ma) as evidenced by the age of the identified magnetic anomalies on the Antarctic plate found immediately to the east of Jane Bank. We conclude that Jane Basin opened prior to the opening of the Scotia Sea and that the spreading center that opened Jane Basin may have jumped to the Scotia Sea and produced the seafloor spreading there.
Grantz, A., S. D. May, P. T. Taylor, and L. A. Lawver, Canada basin, in Geology of North American, Vol. L: The Arctic Ocean Region, edited by A. Grantz, L. Johnson, and J. F. Sweeney, Geol. Soc. Amer., 379-402, 1990, #679
Lawver, L. A., and C. R. Scotese, A review of tectonic models for the evolution of the Canada basin, in Geology of North America, Vol. L: Arctic Ocean Region, edited by A. Grantz, L. Johnson, J. F. Sweeney, Geol. Soc. Amer., 593-618, 1990, 47 citations, #718
Lawver, L. A., R. D. Muller, S. P. Srivastava, and W. R. Roest, The opening of the Arctic Ocean, in Geological History of the Polar Oceans: Arctic Versus Antarctic, edited by U. Bleil and J. Thiede, 29-62, 1990, #761
Mayes, C. L., L. A. Lawver, and D. T. Sandwell, Tectonic history and new isochron chart of the South Pacific, J. Geophys. Res., 95, 8543-8567, 1990, 138 citations, #794
We have developed an internally consistent isochron chart and a tectonic history of the South Pacific using a combination of new satellite altimeter data and shipboard magnetic and bathymetric data. Highly accurate, vertical deflection profiles (1–2 μrad), derived from 22 repeat cycles of Geosat altimetry, reveal subtle lineations in the gravity field associated with the South Pacific fracture zones. These fracture zone lineations are correlated with sparse shipboard bathymetric identifications of fracture zones and thus can be used to determine paleospreading directions in uncharted areas. The high density of Geosat altimeter profiles reveals previously unknown details in paleospreading directions on all of the major plates. Magnetic anomaly identifications and magnetic lineation interpretations from published sources were combined with these fracture zone lineations to produce a tectonic fabric map. The tectonic fabric was then used to derive new poles of rotation for 12 selected times in the Late Cretaceous and Cenozoic. From our reconstructions, we estimated the former location of the spreading centers in order to derive a new set of isochrons (interpreted unes of equal age on the ocean floor). We believe that the use of new Geosat altimeter data in combination with a multi-plate reconstruction has led to an improvement in our understanding of South Pacific tectonics.
Royer, J.-Y., L. M. Gahagan, L. A. Lawver, C. L. Mayes, D. Nurnberg, D. T. Sandwell, and C. R. Scotese, A tectonic chart for the southern ocean derived from GEOSAT altimetry data, in Antarctica as an Exploration Frontier - Hydrocarbon Potential, Geology and Hazards, edited by B. St. John, Amer. Assn. Petrol. Geol. Studies in Geol., 31, 89-100, 1990, #765
Klepeis, K. A., L. A. Lawver, D. T. Sandwell, and C. Small, The morphology and tectonic structure of the Shackleton fracture zone, Antarctic J. of the U. S., Review, 24 (5), 126-128, 1989, #797
Lawver, L. A., and H. Villinger, North Bransfield Basin: R/V Polar Duke cruise PD VI-88, Antarctic J. of the U. S., Review, 24 (5), 117-120, 1989, #796
Nagihara, S., and L. A. Lawver, Heat-flow measurements in the King George Basin, Bransfield Strait, Antarctic J. of the U. S., Review, 24 (5), 123-125, 1989, #795
Barker, P. F., and L. A. Lawver, South American-Antarctic plate motion over the past 50 My, and the evolution of the South American - Antarctic Ridge, Geophysical J., 94, 377-386, 1988, 37 citations, doi:10.1111/j.1365-246X.1988.tb02261.x, #746
Magnetic and bathymetric data from the South American-Antarctic plate boundary east of the South Sandwich trench have been interpreted to produce ocean floor ages, spreading rates and directions. SAM-ANT motion over the past 50 Myr has been slow (10-15 mm yr-1 half rates). About 20 Ma the spreading direction changed from 120°-300° to the present E-W. These results have been combined with similar data from the South Atlantic and Southwest Indian Oceans to calculate six poles and rates of SAM-ANT motion covering the past 50 Myr. The change at 20 Ma appears to have originated the long-offset Bullard and South Sandwich fracture zones. The change may have been facilitated, or even triggered, by ridge crest-trench collision along the South Scotia Ridge, east of the South Orkney Islands. This event however, could not alone have caused a stable change. It is concluded that the global balance of forces may for long periods be imperfectly reflected in plate motions, because of the constraining effects of long fracture zone offsets on the directions of plate motion, and that the 'causes' of abrupt changes in direction may precede them by several million years.
Gahagan, L. M., C. R. Scotese, J.-Y. Royer, D. T. Sandwell, J. K. Winn, R. L. Tomlins, M. I. Ross, J. S. Newman, R. D. Muller, C. L. Mayes, L. A. Lawver, and C. E. Heubeck, Tectonic fabric map of the ocean basins from satellite altimetry data, Tectonophysics, 155, 1-26, 1988, 33 citations, doi:10.1016/0040-1951(88)90258-2, #736
Satellite altimetry data provide a new source of information on the bathymetry of the ocean floor. The tectonic fabric of the oceans (i.e., the arrangement of fracture zones, ridges, volcanic plateaus and trenches) is revealed by changes in the horizontal gravity gradient as recorded by satellite altimetry measurements. SEASAT and GEOSAT altimetry data have been analyzed and a global map of the horizontal gravity gradient has been produced that can be used to identify a variety of marine tectonic features. The uniformity of the satellite coverage provides greater resolution and continuity than maps based solely on ship-track data. This map is also the first global map to incorporate the results of the GEOSAT mission, and as a result, new tectonic features are revealed at high southerly latitudes.
This map permits the extension of many tectonic features well beyond what was previously known. For instance, various fracture zones, such as the Ascension, Tasman, and Udintsev fracture zones, can be extended much closer to adjacent coninental margins. The tectonic fabric map also reveals many features that have not been previously mapped. These features include extinct ridges, minor fracture zone lineations and seamounts. In several areas, especially across aseismic plateaus or along the margins of the continents, the map displays broad gravity anomalies whose origin may be related to basement structures.
Lawver, L. A., and M. J. Lonsdale, Underway geophysics during Leg 113, Proc. Ocean Drilling Prog., Init. Rept., 113, 33-76, 1988, #756
Blackman, D. K., R. P. Von Herzen, and L. A. Lawver, Heat flow and tectonics in the western Ross Sea, Antarctica, in The Antarctic Continental Margin: Geology and Geophysics of the Western Ross Sea, edited by A. K. Cooper and F. J. Davey, CPCEMR Earth Sci. Ser., Circum-Pacific Council for Energy & Mineral Resources, 5B, 179-189, 1987, #701
Lachenbruch, A. H., J. H. Sass, L. A. Lawver, and M. C. Brewer, Temperature and depth of permafrost on the Alaskan Arctic slope, in Alaskan North Slope Geology, edited by I. Tailleur and P. Weimer, Soc. Econ. Paleont. Mineral., Pacific Sect. & Alaskan Geol. Soc., 2, 545-558, 1987, #721
Lawver, L. A., and C. R. Scotese, A revised reconstruction of Gondwanaland, in Gondwana Six: Structure, Tectonics and Geophysics, edited by G. D. MacKenzie, Amer. Geophys. Union/Geol. Soc. Amer., 17-23, 1987, 136 citations, #666
Lawver, L. A., and P. T. Taylor, Heat flow off Sumatra, in Marine Geophysics: A Navy Symposium, edited by E. N. Shor and C. L. Ebrahimi, 67-76, 1987, #716
Lawver, L. A., J. G. Sclater, and L. Meinke, Mesozoic and Cenozoic reconstructions of the South Atlantic, Tectonophysics, 114, 233-254, 1985, 59 citations, doi:10.1016/0040-1951(85)90015-0, #632
The movement of Antarctica with respect to South America has a number of implications for paleocirculation as well as for the reconstructions of Gondwanaland. Recent papers on the Southwest Indian Ridge have published new or revised poles of opening for Africa and Antarctica which can be combined with the poles of opening between South America and Africa to give resultant motions between South America and Antarctica.
The first indication of a complete closure between South America and the Antarctic Peninsula is at anomaly 28 time (64 Ma) as the two continents are now configured. Between anomaly 28 time (64 Ma) and anomaly M0 time (119 Ma) the amount of closure does not change greatly, and the small computed overlap can be explained by minor uncertainties in the rotation poles used for the reconstructions or some slight extension between East and West Antarctica. By 135 Ma some rotation or translation of the Antarctic Peninsula with respect to East Antarctica must be postulated in addition to any presumed extension between East and West Antarctica in order to avoid an overlap of South America with the Antarctic Peninsula.
Having determined what we feel to be a viable reconstruction of Western Gondwanaland and holding South America fixed, we rotated Africa and Antarctica, with respect to South America, for eight different times during the past. Africa moved away from South America in a more or less consistent manner throughout the time period, closure to present, while Antarctica moved away from Africa in a consistent manner only between 160 Ma and 64 Ma. At 64 Ma its motion changed abruptly: it slowed its north-south motion with respect to Africa and began slow east-west extension with respect to South America. This change supports the hypothesis that a major reorganization of the triple junction between Africa, Antarctica and South America occurred between 60 and 65 Ma. The triple junction changed from ridge-ridge-ridge to ridge-fault-fault at the time of the major westward jump of the Mid-Atlantic Ridge just south of the Falkland-Agulhas Fracture Zone.
The Mesozoic opening of the Somali Basin moved Madagascar from its presumed original position with Africa in Gondwanaland. The closure of Sri Lanka with India produces a unique fit for India and Sri Lanka with respect to Africa, Madagascar and Antarctica. This fit juxtaposes geological localities in Southeast India against similar localities in Enderhy Land. East Antarctica. The late Jurassic opening in the Somali Basin is tied to opening of the same age in the Mozambique Basin. Since this late Jurassic movement represents the initial break-up of Gondwanaland, it is assumed that similar movement must have occurred in what is now the western Weddell Sea and may also explain the opening evidenced by the Rocas Verdes region of southern South America.
Lawver, L. A., H. W. Bergh, and P. F. Barker, Evolution of the far South Atlantic during the Late Cretaceous, Antarctic J. of the U. S., Review, 20 (5), 88-90, 1985, #755
Lawver, L. A., B. Della Vedova, and R. P. Von Herzen, Heat-flow measurements in the Jane Basin; a back-arc basin, in northern Weddell Sea, Antarctic J. of the U. S., Review, 20 (5), 87-88, 1985, #1010
Sass, J. H., L. A. Lawver, and R. J. Munroe, A heat-flow reconnaissance of southeastern Alaska, Canadian J. Earth. Sci., 22, 416-421, 1985, 4 citations, doi:10.1139/e85-040, #633
Heat flow was measured at nine sites in crystalline and sedimentary rocks of southeastern Alaska. Seven of the sites, located between 115 and 155 km landward of the Queen Charlotte – Fairweather transform fault, have an average heat flow of 59 ± 6 mW m−2. This value is significantly higher than the mean of 42 mW m−2 in the coastal provinces between Cape Mendocino and the Queen Charlotte Islands, to the south, and is lower than the mean of 72 ± 2 mW m−2 for 81 values within 100 km of the San Andreas transform fault, even farther south. This intermediate value suggests the absence of significant heat sinks associated with Cenozoic subduction and of heat sources related to either late Cenozoic tectono-magmatic events or significant shear-strain heating. At Warm Springs Bay, 75 km from the plate boundary, an anomalously high heat flow of 150 mW m−2 can most plausibly be ascribed to the thermal spring activity from which its name is derived. At Quartz Hill, 240 km landward of the plate boundary, a value of 115 mW m−2 might indicate a transition to a province of high heat flow resulting from late Tertiary and Quaternary extension and volcanism.
Lawver, L. A., L. Meinke, and J. G. Sclater, Reconstructions of the South Atlantic, Antarctic J. of the U. S., Review, 18 (5), 142-145, 1983, #643