- Email: [email protected]
Comments about the age of the Canada Basin
OLR (1985)32 (12)
D. SubmarineGeologyand Geophysics
deformed trench fill bounded by landward dipping thrust faults, separated by a d6collement surface from an underlying ~ l - k m - t h i c k unit of nearly undeformed trench fill, which along with oceanic lithosphere is being underthrust to act as a buffer between offscraped sediment and oceanic basement. USGS, 345 Middlefield Rd., Menlo Park, CA 94025, USA. (hbf)
85:7155 McGinnis, L.D., R.H. Bowen, J.M. Erickson, B.J. Allred and J.L. Kreamer, 1985. East-west Antarctic boundary in McMurdo Sound. Tectonophysics, 114(1-4):341-356. Western McMurdo Sound is capped by a thin veneer of layered reflectors. The absence of deep, layered reflectors suggests the crust is made up primarily of intrusions associated with plutons generated during the Ross Orogeny. Reflection data support earlier interpretations that indicate fundamental differences in the crust beneath McMurdo Sound and the Transantarctic Mountains, perhaps due to Early Paleozoic subduction of the Ross Embayment crust beneath the Transantarctic Mountains. Orogeny has produced an over-thickened crust beneath the Ross orogenic belt which was followed by several periods of reactivation including the Jurassic thermal event and the Early Tertiary uplift of the Transantarctic Mountains. Presence of the McMurdo Volcanics and preliminary data interpretations suggest that the sound is now being thinned by extension. Dept. of Geol., Louisiana State Univ., Baton Rouge, LA 70803-4101, USA.
85:7156 Rangin, C., J.F. Stephan and C. MUller, 1985. Middle Oligocene oceanic crust of South China Sea jammed into Mindoro collision zone (Philippines). Geology, geol. Soc. Am., 13(6):425-428. A summary is provided of the Cenozoic evolution of Mindoro, an island south of Luzon, located at the 'complex junction between the Manila Trench and the collision zone of the North Palawan block with the western Philippines mobile belt.' The age equivalence of Amnay ophiolites and the oldest Middle Oligocene magnetic anomalies of the South China Sea Basin is cited as evidence that the ophiolites may be a piece of South China oceanic crust rotated 20 ° counterclockwise and caught between the San Jose-North Palawan block and the Mindoro-Luzon basement. LA 215, CNRS, 4 ave de Bois Preau, 92506 Rueil-Malmaison Cedex, France. (hbf)
1029
85:7157 Srivastava, S.P., 1985. Evolution of the Eurasian Basin and its implications to the motion of Greenland along Nares Strait. Tectonophysics, ! 14(1-4):29-53. Analysis shows that the Eurasian Basin and Norwegian-Greenland Sea started to evolve at about anomaly 25 time, though active seafloor spreading did not start until anomaly 24 time. Spreading in the Eurasian Basin has been a result of motion only between the North American and Eurasian plates since the beginning, with the Lomonosov Ridge remaining attached to the North American Plate. From Late Cretaceous to Late Paleocene, Greenland moved obliquely to Ellesmere Island; most of this motion was taken up within the Canadian Arctic Islands resulting in little or no motion along Nares Strait. From anomaly 25-21 Greenland continued to move obliquely, resulting in a displacement of 125 km along and of 90 km normal to the Nares Strait. From Mid-Eocene to Early Oligocene another 100 km of motion took place normal to the Strait. Atlantic Geosci. Centre, Bedford Inst. of Oceanogr., Dartmouth, NS B2Y 4A2, Canada. 85:7158 Stagg, H.M.J., 1985. The structure and origin of Prydz Bay and MacRobertson Shelf, East Antarctica. Tectonophysics, 114(l-4): 315 -340. Multichannel seismic and magnetic data indicate that much of Prydz Bay is underlain by a sedimentary basin that is at least 5 km thick and probably represents a failed rift. The sediments are little disturbed by folding and faulting and contain three major unconformities of Triassic-Early Jurassic, Early Cretaceous, and Mid-Miocene-Early Pliocene age. These probably represent rift onset, margin breakup, and glacial advances, respectively. Bur. of Mineral Res., P.O. Box 378, Canberra City, ACT 2601, Australia. (amt) 85:7159 Sweeney, J.F., 1985. Comments about the age of the Canada Basin. Tectonophysics, 114(1-4): 1-10. The Canada Basin appears to have formed over a 60 Ma interval during the Cretaceous period. Continental breakup was widespread ~131 113 Mya along what was to become the polar margin of North America, and seafloor formation was active during an extended Cretaceous interval ~118-79 Mya. Data indicate that all parts of the North American polar margin could have formed at about the same time. Relatively less/slower stretching occurred along the segment southwest of Brock Island and relatively more/faster stretching took place along the
1030
D. SubmarineGeologyand Geophysics
segment to the northeast during margin formation. Pacific Geosci. Centre, Dept. of Energy, Mines and Res., Box 6000, Sidney, BC V8L 4B2, Canada.
D250. Plate and global tectonics 85:7160 Hynes, A. and J. Mott, 1985. On the causes of bagk-are spreading. Geology, geol. Soc. Am., 13(6):387-389.
The characteristics of plate motion within the actively spreading Lau Basin-Havre Trough and Mariana Trough are reviewed in an effort to evaluate the relative importance of several proposed plate-kinematic mechanism theories tied to motions of the upper plate and lower plate and changes in the profile of the lower plate. It is concluded that adjustment of the descending slab dip as a result of changes in subduction rate provides an 'attractive explanation' for trench migration and the recent onset of spreading behind the two arcs and for the fact that spreading in the Lau Basin outpaces spreading in the Havre Trough. Dept. of Geol. Sci., McGill Univ., Montreal, H3A 2A7, Canada. (hbf) 85:7161 Lawver, L.A., J.G. Sclater and Linda Meinke, 1985. Mesozoic and Cenozoic reconstructions of the South Atlantic. Tectonophysics, 114(1-4): 233 - 254. Recently published poles of rotation used to reconstruct the configurations of Antarctica, Africa and South America with respect to each other indicate that the opening between the Antarctic Peninsula and the tip of South America began before 35 Ma and that the peninsula moved away from South America at least 10 Ma before the opening of Drake's Passage, if there was no movement between East and West Antarctica at that time. Results also support the hypothesis that the triple junction between Africa, Antarctica and South America underwent a major reorganization 60-65 Ma, changing from ridge-ridge-ridge to ridge-fault-fault. Madagascar, India, Sri Lanka and the Somali Basin are also discussed. Inst. for Geophys., Univ. of Texas, Austin, TX 78751, USA. (msg) 85:7162 Mutter, J.C., 1985. Seaward dipping reflectors and the eontinent~ boundary at passive ~ t a l nmr~ns. Tectonophysics, 114(1-4):117-131. Multichannel seismic reflection profiles on many passive margins have revealed the presence of remarkable suites of arcuate reflectors, dipping
OLR(1985)32 (12)
seaward to form a wedge-shaped structure. Their general characteristics and velocity structure suggest they may be largely volcanic, but there is no agreed upon model for their origin. Nevertheless it is generally thought that they lie at or close to the boundary between continent and ocean, and as such they are extremely important structural markers that may yield important evidence concerning the structure and evolution of passive margins. LamontDoherty Geol. Observ., Palisades, NY 10964, USA. 85:7163 Mutter, J.C., K.A. Hegarty, S.C. Cande and J.K. Weissel, 1985. Breakup between Australia and Antarctica: a brief review in the light of new data. Tectonophysics, 114(1-4):255-279. The age of breakup was revised from anomaly 22 time to anomaly 34 time. The reconstruction of Broken Ridge and Kerguelen Plateau at anomaly 34 time shows overlap of these two features, but the problem is nearly resolved by anomaly 18 time. Subsidence patterns are interpreted as more consistent with the revised age of Australia-Antarctic breakup. Rapid subsidence was associated with the rift phase of margin development followed by much slower thermally-controlled subsidence during the drift phase, the transition coinciding with the age of breakup ( ~ 6 0 to 110 MyBP). Subsidence curves indicate a west-to-east propagation of breakup along the southern margin, consistent with magnetic anomaly patterns and stratigraphic observations. Lamont-Doherty Geol. Observ., Palisades, NY 10964, USA.
D280. Volcanism, magmatism 85:7164 Fornari, D.J., W.B.F. Ryan and P.J. Fox, 1985. Sea-floor lava fields on the East Pacific Rise. Geology, geol. Soe. Am., 13(6):413-416. SeaBeam and SeaMARC I data west of the East Pacific Rise define a relatively young submarine lava field, which extends over the faulted, eroded flanks of the EPR and laps up against the base of a large seamount with a large caldera. It is suggested that the lava field was produced by seamount magma, which flowed along pre-existing faults, draining shallow magma chambers beneath the seamount, deflating its summit and leaving the caldera. Lamont-Doherty Geol. Observ., Palisades, NY 10964, USA. (hbf) 85:7165 Fujii, Toshitsugu and C.M. Scarfe, 1985. Composition of liquids coexisting with spinel lherzoHte at
D. SubmarineGeologyand Geophysics
deformed trench fill bounded by landward dipping thrust faults, separated by a d6collement surface from an underlying ~ l - k m - t h i c k unit of nearly undeformed trench fill, which along with oceanic lithosphere is being underthrust to act as a buffer between offscraped sediment and oceanic basement. USGS, 345 Middlefield Rd., Menlo Park, CA 94025, USA. (hbf)
85:7155 McGinnis, L.D., R.H. Bowen, J.M. Erickson, B.J. Allred and J.L. Kreamer, 1985. East-west Antarctic boundary in McMurdo Sound. Tectonophysics, 114(1-4):341-356. Western McMurdo Sound is capped by a thin veneer of layered reflectors. The absence of deep, layered reflectors suggests the crust is made up primarily of intrusions associated with plutons generated during the Ross Orogeny. Reflection data support earlier interpretations that indicate fundamental differences in the crust beneath McMurdo Sound and the Transantarctic Mountains, perhaps due to Early Paleozoic subduction of the Ross Embayment crust beneath the Transantarctic Mountains. Orogeny has produced an over-thickened crust beneath the Ross orogenic belt which was followed by several periods of reactivation including the Jurassic thermal event and the Early Tertiary uplift of the Transantarctic Mountains. Presence of the McMurdo Volcanics and preliminary data interpretations suggest that the sound is now being thinned by extension. Dept. of Geol., Louisiana State Univ., Baton Rouge, LA 70803-4101, USA.
85:7156 Rangin, C., J.F. Stephan and C. MUller, 1985. Middle Oligocene oceanic crust of South China Sea jammed into Mindoro collision zone (Philippines). Geology, geol. Soc. Am., 13(6):425-428. A summary is provided of the Cenozoic evolution of Mindoro, an island south of Luzon, located at the 'complex junction between the Manila Trench and the collision zone of the North Palawan block with the western Philippines mobile belt.' The age equivalence of Amnay ophiolites and the oldest Middle Oligocene magnetic anomalies of the South China Sea Basin is cited as evidence that the ophiolites may be a piece of South China oceanic crust rotated 20 ° counterclockwise and caught between the San Jose-North Palawan block and the Mindoro-Luzon basement. LA 215, CNRS, 4 ave de Bois Preau, 92506 Rueil-Malmaison Cedex, France. (hbf)
1029
85:7157 Srivastava, S.P., 1985. Evolution of the Eurasian Basin and its implications to the motion of Greenland along Nares Strait. Tectonophysics, ! 14(1-4):29-53. Analysis shows that the Eurasian Basin and Norwegian-Greenland Sea started to evolve at about anomaly 25 time, though active seafloor spreading did not start until anomaly 24 time. Spreading in the Eurasian Basin has been a result of motion only between the North American and Eurasian plates since the beginning, with the Lomonosov Ridge remaining attached to the North American Plate. From Late Cretaceous to Late Paleocene, Greenland moved obliquely to Ellesmere Island; most of this motion was taken up within the Canadian Arctic Islands resulting in little or no motion along Nares Strait. From anomaly 25-21 Greenland continued to move obliquely, resulting in a displacement of 125 km along and of 90 km normal to the Nares Strait. From Mid-Eocene to Early Oligocene another 100 km of motion took place normal to the Strait. Atlantic Geosci. Centre, Bedford Inst. of Oceanogr., Dartmouth, NS B2Y 4A2, Canada. 85:7158 Stagg, H.M.J., 1985. The structure and origin of Prydz Bay and MacRobertson Shelf, East Antarctica. Tectonophysics, 114(l-4): 315 -340. Multichannel seismic and magnetic data indicate that much of Prydz Bay is underlain by a sedimentary basin that is at least 5 km thick and probably represents a failed rift. The sediments are little disturbed by folding and faulting and contain three major unconformities of Triassic-Early Jurassic, Early Cretaceous, and Mid-Miocene-Early Pliocene age. These probably represent rift onset, margin breakup, and glacial advances, respectively. Bur. of Mineral Res., P.O. Box 378, Canberra City, ACT 2601, Australia. (amt) 85:7159 Sweeney, J.F., 1985. Comments about the age of the Canada Basin. Tectonophysics, 114(1-4): 1-10. The Canada Basin appears to have formed over a 60 Ma interval during the Cretaceous period. Continental breakup was widespread ~131 113 Mya along what was to become the polar margin of North America, and seafloor formation was active during an extended Cretaceous interval ~118-79 Mya. Data indicate that all parts of the North American polar margin could have formed at about the same time. Relatively less/slower stretching occurred along the segment southwest of Brock Island and relatively more/faster stretching took place along the
1030
D. SubmarineGeologyand Geophysics
segment to the northeast during margin formation. Pacific Geosci. Centre, Dept. of Energy, Mines and Res., Box 6000, Sidney, BC V8L 4B2, Canada.
D250. Plate and global tectonics 85:7160 Hynes, A. and J. Mott, 1985. On the causes of bagk-are spreading. Geology, geol. Soc. Am., 13(6):387-389.
The characteristics of plate motion within the actively spreading Lau Basin-Havre Trough and Mariana Trough are reviewed in an effort to evaluate the relative importance of several proposed plate-kinematic mechanism theories tied to motions of the upper plate and lower plate and changes in the profile of the lower plate. It is concluded that adjustment of the descending slab dip as a result of changes in subduction rate provides an 'attractive explanation' for trench migration and the recent onset of spreading behind the two arcs and for the fact that spreading in the Lau Basin outpaces spreading in the Havre Trough. Dept. of Geol. Sci., McGill Univ., Montreal, H3A 2A7, Canada. (hbf) 85:7161 Lawver, L.A., J.G. Sclater and Linda Meinke, 1985. Mesozoic and Cenozoic reconstructions of the South Atlantic. Tectonophysics, 114(1-4): 233 - 254. Recently published poles of rotation used to reconstruct the configurations of Antarctica, Africa and South America with respect to each other indicate that the opening between the Antarctic Peninsula and the tip of South America began before 35 Ma and that the peninsula moved away from South America at least 10 Ma before the opening of Drake's Passage, if there was no movement between East and West Antarctica at that time. Results also support the hypothesis that the triple junction between Africa, Antarctica and South America underwent a major reorganization 60-65 Ma, changing from ridge-ridge-ridge to ridge-fault-fault. Madagascar, India, Sri Lanka and the Somali Basin are also discussed. Inst. for Geophys., Univ. of Texas, Austin, TX 78751, USA. (msg) 85:7162 Mutter, J.C., 1985. Seaward dipping reflectors and the eontinent~ boundary at passive ~ t a l nmr~ns. Tectonophysics, 114(1-4):117-131. Multichannel seismic reflection profiles on many passive margins have revealed the presence of remarkable suites of arcuate reflectors, dipping
OLR(1985)32 (12)
seaward to form a wedge-shaped structure. Their general characteristics and velocity structure suggest they may be largely volcanic, but there is no agreed upon model for their origin. Nevertheless it is generally thought that they lie at or close to the boundary between continent and ocean, and as such they are extremely important structural markers that may yield important evidence concerning the structure and evolution of passive margins. LamontDoherty Geol. Observ., Palisades, NY 10964, USA. 85:7163 Mutter, J.C., K.A. Hegarty, S.C. Cande and J.K. Weissel, 1985. Breakup between Australia and Antarctica: a brief review in the light of new data. Tectonophysics, 114(1-4):255-279. The age of breakup was revised from anomaly 22 time to anomaly 34 time. The reconstruction of Broken Ridge and Kerguelen Plateau at anomaly 34 time shows overlap of these two features, but the problem is nearly resolved by anomaly 18 time. Subsidence patterns are interpreted as more consistent with the revised age of Australia-Antarctic breakup. Rapid subsidence was associated with the rift phase of margin development followed by much slower thermally-controlled subsidence during the drift phase, the transition coinciding with the age of breakup ( ~ 6 0 to 110 MyBP). Subsidence curves indicate a west-to-east propagation of breakup along the southern margin, consistent with magnetic anomaly patterns and stratigraphic observations. Lamont-Doherty Geol. Observ., Palisades, NY 10964, USA.
D280. Volcanism, magmatism 85:7164 Fornari, D.J., W.B.F. Ryan and P.J. Fox, 1985. Sea-floor lava fields on the East Pacific Rise. Geology, geol. Soe. Am., 13(6):413-416. SeaBeam and SeaMARC I data west of the East Pacific Rise define a relatively young submarine lava field, which extends over the faulted, eroded flanks of the EPR and laps up against the base of a large seamount with a large caldera. It is suggested that the lava field was produced by seamount magma, which flowed along pre-existing faults, draining shallow magma chambers beneath the seamount, deflating its summit and leaving the caldera. Lamont-Doherty Geol. Observ., Palisades, NY 10964, USA. (hbf) 85:7165 Fujii, Toshitsugu and C.M. Scarfe, 1985. Composition of liquids coexisting with spinel lherzoHte at