Geokinematics and Lithoplate Structure - Figures
Figure 1. a. Hypothetical hotspot trace, map view; trace includes an apparent distinct change in plate motion relative to hotspot reference frame as well as slight perturbations in location.
Figure 1b. Expected age-distance plot of hypothetical hotspot trace, with two distinct age-distance trends and persistence of activity after volcanic inception.
Figure 1c. Reconstructed data points, rotated to time of origin for hypothetical hotspot trace. Note two elongate “elliptical” clusters oriented in direction of plate motion at time of “cooling”. The scatter is a result of minor scatter in location as well as in age.
Figure 2. Hotspot traces of the east-central Pacific: Magnetic isochrons, seamounts (open diamonds), hotspot trace data points (x), calculated loci anchored at suggested hotspots (lines incremented every five m.y.), restored hotspot trace data points (blue circles: 0-10 Ma, light blue squares: 10-19 Ma; green diamonds: 19 to 29 Ma; light green up triangles: 29 to 38 Ma; light yellow down triangles: 38-48 Ma; yellow left triangles: 48-57 Ma; orange right triangles: 57-67 Ma; red top semicircles: 67-76 Ma; brown bottom semicircles: 76-86 Ma; lavender right semicircles: 86-96 Ma). Note clusters of restored points near inferred hotspots (Easter, Marquesas, Society, Macdonald, Rapa , Foundation) as well as clustering along Austral-Cook trace). Many unrotated data points are not shown as they are outside the mapped area. Latitude-longitude graticules (+) at 15°.
Figure 3. Hawaiian-Emperor trace: Seamounts (open diamonds), hotspot trace data points (x), calculated locus anchored at suggested hotspots (lines incremented every five m.y.), restored hotspot trace data points (blue circles: 0-14 Ma, green squares: 14-28 Ma; yellow diamonds: 28 to 42 Ma; orange up triangles: 57 to 71 Ma; red down triangles: 57 to 71 Ma). Most unrotated data points are not shown as they are outside the mapped area. Latitude-longitude graticules (+) at 5°.
Figure 4. Hotspot traces of the Gulf of Alaska: Seamounts of Pacific and Juan de Fuca plates (open diamonds), hotspot trace data points (x), calculated loci anchored at suggested hotspots (lines incremented every five m.y.), restored hotspot trace data points (blue circles: 0-19 Ma, green squares: 19-38 Ma; yellow diamonds: 38 to 57 Ma; red triangles: 57 to 76 Ma). Most unrotated data points are not shown as they are outside the mapped area. Latitude-longitude graticules (+) at 5°.
Figure 5. Louisville
Figure 6. Hotspot traces of the central Indian Ocean (Reunion and Kerguelen): Hotspot trace data points (x), calculated loci anchored at suggested hotspots (lines incremented every five m.y.), restored hotspot trace data points (small symbols: original dates, large: dates filtered and recalculated by Baksi (1998); blue circles: 0-25 Ma, green squares: 25-50 Ma; yellow diamonds: 50-75 Ma; orange up-triangles: 75-100 Ma; red down-triangles: 100-125 Ma). Dashed lines connect equivalent data points with age range from Baksi. Most unrotated data points are not shown as they are outside the mapped area. Latitude-longitude graticules(+) at 15°.
Figure 7. Central South Atlantic (Tristan): Unrotated hotspot trace data points (x), calculated loci (relative to African and South American plate) anchored at suggested hotspot and alternative location (37°S, 12°W; 40°S, 15°W; lines incremented every five m.y.), restored hotspot trace data points (small symbols: original dates, large: filtered and reinterpreted dates by Baksi (1998); blue circles: 0-25 Ma, green squares: 25-50 Ma; yellow diamonds: 50-75 Ma; orange up-triangles: 75-100 Ma; red down-triangles: 100-125 Ma; brown left-triangles: 125-150 Ma). Most unrotated data points are not shown as they are outside the mapped area. Latitude-longitude graticules(+) at 5°.
Figure 8. Central North Atlantic, Great Meteor Seamount: Calculated loci (relative to African plate, extending to the east, north, and then west, and North American plate, extending to the northwest) anchored at suggested hotspot (“H”: 30°N, 28.5°W; lines incremented every five m.y.), restored hotspot trace data points from North American plate (small symbols: original dates, large: filtered and reinterpreted dates by Baksi (1998); blue circles: 0-25 Ma, green squares: 25-50 Ma; yellow diamonds: 50-75 Ma; orange up-triangles: 75-100 Ma; red down-triangles: 100-125 Ma; brown left-triangles: 125-150 Ma). No unrotated hotspot trace data points are shown as they are all to the west of the mapped region. Latitude-longitude graticules (+) at 5°.
Figure 9. Trinidade – Western South Atlantic: Unrotated hotspot trace data points (x), calculated locus (relative to South America plate, extending to the west) anchored at inferred hotspot (21°S, 28.5°W; lines incremented every five m.y.), restored hotspot trace data points; green squares: 25-50 Ma; yellow diamonds: 50-75 Ma; orange up-triangles: 75-100 Ma; red down-triangles: 100-125 Ma; brown left-triangles: 125-150 Ma). Not all unrotated hotspot trace data points are shown as some are to the west of the mapped region. Latitude-longitude graticules(+) at 5°. Note that no age data are available from oceanic portion of inferred trace.
Figure 10. Island-seamount chains of the South Pacific: Dated sample locations (x) (compiled by Pilger, 2003), calculated Pacific (or Nazca)-Hotspot loci, circles at 5 m.y. intervals (parameters in Table 1), magnetic isochrons (Müller et al., 1997), bathymetry (lavender-shallow, green- deep) (Smith and Sandwell, 1997).
Figure 11. Cartoon (not to scale) illustrating melting of asthenosphere due to rifting that affects lithosphere as well as asthenosphere. Base of lithosphere is the solidus. Note melting may be offset from surface rift.
Fig. 12. Northeastern South Atlantic: Free-air gravity (Sandwell and Smith, 1997); magnetic isochrons with age in Ma italicized (Müller et al., 1995); reconstructed isochrons in Atlantic-Indian hotspot frame with age in Ma (Pilger, 2003); locus of possible hotspot relative to Central African plate, 0-130 Ma, anchored at 17°S, 10°W, 5 m.y. increments; dated volcanic locations (x’s); restored hotspot data points: blue circles: 0-16 Ma, green squares: 16-32 Ma; yellow diamonds: 32-49Ma; orange up-triangles: 49-65 Ma; red down-triangles: 65-81 Ma). Note relative northward movement of Africa in hotspot frame between 90 and 75 Ma (shown both with locus and reconstructed isochrons); as consequence, African plate near locus passes over asthenosphere originally located beneath older South American plate.
Figure. 13. Eastern Pacific plate: Gravity field (+/- 25 mgals; hotter colors negative; Sandwell and Smith, 1997)), magnetic isochrons (Muller et al., 1997), flowlines around contemporary Pacific-Hawaiian hotspot pole, calculated hotspot loci at 5 m.y. increments, 0-70Ma. Heavy lines demarcate older-on-north fracture zones; light lines are interpreted lineations (mostly along negative trends).
Figure 14. K/Ar ages of volcanic rocks from East Africa plotted against Latitude, together with arbitrarily located hypothetical hotspot (6°S, 30°W) locus in Atlantic-Indian hotspot reference frame (data sources in Pilger, 2003). Note parallelism of locus with onset of magmatism.
Figure 15. Approximate boundaries between the three major mesoplates, Hawaiian, Tristan, and Icelandic (after Pilger, 2003).
Figure 16. Cartoon illustrating mesoplate and lithoplate interaction in the early Cenozoic, North American, Kula, Farallon, and Pacific lithoplates and Hawaiian and Tristan mesoplates, looking to northeast. Tristan mesoplate is arbitrarily fixed. Arrows indicate motion relative to Tristan.
Figure 17. Loci of relative motion of four lithoplates (North and South American, Eurasian, and Australian) and two mesoplates (Hawaiian and Tristan) relative to the Pacific plate. Hawaiian, almost by definition, corresponds with the Hawaiian-Emperor island-seamount chain. Note similarity in shape of North American-Pacific and South American-Pacific to Hawaiian-Pacific.
Figure 18. Reconstructions of the boundaries between the Tristan and Hawaiian mesoplates for past 90 m.y. at 10 m.y. intervals, along margin of western North America . Solid: North America relative Tristan. Dashed: Hawaiian relative to Tristan. Note partial parallelism of reconstructed boundaries between 90 and 30 Ma and especially between 70 and 30 Ma.
Figure 19. Hotspots with document Cenozoic traces: blue circles; other proposed hotspots (UTIG, 2003): red circles. Coarse hulls (solid lines) around hotspots, stress indicators, and cross-grain gravity anomalies for mesoplates -- Hawaiian: green; Tristan: teal, and Icelandic: gold. Original mesoplate boundaries (Pilger, 2003): dash-dot line. Modified mesoplate boundaries (this paper): dotted line.
Figure 20. “Hotspot” model for the origin of the Easter-Saly y Gomez island seamount chain and Nazca and Tuamotu ridges (modified from Pilger and Handschumacher, 1981). Nazca Ridge (N.R.), Sala y Gomez Island (S.G.), Tuamotu Ridge (T.R.), Easter Island (E.I.). Magnetic isochrons with ages (Ma) in parentheses.
Figure 21. Tuamotu Islands region. Bathymetry from Smith and Sandwell (1997). Magnetic isochrons from Muller et al. (1997). Calculated hotspot loci at 5 m.y. intervals.
Figure 22. Idealized cartoon illustrating two lithoplates, two shallow mesoplates, and two deeper mesoplates, with their relative motions (heavy arrows, assuming one shallow mesoplate fixed: bull’s-eye) and vertical motion (light arrows) with phase changes at discontinuities, compensating for seafloor spreading and displacement of the subduction zone by the upper lithoplate. Asthenosphere between lithoplates and shallow mesoplates is not shown. Surfaces separating lithoplates and mesoplates and shallow and deep mesoplates largely correspond with inferred phase change-induced seismic discontinuities (e.g., Gu and Dziewonski, 2002. In the Earth there are numerous lithoplates and three major shallow mesoplates. The number of deeper mesoplates is speculative. The lower surface of the deepest mesoplate corresponds with the 1000 km discontinuity.
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