Google Earth is an exciting new visualization platform for geological and geophysical data (as well as other types). It is especially useful for seeing information pertinent to plate tectonics: isotopic ages of “hotspot” and subduction-related magmatism, contemporary and paleo-stress indicators, magnetic isochrons, plate reconstructions, and plate-hotspot models.
I have posted a number of such data sets on the Google Earth Community website. The links below provide access to Google Earth native format (“kmz”) data sets. More information is provided with each post and internally in each data set.
Isotopic Dates from East African Volcanics
US Cordilleran Igneous Isotopic Dates LT 40 Ma
Isotopic Dates from Global "Hotspot" Traces
Average Ages for Pacific Hotspot Sample Locations
Stresses - Present to 130 Ma
Hotspot rotback
Isotopic Dates from Baksi (1999) - Original Data
Recalculated Isotopic Dates from Baksi (1999)
Isotopic Dates Compiled by O'Neill et al (2005)
Magnetic Isochrons from Müller et al (1997)
Ar/Ar Dates from Hawaiian-Emperor Chain
I intend to post more data sets to the Google Earth Community site, with links noted here, too.
Wednesday, August 29, 2007
Monday, August 27, 2007
Geokinematics: Prelude to Geodynamics
Geokinematics: Prelude to Geodynamics ... can be obtained from Amazon. It's also in almost every major U.S. university library.
Improved Plate-Hotspot Modeling
(2/27/05) The recent contribution of Wessel, Harada, and Kroenke at the Fall, 2004, AGU (link) is a natural next step in modeling Pacific plate motions relative to hotspots. By taking the seamount catalog, applying Harada and Hamano's modeling techniques, and leaving hotspot location as an unknown to be solved for, the results WHK have come up with are very promising.
The big limitation, of course, is coming up with precise and accurate isotopic dates to more fully test and time-parameterize the model. My suggestion is: incorporate the Tuamotu and Nazca ridges. I showed (with David Handschumacher) in 1981 that the two ridges probably originated from the same sublithospheric melting anomaly centered on the Pacific-Nazca (Farallon) ridge between magnetic chrons 11 and 21. Thus, when reconstructed, the intersection of the restored ridges provides ages of the ridges. So, assuming a correct geomagnetic time scale, at least part of the kinematic model could be constrained.
Update: (3/2/05) One could also incorporate the islands and seamounts of the Easter to Sala-y-Gomez chain (assuming that they formed from an Easter hotspot largely located beneath the Nazca plate). However, given the need to rotate them to the Pacific plate and their age uncertainty (which would make their rotated locations less certain), and the lack of tightly spaced (in time) Pacific-Nazca reconstructions since 25 Ma, this seems less promising.
The big limitation, of course, is coming up with precise and accurate isotopic dates to more fully test and time-parameterize the model. My suggestion is: incorporate the Tuamotu and Nazca ridges. I showed (with David Handschumacher) in 1981 that the two ridges probably originated from the same sublithospheric melting anomaly centered on the Pacific-Nazca (Farallon) ridge between magnetic chrons 11 and 21. Thus, when reconstructed, the intersection of the restored ridges provides ages of the ridges. So, assuming a correct geomagnetic time scale, at least part of the kinematic model could be constrained.
Update: (3/2/05) One could also incorporate the islands and seamounts of the Easter to Sala-y-Gomez chain (assuming that they formed from an Easter hotspot largely located beneath the Nazca plate). However, given the need to rotate them to the Pacific plate and their age uncertainty (which would make their rotated locations less certain), and the lack of tightly spaced (in time) Pacific-Nazca reconstructions since 25 Ma, this seems less promising.
Original Post Link: http://mesoplates.spaces.live.com/blog/cns!F9234EE50D713CDC!139.entry
New evidence for sublithospheric hotspots
Koppers and Staudigel's (2005) recent contribution to knowledge of the age of Pacific Seamount chains produces a conclusion that can be inverted. The title concisely states their inference: "Asynchronous bends in Pacific seamount trails: a case for extensional volcanism?"
Taking previous speculations that the Gilbert Ridge and Tokelau Seamounts include a "bend" analogous to the Hawaiian-Emperor bend, K&S show that isotopic ages from the two chains are incompatible with the age of the H-E bend and with one another. Within their published figures, they show hypothetical loci generated by a Pacific hotspot model and demonstrate inconsistency with their newly acquired dates. Interestingly, for the Toekalu chain, they also show a locus anchored at Macdonald "hotspot" -- which better fits the new ages of the seamounts.
Comparison of K&S's inferred seamount chains and their included bends with Smith and Wessel's (1999) bathymetry suggests a certain selectivity in interpretation, especially given the short length of the "younger" portions inferred to mimic the younger part of the H-E chain. Putting such subjective observations aside, there is another way to look at the significance of the new data in light of a relatively fixed sub-Pacific hotspot reference frame.
Taking the new data points, along with previously published data, I've reconstructed each sample date back to its location when the isotopic clock started according to the plate-hotspot model of Raymond et al. (2000) as interpolated using my spline methods (Pilger, 2003). Given the age uncertainty, I've included data points +/- 5 m.y. around each data point at 2.5 m.y. intervals (producing a maximum of five data points), thereby defining loci segments.
The restored loci from the Gilbert and Tokelau chains (click thumbnail below) produce a fascinating pattern when combined with the restored segments from the Cook-Austral chain. The two older chains produce loci that intersect with younger segments close to (1) the inferred location of the Macdonald hotspot and (2) another inferred hotspot location.
Previously, available isotopic dates from the C-A chain implied a miinimum of two hotspots (three if the older part of the Foundation chain were included). K&S's new data strengthen this inference.
Additionally, then, the approximate alignment of the three hotspots cannot as readily be ascribed to intraplate stresses as might previously have been inferred. Why? Because the Gilbert and Tokelau chains are not themselves aligned. That is, the melting anomalies responsible for the two older chains are not attributable to a single locus of intraplate extension. The alignment of the "hotspots" post-47 Ma is largely a coincidence.
Thus, the new data of K&S don't strengthen the case for intraplate extension, they undermine it.
Perhaps the revised title could be: "New isotopic ages from Pacific seamount chains: Further evidence for sub-lithospheric hotspots?"
Cited: Koppers and Staudigel (2005) Science, 307, 904. Pilger (2003) Geokinematics: Prelude to Geodynamics. Raymond et al. (2000) AGU Geophys. Mon.121, 359. Smith and Sandwell (1997) Global seafloor topography from satellite altimetry and ship depth soundings, Science, 277, 1957.
Taking previous speculations that the Gilbert Ridge and Tokelau Seamounts include a "bend" analogous to the Hawaiian-Emperor bend, K&S show that isotopic ages from the two chains are incompatible with the age of the H-E bend and with one another. Within their published figures, they show hypothetical loci generated by a Pacific hotspot model and demonstrate inconsistency with their newly acquired dates. Interestingly, for the Toekalu chain, they also show a locus anchored at Macdonald "hotspot" -- which better fits the new ages of the seamounts.
Comparison of K&S's inferred seamount chains and their included bends with Smith and Wessel's (1999) bathymetry suggests a certain selectivity in interpretation, especially given the short length of the "younger" portions inferred to mimic the younger part of the H-E chain. Putting such subjective observations aside, there is another way to look at the significance of the new data in light of a relatively fixed sub-Pacific hotspot reference frame.
Taking the new data points, along with previously published data, I've reconstructed each sample date back to its location when the isotopic clock started according to the plate-hotspot model of Raymond et al. (2000) as interpolated using my spline methods (Pilger, 2003). Given the age uncertainty, I've included data points +/- 5 m.y. around each data point at 2.5 m.y. intervals (producing a maximum of five data points), thereby defining loci segments.
The restored loci from the Gilbert and Tokelau chains (click thumbnail below) produce a fascinating pattern when combined with the restored segments from the Cook-Austral chain. The two older chains produce loci that intersect with younger segments close to (1) the inferred location of the Macdonald hotspot and (2) another inferred hotspot location.
Previously, available isotopic dates from the C-A chain implied a miinimum of two hotspots (three if the older part of the Foundation chain were included). K&S's new data strengthen this inference.
Additionally, then, the approximate alignment of the three hotspots cannot as readily be ascribed to intraplate stresses as might previously have been inferred. Why? Because the Gilbert and Tokelau chains are not themselves aligned. That is, the melting anomalies responsible for the two older chains are not attributable to a single locus of intraplate extension. The alignment of the "hotspots" post-47 Ma is largely a coincidence.
Thus, the new data of K&S don't strengthen the case for intraplate extension, they undermine it.
Perhaps the revised title could be: "New isotopic ages from Pacific seamount chains: Further evidence for sub-lithospheric hotspots?"
Cited: Koppers and Staudigel (2005) Science, 307, 904. Pilger (2003) Geokinematics: Prelude to Geodynamics. Raymond et al. (2000) AGU Geophys. Mon.121, 359. Smith and Sandwell (1997) Global seafloor topography from satellite altimetry and ship depth soundings, Science, 277, 1957.
Originally posted at: http://mesoplates.spaces.live.com/blog/cns!F9234EE50D713CDC!149.entry
GSA Article...The Bend
See a discussion of the kinematic significance of the Hawaiian-Emperor Bend at:
Pilger, R. H., 2007, The Bend: Origin and significance, Bull. Geol. Soc. Am., 119, 302-313.
Pilger, R. H., 2007, The Bend: Origin and significance, Bull. Geol. Soc. Am., 119, 302-313.
Mesoplates
Here's a link to another web log which deals with plate reference frames: http://mesoplates.spaces.live.com/default.aspx.
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