12 September, 2008 Age, spreading rates and spreading asymmetry of the world's ocean crust Reference Muller, R. D., M. Sdrolias, C. Gaina, and W. R. Roest (2008), Age, spreading rates, and spreading asymmetry of the world's ocean crust, Geochem. Geophys. Geosyst., 9, Q04006, doi:10.1029/2007GC001743. ### Version 3 ### age.3.2.img A 10800 by 8640 grid of 2-byte integers = 186,624,000 bytes. Byte order is big_endian. Stored in an integer*2 format without any header or record information. The age units are in millions of years, multiplied by 100 (to enable storage as short integers) Grid cells without data (i.e. on continental crust) are assigned values of 32767. The Mercator projected image spans longitudes from 0 E to 360 E and latitudes from 80.738 N to -80.738 N. A spherical earth is used for the Mercator projection. 2 minute resolution, pixel-registered. age.3.2.nc A short integer netCDF formatted file. The age units are in millions of years, multiplied by 100 (to enable storage as short integers) The geographic grid spans longitudes from 0 E to 360 E and latitudes from 90 N to -90 N. 2 minute resolution, gridline-registered. age.3.2.tif A short integer GeoTiff formatted file. The age units are in millions of years, multiplied by 100 (to enable storage as short integers) The geographic grid spans longitudes from 0 E to 360 E and latitudes from 90 N to -90 N. 2 minute resolution, gridline-registered. age.3.6.nc A short integer netCDF formatted file. The age units are in millions of years, multiplied by 100 (to enable storage as short integers) The geographic grid spans longitudes from 0 E to 360 E and latitudes from 90 N to -90 N. 6 minute resolution, gridline-registered. age.3.6.tif A short integer GeoTiff formatted file. The age units are in millions of years, multiplied by 100 (to enable storage as short integers) The geographic grid spans longitudes from 0 E to 360 E and latitudes from 90 N to -90 N. 6 minute resolution, gridline-registered. age.3.6.xyz A simple ASCII file (long, lat, age). The age units are in millions of years with no scaling. The file spans longitudes from 0 E to 360 E and latitudes from 90 N to -90 N. 6 minute resolution, gridline-registered. ageerror.3.2.img A 10800 by 8640 grid of 2-byte integers = 186,624,000 bytes. Byte order is big_endian. Stored in an integer*2 format without any header or record information. The age units are in millions of years, multiplied by 100 (to enable storage as short integers) Grid cells without data (i.e. on continental crust) are assigned values of 32767. The Mercator projected image spans longitudes from 0 E to 360 E and latitudes from 80.738 N to -80.738 N. A spherical earth is used for the Mercator projection. 2 minute resolution, pixel-registered. ageerror.3.2.nc A short integer netCDF formatted file. The age units are in millions of years, multiplied by 100 (to enable storage as short integers) The geographic grid spans longitudes from 0 E to 360 E and latitudes from 90 N to -90 N. 2 minute resolution, gridline-registered. ageerror.3.2.tif A short integer GeoTiff formatted file. The age units are in millions of years, multiplied by 100 (to enable storage as short integers) The geographic grid spans longitudes from 0 E to 360 E and latitudes from 90 N to -90 N. 2 minute resolution, gridline-registered. ageerror.3.6.nc A short integer netCDF formatted file. The age units are in millions of years, multiplied by 100 (to enable storage as short integers) The geographic grid spans longitudes from 0 E to 360 E and latitudes from 90 N to -90 N. 6 minute resolution, gridline-registered. ageerror.3.6.tif A short integer GeoTiff formatted file. The age units are in millions of years, multiplied by 100 (to enable storage as short integers) The geographic grid spans longitudes from 0 E to 360 E and latitudes from 90 N to -90 N. 6 minute resolution, gridline-registered. ageerror.3.6.xyz A simple ASCII file (long, lat, ageerror). The age units are in millions of years with no scaling. The file spans longitudes from 0 E to 360 E and latitudes from 90 N to -90 N. 6 minute resolution, gridline-registered. rate.3.2.img A 10800 by 8640 grid of 2-byte integers = 186,624,000 bytes. Byte order is big_endian. Stored in an integer*2 format without any header or record information. The spreading rate units are in mm/yr, multiplied by 100 (to enable storage as short integers) Grid cells without data (i.e. on continental crust) are assigned values of 32767. The Mercator projected image spans longitudes from 0 E to 360 E and latitudes from 80.738 N to -80.738 N. A spherical earth is used for the Mercator projection. 2 minute resolution, pixel-registered. rate.3.2.nc A short integer netCDF formatted file. The spreading rate units are in mm/yr, multiplied by 100 (to enable storage as short integers) The geographic grid spans longitudes from 0 E to 360 E and latitudes from 90 N to -90 N. 2 minute resolution, gridline-registered. rate.3.2.tif A short integer GeoTiff formatted file. The spreading rate units are in mm/yr, multiplied by 100 (to enable storage as short integers) The geographic grid spans longitudes from 0 E to 360 E and latitudes from 90 N to -90 N. 2 minute resolution, gridline-registered. rate.3.6.nc A short integer netCDF formatted file. The spreading rate units are in mm/yr, multiplied by 100 (to enable storage as short integers) The geographic grid spans longitudes from 0 E to 360 E and latitudes from 90 N to -90 N. 6 minute resolution, gridline-registered. rate.3.6.tif A short integer GeoTiff formatted file. The spreading rate units are in mm/yr, multiplied by 100 (to enable storage as short integers) The geographic grid spans longitudes from 0 E to 360 E and latitudes from 90 N to -90 N. 6 minute resolution, gridline-registered. rate.3.6.xyz A simple ASCII file (long, lat, rate). The spreading rate units are in mm/yr with no scaling. The file spans longitudes from 0 E to 360 E and latitudes from 90 N to -90 N. 6 minute resolution, gridline-registered. asym.3.2.img A 10800 by 8640 grid of 2-byte integers = 186,624,000 bytes. Byte order is big_endian. Stored in an integer*2 format without any header or record information. The spreading asymmetry units are expressed as percentage of crustal accretion, i.e. symmetric spreading results in values of 50% on conjugate ridge flanks, multiplied by 100 (to enable storage as short integers) Grid cells without data (i.e. on continental crust) are assigned values of 32767. The Mercator projected image spans longitudes from 0 E to 360 E and latitudes from 80.738 N to -80.738 N. A spherical earth is used for the Mercator projection. 2 minute resolution, pixel-registered. asym.3.2.nc Spreading asymmetry grid. A short integer netCDF formatted file. The spreading asymmetry units are in percent times 100. The geographic grid spans longitudes from 0 E to 360 E and latitudes from 90 N to -90 N. 2 minute resolution, gridline-registered. asym.3.2.tif Spreading asymmetry grid. A short integer GeoTiff formatted file. The spreading asymmetry units are in percent times 100. The geographic grid spans longitudes from 0 E to 360 E and latitudes from 90 N to -90 N. 2 minute resolution, gridline-registered. asym.3.6.nc Spreading asymmetry grid. A short integer netCDF formatted file. Byte order is big_endian. The spreading asymmetry units are in percent times 100. The geographic grid spans longitudes from 0 E to 360 E and latitudes from 90 N to -90 N. 6 minute resolution, gridline-registered. asym.3.2.nc Spreading asymmetry grid. A short integer GeoTiff formatted file. The spreading asymmetry units are in percent times 100. The geographic grid spans longitudes from 0 E to 360 E and latitudes from 90 N to -90 N. 2 minute resolution, gridline-registered. asym.3.6.xyz A simple ASCII file (long, lat, asymmetry). The spreading asymmetry units are in percent with no scaling. The file spans longitudes from 0 E to 360 E and latitudes from 90 N to -90 N. 6 minute resolution, gridline-registered. res_basement_GDH1.1.5.nc: Residual oceanic basement depth based on Stein and Stein's (1992) GDH-1 plate model age-depth relationship. Units are in meters. The geographic grid spans longitudes from 0 E to 360 E and latitudes from 90 N to -90 N. 5 minute resolution, gridline-registered. res_basement_PM_Crosby07_1.5.nc: Residual oceanic basement depth based on the modified plate model age-depth relationship from Crosby's PhD Thesis (Cambridge, 2007). Units are in meters. The geographic grid spans longitudes from 0 E to 360 E and latitudes from 90 N to -90 N. 5 minute resolution, gridline-registered. res_basement_TBL_Crosby_1.5.nc: Residual oceanic basement depth based on the North Pacific thermal boundary layer model age-depth relationship from Crosby et al. (2006) Units are in meters. The geographic grid spans longitudes from 0 E to 360 E and latitudes from 90 N to -90 N. 5 minute resolution, gridline-registered. res_basement_PM_PS77_1.5.nc: Residual oceanic basement depth based on the Parsons and Sclater (1977) plate model. This model is not shown in our G-cubed paper, but included here for completeness. In our view it is still a useful reference model. Units are in meters. The geographic grid spans longitudes from 0 E to 360 E and latitudes from 90 N to -90 N. 5 minute resolution, gridline-registered. All grid file names follow the convention to use two numbers to indicate the file version number followed by the resolution in minutes. Therefore age_3.2.img corresponds to version 3 with 2 minute resolution. About .img files: The Mercator projected .img files can be accessed with Wessel and Smith's Generic Mapping Tools (GMT) program img2mercgrd: img2mercgrd age3.2.img -R/// -Gage3.2_myregion.grd -T1 -S0.01 -D-80.738/80.738 The exact usage of img2mercgrd may depend on the GMT version you use. Note that any inverse projection of the Mercator grid is unnecessary, as we provide a geographic age grid: age.3.2.nc The .img files have big_endian byte format (reflecting e.g. old Macs with Motorala CPU's and Sun SPARC computers). GMT's img2grd and img2mercgrd expects the files to be in the big-endian format (as we supply) and will automatically apply a byte swap when used on little-endian hardware (e.g. based on Intel or AMD chips). If you use a program to read these files that require little-endian data input use dd (on unix machines) to byte swap the img files: dd if=orig.img of=new.img conv=swab. The .img files are pixel-registered (i.e. nodes centered on the grid boxes). This differs from gridline-registered grids where nodes are at gridline intersections. Gridline-registered grids therefore have 1 row/column more than pixel-registrated grids. About .nc files: These are netCDF files adhering to the COORDS convention and may be used with any programs that supports such files, such as the GMT programs (eg grdreformat for converting the file to another format if desired, grdmath for division of the grids by 10 (for age, rate, asym and age error grids) and grdimage for plotting. GMT format file code is ns (short integer netCDF format). The 6 minute age, rate and asymmetry grids are provided for users who do not need high-resolution grids. This resolution corresponds to that of our previous age grid (from 1997). Convert short integer .nc files to default GMT grd files as follows (for example). grdmath age.3.6.nc=ns 0.01 MUL = age.3.6.grd=nf -V This example only works for GMT4.1 or above. For older versions of GMT, you may have to run grdreformat and grdmath separately. If you just want to convert a .nc file to xyz, run, for example grd2xyz age.3.2.nc=ns/0.01/0 > age.3.2.xyz The .nc files are gridline-registered (i.e. nodes are at gridline intersections). This differs from pixel-registered grids where nodes are centered on the grid boxes. Gridline-registered grids therefore have 1 row/column more than pixel-registrated grids. All files are compressed with bzip2. Use bunzip2 for unzipping of the files. Known Bugs: Gridding artifacts exist around microplates (e.g. Bauer microplate), along fracture zones (e.g. Central Atlantic) and in areas with highly oblique spreading (e.g. South-West Indian Ridge). Minor interpolation artifacts along the margins of some back-arc basins. Fixes: 11-09-08: Spreading asymmetry for crust without a present day conjugate is included in this version of the grid due to several requests received by the authors. 11-09-08: Adjustment to the location of chron M25 in the westernmost Pacific (Pacific-Izanagi) and to the age assigned to the Pacific triangle 11-09-08: Minor COB modifications around back-arc basins to minimise over-interpolation artifacts from the adjacent subducting ocean floor 04-04-08: Gridding artifact in the Bay of Bengal, eastern India and in the southern Indian Ocean, east of the Enderby Basin was fixed. 04-04-08: Inclusion of the Komandorsky Basin and Bering Sea, North Pacific Contribute: If you would like your work to be included in the next version of the agegrid, please send us an email. Any questions, please email: Dietmar Muller d.muller@usyd.edu.au Maria Seton maria.seton@usyd.edu.au