Files available at this site (".gz" file extension indicates compression
using "gzip").
"GMT" refers to Wessel and Smith's software system.
globalage_1.3.grd.gz < a GMT netcdf grd file of ocean ages>
Version 1.1: Update to Cande and Kent (1995) and
Gradstein et al. (1994) timescales.
The two timescales overlap at an 34,
and we have chosen Gradstein et al's age (83.5 m.y.)
for an 34.
Version 1.2: correct a timescale conversion error
for an 5, and include the area north of 72 deg N
Version 1.3: Replaced Pacific-Nazca isochrons based on
new mag. anom. picks in French Polynesia from
Munschy et al. (1996). Carmen Gaina helped with
constructing new isochrons. The ref. is:
Munschy, M., Antoine, C., and Gachon, A.,
Evolution tectonique de la region des Tuamotu,
ocean Pacifique Central, C.R. Acad. Sci. Paris,
t. 323, serie II a, 941-948, 1996.
In this version, continental crust is coded
with values=300, and oceanic areas not presently
covered with gridded data is set to 999. This
allows you to use different colors (or grays)
in your color pallette file for differentiating
these features in a plot.
globalage_1.3.bint.gz <a short integer binary file of ocean
ages, without header>
<ages are multiplied by 100>
globalage_errors_1.1.grd.gz < a GMT netcdf grd file of age errors>
THIS FILE HAS NOT BEEN UPDATED SINCE VERSION 1.1
(AS PUBLISHED IN JGR 1997).
age_error.ps.gz < an A4 postscript file of the age and error
grids>
You may obtain the grid and other related files using ftp:
(If you are unsure about how to use the ftp protocol contact your system
administrator)
ftp beryl.es.s.u.oz.au
Name (beryl.es.s.u.oz.au:yourname): anonymous
Password: <Your e-mail address>
ftp> cd pub/agegrid
ftp> bin
ftp > get globalage_1.3.grd.gz
ftp > get globalage_errors_1.1.grd.gz
ftp > get age_error.ps.gz
.
.
.
ftp> quit
Areas underlain by continental crust are assigned an age of 300 in the
original age grid, and thus become 30000 in this grid. The binary integer
grid is organised
in rows. Each row contains 3601 values from 0 - 360 E degrees, and
there are
1621 rows, from -72 to 90 degrees N. The grid interval is 0.1 degree
in
latitude and longitude.
--------
c
integer*2 iage(1621,3601)
c
open(2,file='age_short.i2',status='old',form='unformatted',
^access='direct',recl=7202,err=999)
norec=0
agemin=9999.
agemax=-9999.
ave=0.
nage=0
c
do ilat=1,1621
norec=norec+1
read(2,rec=norec)(iage(ilat,jlon),jlon=1,3601)
enddo
do ilat=1,1621
do jlon=1,3601
age=iage(ilat,jlon)/100.
if(age.lt.200) then
if(age.lt.agemin) agemin=age
if(age.gt.agemax) agemax=age
ave=ave+age
nage=nage+1
endif
enddo
enddo
ave=ave/nage
print*,'Average age, min, max: ', ave,agemin,agemax
c
999 continue
end
---------
This program should give the following output for globalage_1.3.bint:
Average age, min, max: 61.7434425 0. 179.979996
Optional files:
The file isochrons.dat contains the seafloor spreading isochrons
the age agrid is based on. The data are stored in "PALEOMAP" format.
Each data "string" starts with a 2 line "header". The 1st line
contains 3 integer numbers you can ignore, and a geographic description
of
the data. The 2nd line contains a 3 digit plate ID (e.g. 301 = Eurasia),
the age of the isochron, another age (default = 999.0), a data type
descriptor (e.g. IS 5 = isochron at magnetic anomaly 5 time), the plate
ID
of the conjugate plate and a few other numbers you can ignore. A list
of
plate ID integers can be found in the file globalage_pid.lst.
The files platebound.dat and platebound_xr.dat contain
present day plate
boundaries and the location of extinct ridges, respectively, in the
same format
as above. Neither file is necessarily complete or correct. In case
you have
more up-to-date data for either present day or extinct plate boundaries
which you may wish to share with us, please let us know.
In order to plot these data with the GMT software system, an awk
script can be used to strip off the headers and create an mutliple
segment GMT lat/lon file:
awk '{
if(NF==3 && $1 != 99.0000)
{
if ($2 < 0) $2 = $2 + 360;
{
if ($3 == 3) printf("> new string\n%s\t%s\n", $1, $2);
else printf("%s\t%s\n",$1,$2);
}
}
}'
Two tar files contain closed right-handed polygons of the major
plates (plate_polygons.tar) and of the boundaries between oceanic
and
continental crust (cob_polygons.tar). All polygons are lat/lon
ascii
files without headers.
COB POLYGONS
"cont" in the filename indicates that the polygon encloses continental
crust while "ocean" in the filename indicates that the polygon encloses
ocean crust within continental crust. The cob_polygons are:
afr_cont_cob.yx African
ant_cont_cob.yx Antarctica
arctic_ocean_cob.yx Arctic Ocean
aus_cont_cob.yx Australia
car_ocean_cob.yx Caribbean
cayman_ocean_cob.yx Caribbean
eur_cont_cob.yx Eurasia
gulfmex_ocean_cob.yx Gulf of Mexico
janmay_cont_cob.yx Jan Mayen
madagas_cont_cob.yx Madagascar
nam_cont_cob.yx North America
nzealand_cont_cob.yx New Zealand
s_georgia_cont_cob.yx South Georgia Microcontinent
sam_cont_cob.yx South America
seychel_cont_cob.yx Seychelles
PLATE POLYGONS
afr_plate.yx Africa
ant_plate.yx Antarctica
arab_plate.yx Arabia
aus_plate.yx Australia
car_plate.yx Caribbean
coco_plate.yx Cocos Plate
east_plate.yx Easter Microplate
eur_plate.yx Eurasia
ind_plate.yx India
juan_plate.yx Juan de Fuca Plate
nam_plate.yx North America
naz_plate.yx Nazca Plate
pac_plate.yx Pacific Plate
sam_plate.yx South America
We provide a C-program named grdage_cor.c which can be used to
update
the agegrid using different timescales. A Makefile is included
to compile the
program (it depends on the GMT and NETCDF libraries which you need
to
have installed). The program reads a grid file in default GMT grd-format
and a table which includes the mapping of old to new ages (see example
age_conv.tab).
The file age.cpt is a GMT color pallette file which can be used
to plot the
agegrid using the GMT software.
Permission is granted to use and freely distribute the age grid.
Copies of a colored, shaded relief map (~34 x 60 in. large) of the
gridded ages can be obtained for US $40 within the USA from:
Geological Data Center
Scripps Institution of Oceanography
9500 Gilman Drive
La Jolla, CA 92093-0223,
Ph. (619) 534 2752.
Outside the USA copies of the map can be obtained for CAN $50 from:
Geophysical Data Centre
Geological Survey of Canada
615 Booth St., Room 241
Ottawa, Ontario K1A 0E6
Canada
Ph. (613) 995 5326.
Send any inquiries about the age grid to
dietmar@es.su.oz.au (Dietmar Mueller)
The University of Sydney
Department of Geology and Geophysics
Edgeworth David Building F05
N.S.W. 2006
AUSTRALIA