Files in this directory (".gz" file 
extension indicates compression using "gzip").
"GMT" refers to Wessel and Smith's software system:

age_1.6.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, submarine 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 these 2 features.

	Version 1.4: Data west and east of Australia added
	Version 1.5/1.6: Some bugs were fixed that crept into v. 1.4

GMT software users:

The digital grids globalage.grd and age_errors.grd are binary grid registered 
GMT NETCDF grd files which can be manipulated and plotted with 
Wessel and Smith's GMT software system. "NaN's" are assigned to nodes with no data.

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.