Importing_Rasters_Tu..
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1. Ma_ I Reset gt Play x Oo View 3D Globe a 178 lat 3 76 lon 127 59 Mouse lat 25 37 lon 147 85 Selected Topology Sections Present day geometry lat lon Figure 10 The Animate window enables you to specify a specific time period to animate on the globe Can you see the slab window Clue Look for a break in the blue blobs Now that we have visualised the slab window lets digitise it In this example we will digitise the position of the slab window at 60 Ma using an oval shape Figure 11 below is an example of the 70 Ma slab window use this as a guide when you make your 60 Ma slab window Figure 11 Digitised slab window at 70 Ma 11 Click the Digitise New Polygon Geometry icon located in the Tool Palette on the left hand side of the globe gt click around the slab window in www gplates org 10 B M perframe MEM oe oe an oval shape use Figure 14 above as a guide Remember that if you make a mistake or you are not happy with the shape of your polygon then you can use the geometry editing tools from the Tool Palette to move the existing ia iY cy vertices add new ones or delete them all together gt Create Feature from the New Geometry Table to the right of the globe gt gpml UnclassifiedFeature gt Next gt Leave the default setting for the property that best indicates the geometry s purpose gt Plate ID 301 the slab window l2. 27 78 1998 Montelli R G Nolet F A Dahlen and G Masters A catalogue of deep mantle plumes New results from finite frequency tomography Geochem Geophys Geosyst vol 7 11 2006 Muller R D M Sdrolias C Gaina B Steinberger and C Heine Long term sea level fluctuations driven by ocean basin dynamics Science vol 319 p 1357 1362 2008 Richards S G Lister and B Kennett A slab in depth Three dimensional geometry and evolution of the Indo Australian Plate Geochem Geophys Geosyst vol 8 12 2007 Wessel P and W H F Smith New improved version of Generic Mapping Tools released EOS Trans Amer Geophys U vol 79 47 pp 579 1998 Whittaker J M R D Muller M Sdrolias and C Heine Sunda Java trench kinematics slab window formation and overriding plate deformation since the Cretaceous Earth Planet Sci Lett vol 255 p 445 457 2007 www gplates org 16
3. format e g age grids 1 jpg where 1 signifies that the image corresponds to 1 Ma Time dependent rasters must correspond to whole number ages 1 e 2 Ma 34 Ma 140 Ma etc NOT 2 2 Ma 3 01 Ma 40 32 Ma etc Ifthe period of time between the individual raster images in a time dependent raster sequence is longer than 1 Myr then each image in the sequence will be updated on the globe at the half way age For example if a time dependent raster sequence is loaded that has an interval of 10 Myr then the 10 Ma raster will be displayed on the globe from 5 Ma 14 Ma then the 20 Ma raster will be displayed from 15 Ma to 24 Ma etc EXERCISE 1 Importing Time Dependent Rasters PART A Dynamic topography is vertical motion of the Earth s surface attributed to mantle processes For example subducting slabs viscously drag down overlying crust as they sink through the upper mantle whereas hot upwellings push up overlying crust For an informative overview of dynamic topography the 2001 Scientific America article Sculpting the Earth from Inside Out by Professor Mike Gurnis is a good place to start http www gps caltech edu gurnis papers html In this exercise we will be importing a sequence of time dependent raster images showing dynamic topography since the Mid Cretaceous 0 100 Ma These images have been generated at 1 Myr intervals 1 File gt Open Time dependent Raster Sequence Figure 1 gt locate f
4. seen as a break in the fast velocity region Note Blues indicate anomalously fast velocities and so we will interpret these regions as subducting slabs Rather than animating 140 Myr worth of data lets use the Animation controls to specify our 70 43 Ma timeframe 10 Reconstruction gt Configure Animation italicised numbers below 10a e need to be entered into the Animate window that opens Figure 10 Animate from 70 00 Ma To 43 00 Ma With an increment of 00 M per frame Frames per second 3 00 you can experiment with this if you like Current time 70 00 Ma When you have finished adjusting the animation controls click the Play button make sure to move or close the Animate window so that it does not block your view of the GPlates globe monosgs www gplates org 9 kei ke LOB To lt G SP P Feature type Plate ID Name Clicked geometry Begin End DI pee Q TFAO Ya od JG p gt A G1 Mon11 04AM Q GPlates Current Feature Plate ID 00O C Animate Valid time N from to Clicked geometry Animate from 70 00 Ma Use Main Window ae Feature collection to 43 00 Ma Use Main Window i with an increment of 1 00 Reverse the Animation by swapping the start and end times Options Frames per second 3 00 Finish animation exactly on end time _ Loop Close this dialog when animation starts Playback Current time 70 00
5. v Show Line Features v Show Polygon Features v Show Multipoint Features yY Show Arrow Decorations Show Text Figure 7 When loading regional rasters you must tell GPlates the surface extent of your images this is achieved using the Set Raster Surface Extent window Set Raster Surface Extent Set the latitude and longitude extent of the raster image Use the Tab key to cycle through the fields Upper right Latitude 30 0000 Longitude 130 0000 Lower left Latitude 20 0000 Longitude 80 0000 y Reset fields to 90 180 90 180 O O E OK Cancel O Figure 8 The Set Raster Surface Extent window allows you to readjust the bounding latitudes and longitudes of regional rasters You should now be able to see a seismic tomography image in the region of Sundaland Figure 9 www gplates org 8 Time 50 00 ma D K gt Figure 9 Snapshot of the Sundaland region with time dependant seismic tomography loaded A Tomography model is Montelli06_S at 0 Ma B Tomography model is MITPO8 at 50 Ma We want to use this raster sequence to find the assumed slab window that was open between 70 43 Ma in the Late Cretaceous Early Tertiary Subduction zones can be identified from seismic tomography images as regions of anomalously fast velocities This 1s because the subducting slab is colder and denser than the ambient mantle It thus follows that a slab window can be
6. GPlates Tutorial Working with Time Dependent Rasters Kara J Matthews Aedon S Talsma amp Theresa Fabien EarthByte Research Group School of Geosciences University of Sydney Australia www gplates org Earth SLite Linking observations to kinematic and dynamic models Importing Raster Images into GPlates AIM This tutorial is designed to teach the user how to import time dependent raster images into GPlates Screen shots have been included to illustrate how to complete new steps within each exercise INCLUDED FILES The data bundle for this tutorial Importing Rasters includes the following GPlates compatible feature files EarthByte Global Rotation Model EarthByte Global Coastline File Outlines of the Carpentaria Basin Queensland Plateau and the Marion Plateau USGS data Well locations for three wells north and northeast of Australia Duyken 1 and ODP Sites 1193 and 1198 And the following raster files Global Time Dependent Dynamic Topography File 0 100 Ma data from EarthByte Time dependent images for seismic tomography modelsPRI SO5 Montelli et al 2006 and MIT P08 Li et al 2008 Global Time Dependent Oceanic Crustal Age Files 0 140 Ma Muller et al 2008 See www earthbyte org Resources earthbyte_gplates html for EarthByte data sets BACKGROUND What are raster images Raster images comprise 2 dimensional grids of pixels or points of colour that are s
7. an then be visualised and saved as a JPEG In future when adapting this workflow only use the commands necessary for the data you have for example if you start off with a set of grid files then ignore the img2grd step as you obviously don t need to convert an IMG file into gridded data Note each set of commands is to be written on a single line You may run each line individually in turn in a terminal or you may write a simple script with all the lines and execute the script in one go The Importing Rasters data bundle contains a folder called Making Gravity and in this folder is an example script making_gravity sh and the IMG file grav img from Sandwell and Smith http topex ucsd edu WWW_html mar_grav html that is required as input GMT COMMANDS img2erd grav img Gworld_gravity grd R 180 180 80 738 80 738 T1 D 80 738 80 738 V m1 E S0 1 img2grd GMT tool to convert the IMG file to a netcdf grid GRD Input IMG file Output GRD file specifies the name of the GRD file Defines the geographic region of interest west east south north Forces GMT to get values at ALL points Forces GMT to use the extended latitude range and not the default 71 006 72 006 a Commands are run in verbose mode tells you when you have done something wrong Specifies the minute width of input IMG pixels minutes of longitude Scaling factor scales the IMG grid value in this case each cell is multiplied by 0 1 to g
8. due to an absence of ocean water to cool the upwelling asthenosphere and form new oceanic crust the plates no longer continue to grow and www gplates org 5 a gap develops and widens Seismic tomography enables us to visualise slab windows from present day and past subduction SEISMIC TOMOGRAPHY Seismic tomography is a method for imaging the Earth s interior revealing regions of past and present subduction and hot mantle upwellings It involves establishing how fast seismic waves elastic waves travel through the mantle for example seismic waves generated by earthquakes This information is then used to infer regions of anomalously hot or cold material anomalous is judged as deviating from a global reference model e g PREM Dziewonski and Anderson 1981 As the speed of seismic waves travelling through the mantle 1s influenced by temperature velocity can be used as a proxy for temperature fast velocities cold material slow velocities hot material However mantle composition also affects the speed of wave propagation and therefore establishing correlations between velocities and mantle structures is not simple The Importing Rasters data bundle includes 2 sequences of regional time dependent raster images showing seismic tomography These images were generated from the seismic tomography model PRI SO5 Montelli et al 2006 and model MIT P08 Li et al 2008 Although seismic tomography is a method for imaging the str
9. et the correct mGal value erd2cpt world gravity grd Chaxby S 60 60 20 V gt gravity cpt erd2cpt GMT tool to make a colour palette from a GRD file world gravity grd GRD file from which cpt file will be created Selects the colour table to be interpolated GMT has a range to choose from Defines the start z value stop z value and interval of the cpt file Commands are run in verbose mode tells you when you have done something wrong gravity cpt Name of generated cpt file erdimage world gravity grd Jx0 07d R 180 180 80 738 80 738 Cgravity_all_test cpt X0c Y0c V gt world _gravity ps www gplates org 13 erdimage GMT tool to create a coloured or greyscale image from 2D netCDF gridded data Input GRD file Specifes projection and size of the image x denotes a non linear projection with 0 07 defining the map scale use X to define map width for example in cm d informs GMT that your data is geographical rather then a Cartesian this is important if you want to also plot other geographical data such as coastlines Specifies the geographic region west east south north Names the colour palette table to be used Specifes the plot origin in this case 0 cm and 0 cm V Commands are run in verbose mode tells you when you have done something wrong world gravity ps Name of generated postscript file J ps2raster gravity_all test ps Tj E300 A P ps2raster GMT command to c
10. exploit this functionality in order to see why dynamic topography is reflected in the geological record of several Australian basins and oceanic plateau Evidence for negative dynamic topography can be expressed as anomalous tectonic subsidence By analysing stratigraphic data obtained from exploration wells we can calculate how a region has subsided over time Anomalous subsidence can then be isolated by removing the predicted subsidence for the area that is subsidence expected from thermal cooling resulting from lithospheric stretching or flexure due to the emplacement of a heavy load Knowledge of the tectonic history of the region in question will further help determine if dynamic topography is a potential cause of the anomalous subsidence Cenozoic anomalous tectonic subsidence induced by mantle convection processes 1s recorded in wells north and northeast of Australia e g DiCaprio et al 2009 Heine et al 2009 DiCaprio et al 2010 This dynamic topography including a 300 m downward tilt of the continent to the northeast is due to the Australian Plate migrating towards the subduction zones of Southeast Asia DiCaprio et al 2009 We will now load into GPlates the outlines of the Carpentaria Basin Queensland Plateau and Marion Plateau focus regions of the above authors 5 File gt Manage Feature Collections gt Open File gt locate and select CarpentariaBasin gpml QueenslandPlateau gpml and MarionTerrane gpml in the I
11. geographically meaningful let s open a coastline file 3 File gt Open Feature Collection gt locate Global_EarthByte_GPlates Coastlines 20091014 gpml in the Importing Rasters data bundle gt Open www gplates org 3 What are we missing Unless we load a rotation file the coastlines and any other datasets we want to visualise will remain fixed in present day coordinates 4 File gt Manage Feature Collections gt Open File gt locate Global_EarthByte GPlates_ Rotation_20091015 rot in the Importing Rasters data bundle gt Open Now use the Animation Controls and or Time Controls in the Main Window above the globe Figure 4 to reconstruct the image sequence back through time Blues indicate negative dynamic topography whereas reds indicate positive dynamic topography To watch the evolution of the dynamic evolution of the Earth s surface since 100 Ma set the Time to 100 00 and then press the Play button See www gplates org user manual Reconstructions html for more details about manipulating animations Time 60 00 Gma gt I 44 b gt Figure 4 Time and Animation controls in the main window You may use these controls to manually enter a time move the slider to reconstruct the globe or animate from a selected time to the present PART B Time dependent raster sequences can be combined with other reconstructable datasets in order to analyse and investigate features in the geological record We will now
12. ies on the Eurasian Plate gt Begin time of appearance 60 00 Ma gt End time of disappearance 60 00 Ma gt Choose a name for the feature e g SundalandSlabWindow60Ma gt Next gt lt Create a new Feature Collection gt gt Create You have now created your 60 Ma slab window and added it to a new Feature Collection However remember that you need to save it so open your Manage Feature Collections dialog File gt Manage Feature Collections and save the feature using a new name H and the gpml format This Feature Collection can now be loaded into GPlates when you next open the program Alternatively you could have exported the polygon geometry as a file of longitudes and latitudes and visualised them for example using GMT Generic Mapping Tools Wessel and Smith 1998 To do this follow the methodology you learnt in the Creating New Features Tutorial i e you would select the Export button in the New Geometry Window to the right of the globe and chose the GMT file format From this exercise we have shown that seismic tomography combined with plate reconstruction software GPlates can help geoscientists to learn about past plate boundary configurations Our slab window helps constrain the location of the spreading ridge that was being subducted 60 Ma the Wharton Ridge This is just an example using one tomography model If you would like to compare the different models go back to step 8 and load a new set of
13. mporting Rasters data bundle gt Open www gplates org 4 We will also load in the locations of several wells that have recorded anomalous tectonic subsidence in the Cenozoic 6 File gt Manage Feature Collections gt Open File gt locate Wells Australia gpml in the Importing Rasters data bundle gt Open Figure 5 2 RR ROZOR Viw 3DGlobe i i OOOOOO le 178 dat 22 29 lon 145 65 Mouse lat 14 28 lon 61 64 off globe 5 Clicked Selected Topology Sections Figure 5 View of the Australian region with basin outlines and well data loaded into GPlates Now play the animation through from 100 0 Ma as you did previously at the end of PART A How does the dynamic topography signal evolve in the focus areas we have loaded You will notice that the negative signal strengthens as Australia migrates in a north northeasterly direction PART C Advanced We will now be using a combination of regional time dependent rasters and reconstructable data sets to reveal an assumed Late Cretaceous Early Tertiary slab window beneath Sundaland Whittaker et al 2007 a region of Southeast Asia comprising the Malay Peninsula Borneo Java Sumatra and the surrounding islands SLAB WINDOWS Slab windows form as a result of spreading ridges intersecting subduction zones Dickinson and Snyder 1979 When ridges are subducted the down going plates continue to diverge yet
14. nates EE KOO E EEIE Feature View 3D Globe a 141 B lat 1 09 lon 115 95 Mouse lat 47 50 lon 65 23 Clicked Selected Topology Sections Feature type Plate ID Figure 12 60 Ma reconstruction of ocean floor ages and present day coastlines Notice that the youngest oceanic crust and hence the spreading ridge is converging with western most Sundaland Rotate the globe to centre on Sundaland and use the Time controls to jump to 60 Ma Figure 12 How does your digitised slab window compare to the location of subduction of the Wharton Ridge and hence the kinematically inferred slab window If you would like to learn more about how seismic tomography is being used to constrain the location of the Wharton Ridge and slab window beneath Sundaland during the Late Cretaceous to Early Tertiary see Fabian et al 2010 EXERCISE 2 Creating JPEGS to Import as Rasters In this exercise we will learn how to create JPEGS that can be loaded into GPlates using the example of a global gravity raster This workflow can then be easily modified to suit other data that you may want to visualise It should first be noted that this exercise assumes that you have GMT Generic Mapping Tools Wessel and Smith 1998 The GMT software is free to download See http gmt soest hawaii edu to learn more www gplates org 12 The following GMT commands will transform an IMG file into gridded data that c
15. older called Dynamic Topography in the Importing Rasters data bundle gt click on the folder and click Choose you cannot select an individual JPEG when loading a Raster Sequence www gplates org 2 Plates fl Edit View Reconstruction Layers Tools 800 0 Open Feature Collection 360 _ GPlates Open Raster F Open Time dependent Raster Sequence E i A View Read Errors Time a Manage Feature Collections 3M View Shapefile Attributes e 2 OD Figure 2 Step 1 Navigating the menu bar to open time dependent raster sequences If you have previously been working with a regional raster image and have not closed and reopened GPlates you will notice that the loaded image has been compressed to fit inside the region you have been working on To fix this problem you must reset the surface extent of the raster image 2 Layers gt Set Raster Surface Extent gt Reset fields to 90 180 90 180 Figure 3 s 5 s Set the latitude and longitude extent of the raster image Use the Tab key to cycle through the fields Lower left Latitude 60 0000 Longitude L00 0000 4 v Upper right Latitude 0 0000 Longitude 180 0000 EJ a v Reset fields to 90 180 90 180 Cok Cancel p a N p a Sc K by Fa A Figure 3 Step 2 Resetting the surface extent of the raster images to fit a global domain To make these rasters more
16. onvert postscript files to other formats using GhostScript Must have GhostScript installed see chostscript com world gravity ps Name of postscript file to be converted to a new format Specifies output format j JPEG Specifies raster resolution in dpi A Adjusts the bounding box to the minimum size actually required a by the image this 1s extremely important for creating JPEGs for GPlates as it eliminates any white empty space around the image P Forces landscape plots to be rotated to portrait orientation Now that you have a global raster your new JPEG try importing it into GPlates following the steps in EXERCISE 1 In this case you must also set the raster extent Although your raster indeed extends from 180 to 180 it only contains data between latitudes 80 738 and 80 738 l Layers gt Set Raster Surface Extent Figure 13 www gplates org 14 L sth A Nae Ths Sa gt Set Raster Surface Enteni Set the latitude and longitude extent of the raster image Use the Tab key to cycle through the fields Lower left Latitude 80 7380 Longitude 180 0000 Upper right Latitude 80 7380 Longitude 180 00001 2 Reset fields to 90 180 90 180 f M a aa i A A gt H a a f wR Figure 13 Step I a the niece extent T T raster image so that it wraps around the globe but only shows data between the specified latitudes What will happen if you don t adjust the
17. pplication File Name File Format Layer Types Actions QueenslandPlateau gpml GPlates Markup M E MarionTerrane gpml GPlates Markup QML Unload the file from GPlates A 2 a GS sl Gs Gs Gs CarpentariaBasin gpml GPlates Markup em 3 Wells_Australia gpml GPlates Markup wm 3 a a eo ec Global_EarthByte_GPlates_Co GPlates Markup ew 7 ri Save All M Open File Figure 6 The eject button under Actions far right allows data files to be unloaded from GPlates We will now load in the seismic tomography raster sequence 8 File gt Open Time dependent Raster Sequence gt locate folder called Montelli06_S in the Importing Rasters data bundle gt click on the folder and click Choose you cannot select an individual JPEG when loading a Raster Sequence We are dealing with a regional raster sequence and therefore we need to adjust the surface extent of the rasters so that they are not stretched out to cover the whole globe Figures 7 and 8 www gplates org 7 9 Layers gt Set Raster Surface Extent Lower left coordinates are 20 0000 latitude and 80 0000 longitude Upper right coordinates are 30 0000 latitude and 130 0000 longitude _ GPlates File Edit View Reconstruction CE Tools Palaeomagnetism Manage Colouring 2 GPlates 0 00 Elma D _ Show Background Raster Set Raster Surface Extent v Show Point Features
18. surface extent of the raster GPlates assumes that rasters extend from 180 to 180 and 90 to 90 therefore it will stretch your JPEG to the poles whereby distorting the image and making impossible to make an accurate analysis of your data REFERENCES DiCaprio L M Gurnis and R D M ller Long wavelength tilting of the Australian continent since the Late Cretaceous Earth Planet Sci Lett vol 278 p 175 185 2009 DiCaprio L R D Miller and M Gurnis A dynamic process for drowning carbonate reefs on the Northeastern Australian Margin Geology vol 38 1 p 11 14 2010 Dziewonski A M D L Anderson Preliminary reference Earth model Phys Earth Planet Int vol 25 4 p 297 356 1981 Fabian T J M Whittaker and R D M ller Ground truthing proposed slab window formation beneath Sundaland using Seismic Tomography ASEG PESA 2010 International Geophysical Conference and Exhibition Sydney Australia August 22 26 Heine C R D M ller B Steinberger and L DiCaprio Integrating deep Earth dynamics in paleogeographic reconstructions of Australia Tect Phys In Press www gplates org 15 Li C R D van der Hilst E R Engdahl S Burdick A new global model for P wave speed variations in Earth s mantle Geochem Geophys Geosyst vol 9 5 2008 Lithgow Bertelloni C and M Richards The dynamics of Cenozoic and Mesozoic plate motions Reviews of Geophysics vol 36 1
19. time dependant rasters Figure 9 from the folder called MIT P08 GPlates can further be employed to compare the location of the slab window inferred from seismic tomography with its location inferred from other data sources for example plate tectonic reconstructions We will now load in EarthByte s time dependent crustal age sequence from the Importing Rasters data bundle 12 File gt Manage Feature Collections gt Open File gt locate and select age grid jpegs in the Importing Rasters data bundle gt Choose This is a global raster sequence so make sure you adjust the raster surface extent 13 Layers gt Set Raster Surface Extent gt Reset fields to 90 180 90 180 Spend some time reconstructing the raster sequence using the Animation and or Time controls you can see how old the oceanic crust is in various areas of the world www gplates org 11 We will now compare the location of the slab window that you inferred from seismic tomography to the location where the youngest oceanic crust and hence the crust adjacent to the spreading ridge is being subducted beneath Sundaland for simplification we will assume that the spreading ridge is positioned at the centre of the youngest oceanic crust Figure 15 In other words we will be comparing our slab window with the approximate location of the slab window inferred from a plate kinematic reconstruction Note youngest crust is coloured red GPlates Coordi
20. tored in image files such as JPEGS Note that they differ from vector images that are composed of points and line segments Rasters in GPlates Global and regional raster images can be displayed in GPlates They are essentially draped over the 3D globe to form an individual layer upon which other data can be superimposed This functionality assists with visualising data sets by placing them in their global context When combined with other reconstructable data sets e g coastlines plate boundaries etc raster images can effectively constrain where points polylines and polygons are digitised GPlates also supports time dependent rasters that is a set of raster images whose pixels change with time www gplates org 1 See the GPlates online manual for further information www gplates org user manual DataFileTypes html IMPORTANT THINGS TO NOTE GPlates currently supports the widely used JPEG image format Rasters can only be viewed on the 3D globe projection GPlates assumes that rasters extend from 180 to 180 longitude and 90 to 90 latitude if this 1s not the case then the bounds of the image must be specified click Layers gt Set Raster Surface Extent Linear projections are preferable however images of any projection can be imported It is important to be careful when interpreting images of other projections as they may be slightly distorted Time dependent rasters must conform to a specific file name
21. ucture of the present day mantle by establishing a relationship between slab depth and slab age i e when the slab was being subducted at the surface NOT the age of the oceanic crust we can use tomography data to learn about past subduction zones By examining the relationship between subducted materials sinking velocity and its current depth we can make estimates about the age of subducted material Table 1 displays the corresponding depth of the age coded tomography slices Depth Slice km Age Ma p24 P1464 8o p84 90 www gplates org 6 Table 1 Age depth relationship for tomography slices based on Lithgow Bertelloni and Richards 1998 To begin we need to unload the data used in PART B that is not necessary for PART C Therefore unload CarpentariaBasin gpml QueenslandPlateau gpml MarionTerrane gpml and Wells Australia gpml We do not need to unload the coastline file as we want to see how the continents specifically the Sunda Block have moved through time with respect to the slabs inferred from the seismic tomography 7 File gt Manage Feature Collections gt click the eject symbol that applies to each of the above mentioned files far right 1con under the Actions tab see Figure 6 Only one raster image sequence can be loaded at one time therefore loading another raster will cause the current one to be replaced Manage Feature Collections Manage the feature collections which are loaded in the a
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