Gondwana


Gondwana

The above animation (uploaded 2020 September 9) demonstrates the central role of the Bouvet mantle plume in the break-up of Gondwana and the dispersal of its constituent continents using model CR20ABHJ.  Some explanation of the colours is given in the blue text below. Higher resolution JPGs of the frames making up an earlier animation are available [here] and will be updated soon  Explanatory notes are in preparation.  Specific queries are welcomed meanwhile. Colin Reeves. 2020 September 9.

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New! (2020 April 3)

Bouvet plume and triple junction in the Early Cretaceous.  51 high-resolution images, 150-100 Ma at 1 myr intervals.  Orthographic projection centred on 60.0 deg S, 5.0 deg W.  Fixed-hotspot reference frame. Model CR20ABBJ.  Available to view and download [here].

Gondwana dispersion, global view,  Mesozoic & Cenozoic. 50 high-resolution images, 300-190 Ma at 10 myr intervals, 185-0 Ma at 5 myr intervals. Orthographic projection centred on 30.0 deg S, 20 deg E. Fixed-hotpsot reference frame. Model CR20ABBI.  Available to view and download [here].

CGMW ocean colours, Mercator projection. 41 high-resolution images, 0-200 Ma at 5 myr intervals. Africa fixed in present-day location. Fragment codes. Available to view and download [here].

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Much of the work and reasoning behind the above animations is set out in Reeves, C.V., 2018: Petroleum Geoscience, vol 24, pp 41-56.  The extended abstract of a paper presented in London in October 2019 (accessible here) addresses many of the more recent developments.  Since that time the role of Africa's Mwembishi shear zone on the early opening of the South Atlantic and Indian oceans has been incorporated into the model. Refinements to the development of the Weddell Sea and the tectonics of Patagonia (up to Models CR20ABBI and CR20ABBJ) are included in the three detailed image series listed below the animation. Model CR20ABHJ, incorporating these refinements, is demonstrated in the animation at the top of the page. These will be explained in a future Research Update.

Precambrian terranes that made up Gondwana are shown in pink. In forward time, the growth of the oceans between them is depicted with the movement of the mid-ocean ridges (red with grey transforms) in relation to the mantle plumes (yellow stars), the creation of the large igneous provinces (blue/orange) and the pattern of transforms and fracture zones now evident in the topogprahy of the ocean floor (blue lines).  The age of the created ocean is indicated by colours similar to those used in the CGMW Geological Map of the World. The animation illustrates how the topographic features of the ocean floor (as well as marine magnetic anomalies that are scarce before about 84 Ma) constrain the interpretation.  The aimation is made from frames at intervals of 2 myr from 188 to 0 Ma. The Atlas software of CPSL was used throughout.  Research Updates describing the recent work appear in Section 4 (follow the link under heading 4 below).  Look out for more updates soon.

You are welcome to copy the above animated GIF and JPG image series into presentations of your own, with appropriate acknowledgment, for teaching and research purposes. Commercial users are requested to make contact with the author. Suggestions for added clarity or leads to new non-confidential data that should be incorporated into the constraints that define the model are always appreciated.

Please contact me with any queries at: reeves.earth@planet.nl

Colin Reeves

2020 September 11


Contents of this Section

1. An Introduction to the Principles of Global Tectonics [click here]  - for the non-specialist.

2. References [click here] - published work as well as the ‘grey’ literature for the specilaist.

3. A 12-Lecture Course on Gondwana Geodynamics [click here] - for those who want to learn.

4. Global Thoughts [click here] - latest Research Updates with recent ideas for discussion.

 

Background

The core of the work over many years has been the quest for a rigorous geometrical model for the re-assembly and dispersal of the whole of Gondwana.  The model comprises a series of Euler interval poles for the plate circuit Madagascar -> Africa -> Antarctica -> India that are available on request. 'Atlas' software from Cambridge Paleomap Services (CPSL) has been the workbench for all these efforts. Insights gained from hands-on experience with the geological reconnaissance through geophysical mapping of many whole countries in eastern and southern Africa, as well as India and Australia, 1970-2018, is brought to bear wherever possible. The work forms part of IGCP-628, the Geological Map of Gondwana [link to IGCP-628].

Much of the Gondwana continent can still be found preserved as rigid Precambrian crustal fragments (shown in pink) that have retained the same size and shape that they had within unified Gondwana at the end of Precambrian times. In the reassembly they are separated by an estimated amount of continental crust that has since been stretched in rifting processes and lost from view below Phanerozoic cover in rift zones and continental margins. Igneous rocks related to the activity of the labelled mantle plumes - mostly large volcanic plateaus in the oceans - are shown in blue.  

Active mid-ocean ridges are shown in red with major transforms in dark grey and extinct ridges dashed in black. Plume loci in a fixed mantle reference frame are shown as yellow circles (initially 1000 km in diameter) in the forward animation. Rifting within Africa is indicated in a somewhat stylised way, Karoo (Permian-Triassic) in orange, Cretaceous rifting in green and the current East Africa rifting in yellow. Karoo deposits, pre-dating Gondwana dispersal, are shown in pale orange and Cenozoic and younger cover in yellow. The animation supercedes that of  model CR18ABHG which is described in Reeves (2018).  The latest developments are explained in the Research Updates (Section 4 above).

What you see at the top of this page is an animated GIF file about 6 Mb in size. By right-clicking on the image and saving it to your computer it may then be imported as a video into a Powerpoint presentation, for example.  The images and the animations are free for teaching or research purposes, with suitable acknowledgment. Please seek permission for commercial use.  Enquiries and suggestions for collaborative studies are always welcome.

Images from model CR20AAAS, 0 to 200 Ma atintervals of 5 myr showing the ocean crust in colour, based loosely (and with permission) on the CGMW Geological Map of the World (2010) may be accessed [here]. [Ref: Geological Map of the World, 3rd edition, scale 1 :25 000 000. Ph. Bouysse et coll. © CCGM-CGMW / 2010. www.ccgm.org]

2020 February 13