My science/technology-related thoughts, sometimes controversial, sometimes can be based on limited knowledge base, logic can be non-perfect as well. I develop my vision in iterations. Don't take this blog as an attempt to convince anybody in anything.
Each post in this blog reflects my level of understanding of Tectonics of the Earth at the time the post was written; so, some posts may not necessarily be correct now.

22 July, 2011

Porphyry Copper. More On Reshaping Pangaea (Gondwana).

Today's documents are:
- U.S. Geological Survey, Open-File Report 2005-1060, Version 1.0. "Porphyry Copper Deposits of the World: Database, Map, and Grade and Tonnage Models" By Donald A. Singer, Vladimir I. Berger, and Barry C. Moring, 2005. ( http://pubs.usgs.gov/of/2005/1060/ ) [Accessed Jul-22, 2011}

- NASA, Earth Observatory, "Alfred Wegener (1880-1930)" by Patrick Hughes, map on Wegener's fossil and geological evidence that the continents were previously connected ( http://earthobservatory.nasa.gov/Features/Wegener/wegener_4.php ) [accessed on Jul-22, 2011]

- "Some General Concepts underlying the Science of Geology", primary author Nicholas M. Short, Sr. , section 2, "The Rock Cycle" ( http://rst.gsfc.nasa.gov/Sect2/Sect2_1b.html ), image showing the positions of the continents from early Pangaean breakup to the Present. [accessed on Jul-22, 2011]


Only Eastern Australia is rich of porphyry copper deposits.
   On the image showing the positions of the continents from early Pangaean breakup to the present there is no porphyry copper deposits for:
- southern part of South America;
- Africa (3 deposits in Africa are too old to fit the discussed time frame);
- Antarctica;
- India;
   Only Eastern Australia (New South Wales and Queensland) are rich of the deposits. The deposits are dated according to mentioned "The tab-delineated text file containing the porphyry copper database", if I understand it correctly:
- 220-300 Mya for Queensland deposits (approx 16 items);
- 440-460 Mya for New South Wales deposits (approx 8 items);
   Also half dozen of deposits are scattered between Western Australia, Victoria, South Australia, the deposits seem to be too old to fit the discussed time frame.
   How did all items of the image managed not to develop porphyry copper and only Queensland and New South Wales got the copper during 220-300 Mya and 440-460 Mya accordingly?

Comparing the shorelines.
   Let's look a bit closer at Queensland/New South Wales shoreline using a map tool. Compare the shoreline to the Chile's shoreline corresponding to Atacama desert. Compare the Australia's fragment between Byron Bay and down to south of Port Macquarie to the Chile's fragment between Arica and down to Tocopilla. Please keep in mind, Australia may had rotated slightly since then. I can be wrong, that's just a suggestion that Australia once was connected to South America. Besides the fragment of Chile's shoreline seems to be complimentary to the mentioned Australia's fragment, Chile, as everyone know, features porphyry copper deposits not even worse than East Australia.


 The porphyry copper pattern as an evidence of the layout of Pangaea.
   I'll check Chile's deposits ages later, the discrepancy in the age can be explained by the fact that the subduction process on the western and eastern sides between diverging Australia and Chile may had initiated at different times (porphyry copper development seems to be related to the subduction process). The porphyry copper development seems to be taking time of steady subduction of the oceanic crust. The suggested by Wegener Australia's post-Pangaea trajectory seems not to fit the 
 picture of steady subduction process against the East Australia. The suggested in "Reshaping Pangaea" ( http://divergent-boundaries.blogspot.com/2011/07/reshaping-pangaea.html ) the Australia's post-Pangaea path seems to fit porphyry copper pattern better. 

India's almost "porphyry copper"-less status.
   Regarding India's almost "porphyry copper"-less status, India seemed to start off the Australia's North-West, that is too far from the subduction zone, and thus had had no chance developing porphyry copper.


Summing things up.
   Well, this was an attempt to prove that Australia was connected to South America at Pangaea times. Then Australia was diverged out to its current position. The diverging was accompanied with the subduction of oceanic crust under the Eastern Australia, thus porphyry copper deposits were developed. The 440-460
 Mya age of New South Wales deposits was, probably, because the deposits were developed on the previous "Ring Of Fire" cycle.

Next stop - nothofagus-less Africa.
   Next attempt to prove "new" Pangaea layout will probably be to talk on nothofagus-less Africa. On Wegener's layout of Pangaea, nothofagus was found on the left from Africa in South America, on the right in Australia, and even on the bottom in Antarctica, but not in Africa. The suggested in "Reshaping Pangaea" ( http://divergent-boundaries.blogspot.com/2011/07/reshaping-pangaea.html ) "new" Pangaea layout takes care of Africa.

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