MSGID: 1:317/3 641a846e   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    'Rock stars' solve long-standing diamond conundrum    
    Queensland University of Technology    
      
     Date:   
         March 21, 2023   
     Source:   
         Queensland University of Technology   
     Summary:   
         Two researchers have used a standard laptop computer and a humble   
         piece of rock -- from the 'waste pile' of a diamond mine -- to   
         solve a long- held geological conundrum about how diamonds formed   
         in the deep roots of the earth's ancient continents.   
      
      
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   FULL STORY   
   ==========================================================================   
   Two QUT researchers have used a standard laptop computer and a humble   
   piece of rock -- from the 'waste pile' of a diamond mine -- to solve   
   a long-held geological conundrum about how diamonds formed in the deep   
   roots of the earth's ancient continents.   
      
      
   ==========================================================================   
   The paper "Deep, ultra-hot-melting residues as cradles of mantle diamond,"   
   has been published in the academic journal Nature by lead author QUT   
   PhD student Carl Walsh, along with QUT Professor Balz Kamber and Emma   
   Tomlinson from Trinity College, Ireland.   
      
   Mr Walsh said the study, for his MSc research, involved computer modelling   
   on a rock from the African continent and recovered from the bottom of   
   the lithosphere, the outer part of the Earth between about 30km and   
   250km below the surface.   
      
   Mr Walsh said the dominant part of a continent was the part that you   
   never see.   
      
   "If you think of an iceberg -- the visible part -- if you just had an   
   iceberg floating on the ocean surface it would tip over like a boat. This   
   is like the keel of an iceberg," Mr Walsh said.   
      
   "We basically had a known starting composition of a rock, which is   
   representative of the earth's mantle at an early time in the history of   
   the earth before all the continents were formed," Mr Walsh said.   
      
   "We took that starting composition and modelled what would happen to it   
   if it was progressively melted, and what would be left over. And that   
   material is what forms the bulk of the roots of ancient continents that   
   are still around today."  Professor Kamber, from QUT's Faculty of Science,   
   School of Earth and Atmospheric Sciences, said the aim of this research   
   was to use a computer model to see how these deep roots might have formed.   
      
   "The model essentially predicts which minerals and melts will be present   
   as you change the temperature of the mantle. So, it's a predictive tool   
   you can compare with the composition of actual minerals and rocks,"   
   Prof Kamber said.   
      
   The piece of rock used for the advanced computer modelling was mined   
   sometime between 1871 and 1914 and ended up in the 'waste-pile' of   
   the legendary Kimberley diamond mine, best known as 'The Big Hole' --   
   a combination open-pit and underground mine -- in Kimberley, Northern   
   Cape in South Africa.   
      
   The piece of rock they have modelled, garnet harzburgite, was brought   
   to the surface in a kimberlite pipe. The rock was retrieved by Professor   
   Kamber -- who specialises in petrology, a branch of geology that studies   
   rocks and the conditions under which they form.   
      
   He carefully sledgehammered the rock down to a size that he could   
   successfully ship home.   
      
   "It contains a jumble of minerals that were entrained on the way up   
   as they ripped through the base of the whole continent in a supersonic   
   volcanic eruption -- the likes of which we have never seen," Professor   
   Kamber said.   
      
   "The minerals in this rock sample are so badly hurt, they are screaming   
   still today, they were absolutely smashed."  "It is so exciting to see   
   this preserved, it is extremely old -- 3.3 billion years old. Probably   
   the oldest rock most people will ever hold in their hands," Professor   
   Kamber said.   
      
   Mr Walsh said the study solved the conundrum of diamonds and the   
   temperatures in which they formed, given a diamond will turn into graphite   
   if heated up too much.   
      
   "But yet, when we look at the rocks that contain diamonds, they must   
   have been heated to massive temperatures," Mr Walsh said.   
      
   "So why is it that it is exactly those rocks that experienced the highest   
   temperatures that ended up having diamonds?"  Their research challenges   
   the existing two-step shallow "melting and stacking" explanation.   
      
   "Previously, it was believed that most of the ancient deep roots of   
   continents would have been host to diamonds, and that these diamonds were   
   destroyed over time, because the base of the continent is continually   
   invaded and eroded by volatile rich melts and fluids," Mr Walsh said.   
      
   "Our work suggests that actually this might not be the case, that diamonds   
   are rare today -- and were in fact always rare."  "And that's because   
   we can for the first time know what is missing from the cradle of the   
   diamond and we can go hunt for it at the surface."  Professor Kamber   
   said on the present-day earth the heat and temperature distribution in   
   the mantle is not uniform.   
      
   "We have areas of relatively uniform mantle temperature, and areas where   
   the mantle is a lot hotter. These are known as mantle plumes. And we   
   have expressions of these in Hawaii and Iceland," Professor Kamber said.   
      
   "What we're studying is the effect of ancient plumes -- when much hotter   
   plumes than we have now would have hit the base of a growing continent."   
   Since conducing the research, Mr Walsh has travelled to Canberra   
   to recreate similar rocks in the lab at the Research School of Earth   
   Sciences at the Australian National University.   
      
       * RELATED_TOPICS   
             o Matter_&_Energy   
                   # Energy_and_Resources # Chemistry # Nature_of_Water #   
                   Thermodynamics   
             o Earth_&_Climate   
                   # Earth_Science # Geology # Climate # Atmosphere   
       * RELATED_TERMS   
             o Ice_age o Landslide o Feldspar_mineral o Glacier o Ocean o   
             Sedimentary_rock o Ocean_current o Metamorphic_rock   
      
   ==========================================================================   
   Story Source: Materials provided by   
   Queensland_University_of_Technology. Note: Content may be edited for   
   style and length.   
      
      
   ==========================================================================   
   Journal Reference:   
      1. Carl Walsh, Balz S. Kamber, Emma L. Tomlinson. Deep,   
      ultra-hot-melting   
         residues as cradles of mantle diamond. Nature, 2023; 615 (7952):   
         450 DOI: 10.1038/s41586-022-05665-2   
   ==========================================================================   
      
   Link to news story:   
   https://www.sciencedaily.com/releases/2023/03/230321112642.htm   
      
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