UQ researchers find world's deepest rocks
University of Queensland researchers have discovered the world's deepest mantle rocks originating from between 400km and 670km beneath the Earth's surface.
Earth Sciences Department Professor Ken Collerson, Research Fellow Dr Balz Kamber and PhD student Sarath Hapugoda published the results of their study of the rocks from the island of Malaita in the Solomon Islands in prestigious international journal Science in mid-May.
Their co-researcher was Dr Quentin Williams from the Earth Sciences Department at the University of California Santa Cruz in the United States.
Touted as possibly the most important rocks ever found at the Earth's surface, they will increase understanding of the nature and origin of the Transition Zone between the upper and lower mantle, a part of the planet once only accessed using seismic imaging, through the study of minute mineral inclusions in diamond or through experimental simulation.
'These rocks contain a variety of high-pressure minerals, including majorite, a silica-rich form of the mineral garnet, that only forms at pressures of 10 to 22 Gpa prevailing between 400km and 670km beneath the Earth's surface where the upper mantle gives way to the lower mantle,' Professor Collerson said.
'In addition to majorite, some of the deep mantle samples also contain micro-diamond.'
Malaita lies east of Papua New Guinea and north-east of Guadalcanal fiercely fought over during World War II. Geologists have known for at least 20 years that 34 million years ago, deep-sourced volcanic pipes burst through 90 to 120-million-year-old submerged lavas known as the Ontong Java Plateau in the central Pacific Ocean.
'Carried by the Pacific Plate, this plateau eventually smashed into the Indo-Australian Plate 15-20 million years ago, creating the island of Malaita. As it drifted westward, the plateau was cut by many pipes. These pipes are similar to the kimberlite pipes of South Africa and elsewhere which commonly carry diamonds originating from depths of more than 150kms to the surface,' Professor Collerson said.
He said further detailed study of the crystal structure of these unique minerals would be carried out with a number of international collaborators and with members of the Centre for Microscopy and Microanalysis at UQ during the next year.
'Trace element and isotope chemical data for these unique rocks, obtained in my world-class isotope facilities will provide exciting new information concerning the chemical stratification of the Planet,' Professor Collerson said.
For more information, contact Professor Ken Collerson (telephone 07 3365 8505) or Shirley Glaister at UQ Communications (telephone 07 3365 2339).
You can send us an email at communications@mailbox.uq.edu.au, visit the web site for UQ Earth Sciences or coverage by BBC news
