GUYANA will be hot news in Italy this week -as GGMC makes presentation on rock with traces of geological crust over four billion years old Written by Clifford Stanley Sunday, 25 August 2013 22:17 GUYANA will be hot news in Florence, Italy this week as there will be a presentation to the Goldschmidt Conference, the world’s premiere international conference on geo-chemistry, by the Guyana Geology and Mines Commission (GGMC) which will show that age dating of a rock from the North Rupununi contains traces of a geological crust which existed in the Hadean eon i.e: over four billion years ago. The rock, a small chunk of granite, was collected by GGMC geologists at Toka in the North Rupununi late 2011 during a geological and geo diversity mapping exercise with the CPRM, the Geological Survey Department of Brazil. It was age dated as being 2.4 billion years old by the University of Nanjing in China in 2012 but was also found to contain tiny minerals called zircon crystals aged 4.2 billion years. Given the scientific evidence that the earth was formed 4.6 billion years ago, the discovery has led to altered perceptions about the true geological age of Guyana, a discovery which it is expected will create a buzz at the Goldschmidt Conference which will be hearing about it for the first time. The GGMC presentation to the Goldschmidt Conference , is to be done by Senior Geologist Dr. Serge Nadeau. He will be one of three presenters each one providing scientific information on the topic: “What do we know of the Hadean after 30 years- zircons, extinct nuclides—and more.” It is captioned: “Guyana, the lost Hadean Crust of South America?” Local Geologists have explained that the Hadean is the first geologic eon of Earth which began with its formation about 4600 million years ago and ended 4,000 million years ago. This geological eon precedes the Archean eon dated between 4,000 million and 2,500 million years ago. The name "Hadean", scientists say, comes from Hades, the ancient Greek god of the underworld due to the "hellish" conditions on Earth at the time: the planet had just formed and was still very hot due to high volcanism, a partially molten surface and frequent collisions with other Solar System bodies. The word “lost” is used in the presentation by Dr, Nadeau because the zircons in the rock found at Toka are the only physical evidence of Guyana as it existed in this first geologic eon of planet earth. Dr Nadeau recently explained that prior to the collection of the Toka rock and its age dating, the oldest known rocks in Guyana were dated at 1.8 to 2 billion years of age a period of time referred to by geologists as the Proterozoic eon –eons being a division of geological time amounting to hundreds of millions of years.. The geological history of Guyana has therefore been thought all along to have begun in the Paleo Proterozoic 2500 million years ago. Additionally, Hadean zircons aged over 4 billion years and Archean zircons aged between 2.5 billion and 4 billion years have been found to date only in rocks in Canada and Australia. Few geological traces remain of the Hadean and the existence of zircons , indicating this crust or even Archean zircons indicating a younger crusts in Guyana, were hitherto unknown. Reporting on the joint geological and geo-diversity mapping survey during which the rock was found Dr Nadeau reported that Uranium Lead ( U-pb dating) was conducted on eighteen rocks from Southern Guyana by the State Key Laboratory of Mineral Deposit Research in Nanjing China. He disclosed that rocks were taken from three main areas in Southern Guyana where hitherto little age age dating had been done. The zircons of granitic rocks in the Southern Guyana Granite Complex, South Rupununi (most southerly) yielded the youngest age ie: 1925 million years (Ma) to 1928 Ma of age. These rocks contained only a few older zircon crystals clustering at 2086 Ma. 2138Ma, 2261 Ma and 2297Ma. The metamorphic age of zircons from the Kanuku Complex obtained from two rock samples was estimated at 1956-1968 Ma of age. Several other rock samples from the Kanuku contained significant proportions of zircons with older age values clustering at 2200-2269 Ma; 2450 Ma; 2,520Ma. (Archean eon) and 2,635 Ma. (Archean eon ) and 2707-2721 Ma (Archean eon). “The zircons over 2,500 million years old is the first ever indication that Guyana existed during the Archean eon,”Dr. Nadeau said. But it was the rocks of the Iwokrama Formation which displayed the largest range of age. Minimum age of crystallization of the volcanic and sub volcanic granitic rocks was 1981-1986Ma. Older zircon xenocrysts clustered at 2196-2202 Ma, 2395-2417 Ma, 2487-2489 Ma, 2852-2882 Ma, 2949 Ma, 3701 Ma, 3778 Ma and 4218 Ma. The oldest age obtained from a zircon core was one with a concordant age of 4219 Ma. A second zircon core determination from the same crystal yielded a slightly discordant age of 4210 Ma. The rim of the same zircon gave an age of 3733 Ma. These findings, the Geologist said, revealed that the age of the zircons in the Iwokrama Formation in the range of 2520-3811 Ma. overlap with Archean aged rocks of the Imataca Complex in Venezuela and of the Amapa Complex of northern Brazil between 2500 Ma and 3700 Ma. He concluded: “From the age dating results, The subvolcanic granite and felsic volcanic rocks of the Iwokrama Formation appear to contain zircons from a “Lost Hadean Crust” representing the oldest component of the Guiana Shield and of South America.” The Goldschmidt conference began yesterday and concludes on August 30. Dr. Nadeau will present his findings on Guyana’s lost Hadean crust on Thursday 29 between 17:30 and 20:00 hours.
Posted on: Mon, 26 Aug 2013 16:05:39 +0000
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