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Geochronology

The ages of the earth

A network is going to spur study on the dating of rocks and the possibility of finding oil fields

Starting from 2006, the University of São Paulo (USP) will gain a laboratory with the power to transform the research panorama in geology within the country. With funding from Petrobras and FAPESP, the Geosciences Institute of USP has ordered from Australia a sensitive high resolution ion micro probe, known by its acronym Shrimp, equipment capable of carrying out punctilious dating on a single crystal of a mineral, as well as determining the age of the geological processes in a faster and more precise manner than that of the available technology, the micro probe will be installed in a laboratory of 800 m2 on the USP campus.

Today the research work in the country in geochronology (the study of the age of rocks and geological event) and isotope geology (study of the composition of a material in order to determine its origin) depends on slow processes in super clean laboratories, where the chemical dissolving of the mineral grains, rocks or sedimentary material and the consequent analysis of the composition of isotopes are carried out. And what is obtained, in some cases, is an average age of the material, composed of a number of events that took thousands of years to occur. When the intention is carry out dating of individual phases of the growth of crystals, the only option is to send the material for analysis in other countries – it is estimated that US$ 200,000.00 is spent on the use of a micro probe of this type abroad. Only ten of these pieces of equipment exist in the world. That of USP will be the first in Latin America.

The acquisition will have an even greater impact because Petrobras, in partnership with the Ministries of Mines and Energy, Science and Technology and the National Geology Service, have decided to make use of the initiative and to widen investments in geological dating research and isotopic analysis. They are purchasing a further three pieces of equipment, with technology different from that of Shrimp (using laser beams instead of a beam of oxygen). This equipment will allow for the analysis of a greater spectrum of materials, although they will not produce results as precise as that of the SHRIMP micro probe. Known as ICP/MS (Inductively Coupled Plasma Mass Spectrometry (ICP-MS)mass spectrometer with a plasma source and multi-collector systems and of laser ablation), they will be donated to the universities of Brasilia, the Federal University of Rio Grande do Sul and the Federal University of Pará.

Bombarding
With the USP probe, a research network will be formed, baptized with the name GeoChronos (national network and geochronology, geodynamics and environmental studies), with the participation of Petrobras and of the Geology Service of Brazil. A committee is going to determine the projects that will be carried out. “The laboratories will be shared on a national level and also for researchers of other countries, above all Latin American countries, by way of specific scientific conventions”, says the geologist Ciro Jorge Appi, the executive manager of GeoChronos. “This is important both for Petrobras and for the National Geology Service, which will improve the knowledge on the potential of all of the South American continent. Today foreign laboratories, to where we remit studies of this nature, enjoy more quickly the benefits of information about our continent.”

USP’s Shrimp micro probe dispenses with the need for chemical dissolving and submits the grains to the bombardment of a beam of oxygen ions. The beam is positioned to hit specific points and minute parts of the rocky grain and to determine the age of each one of them. The bombarding brings about fusion of the desired points and releases ions of uranium and lead. The material passes through a mass spectrometer, of high resolution, capable of separating even isotopes with mass numbers very close to one another, and of high sensibility, capable of measuring very small quantities of elements.

Ion detector cells receive the separated isotopes and provide the necessary data for the calculation of the ages of each one of the points, revealing the history of the geological process of that particular grain. The technology manages to analyze a large quantity of zircons, crystals deposited in sedimentary basins in areas with potential petroleum fields and, in this manner, know the history of its formation and its characteristics. This helps in the evaluation of the potential for crude oil/natural gas reserves.

It also has applications in the dating of all types of rocks, which will allow for the elaboration of geological maps that are more precise and in a shorter time span. This will be helpful for miners since it will facilitate the discovery of new deposits. “With the micro probe it will be possible to take a qualitative jump and to increase the number of Brazilian articles in international magazines”, suggests Colombo Celso Gaeta Tassinari, an incumbent professor at the Geo-Chronology Research Center of USP’s Geosciences Institute, who supervised the laboratory purchase.

The project began to take shape some two years ago, when the USP group, led by  Tassinari and by Umberto Cordani, a professor at the Geology Department, sought out FAPESP in search of funding for the purchase of the micro probe. It was not a simple request. The equipment manufactured by the company Australian Scientific Instruments, costs US$ 2.5 million. “FAPESP promptly agreed to help with a part and recommended that we look for a partner”, recalls Tassinari, who went off to Petrobras. The interest of the national company was immediate. During 2000 the company had already been approached by the University of Brasilia, which had pleaded to the federal government for an allocation to purchase a Shrimp. Petrobras’s participation restricted itself to the construction of a building. The idea did not take off because the main allocation of funds did not come about.

Chronogram
The  cost of purchase of the Shrimp, a project approved by FAPESP within the environment of the Technological Innovation program, will be split  ups, US$ 1.5 million coming from Petrobras and US$ 1 million from FAPESP. The first payment is about to be released  and will define the chronogram of delivery. Each micro probe takes eighteen months to be built – for this reason the equipment will be installed at the earliest during the second semester of 2006. But there is a Shrimp that has been under construction for the last six months – disputed by various countries. If the Brazilian money arrives first, the micro probe will come sooner. The usage time within the laboratory will be divided in two. Researchers from the State University of Campinas (Unicamp) and from the São Paulo State University (Unesp) will have access to the equipment and together with those from USP will be able to make use of it for 50% of the time. The other half will fall to Petrobras, with the involvement of researchers from various institutions in the country.

The Project
Geo-Chronology Laboratory  with a sensitive high resolution ion micro probe: support for the development of High Technology Petroleum Exploration Projects (nº 03/09695-0); Modality Partnership for Technological Innovation (PITE); Coordinator Colombo Celso Gaeta Tassinari –  Geosciences Institute of USP; Investment US$ 1,000,000.00 (FAPESP) and US$ 1,500,000.00 (Petrobras)

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