Nuvvuagittuq greenstone belt

The Nuvvuagittuq greenstone belt is a rock unit at the Hudson Bay in northern Canada in the province of Quebec, which is one with an age of possibly up to 4.3 billion years ago to the oldest rocks of the earth.

Location and geological setting

The Nuvvuagittuq greenstone belt located in the northern part of the Superior craton, the largest well-preserved archaic Kraton Earth. The Superior craton belongs to the Slave craton, the Wyoming craton and the North Atlantic craton to the four surviving archaic cratons the northern United States, Canada, and Greenland. It consists of greenstone belts and metamorphosed sediments, have invaded the intrusives of granitic composition. In the northeast and southwest it contains hochmetamorphe belt of gneisses. The Nuvvuagittuq greenstone belt located in the largest of these gneiss areas, the Minto - belt or Minto block in the northeast of Hudson Bay.

The greenstone belt is broken down in a about 3 × 4 km area right on the Hudson Bay. The name of the unit was chosen after a hill located in the north of the unit, it was formerly known as the Porpoise Cove Formation. It contains metamorphic volcanic and sedimentary rocks in an isoclinal synform, folded over to a more open, incident to the south synform. Surrounded is the occurrence of the so-called Boizard tonalitischem gneiss sequence.

Rocks

A characteristic element of the rock unit are light gray to beige mafic amphibolites with cummingtonite instead of the usually in the Superior craton in the normally dark to black amphibolites occurring hornblende ( faux - amphibolites, ie false or deceptive amphibolite ). The rock occupies the largest part of the greenstone belt. Turned in the ultramafic amphibolite are sills that can be traced back to an original komatiitisches magma, and pegmatites. Rarely occur felsic mica schist, which are activated as former tuffites.

In addition to the igneous rocks also converted sedimentary rocks have been preserved and turned on as band-like deposits in the amphibolite. As in other archaic rock units are oxide and quartz- rich Bändererze ( Banded Iron Formation, BIF) represented. Certain gneisses may be interpreted as conglomeratic units.

There is evidence that the different subunits of the greenstone belt, despite the strong overprint are still in their original stratigraphic association. All rocks were subject to a maximum metamorphism up to upper amphibolite facies and a later retrograde metamorphism ( Diaphthorese ).

Importance

The rocks and their age are still subject of research. First published in scientific journals age dating of these rocks were 3.6 to 3.8 Ga. The possibility that the rocks in Nuvvuagittuq greenstone belt part mya could have an age of up to 4,280, was founded in 2008 by researchers at McGill University discovered in Montreal. These results were questioned by other researchers. More detailed investigations are still underway.

In contrast to the igneous rocks of about the same age Acasta - gneiss from northwestern Canada some rocks of the Nuvvuagittuq Greenstone Belt were similar to that of the 3.8 billion years old Isua Greenstone Belt deposited on the earth's surface ( suprakrustal ). The converted sedimentary rocks are an indication that the time of their deposit already a hydrosphere must have existed. The existence of life at this time is also discussed in connection with the Nuvvuagittuq - rocks.