Geology of Niger
From Wikipedia, the free encyclopedia
The geology of Niger comprises very ancient igneous and metamorphic crystalline basement rocks in the west, more than 2.2 billion years old formed in the late Archean and Proterozoic eons of the Precambrian. The Volta Basin, Air Massif and the Iullemeden Basin began to form in the Neoproterozoic and Paleozoic, along with numerous ring complexes, as the region experienced events such as glaciation and the Pan-African orogeny. Today, Niger has extensive mineral resources due to complex mineralization and laterite weathering including uranium, molybdenum, iron, coal, silver, nickel, cobalt and other resources.
Neoproterozoic (1 billion-539 million years ago)
The oldest rocks in Niger, along the border with Burkina Faso and northern Ghana predate the 2.2 billion year old Proterozoic Birimian rocks common in much of West Africa. The pre-Birimian crystalline basement rocks include gneiss and migmatite metamorphosed to amphibolite grade in the sequence of metamorphic facies. The Liptako region, in the west has amphibolite, chlorite-schist, meta-andesite, meta-arkose, micaceous quartzites and garnet gneiss which are younger. These rocks formed after a granite-gneiss complex in the area, but before the mudstones, tuff, quartzite, conglomerate and greywacke of the Amarasinde and Bellekoire beds. These Upper Birimian Supergroup rocks are intruded by younger granites.
The Air Massif began to form in the Precambrian. More than half of the basement rock in the massif is metamorphic, including the Edoukel mesozonal micaschist, Azanguerene gneiss, Tafourfouzete letpynite[check spelling] and possible ophiolite of the Aouzeueur formation.[1]
The Volta Basin syncline along the border with Burkina Faso contains Neoproterozoic rocks, with the oldest rocks near the edge of the basin. After the 50 percent of basement rocks that are metamorphic, the rest of the rocks in the Air Massif Renatt type and Dabaga type granite, which formed during the Pan-African orogeny mountain building event 600 million years ago. [2]
Paleozoic (539-251 million years ago)
During the Cambrian as multi-cellular life became commonplace, anorogenic magmatism formed ring complexes, that now comprise 30 different massifs in the Niger-Nigerian Younger Granite Province. The oldest, Cambrian massifs formed in the north.
Throughout the Paleozoic ring complexes with significant variety in structure and rock type formed in the Air Massif. In fact, the Air Massif has the largest ring-dike in the world, with a diameter of 65 kilometers. Geologists subdivide the different ring complexes into three different types. The Taghouaji-type has plutonic alkaline rocks and may have peraluminous granites while the Goudai-type is mainly acid volcanic rocks. The Ofoud-type is the most varied, encompassing gabbros, granites and anorthosite.
The Iullemeden Basin at Tamesna began to form in the Paleozoic. The center of the basin was uplifted by the Hercynian orogeny to form the Hoggar Mountains. Sedimentary rocks from the Paleozoic, thicken toward the mountains and to the south. East of Tamesna, Cambrian and Ordovician sedimentary rocks are up to 500 meters thick and include conglomerates and sandstones. There is an unconformity between these deposits and glacial sediments, associated with the widespread glaciation and global cooling of the Ordovician-Silurian extinction event. In ascending order, glacial deposits are overlain by Early Silurian graptolite shales, Devonian sandstones and shales and Early Carboniferous deltaic sandstones.
A coal bearing layer, likely tied to a marine transgression is overlain by shales and limestones, which contain coral and conodont fossils.[3]
Mesozoic-Cenozoic (251-66 million years ago)
A marine transgression in the Cenomanian, during the late Mesozoic topped off the Iulllemeden Basin with marine sedimentary rocks, often on top of Early Cretaceous terrestrial sedimentary rocks. The region remained flooded well into the Cenozoic, throughout the Paleocene, before drying out and shifting from marine sediment deposition to continental sediments.[3]