Tchabal Nganha is a
stratovolcano
A stratovolcano, also known as a composite volcano, is a conical volcano built up by many layers (strata) of hardened lava and tephra. Unlike shield volcanoes, stratovolcanoes are characterized by a steep profile with a summit crater and per ...
on the
Ngaoundere Plateau
The Ngaoundéré Plateau is a highland area in the Adamawa Region of Cameroon. It contains Tchabal Nganha, a large volcano, and many other recent volcanic structures.
Location
The plateau is between the forested south and savannah north of Cam ...
, a highland area in the
Adamawa Region
The Adamawa Region (french: Région de l'Adamaoua) is a constituent region of the Republic of Cameroon. It borders the Centre and East regions to the south, the Northwest and West regions to the southwest, Nigeria to the west, the Central Afr ...
of Cameroon.
Location
Tchabal Nganha is a large composite volcano located within the Ngaoundere volcanic field in the east of the
Adamawa Plateau
The Adamawa Plateau (french: Massif de l'Adamaoua) is a plateau region in west-central Africa stretching from south-eastern Nigeria through north-central Cameroon ( Adamawa and North Provinces) to the Central African Republic. The part of the pl ...
.
It is the only stratovolcano in the field.
Nganha rises about above the surrounding plateau to a height of at Doïtaïa Mounts.
The Adamawa plateau is an asymmetrical
horst bounded by N70°E
faults and tilted to the south.
The plateau has a
Precambrian
The Precambrian (or Pre-Cambrian, sometimes abbreviated pꞒ, or Cryptozoic) is the earliest part of Earth's history, set before the current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian, the first period of the ...
metamorphic
Metamorphic rocks arise from the transformation of existing rock to new types of rock in a process called metamorphism. The original rock (protolith) is subjected to temperatures greater than and, often, elevated pressure of or more, causin ...
basement
A basement or cellar is one or more floors of a building that are completely or partly below the ground floor. It generally is used as a utility space for a building, where such items as the furnace, water heater, breaker panel or fuse box, ...
that is
intruded
Intrusive rock is formed when magma penetrates existing rock, crystallizes, and solidifies underground to form '' intrusions'', such as batholiths, dikes, sills, laccoliths, and volcanic necks.Intrusive RocksIntrusive rocks accessdate: March ...
by
granite
Granite () is a coarse-grained (phaneritic) intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly cools and solidifies undergro ...
and
syenite
Syenite is a coarse-grained intrusive igneous rock with a general composition similar to that of granite, but deficient in quartz, which, if present at all, occurs in relatively small concentrations (< 5%). Some syenites contain larger proport ...
pluton
In geology, an igneous intrusion (or intrusive body or simply intrusion) is a body of intrusive igneous rock that forms by crystallization of magma slowly cooling below the surface of the Earth. Intrusions have a wide variety of forms and com ...
s from the
Paleozoic
The Paleozoic (or Palaeozoic) Era is the earliest of three geologic eras of the Phanerozoic Eon.
The name ''Paleozoic'' ( ;) was coined by the British geologist Adam Sedgwick in 1838
by combining the Greek words ''palaiós'' (, "old") and ' ...
.
It is partly covered by volcanic formations from the
Cenozoic
The Cenozoic ( ; ) is Earth's current geological era, representing the last 66million years of Earth's history. It is characterised by the dominance of mammals, birds and flowering plants, a cooling and drying climate, and the current configura ...
to Recent ages.
The
crust is thick below the plateau.
Although considered by many geologists to be part of the
Cameroon line, the
silicic
Silicic is an adjective to describe magma or igneous rock rich in silica. The amount of silica that constitutes a silicic rock is usually defined as at least 63 percent. Granite and rhyolite are the most common silicic rocks.
Silicic is the group ...
volcanism
Volcanism, vulcanism or volcanicity is the phenomenon of eruption of molten rock (magma) onto the surface of the Earth or a solid-surface planet or moon, where lava, pyroclastics, and volcanic gases erupt through a break in the surface called ...
of the Ngaoundere Plateau is younger (11 to 9 million years old) than silicic volcanism in the
Western Highlands, with much more alkaline
basalt
Basalt (; ) is an aphanite, aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the planetary surface, surface of a terrestrial ...
s than in the western part of the line.
Formation
Basalt
Basalt (; ) is an aphanite, aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the planetary surface, surface of a terrestrial ...
and
trachyte
Trachyte () is an extrusive igneous rock composed mostly of alkali feldspar. It is usually light-colored and aphanitic (fine-grained), with minor amounts of mafic minerals, and is formed by the rapid cooling of lava enriched with silica and al ...
rock samples from Nganha have
K–Ar ages of 7.2, 7.9 and 9.8 Ma (million years).
The volcano was formed in four overlapping phases.
First, many basaltic lava flows erupted throughout the region, creating the generally smooth relief.
Next, voluminous
breccia
Breccia () is a rock composed of large angular broken fragments of minerals or rocks cemented together by a fine-grained matrix.
The word has its origins in the Italian language, in which it means "rubble". A breccia may have a variety of di ...
s were deposited. Most of these have been deeply eroded except where covered by later lava flows.
Thick, radially distributed trachyte and
phonolite
Phonolite is an uncommon extrusive rock, of intermediate chemical composition between felsic and mafic, with texture ranging from aphanitic (fine-grained) to porphyritic (mixed fine- and coarse-grained). Phonolite is a variation of the igneous ...
flows then erupted.
They have steep margins and are separated by deep and narrow valleys.
Later there was basaltic activity at the summit.
Notes
Sources
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{{DEFAULTSORT:
Volcanoes of Cameroon
Adamawa Region
Miocene stratovolcanoes