Manzaz volcanic field is a volcanic field in Algeria. It consists of

scoria cones A cinder cone (or scoria cone) is a steep conical hill of loose pyroclastic fragments, such as volcanic clinkers, volcanic ash, or scoria that has been built around a volcanic vent. The pyroclastic fragments are formed by explosive eruptions o ...

with

lava flows Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a moon onto its surface. Lava may be erupted at a volcano or through a fracture in the crust, on land or un ...

and has been active until recently.

Geography and geomorphology

The field lies in

Hoggar The Hoggar Mountains ( ar, جبال هقار, Berber: ''idurar n Ahaggar'') are a highland region in the central Sahara in southern Algeria, along the Tropic of Cancer. The mountains cover an area of approximately 550,000 km. Geography Thi ...

, close to the

Atakor volcanic field Atakor volcanic field ("Atakor" in Tuareg means "swollen part, knot at the end of something") is a volcanic field in Algeria. It lies in the Hoggar mountains and consists of a variety of volcanic features such as lava flows and about 450 individua ...

. A dome-like

uplift Uplift may refer to: Science * Geologic uplift, a geological process ** Tectonic uplift, a geological process * Stellar uplift, the theoretical prospect of moving a stellar mass * Uplift mountains * Llano Uplift * Nemaha Uplift Business * Uplif ...

has been associated with the volcanism in the region. The presence of volcanism has been explained by tectonic events associated with the collision between Europe and Africa, and the resulting reactivation of ancient tectonic lineaments. The field consists of

scoria cone Scoria is a pyroclastic, highly vesicular, dark-colored volcanic rock that was ejected from a volcano as a molten blob and cooled in the air to form discrete grains or clasts.Neuendorf, K.K.E., J.P. Mehl, Jr., and J.A. Jackson, eds. (2005) ''G ...

s and covers a surface of . Many of these have breaches and are heavily eroded. The cones were strombolianically active and have erupted

lava flow Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a moon onto its surface. Lava may be erupted at a volcano or through a fracture in the crust, on land or und ...

s. Volcanic ash and

pyroclastic Pyroclastic rocks (derived from the el, πῦρ, links=no, meaning fire; and , meaning broken) are clastic rocks composed of rock fragments produced and ejected by explosive volcanic eruptions. The individual rock fragments are known as pyroc ...

s are also found. Oukcem is a

maar A maar is a broad, low-relief volcanic crater caused by a phreatomagmatic eruption (an explosion which occurs when groundwater comes into contact with hot lava or magma). A maar characteristically fills with water to form a relatively shallow ...

in the field that consists of two separate

crater Crater may refer to: Landforms *Impact crater, a depression caused by two celestial bodies impacting each other, such as a meteorite hitting a planet *Explosion crater, a hole formed in the ground produced by an explosion near or below the surfac ...

s with diameters of and respectively. They are surrounded by tuffs and natron is found at the bottom of the larger crater.

Geology

The basement consists of metamorphic and

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 ...

ic rocks of

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 ...

age, which are part of the

Tuareg shield The Tuareg Shield is a geological formation lying between the West African craton and the Saharan Metacraton in West Africa. Named after the Tuareg people, it has complex a geology, reflecting the collision between these cratons and later events. ...

. Outcrops of granite are found in some places. These were first buried by tholeiitic basalts between 35 and 30 million years ago. The field has mostly erupted basalt and

basanite Basanite () is an igneous, volcanic (extrusive) rock with aphanitic to porphyritic texture. It is composed mostly of feldspathoids, pyroxenes, olivine, and plagioclase and forms from magma low in silica and enriched in alkali metal oxides that s ...

. Xenoliths include

peridotite Peridotite ( ) is a dense, coarse-grained igneous rock consisting mostly of the silicate minerals olivine and pyroxene. Peridotite is ultramafic, as the rock contains less than 45% silica. It is high in magnesium (Mg2+), reflecting the high prop ...

and pyroxenite, and

amphibole Amphibole () is a group of inosilicate minerals, forming prism or needlelike crystals, composed of double chain tetrahedra, linked at the vertices and generally containing ions of iron and/or magnesium in their structures. Its IMA symbol is A ...

and feldspar form megacrysts in the rocks. Xenoliths appear to, in part, originate from a metasomatized

mantle A mantle is a piece of clothing, a type of cloak. Several other meanings are derived from that. Mantle may refer to: *Mantle (clothing), a cloak-like garment worn mainly by women as fashionable outerwear **Mantle (vesture), an Eastern Orthodox ve ...

. The total volume of erupted rocks is about .

Eruptive history

Three phases of volcanic activity have been distinguished at Manzaz, the first between 20 and 12 million years ago, the second between 7 and 4 million years ago and the third between 3 and 0.01 million years ago. Volcanic activity continued into the Holocene. Some young volcanoes developed on terraces of Neolithic age.

References

Sources

* * {{refend Volcanic fields Holocene volcanoes Volcanoes of Algeria