How is a Lamprophyre formed?
Distribution. Lamprophyres are usually associated with voluminous granodiorite intrusive episodes. They occur as marginal facies to some granites, though usually as dikes and sills marginal to and crosscutting the granites and diorites. In other districts where granites are abundant no rocks of this class are known.
Where is dolerite formed?
Formation. Dolerite cools under basaltic volcanoes, like those at mid-ocean ridges. It cools moderately quickly when magma moves up into fractures and weak zones below a volcano.
What is the texture of dolerite?
Dolerite. Fine grained, ophitic texture. Primary minerals – plagioclase, pyroxene, hornblende and quartz. Acicular and lath-like plagioclase, equant grains of pyroxene – some alteration to chlorite along cleavage and fissures.
What is the origin of granite?
Origin. Granite is an igneous rock and is formed from magma. Granite magma has many potential origins but it must intrude other rocks. Most granite intrusions are emplaced at depth within the crust, usually greater than 1.5 km and up to 50 km depth within thick continental crust.
What is the origin of basalt?
Basalts are formed by the rapid cooling of basaltic lava, equivalent to gabbro-norite magma, from interior of the crust and exposed at or very close to the surface of Earth. These basalt flows are quite thick and extensive, in which gas cavities are almost absent.
What type of igneous rock is Lamprophyre?
ultrapotassic igneous rock
Lamprophyre is ultrapotassic igneous rock that is occurring as dikes, lopoliths, loccoliths, stocks and small intrussion. It is alkaline silica-undersaturated mafic or ultramafic rocks with high magnesium oxide, >3% potassium oxide, high sodium oxide and high nickel and chromium.
Is dolerite a greenstone?
The majority of greenstone used for hand axes is a medium- to coarse-grained basic intrusive rock (generally dolerite or sometimes gabbro) that may often have undergone low-grade metamorphism with the development of various secondary minerals.
What Colour is dolerite?
diabase, also called Dolerite, fine- to medium-grained, dark gray to black intrusive igneous rock.
Is augite a mineral?
Augite is a common rock-forming pyroxene mineral with formula (Ca,Na)(Mg,Fe,Al,Ti)(Si,Al)2O6. Augite has two prominent cleavages, meeting at angles near 90 degrees.
Is dolerite a basalt?
əˌbeɪs/), also called dolerite (/ˈdɒl. əˌraɪt/) or microgabbro, is a mafic, holocrystalline, subvolcanic rock equivalent to volcanic basalt or plutonic gabbro.
What is the origin of the word lamprophyre?
The term “lamprophyre”, from ” lampros ” and ” porphyros ” (glistening porphyry), was introduced by von Gumbel in 1874 for a group of dark rocks that form minor intrusions, contain phenocrystal brown mica and hornblende, but lack feldspar phenocrysts.
Where do ultramafic lamprophyres come from?
The nature and origin of ultramafic lamprophyres: alnöites and allied rocks. Journal of Petrology, 27 (1), 155-196. • Rock, N. M. (1987).
Where do alkaline lamprophyres come from?
The alkaline lamprophyres are generally interpreted as being derived from hydrous basanitic, or tephritic magmas that evolved in areas of crustal doming, and they may be emplaced during the early stages of continental rifting. They include: camptonite, monchiquite, sannaite, fourchite and other rare rocks.
What are the characteristics of lamprophyre rocks?
Because of their relative rarity and varied composition, lamprophyres do not fit into standard geological classifications. In general, they form at great depth and are enriched in sodium, cesium, rubidium, nickel, and chromium, as well as potassium, iron, and magnesium. Some are also source rocks for diamonds.