What minerals are in harzburgite?
Named for occurrences in the Harz Mountains of Germany, a harzburgite is an ultrabasic igneous rock dominated by essential olivine and orthopyroxene with or without small amounts of clinopyroxene. Accessory minerals include plagioclase, spinel, garnet, ilmenite, chromite and magnetite.
How do you identify harzburgite?
Unserpentinized harzburgite is a dark olivegreen, coarse-grained rock weathering red-brown on the surface. The orthopyroxene tends to resist weathering and serpentinization and forms rough projections on weathered surfaces. The rough surface and darker color serve to distinguish harzburgite from dunite in the field.
What is the composition of lherzolite?
Lherzolite is a type of peridotite containing idiomorphic Olivine with equal share of orthorhombic Orthopyroxene-Bronzite (with irregular grains), and monoclinic Clinopyroxene-Diallage.
How is lherzolite formed?
Lherzolite is common as a mantle xenolith within mantle-derived magmas and is present in the mantle sequence of ophiolites. Mantle lherzolite usually contains Cr-diopside as the clinopyroxene and enstatite as the orthopyroxene. Lherzolite can also form as cumulates within layered intrusions.
Where is Harzburgite found?
Garnet-bearing harzburgite is found as xenoliths in some kimberlite pipes, which are found almost exclusively in ancient continental cratons of Archean or Paleoproterozoic age. The mantle lithosphere under these cratons is particularly thick (up to 200 km or more) and cool.
Where are Ophiolites found?
Ophiolites have been found in Cyprus, New Guinea, Newfoundland, California, and Oman. The Samail ophiolite in southeastern Oman has probably been studied in the greatest detail. The rocks probably formed in the Cretaceous not far from the what is now the Persian Gulf.
Where is kimberlite rock found?
Generally speaking, kimberlites are found only in cratons, the oldest surviving areas of continental crust, which form the nuclei of continental landmasses and have remained virtually unchanged since their formation eons ago.
Where is harzburgite found?
Is lherzolite a basalt?
Partial melting of spinel lherzolite is one of the primary sources of basaltic magma.
Where is lherzolite found?
Lherzolite is known from the lower ultramafic part of ophiolite complexes (although harzburgite is more common in this setting), from alpine-type peridotite massifs, from fracture zones adjacent to mid-oceanic ridges, and as xenoliths in kimberlite pipes and alkali basalts.
How is Harzburgite formed?
Harzburgite typically forms by the extraction of partial melts from the more pyroxene-rich peridotite called lherzolite. The molten magma extracted from harzburgite may then erupt on the surface as basalt.