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Petrologic and geophysical significance of mantle xenoliths in basalts
Author(s) -
MacGregor Ian D.
Publication year - 1975
Publication title -
reviews of geophysics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 8.087
H-Index - 156
eISSN - 1944-9208
pISSN - 8755-1209
DOI - 10.1029/rg013i003p00090
Subject(s) - geology , mantle (geology) , transition zone , basalt , mantle wedge , geochemistry , hotspot (geology) , olivine , geophysics , crust , peridotite , xenolith , crustal recycling , petrology , lithosphere , tectonics , continental crust , seismology
Data on the nature of the earth's upper mantle are derived from a combination of direct and indirect techniques. Indirect techniques, which include investigations of the seismic, thermal, electrical, and magnetic structures, monitor bulk properties of extensive regions of the upper mantle. The indirect measurements lead to estimates of the vertical and lateral structures in terms of the acoustic velocities, density, and thermal and electrical properties of the mantle. In contrast, certain geologic processes bring mantle samples directly to the surface. At these locations mantle rocks can be examined in fine detail and serve as a storehouse of descriptive data to calibrate the estimates of lateral and vertical structures given by the indirect geophysical methods. Geologic examples where mantle rocks have been brought through the crust to the surface include two major types of occurrences. The first group consists of large massifs of mafic and ultramafic rocks such as the ophiolites, alpine peridotites, and high‐temperature peridotites. They are brought to the surface by diapiric uprise of mantle material or tectonic forces resulting in the faulting or thrusting of mantle material into crustal environments. The second group includes inclusions of mantle material transported to the surface by host magmas that have their origin in the mantle. The alkalic magmas such as alkaline‐olivine basalts, mugiarites, nephelinites, and kimberlites are most commonly the host magmas. The mantle inclusions are predominantly accidental and represent direct samples torn from the walls of the conduits channeling the magma to the surface. In this sense they represent reverse churn drill holes into the mantle and offer the most direct technique for getting a single profile at a single locality. This report focuses on the progress made in studies concerned with mantle inclusions, particularly insofar as they contribute to knowledge of the physical structure of the mantle.