Сборник упражнений по грамматике английского языка. Стрелкова М.С. - 29 стр.

to magmas generated at subduction zones, whereas mafic and ultramafic rocks
are broadly comparable with modern tholeiitic basalts.
      54) The rocks are therefore considered to have originated in oceanic island-
arc environments.
      55) Isotopic studies indicate the rocks of the Rinns Complex to have been
formed as newly differentiated (Juvenile) mantle-derived materials.
      56) Provenance studies of locally-derived granitic boulders in younger
sediments show them to be petrographically and chemically similar to compo-
nents of the Rinns Complex.
      57) These data suggest that rocks found in the Rinns Complex were once
much more widespread.
      58) Specialists therefore considered these rocks to have originated in oce-
anic island-arc environments.
      60) Furthermore, Rb – Sr ages from the Diabeg and Applecross Formations
are interpreted to date diagenesis at c. 994 Ma and 977 Ma respectively.
      61) The detrital zircon ages are similar to those from the Moine Super-
group, which suggests the sediments to have been derived from a similar source
region.
      63) These granites are supposed to have been formed as a result of partial
melting of Moine rocks at a deeper crustal level, and recent isotopic dating of
several of these bodies indicates an age of c. 873 Ma for their emplacement.
      64) Field relations indicate these pegmatites to have been emplaced during
regional ductile deformation and metamorphism.
      65) The ages of the shear zones are considered to be c. 806 Ma, based on
the dating of monazite that crystallized during metamorphism.
      66) From the available evidence the Moine Supergroup and Dava are con-
cluded to have been deformed and metamorphosed during the Knoydartian
Orogeny at c. 840–780 Ma.
      67) In many studies the evolution of relief has been proved to be very sen-
sitive to certain crustal movements.
      68) Likewise assymetrical or other anomalous features in drainage basins
have been shown to be dependent on late deformations of the earth’s crust.
      69) Oil is known to be one of the most important sources of energy.
      70) Petroleum is believed to have been formed from decaying plant and
animal remains.
      71) Drilling is considered to be the principal exploration method and it is


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