Page 21 - Global Tectonics

8 CHAPTER 1

nomenclature consequently represented an impedi- changes in sea level in the past, and the changing con-

ment to the recognition of a common causal mecha- figuration of the continents, and the uplift of mountain
nism. The relation of sedimentation to the mobilistic belts would have affected both oceanic and atmospheric
mechanism of plate tectonics (Mitchell & Reading, circulation. The nature and implications of these
1969) allowed the recognition of two specifi c environ- changes, in particular for the Earth’s climate, are
ments in which geosynclines formed, namely rifted, or explored in Chapter 13.
trailing, continental margins and active, or leading, Clearly some of these implications were docu-
continental margins landward of the deep oceanic mented by Wegener, notably in relation to the distribu-

trenches. The latter are now known as subduction tion of fauna and flora in the past, and regional
zones (Chapter 9). Although some workers retain geo- paleoclimates. Now, however, it is realized that plate
synclinal terminology to describe sedimentary associa- tectonic processes impact on the physics and chemistry
tions (e.g. the terms eugeosyncline and miogeosyncline of the atmosphere and oceans, and on life on Earth, in
for sediments with and without volcanic members, many more ways, thus linking processes in the atmo-
respectively), this usage is not recommended, and the sphere, oceans, and solid Earth in one dynamic global
term geosyncline must be recognized as no longer rel- system.
evant to plate tectonic processes. The fact that plate tectonics is so successful in unify-
ing so many aspects of Earth science should not be
taken to indicate that it is completely understood.
Indeed, it is the critical testing of the implications of
1.4 IMPACT OF plate tectonic theory that has led to modifi cations and
extrapolations, for example in the consideration of the
PLATE TECTONICS relevance of plate tectonic processes in continental
areas (Section 2.10.5) and the more distant geologic past
(Chapter 11). It is to be hoped that plate tectonic theory
will be employed cautiously and critically.
Plate tectonics is of very great significance as it repre-

sents the first theory that provides a unifi ed explanation

of the Earth’s major surface features. As such it has
enabled an unprecedented linking of many different
aspects of geology, which had previously been consid- FURTHER READING
ered independent and unrelated. A deeper understand-
ing of geology has ensued from the interpretation of
many branches of geology within the basic framework Hallam, A. (1973) A Revolution in the Earth Sciences: from
provided by plate tectonics. Thus, for example, explana- continental drift to plate tectonics. Oxford University
tions can be provided for the past distributions of fl ora Press, Oxford, UK.
and fauna, the spatial relationships of volcanic rock LeGrand, H.E. (1988) Drifting Continents and Shifting
suites at plate margins, the distribution in space and Theories. Cambridge University Press, Cambridge,
time of the conditions of different metamorphic facies, UK.
the scheme of deformation in mountain belts, or Marvin, U.B. (1973) Continental Drift: the evolution of a
orogens, and the association of different types of concept. Smithsonian Institution, Washington, DC.
economic deposit. Oreskes, N. (1999) The Rejection of Continental Drift:
Recognition of the dynamic nature of the appar- theory and method in American Earth Science. Oxford
ently solid Earth has led to the realization that plate University Press, New York.
tectonic processes may have had a major impact on Oreskes, N. (ed.) (2001) Plate Tectonics: an insider’s history
other aspects of the Earth system in the past. Changes of the modern theory of the Earth. Westview Press,
in volcanic activity in general, and at mid-ocean ridges Boulder.
in particular, would have changed the chemistry of the Stewart, J.A. (1990) Drifting Continents and Colliding Par-
atmosphere and of seawater. Changes in the net accre- adigms: perspectives on the geoscience revolution. Indiana
tion rate at mid-ocean ridges could explain major University Press, Bloomington, IN.