Geoscience Reference
In-Depth Information
Isostatic
uplift
Lithospheric
creep
Sediment
erosion
Subsidence
Figure 10.16
The endogenic (tectonic) and exogenic (geo-
'gone onshore' and the resultant orogen is formed by isostatic
uplift of mélange, flysch and continental slivers around a
granite batholith. Lithosphere creep, which reinforces uplift,
creates subsidence elsewhere, and subsiding basins trap
siliciclastic sediment eroded from the orogen. B-subduction
magmatic eruptions and alpine glaciation ornament the
summits, rock avalanches and debris fans are the products of
rapid uplift and intense denudation.
Photo: Andrew Goudie
Tectonics and climate
NEW DEVELOPMENTS
Earth's most active environments are located at the contact between its crust and outer-lying hydrosphere, biosphere
and atmosphere, in the zone where internal heatflow and convection currents are powerful enough to detach the
lithosphere from the deeper geosphere. Movement and recycling of brittle plates across Earth's surface are exposed
to a gaseous and hydrothermal environment, stirred by radiant energy from the sun. Tectonics exerts the most
comprehensive of all of several major controls on these Earth system processes, through its fundamental mechanisms
of sea-floor spreading and uplift, dispersal of continents and oceans, formation and recycling of crustal rocks and
seismo-volcanic activity. These controls are summarized in
Figure 10.17
,
with specific influences and interactions
developed here and in the boxes of later chapters. The highly interconnected nature of these Earth systems makes
it impossible to consider any in absolute isolation but, for convenience, tectonic impacts on climate via the oceans,
continental denudation and geomorphic systems are left to their appropriate chapters.
Tectonics and climate
Solar radiation was acknowledged in Part Two ('Atmosphere') as Earth's dominant source of energy. Astronomic
controls on its receipt therefore mark out, across the planet's surface, primary zonal patterns of climate, general
circulation and those aspects of biogeochemical cycling it drives directly. This was recognized formerly in the trio of
climate, vegetation and soil classifications of traditional physical geography but considerable progress in our
understanding of climate change and the plate tectonics revolution has changed much of that. We can now assert
that tectonics control or influence every other aspect of climate, commencing with its biogeochemical role in geological
sourcing and processing of atmospheric constituents. This starts with volcanic eruption and continues through
weathering, denudation and recycling through subduction; we return to this below. Next, tectonic dispersal or
clustering and the geographical location of continents and oceans create basic physical distinctions between
continental and maritime climates and also determine the albedo and specific heat capacity of primary surfaces
exposed to incidental solar radiation. This generates substantial anomalies in expected zonal radiation and moisture
balances at hemispheric and regional scales, with positive or negative feedbacks from sequential effects. For example,
active elevation of northern hemisphere mid to higher-latitude land surfaces in the later Cenozoic predisposed them
