Terrestrial Palaeoecology and Global Change

Chapter 5. Tectonic factors of global changes
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with that of the Atlantic (above), but antithetic to that of the Tethys (V.6.5). The Late
Cretaceous – Palaeogene thrust belts are supperimposed, with a dextral offset, upon the
Palaeozoic frame, partly re-shuffling the Caledonian nappes (Elswick, 1984). They are
exposed on Lyakhovski Islands of the New Siberian Archipelago, western De Long
Rise, western Svalbard, the Canadian Archipelago (Eureka Sound) and over the Brooks
Range of Alaska. Like in the Atlantic, a major thrusting event occurred in the Late
Palaeocene to Early Eocene (Saalman & Tiedig, 2001), involving the Cretaceous volcanic/metamorphic
deposits. A large thrust sheet of Cretaceous andesites and silicites is
recorded on the Alpha (Mendeleev) Ridge (Herron et al., 1974), a submerged arcuate
structure over the western border of the Beaufort – Chukchi block, linking the ophiolitic
melanges of the northern Ellesmere Island, Arctic Canada, with those of the Lyakhovski
Islands, New Siberian Archipelago (Savostin & Drachev, 1988).
The peri-Arctic mobile belt is, thus, strikingly similar to the Caribbean (V.6.3) and, as
we shall see, to the Tethys (V.6.5), with the Lomonosov Rise of intermediate crust
corresponding to the Nicaraguan Rise and with fossil volcanic arcs represented by the
Alpha – Mendeleev Ridge and the Aves Rise respectively. In both the recent extensional
zones are controlled by transcurrent fault systems, the Nansen ridge/trough system of
the Arctic Ocean having its equivalent in the Cayman ridge/trough system of the Caribbean.
Both extended over continental borders, the former to the Moma graben of Yakutia
(Volk et al., 1984), the latter – to the Motagua–Polochic fault zone of Guatemala.
The above comparisons show that both the Atlantic and Arctic margins might have
been active over the Mesozoic. Their mosaic block structures, their thrust belts with
ophiolitic melanges are similar to those of the Pacific margin. However, the Atlantic –
Arctic phases of marginal expansion in the Neocomian, thrusting over continental margins
in the mid-Cretaceous and back-thrusting, supposedly with re-orientation of Benioff
zones, in the terminal Cretaceous and Eocene, are antithetic to the roughly synchronous
tectonomagmatic events in the circum-Pacific belt.
V.6.5. Cretaceous Tethys
In the northern mid-latitudes, the peri-Atlantic and circum-Pacific fold belts are linked
by a seismically active zone extending over the Mediterranean and southern Asia. This
zone corresponds to the Cretaceous – Tertiary and older belts of folded marine deposits
that prompted the idea of Tethys, an extinct seaway between the Laurasian and Gondwanic
landmasses. In the classical geotectonics, the Tethys fold belt was ascribed to
contraction closing the seaway. Later the emphasis has shifted to the ophiolite assemblages
as remnants of oceanic crust obducted on continental blocks (microcontinents)
that were rafted across the Tethys Ocean (or the successive Tethys I – Tethys II oceans)
to their random collision with each other and with mainland Asia. A brief overview of the
Tethys would show this as not having been the case.