OROGENY, SEA-LEVEL AND STRONTIUM ISOTOPES

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• OROGENY, SEA-LEVEL AND STRONTIUM ISOTOPES
• A. M. C. Sengör
• ITÜ Maden Fakültesi, Jeoloji Bölümü,
  Ayazaga 34469 Istanbul, TURKEY
• Every advance in understanding has been made at
  the expense of some particular knowledge

Werner Heisenberg, 1949
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The Turkic-type orogens of the later
Neoproterozoic and the Phanerozoic
Pan-Africanides (900-550 Ma)
Altaides and Gondwanides (580-320 Ma) with some
Kuen-Lun Scythide additions
Cordillerides and Nipponides (250-2 Ma) with some
Cimmeride additions
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Definition of Turkic-type orogeny Collisional
orogeny involving the growth of very large
subduction-accretion prisms (commonly with
significant net crustal growth) ALL OROGENS ARE
ACCRETIONARY! WE THEREFORE DO NOT USE THE
TERM ACCRETIONARY OROGENY, WHICH AMOUNTS TO
AN UNINFORMATIVE TAUTALOGY
Altiplano
Pacific Ocean
Cordillera oriental
Subandes
Brasilian Shield
The Central Andes
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Evolution of 87Sr/86Sr in seawater and sea-level
in the Phanerozoic (87Sr/86Sr curve from
McArthur and Howard, 2004, sea-level from Hallam,
1992)
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What are the relationships between orogenic
events and global sea-level ?
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Drop in world-wide sea-level because of
diminished submerged continental volume
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Effect of hard collisions on world-wide
sea-level GLOBAL REGRESSION
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Rise in world-wide sea-level because of enlarged
submerged continental volume
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Effect of the growth of Turkic-type orogens on
world-wide sea-level GLOBAL TRANSGRESSION
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Two of the largest accretionary wedges in the
world today Alaska (above) and Iranian Makran
(below). The wedge in the Pakistani Makran (not
shown here) is almost twice as wide as the one in
the Iranian Makran
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(No Transcript)
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Volume of subduction/accretion complexerosion of
pre-existing materialjuvenile addition
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Global sea-level rise due to Turkic-type
orogeny Submergence of previously subaerial
crust (by erosion and transportation) addition
of juvenile crust to submerged subduction/accretio
n complexes
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Is there a tectonic reason for the late Permian
anomaly? (While global sea-level is dropping,
87Sr/86Sr is rapidly decreasing!)
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WEST
EAST
AN ENDORHEIC SUPERCONTINENT WITH PERIPHERAL
SUBDUCTION AND E-W CLIMATIC ASYMMETRY IN THE
SIMPLEST THREE-PLATE SETTING
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WEST
Marginal basins
EAST
Sabkhas on non-clastic shelves
AN ENDORHEIC SUPERCONTINENT WITH PERIPHERAL
SUBDUCTION AND E-W TOPOGRAPHIC CLIMATIC
ASYMMETRY IN THE SIMPLEST THREE-PLATE SETTING
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N Winter wind direction
Non-clastic shelves
Mountains
Palaeo-Tethys
N Summer wind direction
KUNGURIAN PANGAEA (275-270 Ma)
Deserts
River transport direction
Lake, marginal marine
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N
Guapore Shield
Western Landmass
THE CHACO-TARIJA BASIN (Modified from Eyles et
al., 1995)
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N Winter wind direction
Non-clastic shelves
Mountains
Palaeo-Tethys
N Summer wind direction
KUNGURIAN PANGAEA (275-270 Ma)
Deserts
River transport direction
Lake, marginal marine
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Pangaean wind patterns (Nairn
Smithwick1976) Black N Winter Red N Summer
Northern Siberia
South Tethyan shelf
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N Winter wind direction
Non-clastic shelves
Mountains
Palaeo-Tethys
N Summer wind direction
KUNGURIAN PANGAEA (275-270 Ma)
Deserts
River transport direction
Lake, marginal marine
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Reciprocal relationships between
mountain-building, glaciation, global sea-level,
87Sr/86Sr in sea water, and continental positions
and flooding
87Sr/86Sr
Andean Altiplano
Main Alpide collisions
Marginal Cimmeride collisions
Main Cimmeride collisions
Cape Altiplano
Pangaean desert basins
Final Uralide/Scythide/Hercynide/Appalachide
collisions
Final Caledonian collisions
Final Pan-African collisions
Sea-level High Low
Ice More Less
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The Turkic-type orogens of the later
Neoproterozoic and the Phanerozoic
Pan-Africanides (900-550 Ma)
Altaides and Gondwanides (580-320 Ma) with some
Kuen-Lun Scythide additions
Cordillerides and Nipponides (250-2 Ma) with some
Cimmeride additions
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Reciprocal relationships between
mountain-building, glaciation, global sea-level,
87Sr/86Sr in sea water, and continental positions
and flooding
87Sr/86Sr
Andean Altiplano
Main Alpide collisions
Marginal Cimmeride collisions
Main Cimmeride collisions
Cape Altiplano
Pangaean desert basins
Final Uralide/Scythide/Hercynide/Appalachide
collisions
Final Caledonian collisions
Final Pan-African collisions
Sea-level High Low
Ice More Less
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How much do global plate velocities control
world-wide sea-level? (And hence hydrothermal
activity the abundance of 86Sr)
Tethyan ophiolite obductions and beginning
collisions
End-Palaeozoic collisions and the Cape Altiplano
Pangaean anomaly!
Final Caledonide collisions
Caledonide/Appalachide ophiolite obductions and
beginning collisions
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major continental glaciation
major continental glaciation
Neither glacial nor Turkic-type growth history is
well-known here
More Ice Less
Largest glaciations in the history of the earth
correlate with termination of major Turkic-type
growth on the planet. WHY SHOLD THIS BE SO?
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Rise in world-wide sea-level because of enlarged
submerged continental volume
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Effect of the growth of Turkic-type orogens on
world-wide sea-level GLOBAL TRANSGRESSION, which
is not conducive to generating large continental
ice-caps
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CO2 released to atmosphere
CaCO3 subduction facilitated by flysch cushion
Accretionary prism(flysch cushion)
CaCO3 decomposed
Widesprad weathering CaSiO3CO2SiO2CaCO3
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Sea-level lowering
Turkic-type crustal growth leads to a CO2-rich
atmosphere Turkic-type collisions deplete the
atmosphere of CO2
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Major hard collisions of Alpine/Himalayan type
do not explain the main pattern of continental
glaciation, but explain details of major patterns
determined by Turkic-type evolution
Neither glacial, nor accretionary history
well-known here
Major continental glaciation
Major continental glaciation
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Regrettably, the precision of the timing of the
termination of Proterozoic glaciations is only
within 50 Ma. This and a similar imprecision in
the dating of the end of major Turkic-type
developments in the Proterozoic do not allow us
to test rigorously the hypothesis that ending of
a major Turkic-type growth triggers an ice-age.
Nevertheless, glaciations in the end of the
Proterozoic (between 640 to 590 Ma and 585 and
520 Ma) do correlate with the terminal
Pan-African collisions, i.e. end of major
Turkic-type growth in Gondwana-Land. The 750-700
Ma glaciation correlates with the end of the
Gapuvalli (India) and Chengjiang (China)
Turkic-type growth. For still earlier what we now
know of the record is just not good enough to say
anything.
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CONCLUSIONS Orogenic styles fluctuate with time
following the capricious dance of the continents,
now embracing, now disentangling. They seem to
control sea-level and trigger glaciations with
the help (or hindrance) of continental positions
and Milankovitch cyclicity. Earth history is
easily understandable, but not retrodictable,
because it is, at our presently available level
of observational capabilities, not deterministic.
As Werner Heisenberg often emphasised for
physics, geology has reached a level of abstract
understanding at the cost of particular
knowledge. This is the main bone of contention
between "field geologists" and "theoretical
geologists". Neither can do without the other,
but both will continue advancing towards an ever
enlarging field of understanding so long as both
appreciate what the game is about.