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| Titel |
Characterising the world's most catastrophic volcanism: constraints from trace elements and radiogenic isotopes of the Siberian Traps large igneous province |
| VerfasserIn |
Marc K. Reichow, Andrew D. Saunders, Ian L. Millar, Victor N. Puchkov, Inna Yu. Safonova, Mikhail Buslov, Robert A. Scott, Alexander Ya. Medvedev, Alexander I. Al'Mukhamedov |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250042682
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| Zusammenfassung |
| Radiometric dating strongly indicates that the bulk of the Siberian large igneous province is
contemporaneous with the end-Permian mass extinction, approximately 251 m.y. ago. The
most visible manifestation of the Siberian Traps are outcrops on the Siberian craton (Noril’sk,
Putorana Plateau, Maymecha-Kotuy and Tunguska Basin), which are also the most
intensively sampled and analysed regions of the province. However, the greater province
extends beneath the West Siberian Basin (WSB) to the central (Chelyabinsk) and polar
(Vorkuta) Urals, north to the Taimyr Peninsula, and south to the Kuzbass. Many of these
areas appear not to be contiguous, either because they were erupted as discrete
subprovinces, or because tectonic activity and erosion has subsequently isolated them.
The genetic link between these areas continues to be a subject of active debate;
questions remain as to the contributing source materials and the process of their
formation.
The thick sections of basalts at Noril’sk have provided the defining characteristics (elemental
and isotopic) of the Siberian suites. In summary, these show a series of lower suites, typified
by high Gd/Yb ratios which indicate higher pressure melting, and high La/Sm and ε Nd2. Suites of the upper series
display generally low La/Sm and Gd/Yb indicating low pressure melting combined with ε
Nd>0 expect for the strongly crustally contaminated Nadezhdinsky suite with high La/Sm
and negative ε Nd. The latter are followed by Morongovsky suite basalts with transitional less
contaminated composition between basalts of the last Nadezhdinsky and the first
Morongovsky suite.
We present new major and trace element data, and radiogenic Sr, Nd, Hf, and Pb isotope data
for over 50 samples taken from the Siberian large igneous province in order to
understand the process of their formation. The basaltic rocks of the Province as a
whole can broadly be divided into low- and high-Ti groups; all our analysed samples
belong to the low-Ti group. From trace element data we infer that these low-Ti
basalts were derived by large degrees of partial melting. Basalts from the WSB,
and the Taimyr, Kuzbass, and central to polar Urals regions, exhibit major and
trace element characteristics typical of evolved, crustally-contaminated continental
flood basalts (e.g., low Mg#, negative Nb anomaly, high La/Sm) showing affinities
with the Noril’sk Nadezhdinsky suite of the main Traps. The trace element data are
consistent with a process of fractional crystallisation coupled with assimilation of
incompatible-element-enriched lower crust. Despite the elemental similarities, however, the
radiogenic isotope compositions of the igneous rocks west and south of the Siberian
craton (WSB, Kuzbass, and central to polar Urals regions) are very different from
those of the Nadezhdinsky suite. The WSB, Kuzbass and Urals regions basalts
display remarkably small ranges in initial Hf and Sr ratios (0.2827-0.2829 and
0.7043-0.7056, respectively) and ε Nd (2.26-4.16), although their Pb isotope ratios are
more varied (e.g. 206Pb/204Pb between 18.15 and 19.73). In terms of the isotope
data, the basalts of the WSB, Kuzbass, and central to polar Urals are similar to
the Noril’sk Morongovsky and Mokulaevsky Upper Series basalts, but from the
elemental data, these two Upper Series appear to be far less contaminated by upper
crust.
The isotopic composition of these rocks indicates the involvement of several distinct mantle
and lithospheric sources. Given the large areal extent of the Siberian large igneous province,
this is not altogether surprising, but the data do indicate that the subprovinces were derived
locally and not from a single point source or single rift system. This is a likely scenario
considering the varied composition of the continental crust even on a small scale. |
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