 |
| Titel |
Contrasting crustal evolution processes in the Dharwar craton |
| VerfasserIn |
Penelope J. Lancaster, Sukanta Dey, Craig D. Storey, Anirban Mitra, Rakesh K. Bhunia |
| Konferenz |
EGU General Assembly 2015
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250101097
|
| Publikation (Nr.) |
 EGU/EGU2015-164.pdf |
|
|
|
|
|
| Zusammenfassung |
| Archaean cratons provide a critical window into early Earth dynamics, preserving a record of
crustal evolution processes that include the start of ‘modern’ plate tectonics and the
development of supercontinents. However, these same processes can also destroy or rework
substantial volumes of crust, and the oldest extant Archaean terrane is only ~3.9 Ga. Where
Archaean rocks are exposed, bulk techniques such as Pb and Nd isotopes can provide
considerable information about continental formation, but these may have been altered by
later metamorphic events. Another method is to examine sedimentary units, which can
preserve fragments of the crust that are no longer exposed at the Earth’s surface. Resistant
detrital minerals such as zircon have particular use in these studies, as they incorporate a
range of isotopic and geochemical tracers and can survive multiple crystallisation
and/or sedimentary events. In this manner, a more complete record of a craton’s
evolution may be obtained, with the benefit of contributions from contrasting isotopic
systems.
The Dharwar craton of southern India is one such Archaean block, comprising >2.7 Ga
trondjhemite-tonalite-granodiorite (TTG) gneisses, volcano-sedimentary belts (>3.0 and
2.9–2.6 Ga) and 2.7–2.5 Ga calc-alkaline to potassic granitoids. These rocks preserve
evidence for several cycles of supracrustal formation, deformation, metamorphism and
granitic activity during the Precambrian. New in situ U–Pb-Hf analyses of detrital zircons
from across the craton indicate significant juvenile crustal extraction events at ~3.3 and 2.7
Ga, and continuous extraction from 3.7–3.3 Ga. Reworking in the older western block at
~3.0 Ga marks the onset of cratonisation, most likely due to ‘modern’ plate tectonic
processes, while reworking in both the western and younger eastern block at 2.55–2.50 Ga
indicates accretion of the two terranes and final cratonisation much later than in
most other Archaean terranes (~2.7 Ga). Different patterns of disturbance to the
zircon U–Pb systematics reflect variations in both the U content of parent rocks and
later metamorphic conditions. Tectonic links are observed between the Kaapvaal
and western Dharwar cratons, and between the north China and eastern Dharwar
cratons, though none of these links necessarily requires a consanguineous origin. |
|
|
|
|
|
|