 |
| Titel |
Fluid-controlled rheological responses during intraplate orogeny |
| VerfasserIn |
Tom Raimondo, Daniel Howlett, Martin Hand, Chris Clark |
| Konferenz |
EGU General Assembly 2016
|
| Medientyp |
Artikel
|
| Sprache |
en
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250130375
|
| Publikation (Nr.) |
 EGU/EGU2016-10624.pdf |
|
|
|
|
|
| Zusammenfassung |
| The intraplate Alice Springs Orogen, central Australia, is characterised by fluid-rock systems
that systematically vary in their depth, structural style, fluid sources and magnitude of
rehydration and reworking. Discrete metre-scale cataclastic faults in the northwestern
Reynolds–Anmatjira Ranges progress into ten- to hundred metre-scale metasomatised shear
zones at the southeastern margin of this terrane, associated with low δ18O and δD values
indicative of a meteoric fluid source. Continuing along strike to the southeast, these structures
are succeeded by kilometre-scale schist belts transecting Palaeoproterozoic granulites in the
Strangways Metamorphic Complex, followed by a ∼7500 km2 zone of pervasive
Palaeozoic amphibolite facies retrogression and voluminous partial melting in the Harts
Range and Entia Gneiss Complex further east. Strongly deformed outcrops of the
basal sedimentary unit of the Amadeus Basin (Heavitree Quartzite) are preserved in
these areas, and discrete shifts to elevated δ18O values suggest that shear zones of
the Strangways Metamorphic Complex contain fluids sourced from its prograde
dewatering.
Intriguingly, despite being part of a laterally-continuous, anastomosing shear belt that
forms the dominant structural network of the Alice Springs Orogen, the fluid-rock systems
described above appear to be diachronous. Garnet Sm-Nd and monazite U-Pb geochronology
from garnet-staurolite-biotite-muscovite-quartz ± kyanite ± sillimanite schists of the
Strangways Metamorphic Complex indicate metamorphic ages of ca 445 Ma, ca 380
Ma, ca 360 Ma and ca 330 Ma, spanning approximately 120 Myr of fluid-rock
interaction and partial melting. P–T evolutions constrained by petrography, EPMA
X-ray maps and calculated pseudosections also demonstrate multiple prograde
thermal cycles across this interval, while field relationships indicate the reactivation of
contractional structures by overprinting extensional ultramylonites, attesting to a prolonged
and episodic history of fluid-driven metamorphism and deformation. The Alice
Springs Orogen therefore represents a remarkable natural laboratory to investigate the
contribution of metasomatic processes to intraplate orogenesis through space and
time.
We explore the possibility that the fluid-rock interaction history of this intraplate orogenic
event had a profound impact on its structural/metamorphic expression, and by inference the
rheological response of the lithosphere. In particular, we suggest that the spatial and temporal
evolution of Alice Springs shear zones may be linked to the availability of fluids in the deep
crust and their effects on lithospheric strength through processes such as hydration and
reaction softening. Far from being a purely local phenomena, therefore, deep crustal
metasomatism had a profound impact on the dynamics of basement reactivation, acting in
concert with other factors such as regionally elevated heat production to critically reduce the
long-term strength of intraplate lithosphere and provide impetus for large-scale reworking. |
|
|
|
|
|
|