Das Problem der paläomagnetischen Quantifizierung von 'Greater India'
Physik des Erdkörpers
Zusammenfassung der Projektergebnisse
Knowing the pre-collisional extent of the northern Indian Plate margin (‘Greater India’) is vital to understanding the tectonic evolution of the India-Asia collision and the formation of the Himalayan- Tibetan orogen. However, suitable geological units for paleomagnetic investigations along the Himalayan belt are limited, which makes it difficult to reconstruct Greater India during the precollisional period in Late Cretaceous to Paleogene. Often the paleomagnetic results from the Zongpu Formation at Gamba in southern Tibet (~88.5°E) were used for estimates of Greater India, but their validity was recently questioned. As a contribution to closing the data gap, we performed a paleomagnetic study of the Paleocene/Lower Eocene Dibling limestone (DL) in the western Tethyan Himalaya of Zanskar (34.0°N/76.6°E). The results from 27 sites revealed a well grouping (k=71.7) syntectonic magnetization with best grouping at 52% unfolding. The remagnetization of the DL was acquired shortly after ~54 Ma, at the latest at ~49 Ma, and is probably carried by fine-grained magnetite formed during the early orogenic phase. Assuming proportional tilting of the fold limbs, the corresponding paleolatitude of 11.8 ± 2.4 °N suggests a maximum Greater India extent of 810 ± 420 km and a first continental contact with the southern Eurasian margin at ~12°N in the western part of the suture zone. The tectonostratigraphic equivalence of the DL with the Zongpu Formation at Gamba and a great similarity in their magnetic properties supports a secondary origin of the Gamba results. Through understanding the mechanism of remagnetization in the DL, an early orogenic remanence acquisition is also indicated for the Zongpu Formation, and thus the Gamba results deserve further credit for Greater India reconstructions. However, we notice a large inconsistency of the available Late Cretaceous and Paleogene paleolatitude data from the Tethyan Himalaya by up to ~20°, corresponding to differences of up to ~2000 km in the size of Greater India. These discrepancies require further paleomagnetic work in the Tethyan Himalaya, and in particular we recommend comparative studies at same locations and of same units.
Projektbezogene Publikationen (Auswahl)
- On the diversity of paleomagnetic results used for Greater India reconstruction. 34th Himalaya-Karakoram-Tibet Workshop 2019, Bozeman/Montana (USA)
Appel E.
- Paleomagnetic record of Greater India in Paleocene limestones of the Western Himalaya. 34th Himalaya-Karakoram-Tibet Workshop 2019, Bozeman/Montana (USA)
Dannemann S., Appel E., Rösler W., Nag D.
- (2022). Paleomagnetic indication for India-Asia collision at 12°N and maximum 810 km Greater India extent in the western suture zone. Geophysical Journal International, 229, 1193–1211
Dannemann S., Appel E., Rösler W., Neumann U., Liebke U., Nag D.
(Siehe online unter https://doi.org/10.1093/gji/ggab528)
