Large Accretionary Complexes of the World: Evolution of the southern segment of the Central Asian Orogenic Belt
Final Report Abstract
The Central Asian Orogenic Belt (CAOB) is one of the world’s largest accretionary orogens, which was active during most of the Paleozoic. In recent years it has again moved into focus of the geological community debating how the accreted lithospheric elements were geographical arranged and interacting prior and/or during the final amalgamation of Kazakhstania. Two families of competing models exist. One possible geodynamic setting is based on geological evidence that a more or less continuous giant arc connecting Baltica and Siberia in the early Paleozoic was subsequently dissected and buckled. Alternatively an archipelago setting, similar to the present day south west Pacific was proposed. During the duration of this project we were able to shed new light on the paleogeography of the south western part of the CAOB from the early Paleozoic until the latest Paleozoic to earliest Mesozoic. It is shown how fragments of Precambrian to early Paleozoic age are likely to have originated from Gondwana at high southerly paleolatitudes (∼ 500 Ma), subsequently accreted during the Ordovician (∼ 460 Ma) to form Kazakhstania, before migrating further northwards across the paleo-equator. During the Devonian and the latest Early Carboniferous (∼ 330 Ma) Kazakhstania occupied a stable position at about ∼ 30◦ N. At least since this time the area underwent several stages of counterclockwise rotational movements accompanying the final amalgamation of Eurasia (∼ 320 − 270 Myr). This overall pattern of roughly up to 90◦ counterclockwise bending was replaced by internal relative rotational movements in the latest Paleozoic, which continued probably until the early Mesozoic or even the Cenozoic. In the Karatau range of Kazakhstan we could identify widespread remagnetization acquired during during folding in the Carboniferous. Comparison of these results to coeval data from Baltica and Siberia lead to a documentation and quantification of rotational movements within the Karatau Mountain Range. Based on this results it is very likely that the rotational reorganization started in the Carboniferous and was active until at least the early Mesozoic. Additionally, the data shows that maximal declination deviation increases going from the Karatau towards the Tianshan Mountains (i.e. from North to South). This observation supports models claiming that the Ural mountains, Karatau and Tianshan once formed a straight orogen subsequently bent into a orocline. The hinge of this orocline is probably hidden under the sediments of the Caspian basin. Our study of Carboniferous rocks from the northern Tianshan demonstrates that the region has been affected by inclination shallowing inclination shallowing has affected the red terrigenous sediments of Carboniferous age resulting in faulty estimates of the paleoposition of this region. The corrected inclination values put this part of the Tianshan in a paleolatitude of around 30◦ N during Carboniferous times suggesting a stable stable latitudinal position between the Devonian and the Carboniferous.
Publications
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2011. Evolution of the southern segment of the Central Asian Orogenic Belt using Paleomagnetic data. American Geophysical Union, Fall Meeting 2011, abstract T23D-2423, 2011AGUFM. T23D2423B
Bachtadse, V., Kirscher, U., Mikolaichuk, A., Alexeiev, D.
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2012, Constraints on the structural evolution of the southern segment of the Central Asian Orogenic Belt by Paleomagnetic data EGU General Assembly 2012, held 22-27 April, 2012 in Vienna, Austria., p.9511
Kirscher, U., Alexeiev, D., Mikolaichuk, A., Bachtadse, V.
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2013 Constraints on the Tectonic Evolution of the Southern Segment of the central Asian Orogenic Belt by Paleomagnetic Data, 1st International Workshop on Geodynamic Evolution of the Central Asian Orogenic Belt. St. Petersburg, Russia
Kirscher, U., Mikolaichuk, A., Alexeiev, D.V. Bachtadse, V.
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2013. Paleomagnetism of Paleozoic sedimentary rocks from the Karatau Range, Southern Kazakhstan: Multiple remagnetization events correlate with phases of deformation. Journal of Geophysical Research - Solid Earth, 118:1-15
Kirscher, U., Zwing, A., Alexeiev, D.V., Echtler, H., Bachtadse, V.
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2014. Correcting for inclination shallowing of early Carboniferous sedimentary rocks from Kyrgyzstan - indication of stable subtropical position of the North Tianshan Zone in the mid-late Paleozoic. Geophysical Journal International, 198(2), 1000-1015
Kirscher, U., Bilardello, D., Mikolaichuk, A., and Bachtadse, V.
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2014. Paleozoic Paleogeography of the South Western Part of the Central Asian Orogenic Belt-Paleomagnetic Constraints, Doctorate thesis, Ludwig-Maximilians-Universitat München
Kirscher, Uwe
