Monday, June 24, 2013

A Collision of Sea Mounts and Plates From the Silurian to Carboniferous

Restoring the Silurian to Carboniferous northern active continental margin of the Mongol-Okhotsk Ocean in Mongolia - Hangay-Hentey accretionary wedge and seamount collision


1. Désirée Ruppen (a)
2. Alice Knaf (a)
3. Denise Bussien (a)
4. Wilfried Winkler (a)
5. Anaad Chimedtseren (b)
6. Albrecht von Quadt (c)


a. Geological Institute, Department of Earth Sciences, ETH Zurich, Sonneggstrasse 5, 8092 Zurich, Switzerland

b. Mongolian University of Science and Technology, Ulaanbaatar 210646, P.O.Box 46/225, Mongolia

c. Institute of Geochemistry and Petrology, Department of Earth Sciences, ETH Zurich, Clausiusstrasse 25, 8092 Zurich, Switzerland


Trapped between the Siberian Craton to the north, and the Tarim and North China blocks to the south, the Mongol-Okhotsk Belt represents a young portion of the Central Asian Orogenic Belt. The Andean-type orogeny was caused by the closure of the Mongol-Okhotsk Ocean, whose timing and mode of geodynamic evolution still needs to be clarified in more detail. This paper investigates the lithostratigraphic units of the Gorkhi Formation, which are comprised in the Hangay-Hentey terrane representing the accretionary prism of the northern continental margin of the Mongol-Okhotsk Ocean. In the tectonically disrupted slices of the Gorkhi Formation we identify a typical ocean plate stratigraphy with pelagic to hemipelagic and turbiditic sequences. Locally, shallow marine limestones are found associated with mafic volcanic rocks. XRF and LA-ICPMS measurements of these volcanic rocks clearly indicate an OIB signature. The geochemistry together with lithostratigraphic observations permit us to reconstruct the evolution of a seamount, ranging from its growth in shallow water depths and drowning due to subduction-related subsidence linked with subsequent radiolarian chert, hemipelagic shale and turbiditic sandstone cover sedimentation. Calc-alkaline felsic dikes later intruded the accreted silt and sandstone deposits. Standard sandstone provenance analysis, detrital zircon U-Pb laser ablation ICP-MS dating and Hf isotope ratios in the sandstones document a prevailing continental volcanic arc sourcing during Carboniferous from the northern margin of the Mongol-Okhotsk Ocean.

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