--> ABSTRACT: The Paleo-Tethyan History of North Karakorum Terrane, by Gaetani, Maurizio; #90135 (2011)

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The Paleo-Tethyan History of North Karakorum Terrane

Gaetani, Maurizio 1
(1)Earth Sciences, Università di Milano, Milano, Italy.

The North Karakorum is part of the Peri-Gondwanan Fringe that detached from Gondwana during the Permian to eventually collide with the Asian margin towards the end of the Triassic, following the fate of the Paleo-Tethyan ocean. Other similar blocks in the area are the South Pamir in Tajikistan and the Helmand Block in Central Afghanistan.

Sedimentary rocks testify to its evolution since the Early Ordovician. The first 90 MY, from Ordovician to Middle Devonian are represented by a stable shelf with shaly deposits gradually replaced by carbonates. During the Givetian a first extensional episode occurred, with outpouring of basalts, and local unconformities. The next interval, up to the top of the Pennsylvanian, lasting additional 100 MY, is characterized by a complex intermingling of rifting episodes coupled with eustatic oscillations linked to the Gondwana glaciations. However, no glacigenic sediments are know in Karakorum. Synsedimentary extensional faults were identified, separating different blocks. Around the Pennsylvanian/Permian boundary, a major unconformity, interpreted as the break-up unconformity, brought a huge clastic wedge to seal the rifted blocks. With the demise of the Gondwana glaciation, shallow water carbonate sedimentation recovered. To northward instead, a deeper sea-way, driven by extension, created room to accommodate the very thick clastic wedge of the Wakhan Slates, presently in anchimetamorphic facies. By the Middle Permian, the eastern part of the Karakorum was further dissected and that area sunk to bathyal condition. Knobby and platy cherty limestones, megabreccias originating from the margin of the shelf, represent the interval from Late Permian to the base of the Upper Triassic (Carnian). To the west instead, a peritidal carbonate platform, with repeated emersion episodes, including occasional clastic inputs, are present. Some of them are now lateritic.

With the Carnian all the N Karakorum resumed to shallow water conditions or emerged, locally being karstsified. The inversion is linked to the approaching of the terrane to the Asian active margin and the onsetting Cimmerian orogeny. Karakorum was not deeply affected by the deformation, that occurred mostly northward, in Pamir. However, some of the previous basinal areas, shortly returned to shallow conditions, were newly drowned in latest Triassic, acting as distal foredeep, receiving the clastics originating from the Cimmerian mountains.

 

AAPG Search and Discovery Article #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011.