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Subhorizontal boundary between ultrahigh‐pressure and low‐pressure metamorphic units in the Sulu–Tjube area of the Kokchetav Massif, Kazakhstan
Author(s) -
Ishikawa Masahiro,
Kaneko Yoshiyuki,
Anma Ryo,
Yamamoto Hiroshi
Publication year - 2000
Publication title -
island arc
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.554
H-Index - 58
eISSN - 1440-1738
pISSN - 1038-4871
DOI - 10.1046/j.1440-1738.2000.00281.x
Subject(s) - metamorphic rock , massif , geology , geochemistry , mantle (geology) , shear zone , petrology , shear (geology) , metamorphism , coesite , tectonics , eclogite , seismology , subduction
The Kokchetav Massif of Kazakhstan includes high to ultrahigh‐pressure (HP–UHP) metamorphic rocks (some of which were recrystallized at depths in excess of 150 km), juxtaposed against much lower pressure metamorphic components. We investigated the relationship between the HP–UHP metamorphic unit and the low pressure (LP) unit (Daulet Suite) in the Sulu–Tjube area, where the metamorphic rocks have previously been interpreted as constituting a megamelange with subvertical structural attitudes. Analyses of fold structures suggest that the HP–UHP metamorphic unit overlies the LP unit across a west‐dipping subhorizontal boundary. In addition, kinematic indicators display top‐to‐the‐north senses of shear along the tectonic contact between the two units, indicating that the HP–UHP unit has been extruded northward onto the LP unit. Following the juxtaposition of the two units, upright folds developed in both units, and these are associated with the previously reported steeply dipping metamorphic foliations. These data have important implications for the mode of exhumation of the UHP rocks from upper mantle to shallow crustal depths.