The andalusite-sillimanite-type low-pressure Daulet Suite underlies the Kokchetav ultrahigh-pressure-high-pressure (UHP-HP) massif of northern Kazakhstan. The Daulet Suite is composed of pelitic-psammitic gneisses or schists an quartz schist with minor amounts of metacarbonate and metabasite. About 300 thin sections were examined from the, Daulet metapelites: rocks were divided into two mineral zones. Zone A is characterized by andalusite + cordierite + biotite, and zone B by sillimanite + cordierite + biotite with excess K-feldspar, quartz, and plagioclase in both zones. K-feldspar appears with andalusite at lower temperatures than the first formation of sillimanite. Pressure-temperature conditions of the Daulet metamorphism range from 580 to 680°C at a nearly constant pressure of ∼2 kbar. Comparison of compositions of solid-solution minerals with a buffered assemblage indicates that the metamorphic grade increases towards the boundary with the overlying UHP-HP unit. Detailed mapping revealed that the primary structure of both the Kokchetav UHP-HP massif and its surrounding units is subhorizontal; the UHP-HP unit has been thrust over the Daulet Suite with a top-to-the-north movement. The thermal structure of the Daulet Suite is subhorizontal and metamoorphic grade increases upwards-i.e., toward the boundary with the UHP-HP unit-whereas the thermobaric maximum of the UHP-HP unit occurs at an intermediate structural level, The upward increase in metamorphic grade within the Daulet Suite implies contact metamorphism by the tectonic juxtaposition of the "hot" Kokchetav UHP-HP unit at shallow crustal levels.
|Number of pages||12|
|Journal||International Geology Review|
|Publication status||Published - Sep 2002|
ASJC Scopus subject areas