Thermobaric structure of the Kokchetav ultrahigh-pressure-high-pressure massif deduced from a north-south transect in the Kulet and Saldat-Kol regions, northern Kazakhstan

Tsutomu Ota, Masaru Terabayashi, Christopher D. Parkinson, Hideki Masago

Research output: Contribution to journalArticle

49 Citations (Scopus)

Abstract

To investigate the regional thermobaric structure of the diamondiferous Kokchetav ultrahigh-pressure and high-pressure (UHP-HP) massif and adjacent units, eclogite and other metabasites in the Kulet and Saldat-Kol regions, northern Kazakhstan, were examined. The UHP-HP massif is subdivided into four units, bounded by sub-horizontal faults. Unit I is situated at the lowest level of the massif and consists of garnet-amphibolite and acidic gneiss with minor pelitic schist and orthogneiss. Unit II, which structurally overlies Unit I, is composed mainly of pelitic schist and gneiss, and whiteschist locally with abundant eclogite blocks. The primary minerals observed in Kulet and Saldat-Kol eclogites are omphacite, sodic augite, garnet, quartz, rutile and minor barroisite, hornblende, zoisite, clinozoisite and phengite. Rare kyanite occurs as inclusions in garnet. Coesite inclusions occur in garnet porphyroblasts in whiteschist from Kulet, which are closely associated with eclogite masses. Unit III consists of alternating orthogneiss and amphibolite with local eclogite masses. The structurally highest unit, Unit IV, is composed of quartzitic schist with minor pelitic, calcareous, and basic schist intercalations. Mineral assemblages and compositions, and occurrences of polymorphs of SiO2 (quartz or coesite) in metabasites and associated rocks in the Kulet and Saldat-Kol regions indicate that the metamorphic grades correspond to epidote-amphibolite, through high-pressure amphibolite and quartz-eclogite, to coesite-eclogite facies conditions. Based on estimations by several geothermobarometers, eclogite from Unit II yielded the highest peak pressure and temperature conditions in the UHP-HP massif, with metamorphic pressure and temperature decreasing towards the upper and lower structural units. The observed thermobaric structure is subhorizontal. The UHP-HP massif is overlain by a weakly metamorphosed unit to the north and is underlain by the low-pressure Daulet Suite to the south; boundaries are subhorizontal faults. There is a distinct pressure gap across these boundaries. These suggest that the highest grade unit, Unit II, has been selectively extruded from the greatest depths within the UHP-HP unit during the exhumation process, and that all of the UHP-HP unit has been tectonically intruded and juxtaposed into the adjacent lower grade units at shallower depths of about 10 km.

Original languageEnglish
Pages (from-to)328-357
Number of pages30
JournalIsland Arc
Volume9
Issue number3
DOIs
Publication statusPublished - 2000
Externally publishedYes

Fingerprint

eclogite
transect
amphibolite
schist
coesite
garnet
orthogneiss
metabasite
quartz
gneiss
clinozoisite
zoisite
omphacite
porphyroblast
phengite
augite
kyanite
mineral
epidote
rutile

Keywords

  • Eclogite
  • Kokchetav
  • Thermobaric structure
  • Ultrahigh-pressure metamorphism

ASJC Scopus subject areas

  • Earth and Planetary Sciences (miscellaneous)

Cite this

Thermobaric structure of the Kokchetav ultrahigh-pressure-high-pressure massif deduced from a north-south transect in the Kulet and Saldat-Kol regions, northern Kazakhstan. / Ota, Tsutomu; Terabayashi, Masaru; Parkinson, Christopher D.; Masago, Hideki.

In: Island Arc, Vol. 9, No. 3, 2000, p. 328-357.

Research output: Contribution to journalArticle

Ota, Tsutomu ; Terabayashi, Masaru ; Parkinson, Christopher D. ; Masago, Hideki. / Thermobaric structure of the Kokchetav ultrahigh-pressure-high-pressure massif deduced from a north-south transect in the Kulet and Saldat-Kol regions, northern Kazakhstan. In: Island Arc. 2000 ; Vol. 9, No. 3. pp. 328-357.
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abstract = "To investigate the regional thermobaric structure of the diamondiferous Kokchetav ultrahigh-pressure and high-pressure (UHP-HP) massif and adjacent units, eclogite and other metabasites in the Kulet and Saldat-Kol regions, northern Kazakhstan, were examined. The UHP-HP massif is subdivided into four units, bounded by sub-horizontal faults. Unit I is situated at the lowest level of the massif and consists of garnet-amphibolite and acidic gneiss with minor pelitic schist and orthogneiss. Unit II, which structurally overlies Unit I, is composed mainly of pelitic schist and gneiss, and whiteschist locally with abundant eclogite blocks. The primary minerals observed in Kulet and Saldat-Kol eclogites are omphacite, sodic augite, garnet, quartz, rutile and minor barroisite, hornblende, zoisite, clinozoisite and phengite. Rare kyanite occurs as inclusions in garnet. Coesite inclusions occur in garnet porphyroblasts in whiteschist from Kulet, which are closely associated with eclogite masses. Unit III consists of alternating orthogneiss and amphibolite with local eclogite masses. The structurally highest unit, Unit IV, is composed of quartzitic schist with minor pelitic, calcareous, and basic schist intercalations. Mineral assemblages and compositions, and occurrences of polymorphs of SiO2 (quartz or coesite) in metabasites and associated rocks in the Kulet and Saldat-Kol regions indicate that the metamorphic grades correspond to epidote-amphibolite, through high-pressure amphibolite and quartz-eclogite, to coesite-eclogite facies conditions. Based on estimations by several geothermobarometers, eclogite from Unit II yielded the highest peak pressure and temperature conditions in the UHP-HP massif, with metamorphic pressure and temperature decreasing towards the upper and lower structural units. The observed thermobaric structure is subhorizontal. The UHP-HP massif is overlain by a weakly metamorphosed unit to the north and is underlain by the low-pressure Daulet Suite to the south; boundaries are subhorizontal faults. There is a distinct pressure gap across these boundaries. These suggest that the highest grade unit, Unit II, has been selectively extruded from the greatest depths within the UHP-HP unit during the exhumation process, and that all of the UHP-HP unit has been tectonically intruded and juxtaposed into the adjacent lower grade units at shallower depths of about 10 km.",
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AU - Masago, Hideki

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N2 - To investigate the regional thermobaric structure of the diamondiferous Kokchetav ultrahigh-pressure and high-pressure (UHP-HP) massif and adjacent units, eclogite and other metabasites in the Kulet and Saldat-Kol regions, northern Kazakhstan, were examined. The UHP-HP massif is subdivided into four units, bounded by sub-horizontal faults. Unit I is situated at the lowest level of the massif and consists of garnet-amphibolite and acidic gneiss with minor pelitic schist and orthogneiss. Unit II, which structurally overlies Unit I, is composed mainly of pelitic schist and gneiss, and whiteschist locally with abundant eclogite blocks. The primary minerals observed in Kulet and Saldat-Kol eclogites are omphacite, sodic augite, garnet, quartz, rutile and minor barroisite, hornblende, zoisite, clinozoisite and phengite. Rare kyanite occurs as inclusions in garnet. Coesite inclusions occur in garnet porphyroblasts in whiteschist from Kulet, which are closely associated with eclogite masses. Unit III consists of alternating orthogneiss and amphibolite with local eclogite masses. The structurally highest unit, Unit IV, is composed of quartzitic schist with minor pelitic, calcareous, and basic schist intercalations. Mineral assemblages and compositions, and occurrences of polymorphs of SiO2 (quartz or coesite) in metabasites and associated rocks in the Kulet and Saldat-Kol regions indicate that the metamorphic grades correspond to epidote-amphibolite, through high-pressure amphibolite and quartz-eclogite, to coesite-eclogite facies conditions. Based on estimations by several geothermobarometers, eclogite from Unit II yielded the highest peak pressure and temperature conditions in the UHP-HP massif, with metamorphic pressure and temperature decreasing towards the upper and lower structural units. The observed thermobaric structure is subhorizontal. The UHP-HP massif is overlain by a weakly metamorphosed unit to the north and is underlain by the low-pressure Daulet Suite to the south; boundaries are subhorizontal faults. There is a distinct pressure gap across these boundaries. These suggest that the highest grade unit, Unit II, has been selectively extruded from the greatest depths within the UHP-HP unit during the exhumation process, and that all of the UHP-HP unit has been tectonically intruded and juxtaposed into the adjacent lower grade units at shallower depths of about 10 km.

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