Intrusion of UHP metamorphic rocks into the upper crust of Kyrgyzian Tien-Shan: P-T path and metamorphic age of the Makbal Complex

Abstract

Coesite occurs in garnets from quartz schists and pelitic schists in the Makbal Complex of Kyrgyzian TienShan. The thick quartz schists interbedded with pelitic schists are the transitional facies after coesite schists. Quartz -pseudomorph after coesite also appears widely in pelitic schists and quartz schists, but is rare in eclogitic rocks. The growth zoning of garnets and Na -Ca amphiboles in eclogites and the garnet -omphacite geothermometry indicate that the metamorphic P -T paths of eclogites are different from each. Ultra -high (UHP) pressure metamorphic rocks of the Makbal Complex are mainly composed of pelitic and quartz schists. All eclogite lenses are included in the host UHPM rocks, although most of them do not contain UHP metamorphic (UHPM) evidences. The K -Ar ages of phengite in a host pelitic schist and of paragonite in an eclogite are approximately 500 Ma, while those of biotite and phengite in a biotite -bearing mica schist and of winchite in a winchite schist are approximately 769 -717 Ma and 881 Ma, respectively. The evidence indicates that this complex is a tectonic mélange. These geological relationships suggest that the ascending substances must be pelitic and quartz schists. The UHPM rocks in the ascending material capture many exotic blocks as xenoliths during intrusion into the upper crust.

Field and microanalytical isotopic investigation of ultradepleted in 18O Paleoproterozoic “Slushball Earth” rocks from Karelia, Russia

“…Within the age range between 1.89 and 1.85 Ga, we observe a nearly linear increase in δ 18 O of ~1-1.5‰. This temporal variation is too large to be caused by increasing zirconwhole-rock fractionation (1000lnα 18 O(zircon-WR) during retrograde metamorphism and instead refl ects a subtle increase in δ 18 O for (Dobrzhinetskaya et al, 1996) Garnet peridotite 5.39 P >10-12 7-AA96-1 Garnet Alpe Arami, Italy (Dobrzhinetskaya et al, 2002) Kyanite eclogite 3.93 P = ~7, T = 1100 ED05 Garnet Erzgebirge, Germany (Dobrzhinetskaya et al, 2006) Garnet-quartz-biotite gneiss with diamonds 10.58 P >7, T = 1200 20/1-93 Garnet Fiortoft, Norway (Dobrzhinetskaya et al, 1995) Garnet-biotite-kyanite gneiss with diamonds 12.18 P >4, T = 900 20-1/93 Garnet Fiortoft, Norway (Dobrzhinetskaya et al, 1995) Same with lenses of eclogite 7.29 P >4, T = 800 (Dobrzhinetskaya et al, 2003) Garnet-biotite-gneiss with diamonds 6.54 P >6-9, T = 980-1200 MakBal Garnet Makbal, Tajikistan # (Tagiri et al, 2010) Garnet-eclogite with coesite 6.87 P = 2-3, T = 800 *Sample courtesy of M. Perraki. † Mposkos and Kostopoulos (2001).…”

Micro-excavation and direct chemical analysis of individual fluid inclusion by cryo-FIB-SEM-EDS: Application to the UHP talc-garnet-chloritoid schist from the Makbal Metamorphic Complex, Kyrgyz Tian-Shan

“…Talcgarnet-chloritoid schists are found in the quartzites as layers measuring hundreds of meters to a few kilometers long. UHP metamorphism has been confirmed by the finding of coesite inclusions within garnet from both Tlc-Grt-Cld schists and surrounding quartzites (Tagiri et al, 2010;Orozbaev et al, 2015). The peak P-T conditions of Tlc-Grt-Cld schists have been variously estimated by different methods to be 530-580∞C and 2.8-3.3 GPa by petrogenetic grid (Orozbaev et al, 2015) and approximately 580∞C and 2.85 GPa by pseudosection modeling (Meyer et al, 2014).…”

“…The Makbal metamorphic complex is located in the western part of Northern Kyrgyz Tian-Shan ( Fig. 1) and consists of two main units, namely, upper Sharkyrak Group characterized by greenschist facies metamorphism, and the lower Akdjon Group that exhibits higher-grade metamorphism (HP-UHP conditions) (Bakirov, 1978;Bakirov et al, 1998;Tagiri et al, 2010). The Akdjon Group is subdivided into the Neldy and Makbal Formations.…”

“…The peak P-T conditions of Tlc-Grt-Cld schists have been variously estimated by different methods to be 530-580∞C and 2.8-3.3 GPa by petrogenetic grid (Orozbaev et al, 2015) and approximately 580∞C and 2.85 GPa by pseudosection modeling (Meyer et al, 2014). Paleozoic metamorphic ages of the Tlc-Grt-Cld schists are reported by different methods; U-Pb SHRIMP age of 502 ± 10 Ma for metamorphic zircon rims (Konopelko et al, 2012), phengite K-Ar age of 509 ± 13 Ma (Tagiri et al, 2010), and Th-Pb CHIME monazite ages of 481 ± 26 Ma and 480 ± 56 Ma (Togonbaeva et al, 2009).…”

Subduction and exhumation mechanisms of ultra‐high and high‐pressure oceanic and continental crust at Makbal (Tianshan, Kazakhstan and Kyrgyzstan)

“…Some Grt‐Cld‐Tlc schists provide evidence of UHP metamorphism as can be inferred from rare coesite inclusions in garnet (e.g. Togonbaeva et al ., ; Tagiri et al ., ; Konopelko et al ., ; this study). Thus, this Grt‐Cld‐Tlc assemblage, indicative of UHP, has the potential from petrological and thermodynamic modelling to constrain the metamorphic conditions and so aid in the reconstruction of subduction and exhumation mechanisms accompanying deep subduction.…”