TY - JOUR

T1 - Ubiquitous post-peak zircon in an eclogite from the kumdy-kol, kokchetav uhp-hp massif (Kazakhstan)

T2 - Significance of exhumation-related zircon growth and modification in continental-subduction settings

AU - Skuzovatov, Sergei Yu

AU - Shatsky, Vladislav S.

AU - Ragozin, Alexey L.

AU - Wang, Kuo Lung

N1 - Funding Information: Council of the Russian Federation President Grants, Grant/Award Number: MK-67.2020.5; Ministry of Science and Technology, Taiwan, Grant/Award Number: MOST 106-2811-M-001-035 Funding Information: This work has been conducted within the framework of the State Assignment Projects of IGC and IGM. Zircon studies were partially performed under postdoctoral program from IES with support from Ministry of Science and Technology of Taiwan (MOST 106-2811-M-001-035). SYuS also acknowledges support from the Council of the Russian Federation President Grants (MK-67.2020.5). We are indebted to Jaroslaw Majka and an anonymous referee for their helpful reviews, as well as to Tatsuki Tsujimori and Dmitry Zedgenizov for the editorial handling. Publisher Copyright: © 2020 John Wiley & Sons Australia, Ltd. Copyright: Copyright 2021 Elsevier B.V., All rights reserved.

PY - 2021/1/1

Y1 - 2021/1/1

N2 - U–Pb geochronological, trace-element and Lu–Hf isotopic studies have been made on zircons from ultrahigh-pressure (UHP) mafic eclogite from the Kumdy-Kol area, one of the diamond-facies domains of the Kokchetav Massif (northern Kazakhstan). The peak eclogitic assemblage equilibrated at > 900°C, whereas the bulk sample composition displays light rare-earth element (LREE) and Th depletion evident of partial melting. Zircons from the eclogite are represented by exclusively newly formed metamorphic grains and have U–Pb age spread over 533–459 Ma, thus ranging from the time of peak subduction burial to that of the late post-orogenic collapse. The major zircon group with concordant age estimates have a concordia age of 508.1 ±4.4 Ma, which corresponds to exhumation of the eclogite-bearing UHP crustal slice to granulite-or amphibolite-facies depths. This may indicate potentially incoherent exhumation of different crustal blocks within a single Kumdy-Kol UHP domain. Model Hf isotopic characteristics of zircons (εHf(t) +1.5 to +7.8, Neoproterozoic model Hf ages of 1.02–0.79 Ga) closely resemble the whole-rock values of the Kumdy-Kol eclogites and likely reflect in situ derivation of HFSE source for newly formed grains. The ages coupled with geochemical systematics of zircons confirm that predominantly late zircon growth occurred in Th–LREE-depleted eclogitic assemblage, that experienced incipient melting and monazite dissolution in melt at granulite-facies depths, followed by amphibolite-facies rehydration during late-stage exhumation-related retrogression.

AB - U–Pb geochronological, trace-element and Lu–Hf isotopic studies have been made on zircons from ultrahigh-pressure (UHP) mafic eclogite from the Kumdy-Kol area, one of the diamond-facies domains of the Kokchetav Massif (northern Kazakhstan). The peak eclogitic assemblage equilibrated at > 900°C, whereas the bulk sample composition displays light rare-earth element (LREE) and Th depletion evident of partial melting. Zircons from the eclogite are represented by exclusively newly formed metamorphic grains and have U–Pb age spread over 533–459 Ma, thus ranging from the time of peak subduction burial to that of the late post-orogenic collapse. The major zircon group with concordant age estimates have a concordia age of 508.1 ±4.4 Ma, which corresponds to exhumation of the eclogite-bearing UHP crustal slice to granulite-or amphibolite-facies depths. This may indicate potentially incoherent exhumation of different crustal blocks within a single Kumdy-Kol UHP domain. Model Hf isotopic characteristics of zircons (εHf(t) +1.5 to +7.8, Neoproterozoic model Hf ages of 1.02–0.79 Ga) closely resemble the whole-rock values of the Kumdy-Kol eclogites and likely reflect in situ derivation of HFSE source for newly formed grains. The ages coupled with geochemical systematics of zircons confirm that predominantly late zircon growth occurred in Th–LREE-depleted eclogitic assemblage, that experienced incipient melting and monazite dissolution in melt at granulite-facies depths, followed by amphibolite-facies rehydration during late-stage exhumation-related retrogression.

KW - Eclogite

KW - Hf isotopes

KW - Kokchetav Massif

KW - Retrograde partial melting

KW - UHP metamorphism

KW - U–Pb age

KW - Zircon

UR - http://www.scopus.com/inward/record.url?scp=85099836782&partnerID=8YFLogxK

U2 - 10.1111/iar.12385

DO - 10.1111/iar.12385

M3 - Article

AN - SCOPUS:85099836782

VL - 30

SP - 1

EP - 19

JO - Island Arc

JF - Island Arc

SN - 1038-4871

IS - 1

M1 - e12385

ER -