Petrology, geochemistry and zirconology of impure calcite marbles from the Precambrian metamorphic basement at the southeastern margin of the North China Craton
Abstract Impure calcite marbles from the Precambrian metamorphic basement of the Wuhe Complex, southeastern margin of the North China Craton, provide an exceptional opportunity to understand the depositional processes during the Late Archean and the subsequent Palaeoproterozoic metamorphic evolution of one of the oldest cratons in the world. The studied marbles are characterized by the assemblage calcite+clinopyroxene+plagioclase+K-feldspar+quartz+rutile±biotite±white mica. Based on petrography and geochemistry, the marbles can be broadly divided into two main types. The first type (type 1) is rich in REE with a negative Eu anomaly, whereas the second type (type 2) is relatively poor in REE with a positive Eu anomaly. Notably, all marbles exhibit remarkably uniform REE patterns with moderate LREE/HREE fractionation, suggesting a close genetic relationship. Cathodoluminescence imaging, trace elements and mineral inclusions reveal that most zircons from two dated samples display distinct core-rim structures. Zircon cores show typical igneous features with oscillatory growth zoning and high Th/U ratios (mostly in the range 0.3–0.7) and give ages of 2.53−2.48Ga, thus dating the maximum age of deposition of the protolith. Zircon rims overgrew during granulite-facies metamorphism, as evidenced by calcite+clinopyroxene+rutile+plagioclase+quartz inclusions, by Ti-in-zircon temperatures in the range 660–743°C and by the low Th/U (mostly Positive Eu anomalies and high Sr and Ba contents in type 2 marbles are ascribed to syn-depositional felsic hydrothermal activity which occurred at 2.53−2.48Ga. Our results, together with other published data and the inferred tectonic setting, suggest that the marbles' protolith is an impure limestone, rich in detrital silicates of igneous origin, deposited in a back-arc basin within an active continental margin during the late Archean and affected by synchronous high- T hydrothermalism at the southeastern margin of the North China Craton. Highlights The protolith of the impure calcite marbles was deposited in the late Archean in a back-arc basin setting. The impure marbles experienced 1.83−1.85Ga granulite-facies metamorphism. Granulite-facies impure marbles from the Precambrian basement occur at southeastern margin of the North China Craton.
유료 다운로드의 경우 해당 사이트의 정책에 따라 신규 회원가입, 로그인, 유료 구매 등이 필요할 수 있습니다. 해당 사이트에서 발생하는 귀하의 모든 정보활동은 NDSL의 서비스 정책과 무관합니다.
원문복사신청을 하시면, 일부 해외 인쇄학술지의 경우 외국학술지지원센터(FRIC)에서
무료 원문복사 서비스를 제공합니다.
NDSL에서는 해당 원문을 복사서비스하고 있습니다. 위의 원문복사신청 또는 장바구니 담기를 통하여 원문복사서비스 이용이 가능합니다.
- 이 논문과 함께 출판된 논문 + 더보기