title: Diversity in early crustal evolution: 4100 Ma zircons in the Cathaysia Block of southern China.
abstract: Zircons are crucial to understanding the first 500 Myr of crustal evolution of Earth. Very few zircons of this age (>4050 Ma) have been found other than from a ~300 km diameter domain of the Yilgarn Craton, Western Australia. Here we report SIMS U-Pb and O isotope ratios and trace element analyses for two ~4100 Ma detrital zircons from a Paleozoic quartzite at the Longquan area of the Cathaysia Block. One zircon ((207)Pb/(206)Pb age of 4127 ± 4 Ma) shows normal oscillatory zonation and constant oxygen isotope ratios (δ(18)O = 5.8 to 6.0‰). The other zircon grain has a ~4100 Ma magmatic core surrounded by a ~4070 Ma metamorphic mantle. The magmatic core has elevated δ(18)O (7.2 ± 0.2‰), high titanium concentration (53 ± 3.4 ppm) and a positive cerium anomaly, yielding anomalously high calculated oxygen fugacity (FMQ + 5) and a high crystallization temperature (910°C). These results are unique among Hadean zircons and suggest a granitoid source generated from dry remelting of partly oxidizing supracrustal sediments altered by surface waters. The ~4100 Ma dry melting and subsequent ~4070 Ma metamorphism provide new evidence for the diversity of the Earth's earliest crust.
authors.affiliation: Nanjing Institute of Geology and Mineral Resources, China geological survey, Nanjing 210016, PR China.
authors.forename: Guang-Fu
authors.initials: GF
authors.lastname: Xing
authors.affiliation: 1] State Key Laboratory for Mineral Deposits Research, School of Earth Science and Engineering, Nanjing University, Nanjing 210093, China [2] WiscSIMS, Department of Geoscience, University of Wisconsin, 1215 W Dayton Street, Madison, WI 53706, USA.
authors.forename: Xiao-Lei
authors.initials: XL
authors.lastname: Wang
authors.affiliation: Beijing SHRIMP Center, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China.
authors.forename: Yusheng
authors.initials: Y
authors.lastname: Wan
authors.affiliation: Nanjing Institute of Geology and Mineral Resources, China geological survey, Nanjing 210016, PR China.
authors.forename: Zhi-Hong
authors.initials: ZH
authors.lastname: Chen
authors.affiliation: Nanjing Institute of Geology and Mineral Resources, China geological survey, Nanjing 210016, PR China.
authors.forename: Yang
authors.initials: Y
authors.lastname: Jiang
authors.affiliation: WiscSIMS, Department of Geoscience, University of Wisconsin, 1215 W Dayton Street, Madison, WI 53706, USA.
authors.forename: Kouki
authors.initials: K
authors.lastname: Kitajima
authors.affiliation: WiscSIMS, Department of Geoscience, University of Wisconsin, 1215 W Dayton Street, Madison, WI 53706, USA.
authors.forename: Takayuki
authors.initials: T
authors.lastname: Ushikubo
authors.affiliation: WiscSIMS, Department of Geoscience, University of Wisconsin, 1215 W Dayton Street, Madison, WI 53706, USA.
authors.forename: Phillip
authors.initials: P
authors.lastname: Gopon