In-situ trace element analyses of zircons from Dabieshan Huangzhen eclogite: Trace element characteristics of eclogite-facies metamorphic zircon

The internal structures of zircons in eclogite from Huangzhen have been studied by cathodoluminescence (CL) microscopy. Two growth stages were distinguished: protolith magmatic cores and metamorphic overgrowth rims. These different domains were analyzed for trace elements using LAM-ICP-MS. The protolith and the overgrowth zircons have different trace elements characteristics. The trace element contents of protolith zircons are high and very variable. The overgrowth zircons show a typical trace element feature of equilibrium with garnet, e.g. low contents of HREE (132.2–197.6 μg/g) and small differential degree of HREE ((Yb/Gd)CN=8.6–11.9). The contents of Nb, Ta and the ratio of Nb/Ta are lower in the metamorphic domains (0.5–1.4 μg/g, 0.7–1.5 μg/g, 0.3–1.3, respectively) than in the protolith domains (3.8–19.7 μg/g, 2.7–12.1 μg/g, 1.0–4.6, respectively). This is the first time to give the evidence that the metamorphic zircon equilibrates with the rutile, which formed during the peak metamorphic stage. The REEs and other trace elements data demonstrate that the metamorphic zircons overgrow in the eclogite-facies conditions. The trace element composition of zircon can therefore give new ways to constrain their formation conditions.

[1]  H. Fan,et al.  Mineral Inclusions in Zircon from Gneisses in the Ultrahigh‐Pressure Zone of the Dabie Mountains, China , 2001, The Journal of Geology.

[2]  I. Katayama,et al.  Ion micro-probe U-Pb zircon geochronology of peak and retrograde stages of ultrahigh-pressure metamorphic rocks from the Kokchetav massif, northern Kazakhstan , 2001 .

[3]  J. Hermann,et al.  Multiple zircon growth during fast exhumation of diamondiferous, deeply subducted continental crust (Kokchetav Massif, Kazakhstan) , 2001 .

[4]  Y. Liu,et al.  Geochronology and geochemistry of single-grain zircons: Simultaneous in-situ analysis of U-Pb age and trace elements by LAM-ICP-MS , 2000 .

[5]  T. Ireland,et al.  Rare earth element chemistry of zircon and its use as a provenance indicator , 2000 .

[6]  Barth,et al.  Rutile-bearing refractory eclogites: missing link between continents and depleted mantle , 2000, Science.

[7]  D. Gebauer,et al.  Dating of eclogite-facies zircons: the age of Alpine metamorphism in the Sesia–Lanzo Zone (Western Alps) , 1999 .

[8]  Yong‐Fei Zheng,et al.  Hydrogen and oxygen isotope evidence for fluid–rock interactions in the stages of pre- and post-UHP metamorphism in the Dabie Mountains , 1999 .

[9]  D. Gebauer,et al.  Growth, annealing and recrystallization of zircon and preservation of monazite in high-grade metamorphism: conventional and in-situ U-Pb isotope, cathodoluminescence and microchemical evidence , 1999 .

[10]  Liang Xi.  Simultaneous Determination of U Pb Ages and Trace Elements in Single Zircon by Using LAM ICPMS , 1999 .

[11]  D. Gebauer,et al.  Jurassic formation and Eocene subduction of the Zermatt–Saas-Fee ophiolites: implications for the geodynamic evolution of the Central and Western Alps , 1998 .

[12]  Robert D. Tucker,et al.  Ages of ultrahigh pressure metamorphism and protolith orthogneisses from the eastern Dabie Shan: U/Pb zircon geochronology , 1997 .

[13]  D. Gebauer,et al.  35 Ma old ultrahigh-pressure metamorphism and evidence for very rapid exhumation in the Dora Maira M , 1997 .

[14]  P. O'Brien,et al.  Thermobarometry of phengite‐bearing eclogites in the Dabie Mountains of central China , 1997 .

[15]  D. Gebauer,et al.  Multiple zircon growth and recrystallization during polyphase Late Carboniferous to Triassic metamorphism in granulites of the Ivrea Zone (Southern Alps): an ion microprobe (SHRIMP) study , 1996 .

[16]  A. Okay.  Petrology of a diamond and coesite-bearing metamorphic terrain; Dabie Shan, China , 1993 .

[17]  B. Upton,et al.  The chemistry of zircon: Variations within and between large crystals from syenite and alkali basalt xenoliths , 1991 .