Wang, X.
Griffin, W.L. and Chen, J. (2011) U and Th Contents and Th/U Ratios of Zircon in Felsic and Mafic Magmatic Rocks Improved Zircon -Melt Distribution Coefficients. Acta Geologica Sinica, English Edition, 85, 164-174.
A population of captured magmatic zircons indicates another pulse of magmatism at similar to 143 Ma. A barren granite intrusion near the deposit gives a zircon U -Pb age of 148.1 +/- 1.1 Ma.
Zircons from the TMG exhibit oscillatory or planar zoning under CL and have Th/U ratios ranging from 0.39 to 2.00, consistent with a magmatic origin [ 62 ]. U – Pb dating results for 23 zircons,, Eleven analyses on magmatic zircon rims from YCL0722 have rel- atively low U and Th contents of 45 – 553 ppm and 35 – 204 ppm re- spectively, but their Th/U ratios (0.29 to 1.57) are parallel …
They show depletion in Nb and Ta on N-MORB-normalized trace-element spider-diagrams and have high Th /Yb ratios , suggesting their precursor magmas were generated in a subduction-related environment.
rutile and titanite generally contain 5–10 times less U than zircon , thus metamictisation of these minerals is relatively rare. Consequently, in rocks with U -rich zircon and titanite or rutile, the zircon might show metamictisation, and there-fore would be more prone to degradation during transport, 3/1/2018 · Even so, the MMEs still have lower silica contents (62.1–63.4 wt%) than those of the phase 1 intrusion (63.4–70.5 wt%), and this indicates that direct magma mixing of basaltic and felsic melts …
lithosphere can be characterized by a distinct Th/U ratio that can be traced using 230Th/232Th activity ratios . This last point will be discussed in section IIIc. At shallow pressure (less than 1 GPa), Th becomes slightly more compatible than U in clinopyroxene (Landwehr et al. 2001) and garnet is not stable even in pyroxenite or eclogite.
reco rded by our samp les. Th us , if the sp read – ing rate we re co ns tant du ring the form ation of At lantis Ba nk , the differenc e in time betwe en the U – P b zircon crys tallization ag e an d the ma gn etic ag e is a proxy for the de pth at wh ich zircon crys tallize d. Th e ag e range of our an oma lous ly old samp les (0.7 to 2.5 my r), Th ere are some concerns that the monitors of oxidation state may be reset by metasomatic impregnation 93 , but specifi c trace-element concentrations and ratios promise to see through these modifi cations to provide information about earlier states 94 . Th e underlying asthenospheric mantle will also be more reduced than at shallower levels, as …
