Extended Data Fig. 3: Y/Yb systematics of terrestrial rocks.
From: Widespread two-layered melt structure in the asthenosphere
a, Plots of Y versus Yb and Y/Yb versus Fe2O3 for the Xu-Huai eclogite/garnet-pyroxenites. b, Plot of Y versus Yb for xenolithic spinel-facies peridotites in Cenozoic basalts from the eastern NCC. Spinel-facies peridotites have Y and Yb contents lower than primitive mantle values but near-chondritic Y/Yb ratios, indicating that melting of peridotites within the spinel stability field does not fractionate Y from Yb significantly. c, Y/Yb values of oceanic and continental crust. d, Plot of Y versus Yb for global MORB, Moon and Mars. The Moon and Mars have chondritic Y/Yb values, implying that planetary differentiation could not fractionate Y from Yb. e, Plots of Y versus Yb and Y/Yb ratio versus K2O for ancient glacial diamictites. Fine-grained glacial diamictites deposited in the Mesoarchean, Paleoproterozoic, Neoproterozoic, and Paleozoic eras define a positive relationship between Y and Yb (R2 = 0.98) and have chondritic Y/Yb ratios (Y/Yb = 9.81 ± 0.65, 1 SD), which are independent of K2O content (potassium is known as a highly fluid-mobile element, and is sensitive to chemical weathering34). In particular, these glacial diamictites have high CIA (chemical index of alteration, a measure of chemical weathering intensity) ranging from 54 to 89, and show decoupled variation between Y/Yb ratios and CIA82. These observations indicate that the fractionation of the Y/Yb ratio is insensitive to chemical weathering of upper crustal rocks. Data sources: Xu-Huai eclogite/garnet-pyroxenite xenoliths83 and peridotite xenoliths in Cenozoic basalts84 from the eastern NCC; continental crust34; chondrite and primitive mantle21; Moon85; Mars86; glacial diamictite82; Siberian Udachnaya eclogites87; Koidu low- and high-MgO eclogites from West Africa88,89. LCC, MCC and UCC represent lower, middle and upper continental crust, respectively34. The horizontal or vertical shaded areas in a, c and e represent the upper and lower bounds based on mean values ± 1 SD. Error bars in c are 1 SD and are smaller than symbol size where absent. Data in c are presented as mean values ± 1 SD. R2, correlation coefficient. Full data for MORB (including Pacific, Indian, Atlantic, Arctic, Pacific-Antarctic, Ninetyeast, Galapagos Spreading Center, South China Sea and Juan de Fuca) are listed in Supplementary Table 1.
