Clay crustal dating environment in isotope tracing
The decoupling of clay-sized Hf-Nd isotopic compositions may explain the different Hf-Nd correlation patterns between SKTC and CAOB.
It is noted that the SKTC clay-sized array has a higher radiogenic Hf isotopic composition for its corresponding Nd isotopic composition than the CAOB array.
REE barely fractionate during weathering and have been used for studying the provenance of detrital sediments.
More specifically, ratios such as REE ratio and Nd isotopic compositions of weathered material, are considered to represent the compositions of source rocks2 μm fraction (0.05), whereas the Sm/Nd ratio remains the same (0.18) (Table S3, and Figure S3 in Supplementary information), suggesting the difference or decoupling of Hf to REE during weathering process.
The Chinese deserts have ε from −5.94 to 4.63 (mean = −0.97).
The Mongolian Gobi is more radiogenic in Nd and Hf isotope compositions which ranges from −5.99 to −2.67 (mean = −4.43; n = 9) and from −2.56 to 3.68 (mean = 0.81; n = 9), respectively.
It is clear that the clay-sized fractions have higher radiogenic Hf isotopic composition than silt-to-sand silicate fractions (Map showing the distribution of Gobi and sandy deserts in northern China and southern Mongolia, including the Gobi desert in southern Mongolia (MG) and northern China, Tengger (TG), Badain Juran (BJ), Mu Us (MU) and Hobq (HB) sandy deserts in northern China, Taklimakan (TK) and Gurbantunggut (G) desert in northwestern China, Qtingdag (OT), Hulun Buir (HL) and Horqin (HQ) sandy lands in northeastern China, and Qaidam Desert (QD) in the northern Tibetan Plateau.
Both Red and blue dots indicate location of surface desert samples studied. North Pacific margin provenance (NPM, red circle) and North Pacific center provenance (NPC, half green circle) indicate the locations of Asian dust in North Pacific Ocean.
This is attributable to the SKTC being older and thereby containing less radiogenic Nd than CAOB as demonstrated above.
1) What controls the Hf-Nd isotopic composition of clay-sized fractions within desert sands?