Rare earth element chemistry indicates chemical alteration of zircons during the evolution of weathering profile

Although rare earth elements(REEs)in magmatic zircons have been widely used to identify the type and compositional evolution of host rocks,REE distribution patterns during the chemical alteration of zircons need clarification.We investigated REE characteristics in zircons with different degrees of chemical weathering through systematic observation of a granodiorite-weathering profile in southeast China.Despite the relatively stable provenance of the studied profile(zircon U–Pb ages are95.2±4.8 Ma),the zircon REEs exhibited systematic differences in abundance and fractionation patterns from the bedrock to upper layers,e.g.∑PREE,(LREE/HREE)_(CN),and Ce/Ce*.This evidence suggests chemical alteration of zircons during intensive chemical weathering and an expected influence on REE variability in the weathered products due to the presence of REE-bearing minerals.

The hydrogen and oxygen isotopic compositions of hydroxyl in clay mineral from a weathering profile： New proxies for paleo-climate change？

Recent studies suggest that the hydrogen and oxygen isotopic compositions of clay minerals can indicate paleoclimate.Here,we report mineralogy and stable isotopic records(d D and δ^(18)O_(OH))of a weathering profile located in the Fujian Province,aiming to validate whether hydroxyl stable isotopes can indicate paleo-precipitation and paleo-temperature.Our results indicate that the d D and δ^(18)O_(OH)changes in the kaolinite hydroxyl of the weathering profile are basically determined by the isotopic composition of paleo-meteoric water and paleotemperature,respectively.Nevertheless,whether the d D and δ^(18)O_(OH)of kaolinite can quantitatively indicate paleo-precipitation and paleo-temperature needs to be verified further,and especially,the structural oxygen isotopic composition that is the essential element for the kaolinite formation temperature calculation has to be constrained in future work.

Geochemical Trends in Weathering Profiles and Their Underlying Precambrian Basement Rocks in Akure,Southwestern Nigeria

Akure area in southwestern Nigeria falls within the basement complex underlain by migmatite,quartzite granite and charnockite.Geochemical features of these crystalline rocks and their overlying in-situ weathering profiles are investigated and reported.Analytical result from ICP-MS facility at the University of Malaya reveals average SiO_(2) content in quartzite(91.1%),granite(73.8%),migmatite(67.4%)and charnockite(58.6%)categorize the rocks as siliceous.SiO_(2) contents in the weathering profiles above these rocks are 61.9%,60.2%,52.2%and 54.6%respectively.Alumina contents in the weathering profiles overlying quartzite(23.8%),granite(19.9%),migmatite(26.3%)and charnockite(24.3%)are substantially higher than the precursor rocks.In the same order,average alkali(Na_(2)O+K_(2)O)contents in the profiles are 3.38%,3.42%,3.48%and 2.68%.Chemical features of the profiles reflect that there exists some correlation between the chemistry of crystalline basement and their in-situ weathering profiles.The residual soils contain low plastic clays with kaolinitic characteristics and compare well with other clays reported from other parts of Nigeria basement complex.