One size does not fit all: Refining zircon provenance interpretations via integrated grain shape, geochronology, and Hf isotope analysis

Sediment provenance studies commonly utilize isotopic signatures to resolve detrital mineral sources and routing.However,non-unique ages and geochemical characteristics across geographically distinct crystalline source regions can lead to significant ambiguities in mineral provenance interpretations.Such ambiguity is apparent in southern Australia’s Cenozoic Eucla Basin,which hosts world-class heavy mineral sand resources.Here,new Hf isotope data are provided from four heavy mineral prospects(N=8,n=844[N=samples,n=grains]).Zircon grain shape data are also presented for a suite of detrital Eucla Basin samples(N=22,n=35,604)and the basin’s underlying basement,the Coompana Province(N=13,n=824).The data are integrated with published detrital and non-detrital primary zircon data to investigate the efficacy of grain shape analysis to better resolve the basin’s mineral provenance.Zircon Hf isotope compositions indicate a primary Mesoproterozoic juvenile source for zircon melts(~1250-1000 Ma,-2.5<εHf>~+5)with additional contributions from a range of juvenile to evolved late Archean to Phanerozoic-aged zircon bearing magmas(-28.0<εHf>+11).U-Pb geochronology and Hf isotopes are incapable of differentiating Mesoproterozoic-aged source rocks bounding the region for the majority of heavy mineral deposits analyzed as potential sources express overlapping crystallization ages and similarities in Hf-isotope characteristics.However,distinct zircon grain shapes(i.e.,perimeter,major axis and circularity)facilitate improved differentiation across these Mesoproterozoic sources.Filtering of U-Pb age,Hf isotope and shape data implicate the underlying Madura and Coompana provinces as dominant sediment sources for Eucla Basin detritus aged~1400-1000 Ma.The lack of direct sediment pathways between the underlying basement provinces and placer sediments analyzed demonstrates the significance of zircon reworking from intermediate sedimentary basins in the formation of the economically significant Eucla Basin beach placers.Zircon grain shape represents a cheaply acquired and readily incorporated grain characteristic that can enhance provenance investigations.

δ^(15)N-stable isotope analysis of NH_(x): An overview on analytical measurements, source sampling and its source apportionment

Agricultural sources and non-agricultural emissions contribute to gaseous ammonia(NH_(3))that plays a vital role in severe haze formation.Qualitative and quantitative contributions of these sources to ambient PM_(2.5)(particulate matter with an aerodynamic equivalent diameter below 2.5µm)concentrations remains uncertain.Stable nitrogen isotopic composition(δ^(15)N)of NH_(3)and NH_(4)+(δ^(15)N(NH_(3))andδ^(15)N(NH_(4)+),respectively)can yield valuable information about its sources and associated processes.This review provides an overview of the recent progress in analytical techniques forδ^(15)N(NH_(3))andδ^(15)N(NH_(4)+)measurement,sampling of atmospheric NH_(3)and NH_(4)+in the ambient air and their sources signature(e.g.,agricultural vs.fossil fuel),and isotope-based source apportionment of NH_(3)in urban atmosphere.This study highlights that collecting sample that are fully representative of emission sources remains a challenge in fingerprintingδ^(15)N(NH_(3))values of NH_(3)emission sources.Furthermore,isotopic fractionation during NH_(3)gas-to-particle conversion under varying ambient field conditions(e.g.,relative humidity,particle pH,temperature)remains unclear,which indicates more field and laboratory studies to validate theoretically predicted isotopic fractionation are required.Thus,this study concludes that lack of refinedδ^(15)N(NH_(3))fingerprints and full understanding of isotopic fractionation during aerosol formation in a laboratory and field conditions is a limitation for isotope-based source apportionment of NH_(3).More experimental work(in chamber studies)and theoretical estimations in combinations of field verification are necessary in characterizing isotopic fractionation under various environmental and atmospheric neutralization conditions,which would help to better interpret isotopic data and our understanding on NH_(x)(NH_(3)+NH_(4)+)dynamics in the atmosphere.