『Abstract
Given the relevance of desert aerosols to environmental issues
such as dust storms, climate change and human health effects,
we provide a demonstration of how the bedrock geology of an arid
area influences the mineralogy and geochemistry of even the finest
particulate matter (i.e., the inhalable fraction <10μm in size:
PM10). PM10 samples
extracted from desert sediments at geologically contrasting off-road
sites in central and southeastern Australia (granitic, high grade
metamorphic, quartzitic sandstone) were analyzed using X-ray diffraction
(XRD), scanning electron microscopy (SEM), inductively coupled
plasma atomic emission spectrometry (ICP-AES) and inductively
coupled plasma mass spectrometry (ICP-MS
). The “granitic” PM10 are highly alkali
feldspathic and illitic, with a wide range of accessory minerals
including rutile (TiO2), monazite [(Ce, La,
Nd, Th, Y)PO4], xenotime (YPO4),
apatite [Ca5(PO4)3(F,OH,Cl)], hematite(magnetiteの間違い)
(Fe3O4), zircon (ZrSiO4) and thorite (ThSiO4).
This mineralogy is reflected in the geochemistry which shows notable
enrichments in rare earth elements (REE) and most high field strength
elements (both held in the accessory minerals), and higher than
normal levels of low (<2.0) ionic potential elements (Na, K, Li,
Cs, Rb: held in alkali feldspar and illite). The “metamorphic”
resuspended PM10 define a mineralogy clearly
influenced by local exposures of pelitic and calc-silicate schists
(sillimanite, muscovite, calcite, Ca-amphibole), a dominance of
monazite over other REE-bearing phases, and a geochemistry distinguished
by enrichments in alkaline earth metals (Ca, Mg, Ba, Sr) and depletion
in heavy REE. The “quartzite”PM10, derived
from rocks already recycled by Precambrian erosion and sedimentary
transport, show a sedimentologically mature mineralogy of mostly
quartz and kaolinite, detrital accessory ilmenite, rutile, monazite
and hematite, and the strongest geochemical depletion (especially
K, Rb, Cs, Na, Ca, Mg, Ba).
Keywords: PM10; Mineralogy; Geochemistry;
Australian desert dust; Resuspension』
Introduction
Materials and methods
Sample localities
Ormiston pound
Wilpena pound
Silverton
Analytical methodology
Results and interpretations
X-ray diffraction
Scanning electron microscope
Inductively coupled plasma atomic emission and mass spectrometry
Discussion and conclusions
Acknowledgments
References