A study on the alteration mechanism of phlogopite phenocrysts in the Lujing Kimberlitic lamprophyre in the Anyuan area,Jiangxi Province
The alteration evolution process of phyllosilicate minerals can record genetic informations of diagenesis and metallogenesis and changes of geological environmental conditions.Trioctahedral mica is a common phyllosilicate mineral in the ultra basic rocks.Its mineralogical characteristics have been proved to be effective in reflecting the crystallization conditions at depth/and reflects alterations in host rocks.However,the secondary evolution process of mica in ultrabasic rocks have not been systematically investigated.In oreder to explore the late-stage evolutionary regulation and internal mechanism of original mical in ultrabasic rocks,by using multiple microzone microbeam techniques,including the micro-XRD spectrometer,electron probe microanalyzer,X-ray photoelectron spectroscopy,focused ion beam scanning electron microscopy,and high-resolution transmission electron microscope(TEM),we here have analyzed phlogopite and its evolutionary products in the Lujing kimberlitic lamprophyres in Jiangxi Province,China.Our study reveals that phlogopite could be altered to various secondary phyllosilicates simultaneously at different crystallographic sites.In the alteration process,most Si ions were remained within phlogopite,while Fe,Ti,Mn,K,and Na ions were largely migrated into hydrothermal fluids,secondary titanium-iron oxides,and carbonates(rather than silicate products).The alteration reaction of phlogopite spreads outward from the defect site.The alteration sequence products such as chlorite,kaolinite,serpentinite were formed at the defect sites through dissolution and recrystallization,then illite was filled in the fissure through epitaxial growth,and interlayer-deficit phlogopite was formed at the weakly altered site through solid phase transformation.The formation sites of alteration products are controlled by the phase transformation mechanism.With the decrease of alteration degree,the structural similarity between products and the parent mineral phlogopite is gradually increased.
Phlogopitephyllosilicatescrystal structureelemental migrationtransmission electron microscopy
万方数据
维普
