Geochronology,petrogenesis and geological implication of Early Cretaceous lamprophyre in Chaohu area,Anhui Province
Lamprophyre is a typical ultrabasic-intermediate and rich in volatile matter.As a deep mantle source rock,lamprophyre can well reflect the geochemical properties of the mantle source,and provide a favorable window for exploring the deep tectonic and magmatic processes of the earth.This paper takes Chaohu spessartites as the research object,and carries out apatite geochronology,Sr-Nd isotopes and whole-rock major and trace elements analysis based on field geological surveys and petrographical studies.Through quantitative data simulation,this study analyzes the magmatic processes and characteristics of the mantle source,and explores the tectonic setting of the Chaohu spessartites formation.The results indicate that the apatite LA-ICP-MS 206Pb/238U weighted mean ages of Chaohu spessartites(22CH09,22CH14 and 22CH17)are 119±18 Ma,116.4±7.5 Ma and 114±13 Ma,respectively,all formed during the Early Cretaceous period.The Chaohu spessartites have low SiO2(39.80％～43.52％),high Mg# values(63～70)and K2O content(1.60％～2.46％),belong to alkaline lamprophyre.The Chaohu spessartites are enriched in large ion lithophile elements(LILEs,e.g.Ba,K,Cs)and depleted in high field strength elements(HFSEs,e.g.Nb,Ta,Zr,Hf),similar to arc-related magmatic rocks.Their low(Hf/Sm)N(0.60～0.67)and(Ta/La)N(0.27～0.38)ratios indicate that their mantle source has undergone metasomatism of subduction slab fluids.The high Zn/Fe(0.001 2～0.001 5)and Fe/Mn(65.54～84.49)suggest that the mantle source of the Chaohu spessartites is mainly composed of pyroxenite.Numerical quantitative calculations indicate that the Chaohu spessartites were generated from small-scale partial melting of garnet pyroxenite(＜4％),and followed by 3％olivine fractional crystallization.The in-situ 87Sr/86Sr(t)values of spessartites apatite range from 0.706 9 to 0.707 8 and εNd(t)values from-9.5 to-6.8,which are similar to the Sr-Nd isotopic compositions of the same period basic rocks in the lower Yangtze River belt,indicating that they originated from the enriched lithosphere mantle with similar isotopic compositions.The Mesozoic lithosphere mantle in the Chaohu area has high affinity with the Lower Yangtze River belt,and the lithosphere mantle boundary between the Lower Yangtze River belt and the southern segment of the Tan-Lu fault zone may be between the Chaohu spessartites and Feidong complex.Based on the characteristics of regional magmatic activity,the Chaohu spessartites are considered to be the product of the retreat of the paleo-Pacific subduction slab and formed in the back-arc extensional tectonic setting.
Chaohu spessartiteSouth segment of Tan-Lu fault zoneEarly CretaceousPyroxenite mantle sourcePetrogenesis
万方数据
维普
