The　Xiadu　Formation　is　a　key　unit　of　volcanic　strata　from　the　Late　Mesozoic　in　western　Fujian.　The　age　of　the　Xiadu　Formation　remains　controversial,　and　there　is　a　lack　of　systematic　rock　chemistry　analysis,　age　attribution,　and　rock　genesis　studies.　These　issues　restrict　the　division　and　correlation　of　regional　strata.　This　study　focuses　on　the　volcanic　rocks　of　the　Xiadu　Formation　in　Yong＇an,　western　Fujian.　We　conduct　LA-ICP-MS　zircon　U-Pb　age　dating,　whole-rock　major　and　trace　element　analysis,　and　whole-rock　Sr-Nd　isotope　analysis　to　explore　the　age,　petrogenesis,　and　tectonic　setting　of　the　Xiadu　Formation.　The　rocks　of　the　Xiadu　Formation　are　primarily　composed　of　rhyolitic　breccia　tuff,　breccia　ignimbrite,　ignimbrite,　and　tuff,　occasionally　interbedded　with　tuffaceous　sandstone　and　tuffaceous　mudstone.　The　age　of　the　tuff　in　the　top　part　of　the　Xiadu　Formation　is　130.4　±　1.5　Ma.　The　analysis　of　the　whole-rock　major　and　trace　elements　shows　that　the　tuff　has　high　silicon　content　［w　(SiO2)　=　71.40%～73.40%］,　is　rich　in　aluminum　［w　(Al2O3)　=　13.70%～14.85%］,　and　has　an　abundance　of　alkali　［w　(K2O　+　Na2O)　=　5.91%～　9.75%］.　It　also　has　low　titanium　［w　(TiO2)　=　0.21%～0.38%］　and　low　magnesium　［w　(MgO)=0.05%～0.65%］　contents.　The　rocks　belong　to　the　high-potassium　calc-alkaline　series　to　the　potassium　basalt　series　of　acidic　volcanic　rocks.　The　rocks　are　enriched　with　large-ion　lithophile　elements　Rb,　Th,　U,　and　K　and　light　rare　earth　elements,　and　depleted　in　high-field-strength　elements　Nb,　Ta,　P,　and　Ti　and　heavy　rare　earth　elements.　We　also　find　a　pronounced　negative　Eu　anomaly.　The　whole-rock　Sr-Nd　isotope　analysis　results　show　that　εNd(t)　varies　between　–12.17　and　–9.94,　while　T2DM　ranges　from　1　659　Ma　to　1　507　Ma.　This　study　indicates　that　the　volcanic　rocks　of　the　Xiadu　Formation　in　Yong＇an　formed　in　the　Late　Jurassic　to　Early　Cretaceous,　when　the　ancient　Pacific　plate　subducted　beneath　the　Eurasian　plate,　which　formed　a　compression　environment　along　an　active　continental　margin.　The　magma　mainly　originated　from　partial　melting　of　the　lower　crust　during　the　Proterozoic　era　and　underwent　contamination　from　the　middle　and　upper　crust.　©　2025,　Chengdu　University　of　Technology.　All　rights　reserved.