1. Shenzhen Branch of CNOOC Ltd.，Shenzhen 518000，Guangdong，China; 2. CNOOC Deepwater Development Ltd.，Shenzhen 518000，Guangdong，China

In this paper，the authors present a systematic study of the petrology，zircon U--Pb geochronology and geochemistry of the Early Cenozoic volcanic rocks exposed by drilling in the Huizhou sag of the Pearl Ｒiver Mouth Basin ( PＲMB) ，in order to explore their petrogenesis and tectonic environment． Petrological and geochemical analyses show that the studied volcanic rocks are composed of andesite，dacite and trachyandesite． LA--ICP--MS zircon U--Pb geochronology reveals that the crystallization age of the volcanic rocks are ( 60. 8 ± 1. 0) ～ ( 56. 7 ±1. 7) Ma，i. e.，the age is Paleocene． The studied rocks have w ( SiO2 ) of 57. 59% ～ 66. 63% ，w ( Na2O + K2O) of 3. 98% ～ 9. 85% ，w ( Al2O3 ) of 16. 93% ～ 20. 50% ，w ( MgO) of 1. 37% ～ 3. 12% ，w ( TiO2 ) of 0. 49% ～0. 74% ，w ( TFe2O3 ) of 3. 77% ～ 6. 78% ，and Mg# value of 21. 98 ～ 28. 30． These rocks belong to calc-alkaline，high-K calc-alkaline，shoshonite and qusi-aluminous series． The rocks exhibit enrichments in LＲEE with the LＲEE /HＲEE ratios of 7. 88 ～ 10. 16 and ( La /Yb) N ratios of 9. 64 ～ 11. 92 ( 11. 08 on average) ，and show slight negative Eu anomalies with δEu values of 0. 70 ～ 1. 01 ( 0. 88 on average) ． These samples are relatively enriched in LILEs such as Ba and K，and depleted in HFSEs such as Nb，Ta and Ti． Petrogenesis analysis shows that the Paleocene intermediate-acid volcanic rocks originated from the mafic lower crust in high pressure conditions，and they are the partial melting products under garnet or amphibolite facies． Combined with regional data，we propose that the PＲMB was in a volcanic arc enviroment related to the subduction of the Paleo--Pacific slab beneath the South China block in the Paleocene．