Researching on the Mesozoic magmatism is critical to understanding the tectonic evolution of the Cathaysia Block

and therefore has become a hot topic in the past decade. Numerous petrological and geochemical studies were implemented in the eastern and middle parts of the block

but few studies focused the southernmost area in western Guandong Province. Therefore

the geochronological

geochemical

and Hf isotopic data from the Fenghuangshan granitoids

which are located at the southern margin of the Cathaysia Block

were used to constrain the crystallization age

petrogenesis and tectonic environment. The Fenghuangshan granitoids are dominated by biotitebearing monzogranites and biotite-bearing syenogranites. LA-ICP-MS zircon U-Pb data show that the former is (156±2) Ma and the latter is (158±3) Ma

respectively. All of the samples contain high silicon (SiO

2

=72.66%-76.63%)

high alkali (Na

2

O+K

2

O =7.89%~9.43%)

and low magnesium (MgO=0.05%-0.54%) concentrations. They show weakly peraluminous characteristics (A/CNK=1.02~1.04). The samples are enriched in Rb

Th

K and depleted in Ba

P

Sr

Ti

with a negative correlation between SiO

2

and P

2

O

5

. Mineralogical and geochemical features suggest that the biotite-bearing syenogranite is I-type granite. By contrast

the biotite-bearing monzogranite falls into the area of highly fractionated I-type granite

with high differentiation index (DI=93.91-95.74)

high Rb/Sr (=99.12-243.75) and Rb/Ba (=67.45-203.80) ratio

low consolidation index (SI=0.48-0.66) as well as significant negative Eu anomalies (

δ

Eu=0.01~0.02). The samples of monzogranite and syenogranite have relatively homogeneous Hf isotopic compositions

with

ε

Hf(

t

)  values and two-stage model ages (T

DM2

) of -9.4 to-5.4 and 1 545-1 804 Ma

respectively. The Hf isotopic features indicated that the monzogranites and syenogranites might share a same magma source

which was sourced from reworking of the Paleoproterozoic-Mesoproterozoic crust in the Jurassic. Combined with the previous studies

the Fenghuangshan pluton was suggested to be formed by underplating of the mantle-derived magma in an extensional tectonic setting

which was related to the roll-back or breakup of the subducting oceanic lithosphere.