The Mesozoic volcano-plutonic belt of SE China is characterized, in th
e Kuiqi area, by acid volcanics followed by the Yanshan granites. The
Kuiqi granitic complex, which belongs to the latter unit, is made up o
f a calc-alkaline and a peralkaline group. The calc-alkaline group con
sists of two intrusions, the Danyang monzogranite and the Fuzhou syeno
granite, emplaced 103 +/- 10 Ma and 104 +/- 5 Ma ago, respectively (Rb
-Sr whole-rock isochrons). Formation of the Danyang monzogranite can b
e explained by a three-stage model: (1) partial melting of a metasomat
ized mantle generated a dioritic magma known in the area as the Nanyu
diorite; (2) the magma was contaminated (approximately 25%) by lower c
ontinental crust; (3) large amounts (70-80%) of fractional crystalliza
tion of hornblende and plagioclase at depth gave rise to the magmatic
suite. The Fuzhou syenogranite is more fractionated and its formation
involved crystallization of plagioclase + biotite + K-feldspar + apati
te. Intrusion of the peralkaline group is dated at 93 +/- 1 Ma (Kuiqi
peralkaline granite) and at 91.8 +/- 0.9 (Bijiashan peralkaline granit
e). These units are homogeneous and their petrogenesis is less constra
ined than for the calc-alkaline suite. Nevertheless, a multistage proc
ess can be proposed: (1) partial melting of a metasomatized mantle pro
duced a dioritic magma; (2) fractional crystallization began with segr
egation of hornblende + plagioclase +/- ilmenite and/or magnetite; sub
sequently, hornblende no longer crystallized; (3) the last stage of fr
actionation corresponded to the crystallization of K-feldspar + plagio
clase + REE-rich accessory phases. Mineralogical study indicates that
during the last stage, fluids played a prominent role and controlled t
he nature of the crystallizing minerals. The magma evolved from F- and
S-rich, and water-undersaturated to water-oversaturated, leading to t
he exsolution and dissociation of an H2O vapour phase and to the loss
of H-2. The change from calc-alkaline to peralkaline magmatism is rela
ted to inferred changes in the tectonic environment. The calc-alkaline
granites were generated in a subduction setting in which water was su
pplied by dehydration of the downgoing slab. The peralkaline granites
were produced in a crustal thinning environment where little water was
available, thus necessitating high temperatures to initiate partial m
elting. On the other hand, petrogenetic modelling shows that both calc
-alkaline and peralkaline granites could have been derived from the sa
me source which is metasomatized mantle. This possibly indicates that
the volcanic arc source, active during subduction, persisted beneath t
he continent and was reactivated during the post-orogenic magmatism. T
he reactivation was caused by a deep crustal fault.