Geochronological framework and petrogenesis of Indosinian-Yanshannian granites in Hainan Island
In recent years,a series of work on granites have been conducted on the widespread Indosinian-Yanshannian granites in Hainan Island which constitute part of the magmatic rocks of South China.However,the geochronological framework,genetic type and regional tectonic setting of these granites still need to be constrained.We made a detailed analysis of relevant literature as well as our own study regarding the ages and geochemical properties of the Indosinian-Yanshannian granites in Hainan Island,and a further discussion on the magmatic source and tectonic background controlling them.In Hainan Island,the Indosinian granites are mainly composed of granodiorite and monzogranite,and part of them show gneissic structure.The summary of high precision geochronology data suggests that they emplaced during 278～225Ma,and the main age peak is ca.240Ma.The geochemical features indicate they can be divided into S-,I-and A-type granites.Both S-type(278～241 Ma)and I-type(272～233Ma)granites are high-K calc-alkaline,and their whole-rock zircon saturation temperatures(average＜750℃)are lower than the dehydration melting of amphibolite,indicating that these two types of granites might be products of water-flux melting.In contrast,the high whole-rock zirconium saturation temperatures(＞800℃)of A-type granites(257～225Ma)indicate they are generated from vapour-absent melting of the residue remaining in the lower crust after production of a previous granite.Furthermore,there are very limited Jurassic magmatic rocks developed in Hainan Island,i.e.,the newly identified 161 Ma granite is high-K calc-alkaline with Ⅰ-type affinity;while the Cretaceous granites(mainly monzogranite and granodiorite)can be divided into three periods:ca.120Ma,ca.110～90Ma and ca.70Ma,with a peak at ca.100Ma.The geochemical evidence implies that these granites are I-type granites with the source involving juvernile mantle components.On the basis of the above information,we propose that:(1)the large volume Indosinian-Yanshannian magmatic rocks are developed under the subduction of the Paleo-Pacific plate;(2)the initiation of the Paleo-Pacific plate subduction started since Early Permian(ca.280Ma),and the Andean-type active continental margin of South China lasted to Late Cretaceous(ca.70Ma);(3)Hainan Island preserves the subduction-related Indosinian-Yanshannian magmatism under the setting of the Andean-type active continental margin of east-southeast Asia.
GraniteHainan IslandIndosinianYanshannianPaleo-Pacific plate subductionSouth China
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维普
