Abstract:

The Late Ordovician Helin intrusive complex in the southeast of Xiaoxinganling Mountains consists of a series of different rocks，including amphibole gabbro，(quartz)diorite，tonalite and monzonitic granite. Intrusive, inclusive and gradual transitional contact relationship has been recognized among different rock types. Some microgranular dioritic enclaves have been discovered in(quartz）diorite, tonalite and monzonitic granite. The enclaves have mainly ovoidlike shape, possibly caused by plastic flow, typically magma structure, acicular apatite as well as K-feldspar and quartz phenocrysts of host rocks, indicating an origin of magma mingling enclaves(MME). The intrusive complex is characterized by enrichment of large ion lithophile elements LILE(Ba，Sr，Rb)and HFS (U，Th，Zr，Ce)relative to primitive mantle, suggesting derivation of crust. However relatively high ε_Nd（t）values（-2.38 to -3.77）reflects a mantlederived source. In summary, petrographic petrochemical and geochemical characteristics of the Helin complex suggest mixed crustmantle origin. It can be attributed to underplating of mafic magma in an active continent marginal arc setting.

Key words: magma intrusive complex, microgranitoid mafic enclave(MME), magma mingling, southeastern Xiaoxinganling Mountains, Late Ordovicia