Late Pan-African magmatism in northeastern China: SHRIMP U–Pb zircon evidence from granitoids in the Jiamusi Massif

We present the first evidence of late Pan-African magmatism in the Jiamusi Massif of northeastern China. Recent SHRIMP U–Pb zircon studies of the Mashan Complex have identified a major ∼500 Ma granulite facies metamorphic event in the area, but no older igneous rocks have previously been dated. Two granitoid samples have been analysed using SHRIMP U–Pb zircon techniques: a deformed granitoid from near Sandaogou contains zircons with well-defined oscillatory zoning that define a weighted mean 206Pb/238U age of 523±8 Ma, taken to be the age of the granite protolith; and a weakly-deformed porphyritic granite from near Jiamusi, which also contains zircons with oscillatory zoning of igneous origin, has a weighted mean 206Pb/238U Ma crystallisation age of 515±8 Ma. In addition, a deformed pegmatite from Liu Mao, which contains oscillatory-zoned igneous zircons, was also analysed. These zircons are rich in uranium and the data are discordant, so their interpretation is not equivocal. If the four oldest 207Pb/206Pb ratios are taken to represent the minimum age of zircon crystallisation, they define an age of 501±18 Ma. Several zircon crystals from both granite samples also reveal evidence of recrystallisation in cathodoluminescence (CL) images and this has been dated at 505±4 and 497±5 Ma in the Sandaogou and Jiamusi samples, respectively. This is the timing of granulite facies metamorphism in the southern area of the Mashan Complex and these ages are only slightly older than the ∼490 Ma granulite facies metamorphism identified in southern Siberia, possibly indicating that they had a common evolution. Alternatively, the presence of plutonic igneous rocks with ages between ∼515 and ∼525 Ma in the Jiamusi Massif is comparable to several other late Pan-African terranes. In particular, the timing of granite emplacement at ∼515 Ma and high-grade metamorphism at ∼500 Ma is identical to events recorded in the Delamerian Orogen of South Australia. The recent discovery of ∼500 Ma metamorphic zircons in the Halls Reward metamorphic belt in Queensland, NE Australia, may indicate a continuation of late Pan-African events across Australia, supporting the view that the Jiamusi Massif lay along the northern margin of Australia at this time, together with the Tarim, North China and South China blocks.