The Geochronological Studies Of Liuhe Diopside-syenite-porphyry Of Heqing County In Dianxi, SW China And Its Geological Implications

Alkaline rocks are often associated with extensional tectonism and regarded as the characteristic products occurring in continental margins or rift zones. They were usually generated in deep-large-fault zone and closely connected with basic/ultrabasic rocks in space. Therefore, alkaline rocks are of significance in tectonic petrology. A set of Tertiary alkali-rich porphyries occurs in the Jinshajiang River-Ailao Mountain fault belt, western Yunnan Province. And many types of deep-derived xenoliths have been discovered in some of the alkali-rich porphyries. At the beginning of the 1980s, geological and geophysical studies were nerformed in the Jinshajiang River-Ailao Mountain fault belt, western Yunnan Province. However, these studies most involved geology and petrochemistry of the ring alkali complexes. The geochronological study was conducted during the 1990s.Geochronological, geochemical and Sr,Nd,Pb isotopic data are reported for the Liuhe diopside-syenite-porphyry of Heqing County in Dianxi, SW China. The zircons from diopside-syenite-porphyry (located in Heqing County Liuhe) can be divided into two groups: igneous zircons and the inherited zircon with growthing zone. The SHRIMP zircon dating implies that the forming age is 38.0Ma±1.5 Ma by dating the igneous zircon and the new growthing zone, which belongs to early Himalayan movement correspond early Oligocene. The Liuhe diopside-syenite-porphyry is strongly enriched in K(K₂O/Na₂O=1.44-2.22), Ca(CaO=3.22%-5.23%), LILE(Sr=642 -831×10^-6,Ba=2221-2969×10^-6,Rb=221-223×10^-6),LREE(La/Yb_N= 12.48-20.53) and pinched in LILE (Zr=208-229×10^-6,Hf=5.46-6.4×10^-6,Nb=11.7-15.5×10^-6,Ta=0.48-0.71×10^-6) . According to the study with the Geochronological and geochemical of Liuhe diopside-syenite-porphyry, we interpret that Liuhe diopside-syenite-porphyry might be not similar to I-type granite and formed in post-collision arc settings.The magmas of alkali-rich porphyries originated near the EM II enriched mantle bottom(about 100 km in depth) of the the mixing of the lower crust and the mantle in western Yunnan. The old cores of the igneous zircon are prized from the path not from the source region.