SHRIMP U-Pb Zircon Geochronology And Geochemistry Study Of Neoproterozoic Granites In The Northern Margin Of Yangtze Continental

Neoproterozoic volcanic massif and granite intrusion which widely distributed in the northern margin of Yangtze block are generally considered having a close relationship with Rodinia supercontinent evolution. Some previous geochemical and geochronology study have been made on these magma activities, but different people have different opinions on age and tectonic setting of the magma activities. Because the study area located special tectonic position that is key joint field of several tectonic units such as Yangtze block, Songpan terrane, Qinling orogeny belt and Longmenshan orogeny belt, detailed study on the age and formation environment of the magma activities can offer a helper to pursuit the tectonic Pattern and evolution of North margin in the Yangtze bloke during the Neoproterozoic era.This paper choose Ziwu intrusion in Hannan intrusive complex in the northern margin of Yangtze block, Tiewadian intrusion in the south Qinling orogeny belt and mylonitize granite body intruded in Xixiang group as study objects, using zircon SHRIMP U-Pb dating method combined obtain more accurate age data, using the geochemistry data to study the formation environment, tectonic setting and source area nature of these intrusions.The conclusions reached are as followed:(1)Tiewadian intrusion is typical kalium rich calc-alkaline granite. On the Y-Nb and Rb/30-Hf-Ta*3 discrimination diagrams, the intrusion plot exclusively into the volcanic arc granitoid field, suggesting that they were formed in an active continental margin and syn-collisional tectonic setting. (2)Intrusions in the study area formed at Neoproterozoic granite. SHRIMP U-Pb age of Tiewadian intrusion is 802±16Ma.Ziwu intrusion formed at 773±9Ma and are basically consistent with other intrusions in Hannan intrusive complex. This indicated that the formation age of Hannan intrusive complex mainly between 790~760Ma. Zircon SHRIMP U-Pb age of mylonitize granite body intruded in Xixiang group is 962±12Ma, and this indicated that Xixiang group formed at early-Neoproterozoic. (3)The rock geochemistry characters of Tiewadian intrusion is similar with the one of Hannan intrusive complex suggesting that Tiewadian region that nowadays located at Qinling Oregon belonged to Yangtze block in Proterozoic. (4)Ar-Ar plateau age of diorite from Huangjiaying granite and granite of Yaolinghe group is 764.9±5.6Ma and 858±8Ma respectively. The age data corresponds with two different metamorphic events, and related with break-up of Rodinia supercontinent. It illustrate that the break-up of Rodinia has two stages.