Garnet Amphibolite And Maific- Ultramafic Rocks In The Longyou Area Of Zhejiang:New Evidence Of The Caledonian Orogenic Event In The Cathaysia Block

South China consists of Yangtze Block and Cathaysia Block with the northeasterly trending Jiang-Shao fault acting as the Neoproterozoic suture zone between the two block. The Cathaysia region, as been termed as the South China Caledonian Fold Belt, Early Paleozoic orogen of the South China Block or Wuyi-Yunkai orogen in previous literature, stretches for ca.2000 km in NE-SW direction in South China. The significant feature of the Cathaysia Block is the important tectonothermal event in the early Paleozoic, leading to an angular unconformity between post-Silurian cover and metamorphosed pre-Devonian strata with the intrusion of voluminous granites in this block, as well as in adjacent areas in the Yangtze Block.So far, diverse models have been proposed for the tectonic evolution of this region, among which the most popular ones include:intracontinental orogeny and collision belt. However, there are still some problems for the intracontinental orogeny model.Some recent studies show that there may be some important relationship between Gondwana supercontinent and early Paleozoic global geodynamics of South China. That is, during the Gondwana supercontinent assembly, south China may relate to India block through qiangtang block, and the Cathaysia and Yangtze block didn’t collide together until Caledonian.During the past years, there found garnet amphibolite, serpentinized pyroxene peridotite, pyroxenite and gabbros in longyou area of Zhejiang province. As a special advanced mafic metamorphic rocks, garnet amphibolite can well record the temperature and stress during the metamorphic process. In this paper, we conducted detailed petrology, geochemistry and geochronology study as to the garnet amphibolite, serpentinized pyroxene peridotite, pyroxenite and gabbros in order to confirm their origin and implication. Through the detailed study and analysis, we confirmed that longyou garnet amphibolite is a retrograded eclogite and serpentinized pyroxene peridotite, pyroxenite and gabbros belong to the intrusions formed in the post-orogen.Both of them provided new evidences for the Caledonian orogeny, and we argue that the transition from collision to post collision most possibly took place at ca.430 Ma.