The Multiphase Of Magmatic And Metamorphic Events In The Northern Sulu Orogenic Belt And Their Tectonic Implications

The Sulu orogen belt was formed by the Triassic subduction and collision between the Yangtze Block and the North China Block, and therefore is a natural laboratory to study the collisional orogeny and geodynamics. Although the Triassic ultrahigh-pressure metamorphic rocks have been widely studied, tectonic evolutionary histories of the Precambrian meta-supracrustal rocks within the orogen still remain debated. In this thesis, I present a detailed study of petrology and zircon chronology of the meta-supracrustal rocks and late intrusive rocks from the Weihai area of the southern Sulu orogen. The obtained results show that the meta-supracrustal rocks consist mainly of schists, gneisses, marbles, calc-silicate rocks, amphibolite, quartzites and granulites. The pelitic granulite(S12-06-1) is composed of garnet, sillimanite, plagioclase, perthite, antiperthite, quartz, biotite, muscovite and rutile. The biotite and muscovite commonly occur as symplectitic corona around garnet and sillimanite, representing the retrograde phase of the granulite. Phase equilibria modeling indicates that the pelitic granulite was metamorphosed under P-T conditions of ~1.2GPa and >940°C. Ti-in-quartz thermobarometry calculation shows that the lower limit of the peak metamorphic temperature of the pelitic granulite is ~980°C. Zircons from the metapelitic granulite are nearly isometric form, and show sector zoning. Most zircons are characterized by flat or even depleted HREE patterns with negative Eu anomalies, typical of granulite-facies metamorphic zircon. LA-ICP-MS U-Pb dating of the zircons yielded a weighted mean 207Pb/206 Pb age of 1845±9Ma, indicating the peak-metamorphic age of the pelitic granulite. Zircons from an amphibolite(S12-06-3) are of typical magmatic origin, yielded a weighted mean 206Pb/238 U age of 758±26Ma. Zircons from another amphibolite(S12-02-3) are elliptical form and of metamorphic origin; the zircons with light luminescence and characterized by flat HREE patterns yielded a weighted mean 206Pb/238 U age of 230±4.7Ma, whereas the zircons with weak luminescence yielded a weighted mean 206Pb/238 U age of 214±6.5Ma. Zircons from a garnet-bearing granitic(S12-02-4) vein have the rim-core structure. The rim of the zircons is typical magmatic zircon and yielded a weighted mean 206Pb/238 U age of 200±3.0Ma. These results reveal:(1) the metapelitic granulite underwent the Paleoproterozoic(~1845Ma) ultrahigh-temperature under conditions of ≥980°C and ~1.2GPa;(2) the protolith age of the mafic magmatic rock(amphibolite) is ~758Ma;(3) the amphibolite underwent Triassic(~230Ma) ultrahigh-pressure metamorphism and late(~214Ma) retrograde metamorphism;(4) the crystallization age of garnet-bearing granitic vein is at ~200Ma. Together with available other data, it is speculated that the Paleoproterozoic ultrahigh-temperature metamorphism was related to the accretionary orogeny along the northern margin of the Yangtze Block, the Neoproterozoic magmatism responded to break-up of the Yangtze block, and the Triassic metamorphic and magmatic events were related to the collisional orogeny between the North China and Yangtze Blocks.