Age And Environment Of Ophiolit And Ophiolitic Melange Of Jinshajiang Belt Northwestern Yunnan

This paper is about forming settings and forming times.of ophiolite, Ophiolitic melonges of Jinshajiang orogenic belt and Discussing the result and lodging farther study spatial—temporal in Jinshajiang orogenic belt.Based on the research about the petrology, geochemistry and so on. Expecially the basalts studied date which is the best forming of ophiolite assemblage and thimeaning of the tectonic setting distinguish. The plate show that chemical consitituent of Gongka-Shusong basalts is the feature same as the MORB consitituent, By — /MgO diagram, /MgO — TiO₂ diagram, ATK diagrarn, AFM diagram and TiO₂^P₂O₅, all samples of low fall into MORB, The patterns of the REE and Ce_N/Yb_N, La_N/Yb_N is N-MORB and T—MORB, by the tectonic setting distinguish diagram, such as Ti/V, Ti/Zr, Ti/G, Zr/Y and V -Ti, Ti—Zr, Ti-Zr—Y, Zr/Y-Zr, Ti—Cr, Ti/Cr-Ni all most samples fall into MORB; at the trace element distribution of basalts, the high incompatible elements is enriched, the middle incompatible elements is trend right, the low incompatible elements and compatible elements is plate, it is similar to N—MORB. so foming settings of jinshajiang ophioites is N-MORB and T—MORB.The amphibole gabbro of the Zhiyong, Derong country, Baimaxueshan gabbro and Susong mafic rock, Their age indicating the foming time of ocean crust. On the basis of the determination of SHRIMP zircon U—Pb ages, in westen Yunnan province, the zhiyong amphibole gabbro is dated at 328 ± 8Ma; the Susong anorthosite, 329±7Ma, and the Baimaxueshan gabbro, 282²85Ma. The study also reveals a few older zircons, such as Susong anorthosite, 368±7Ma, Zhiyongamphibole, 375 + lOMa. Indicating that the magmatic activity in this part of Paleo — Tethys ocean started in the late Devonian, the late Devonian.About this working, In the Tongduo, Benzhilan and Shusong the author found silicahtes in ophiolitic melonges which is closed with ophiolite biock, which is the best large of the existing, The block is about 50 meter in length and 30 meter in width In the round of the block, The Fe Mg is high, radiolarians fossil is very productive but all of they are very small roll. Their faulted contact with olivine> basalts and limestone. And their have not feature of radiolarians, so it is not obvious and diffcult to distinguish.Only distinguish Latentifistula sp and Entactinia sp. The geologicera is Carboniferous — Permian, indicating in the prime of Jingshajiang ocean basin growing is Carboniferous—Permian.The newest era of fassil in the ophiolitic melange can acquire the ages of plate collision, bettwen limestone and black silicalites we can test richless fassil about Carboniferous and Permian, In limestone block the newest ages fossi is middle Permian, fusulinids palaeofusulina sp.; foraminiferas colaniella; In black silicalites is late Permian radiolarians copicyntra sp.So it is indicating the newest ear of outside biock is late Permian, the age of plate collision is Late-Permian to E ary-middle Triassic. Molasses is the sedimentary record of orogenic stage, and it is most important sign of ocean basin closed. Continent lithospheric plate or arc-continent collision. Molasses formation of Jinshajiang is Jiapila, which is angular discordance above on ophilitic melonges, and it indicating the age of melonge rocks is middle Triassic.On the basis of the biostratanu magmation, it proves the evolution history of Jinshajiang orogenic belt in westen Yunnan: The continental cracking is Devonian, ocean basin spreading is Late-Carboniferous to Late-Permian, subducation is lated...