Tectonic Properties Of Yichun-yanshou Tectonic Zone During Early Paleozoic

Yichun-yanshou tectonic zone situated in middle part of Hei long-jiang province,between theXiao Hinggan Mountain-Songnen massif and Jia musi massif,along north and south. TheMudanjiang fault is the boundary between Yichun-yanshou tectonic zone and Jia musi massif.Andthe Xunke-Tieli-Shangzhi fault is between with Songnen basin.Dunmi fault may be its southernboundary.And it extends to Russia towards to north.There are Xilin Group,Baoquan Formation and Xiaojingou Formation which local onYichun-yanshou tectonic zone.The Xilin Group is Proterozoic, and the Baoquan Formation andXiaojingou Formation are Middle-lower Ordovician.The Yichun-yanshou tectonic zone consist ofclastic rock and carbonate rock.These rocks mainly consist of sedimentary rocks andmetasedimentary rocks，such as sandstone，siltstone，pelite，slate and phyllite.The rock type ofthe Baoquan Formation consist of igneous rock and clastic rock.The Xiaojingou Formation iscomposition of igneous rock, clastic sediment and carbonate sediment.Granite formed a large north and south belt in the Yichun-yanshou tectonic zone.Manyscholar has considered the time when these granite form, as Hercynian,and know as the Hercyniangranite belt.These granite are associate with the late Hercynian orogeny.But the latest researchresults show that the most granite of the Granite Belt is Indosinian granite,while the presence of asmall amount of the late Hercynian granite and a small amount of Caledonian granite.As is knownto all,there is a Caledonian granite belt at the eastern side of this granite belt.They represent theearly Paleozoic orogenic movement,which are the Caledonian granite belt,the early Paleozoicstratum,fold and thrust fault which formed by the early Paleozoic stratum. On the stratum of the tectonic zone, structure and magmatic rocks, the predecessors havedone a lot of work, but for some key geological problems, there is still no good solution ordifferent understand.Such as, the tectonic setting when the Xilin Group,the Baoquan Formationand the Xiaojingou Formation formed,the sedimentary timing of the Chenming Formation,thelocation which is the Chenming Formation at the sequence of the Xilin Group,and the tectonicsetting when the early Paleozoic granite.We have done a lot of work that about these problems.The lithology, lithofacies and rockformation of sedimentary and igneous rock,were studied under microscopy,and through fieldresearch and make profiles in fact.We researched many problems which are the tectonic setting ofXilin Group,the time when Chenming Formation formed,the location at the sequence of XilinGroup and the tectonic setting that the Early Paleozoic granites formed,through analyzing thegeochemical characteristics,studying zircon geochronology and making the w（SiO₂）-w（K₂O/Na₂O）diagram.And the following major conclusions can be draw:1．We can know that the Xilin Group is mainly composed by thick layers of limestone,withsome pelite,sandstone,siltstone and slate.These rocks are formed mainly by chemical depositionand clastic deposition.The deposition phase of Xilin Group is stability.These fact represent that thesedimentary environment of the Xilin Group is a stable environment.But the fact that there arerepresents that the local crustal is turbulence.2．The sedimentary rock of the Xilin Group are different to each other in the major elementcontents.The trace element is similar between Wuxingzhen Formation and ChenmingFormation.And,they show similar REE patterns with distinct LREE elements.And, their REEpatterns are similar with NASC.On the w（SiO₂）-w（K₂O/Na₂O） diagram,most samples local at thearea of passive continental margin.The conclusion is consistent with stratum.These indicate thatthe tectonic setting of Yichun-Yanshou Structural Zone is passive continental margin n the EarlyCambrian.It may be due to local crustal upheaval that feldspar standstone of the ChenmingFormation local at active continental margin area on the w（SiO₂）-w（K₂O/Na₂O） diagram.Thisdoesn’t influence the discrimination of tectonic setting.3．Considering petrologic characteristics of the Early Paleozoic granites in the Chenmingcalm,we can further divide them into two groups:group and group.Both are rich in SiO₂, Al₃O₂andK₂O, but poor in TiO₂and Fe₃O₂. They are High-K Calc-alkaline Rock Series,and are weak peralunimous.Their REE patterns are similar with that.Their trace element characteristics aresimilar to collision granite on North margin of the Erguna Block during the Early Paleozoic.Theylocal at Syn-collisional area and Post-collisional area on these discrimination diagrams of tectonicsetting.4． The youngest age that comes form detrital zircons of Chenming Formation is559±6Ma.According to the deposition time of the sedimentary rock,it should be the lowercambrian.5．When we study the geochemical characteristics of the Xilin Group,we research its sourceprovenance.And the study indicates that the matter comes form the dissectedisland arc.