| Main study area is located in tianshui area of gansu provinces,that is a combination of qilian orogenic belt and north qinling orogenic belt,in this paper,the main study object is the granitoid body of niutou river,with outdoors detailed survey and indoor petrography,chronology,geochemistry methods,including:identification of rock and mineral,the major and trace element determination,EPMA test and U-Pb zircon SHRIMP dating,etc.we study it to get the formation age,the identification of the rock types and tectonic environment.the discussion of genetic relationship with acidic volcanic rock of northern Chenjiahe group and caochuangpu granitoid mass.According to the research,we get the main new progress and preliminary understanding as follows:1?Granitoid body of niutou river is Mainly consists of granite diorite,tonalite,SHRIMP zircon U-Pb age is(420.8±3.9)Ma,namely the early Silurian;Geochemical characteristics show that the mass is rich in silicon,alkali,and poor of calcium and titanium,LILE:enrichment of Ba,U,Th,HESE:deficit of Sm,Ta,Yb,and an obvious negative abnormality of Nb,the chondrite-normalized REE patterns show enrichment of LREE,deficit of HREE,right pattern,and has moderate negative abnormality of Eu so it belongs to the moderate potassic peraluminous calc-alkaline I type granite of caledonian period,and formed in a continental margin arc environment.2?Reference to previous data,Caochuanpu mass is Mainly consists of granite and adamellite,and is different in rock type but connected in space and has the same geochemistry and volcanic arc setting with the Niutou river rock,in addition,they are have the same emplacement age:434±10Ma.So the Niutouhe Rock and the Caochuanou Grante Rock are all plutons having the same tectonic environment and construct subduction zone.3?Reference to previous data,acidic volcanic rocks metamorphic in the main of metamorphic rhyolite and dacite in Chenjiahe group,and it has different petrofacies and near in space,basically the same geochemical characteristics and consistent magmatic arc feature with this article study on granitoid mass of Niutou river.Besides,they basically have the consistent age which explains they have some causes' connection,that means they are the different phases of magmatic rock in the same era and similar environment but differenttectonic subduction zone.This new understanding has very important meaning of the future research on tectonic pattern,structural evolution and the relation North Qinling with North Qilian in East of North Beiqilian orogenic belt.4?The comparative study between Niutou river granite body and Caochuanpu rock mass,Niutou river granite body and Chenjia river intermediate-felsic volcanic rocks,will provide basic data for exploring the characteristics of tectonic evolution of this area,as well as for the existing of trench-arc-basin system in qinling and qilian orogenic belts which formed in the plate subduction of eastern segment of north qilian betided in Middle-Late Caledonian stage. |
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