Intermediate-acidic Intrusive Rocks Formation Spatio-temporal Distribution In Mesozoic Of Zayuensis-poindo Tectonomagmatic Stage

For the geologists,Tibet plateau always be considered the birthplace of geological sciences recentstudieson for a long time. Research in Zayuensis-Poindo tectonomagmatic belt indicate that the extensive areas from the northern of Lhari-Xiangyangri fracture to the southern of Zhikong- Songduo-Gongbujiangda riftzone. Large quantities of Earth's tectonic evolution event record,is the focus of domestic and international geology concern.The magmatism of Tibet plateau was violent,the process in Tibet plateau uplifting accompany with magmatic activities in different times,also closeness to the formation of Qinghai-Tibet Plateau. Gangdise-Nyainqêntanglha tectonic magmatite belts is the most intense magmatism activity area, Poindo-Zayuensis tectonic magmatite belts is subzone of Gangdise-Nyainqêntanglha tectonic magmatite belts.Petrology,Metallotectonics,Petrotectonic,Magma dynamics et al as scientific guidance,aim at existing questions and shortage problem of intrusive rock in the east segment of the Gangdise magmatic subzone, close connection with intrusive rock and geotectonics as the way, tectonic-magma geologic event's internal relation as clue to research in intrusive rock of this area.According to the request of"the National assessment of mineral resources potential project", the general idea about structural evolution in research area for long periods."the National assessment of mineral resources potential project"put the area of Brahmaputra and Bangong-Nujiang suture zone in Tibet Plateau divided into four tectonic magmatite subzone,these are:western Gangdese tectonic magmatite subzone, Shiquanhe-Xainza-Jiali tectonic magmatite subzone, Nianqing Tanggula tectonic magmatite subzone,and southern Gangdise tectonic magmatite subzone.Research area divided into three groups:Ningzhong-Menba group,Basum-Demula group,Luobadui-Songduo-Gongbujiangda group.Preliminary research found that intrusive rock of Triassic period in research area mainly are Late Triassic epoch intrusive mass.From spatial position,intrusive rock in late Triassic period prior to Ordovician-Permian stratum,local area intruded in granite of Upper Crataceous. Intermediate-acidic intrusive rocks has obvious zonation,from west to east,lithology characters from granodiorite developed into monzogranite.Chemical composition of rock with obvious trend,at the same time,silica from high to low and then from low to high, sodium oxide gradually decline, potassium oxide increase gradually, K₆₀ gradually increase. K₆₀ variation trend indicate that Magma source area gradually deepen.Intermediate-acidic intrusive bodies of Jurassic Period comparatively centralized,mainly in Menba area&Motuo area,rock type mainly are monzogranite, granodiorite and granite,et al.Formation time of intrusive bodies of Jurassic Period:from south to north,from old to new. Isotopic age of southern area mainly focus on 198-187Ma, Isotopic age of northern area mainly focus on 140Ma or so on.In study area, Mesozoic magmatism reach the highest estate in the Crataceous period,in the Early Crataceous Epoch also intense.Early Crataceous intermediate-acidic intrusive rock structurally controlled by nearly west east&northwest-southeast direction,spatially distributed as string shape which apparently nearly east-west direction or northwest-southeast direction. Monzogranite intrusive body belongs to Sangri & Luoqingla mainly are batholith, genetic type belongs to S-type granites, structural setting roughly belongs to Collision tectonic environment. I-S type intermediate-acidic intrusive rock of Lilong county in Nyingchi.Magmatism activity in the Late cretaceous period still intense,mainly focus on 99-65Ma.Early stage on Tangbula,nuri,duogacuo area of Nyingchi county.Along with the fracture are monzonitic granite batholith;till the Mid-Late period mainly are syenogranite,granite and monzonitic granite batholith in the area of Jiali&Menba area.Granite intruded into Jurassic strata,and intruded in Early Crataceous granite,which indicate magmatism activity in the Cretaceous period are continuous.The outcrop of Intermediate-acidic intrusive rock mainly are S-type granite, structural settings mainly are collision.Magmatism activity in the Crataceous period intensely,intrusive rock widely distributed,the time of magmatism activity,space distribution closely related to tectonic movement stage&tectonic settings. The outcrop of intrusive rock types mainly are granodiorite, quartzdiorite, tonalite, monzonitic granite, syenogranite and granite,et al.As a whole, as time goes on,magmatism activity from north to south gradually intense,mainly displays in the outcrop area,the outcrop area of Late cretaceous intrusive bodies mainly focus on south area,but the outcrop area of Early cretaceous intrusive bodies mainly focus on north area.In the while area,magmatism activity with two mainly active stage: 107-133Ma&99-65Ma. To sum up the temporal distribution of intermediate-acidic intrusive rocks of Mesozoic period in the research area are:1.Early-Middle Triassic period intermediate-acidic intrusive rocks covered;2.Late Triassic period intermediate-acidic intrusive rocks exposed only a small area;3.Jurassic Period magmatism activity appears strong-weak-strong tendency;4.The cretaceous magmatism in the Mesozoic period is most active,which appears the outcrop area of intrusive rock in the Crataceous period was much bigger than the others.