Full-Text Search:
Home|About CNKI|User Service|中文
Add to Favorite Get Latest Update

Precambrian geological events on the western margin of Songnen massif: Evidence from LA-ICP-MS U-Pb geochronology of zircons from Paleoproterozoic granite in the Longjiang area

ZHANG Chao;WU XinWei;LIU ZhengHong;ZHANG YuJin;GUO Wei;QUAN JingYu;College of Earth Sciences,Jilin University;Shenyang Center of Geological Survey,CGS;Shenyang Tests Research Centre,Northeast China Coal Field Geology Bureau;  
The Songnen massif is located to the east of the Central Asian Orogenic Belt.However,there is always controversial about the scale and nature of its Precambrian crystalline basement.Mashan monzonitic granite with an age of~1.8Ga was discovered in Longjiang area,reflecting the existence of the Paleoproterozoic crystalline basement.The geochemistry,zircon LA-ICP-MS U-Pb geochronology and Hf isotope of Mashan monzonitic granite were studied in order to provide important information about the tectonic evolution of the western margin of Songnen massif in Late Paleoproterozoic.The results showed that the zircons from Mashan monzonitic granite had oscillatory CL and high Th/U ratios(1.30~2.64),indicating they were of magmatic origin.The magmatic zircons had~(207)Pb/~(206)Pb weighted average age of 1808±14Ma,indicating they formed in Late Paleoproterozoic.The mashan monzonitic granite is high in Si O_2(69.50%~75.11%),Fe O~T(2.86%~4.53%)and alkali(K_2O+Na_2O=5.30%~8.69%),and low in Ca O(0.46%~1.87%),MgO(0.25%~0.93%).It is high in total REE contents(357.2×10~(-6)~587.1×10~(-6))with a"seagulltype"pattern of stronger REE fractionation between LREE and HREE((La/Yb)_N=12.2~17.6)and exhibit prominent negative Eu anomaly(δEu=0.27~0.77).In trace element,the granite shows enrichment of LILEs(Rb,Ba)and depletion of HFSEs(Nb,Ta,Ti),P,Sr,with high contents of Zr+Nb+Ce+Y(772.1×10~(-6)~911.1×10~(-6))and 10000×Ga/Al ratios of 2.41~3.17.Whole rock zircon saturation temperatures range from 891℃to 940℃,which is consistent A-type granite with the high temperature feature,further belonging to the A_2-type granite formed in a post-collisional environment.The zircons in Mashan granite hadε_(Hf)(t)values of-9.2~-2.8 and t_(DM2)of 2992~3520Ma,showing similar Hf model age with the magmatic rocks(~1.8Ga)occurred in the northern margin of the North China Plate.Due to the underplating of mantle-derived magmas,Mashan A-type granite was dominantly derived from the partial melting of Meso-Neoarchaean crustal rocks.Since Columbia supercontinent breakup occurred in the western margin of the Songnen massif,continental crust was in extensional tectonic setting.Based on the analyses above,it was discovered that the Neoarchean-Mesoproterozoic magmatic event occurred in the Songnen massif corresponded to the coeval tectonic geological event of the North China Craton.Thereby,it was inferred that the Songnen massif had a certain affinity with the North China Craton.
Download(CAJ format) Download(PDF format)
CAJViewer7.0 supports all the CNKI file formats; AdobeReader only supports the PDF format.
©CNKI All Rights Reserved