Chronology Of "Precambrian" Metasedimentary Rocks In Changning-Menglian Belt And Its Geological Significance

The evolution of Proto-Palaeo-Tethys has been paid much attention by scholars at home and abroad,and Sanjiang area in the west of Yunnan Province is located in the east of the Tethys tectonic domain,which has relatively important geological evidence of the evolution of Proto-Palaeo-Tethys for a long time,.The Changning-Menglian tectonic belt in western Yunnan is sandwiced between the Simao block on the west and the Baoshan block on the east,which is considered to separate the Gondwana continent from the Yangtze block.A large number of metamorphic units and ophiolite belts are developed intermittently in the belt,which records the evolution of the formation and closure of the Proto-Tethys Ocean and the Paleo-Tethys Ocean.However,due to the multi-stage magmatism and tectonic transformation,the geological conditions of the belt are relatively complex.There are differences in understanding whether the Proto-Tethys Ocean and Paleo-Tethys Ocean evolved continuously or existed the closed Proto-Tethys Ocean orogeny at the end of the Early Paleozoic.On the basis of previous studies,this paper chooses the Precambrian metasedimentary rock series in the Changning Menglian belt as the object of study,and analyzes their field geological characteristics and petrography.Combined with detrital zircon chronology,the relationship between them and the evolution of the Tethyan Ocean is discussed.The Precambrian metasedimentary rocks are widely exposed in the Changning-Menglian tectonic belt and divided into several stratigraphic units,including the Lancang Group,Damenglong Group,Chongshan Group,Mengtong Group and Ximeng Group.The rocks of different sizes are exposed in the Changning-Menglian tectonic belt.The detrital zircon geochronology shows that,The detrital zircons in the Lancang Group range in age from 2424.7 to 508.6 Ma,with peak values of 508 Ma and1199 Ma.The detrital zircons from the Damenglong Group range in age from 3534.9 to426.7 Ma and from 2552.2 to 604.5 Ma,with peak ages of 444 Ma,927 Ma and 1095 Ma,1700 Ma and 2488 Ma,respectively.The detrital zircons from the Chongshan Group range in age from 2605.4 to 402.1 Ma,with peaks of 439.6 Ma and 1850 Ma.The age of detrital zircons in the Mongtong Group ranges from 3552.4 to 521.7 Ma,with peak values of 594 Ma,974 Ma and 2478 Ma.Combined with the chronological data of volcanic intercalations and intrusive magmatic intrusions in each block and the angular unconformity contact relationship with the Late Paleozoic sequence stratigraphy,the sedimentary age of the Lancang Group is 471.5?459 Ma,belonging to the Middle and late Ordovician.The sedimentary age of Mong Tong Group is 487?460 Ma,that is,Middle Ordovician.The sedimentary age of Ximeng Group is 504?460 Ma,which belongs to Late Cambrian-Middle Ordovician.The sedimentary age of the Chongshan Group is from Early Silurian(440 Ma)to Late Silurian(427 Ma).The sedimentary age of Dameng Long Group is from Late Ordovician(444 Ma)to Late Silurian(427 Ma).All the Precambrian metasedimentary rock series(blocks)were formed in the Early Paleozoic.The geochronological characteristics of detrital zircons show that the sedimentary materials of Lancang Group,Mengtong Group and Ximeng Group are derived from Baoshan Block on the west side of the tectonic belt,while the materials of Dameng Long Group and Chongshan Group are derived from Simao Block on the east side of the tectonic belt.The Wanhe ophiolite in the tectonic belt may be the remnant of the proto-Tethys oceanic crust.The results of this article think,chang ning-Meng Lian tectonic belt in the Precambrian sedimentary source rocks are early Paleozoic sedimentary era,in the late early Paleozoic to accompany the original die tethys ocean subduction orogeny has been subjected to intense deformation metamorphic-transformation,and has been since the late palaeozoic devonian sequence stratigraphy Angle unconformity cover.The Proto-Tethys Ocean and the Paleo-Tethys Ocean are not continuous evolvement oceans.The Early Paleozoic orogeny is closely related to the Proto-Tethys Ocean in western Yunnan.For a long time,the evolution of Proto-Palaeo-Tethys has been paid much attention by scholars at home and abroad,and Sanjiang area in the west of Yunnan Province is located in the east of the Tethys tectonic do Main,which has relatively important geological evidence of the evolution of Proto-Palaeo-Tethys.The Changning-Menglian tectonic belt in western Yunnan is sandwiced between the Si Mao block on the west and the Baoshan block on the east,which is considered to separate the Gondwana continent from the Yangtze block.A large number of metamorphic units and ophiolite belts are developed intermittently in the belt,which records the evolution of the for Mation and closure of the Proto-Tethys Ocean and the Paleo-Tethys Ocean.However,due to many times of Magma and tectonic reformation,the geological conditions of the belt are relatively complex.There are differences in understanding whether the Proto-Tethys Ocean and Paleo-Tethys Ocean evolved continuously or existed the closed Proto-Tethys Ocean orogeny at the end of the Early Paleozoic.On the basis of previous studies,this paper chooses the Precambrian metasedimentary rock series in the Changning Menglian belt as the object of study,and analyzes their field geological characteristics and petrography.Combined with detrital zircon chronology,the relationship between them and the evolution of the Tethyan Ocean is discussed.