Genetic Connection And Tectonic Significance Of Indosinian Granites And Migmatites In The Hetai Gold Deposit Area, Guangdong

After the Yangtze plate and the Cathaysia plate merged to form the South China plate since the Neoproterozoic,the South China plate tectonic activity was violent in the Mesozoic,which triggered strong tectonic deformation,regional metamorphism and large-scale magmatic activity within the plate,at least successively experienced Caledonian The three phases of tectonic-thermal events during the period,Indosinian period and Yanshan period.Affected by multiple tectonic-thermal events,the Caledonian,Indosinian,and Yanshanian granitic intrusions are widely distributed in the Yunkai area,and large areas of mixed rocks and multiple ductile shear zones are also developed.There has been a long-standing controversy over the genesis of Indosinian granites in South China,and scholars at home and abroad have different opinions on this.In genetic petrology,studying the genetic relationship between granite and migmatite has become a frontier scientific issue.The Hetai gold mining area in Guangdong Province is located in the Yunkai area at the junction of Guangdong and Guangxi.Indosinian granite,migmatite and ductile shear zone coexist in the mining area.Based on this,the Hetai gold mining area is a good place in Guangdong has become a domestic research on the genetic relationship between granite and migmatite.This paper conducts systematic field geology,petrography,whole-rock geochemistry,Sr-Nd isotope,biotite chemical composition analysis,and LA-ICP-MS zircon U-Pb geochronology research,focusing on the rock genesis of Yunlougang pluton and Yunkai Group migmatite,source of diagenetic materials,genetic relationship between the two,and tectonic significance.The latest research results mainly achieved the following understandings:(1)The main lithology of the Yunlougang pluton is granodiorite,the diagenetic age is 253±1.6 Ma,the A/CNK is 1.17?1.21>1.1,the Ritman index?is1.30?1.64,the average is 1.47<3.3,the initial ratio(⁸⁷Sr/⁸⁶Sr)_iis 0.71394?0.71773.The geochemical characteristics of the whole rock show that it has the characteristics of S-type granite,which belongs to the peraluminous high-K calc-alkaline series S-type granite.Low SiO₂content(65.94?68.68wt.%),low Rb/Sr ratio(1.41?1.80),Nb/Ta ratio(4.30?12.60),?_Nd(T)<0,indicating that the source rock comes from Crust.Enrichment of large ion lithophile elements such as Rb,Th,U,La,K,strong depletion of high field strength elements such as Ba,Nb,Sr,P and Ti,enrichment of light rare earth elements LREE((La/Sm)_N=3.68?4.01),depleted heavy rare earth element HREE((Ga/Yb)_N=4.12?4.70).The whole rock Nd depleted mantle model age(T_DM2)is 1821?1692Ma.The biotite in the rock mass is magnesian recrystallized biotite.The formation temperature is 589?679?,the average is 651?,the pressure is 245?278 MPa,the average is 266MPa,which is equivalent to 9.27?10.51km,and the average is 10.08km.Features of silicon,aluminum,iron,magnesium,potassium,poor in sodium and manganese,and low Ti O₂content.(2)The Yunkai Group migmatite is a full lava migmatite with a migmatization age of 240.3±5.1Ma,Within the analysis error range,the Yunlougang granodiorite formed about 10 Ma earlier than the Yunkai Group mixed rock..Yunkai Group mixed rocks,Yunlougang granodiorite and Yunkai Group metamorphic sedimentary rocks have similar geochemical characteristics.They are all peraluminous and have high K₂O content,Fe₂O₃/Mg O ratio,Rb,Pb,LREE and the initial ⁸⁷Sr/⁸⁶Sr(I_Sr)ratio,?_Nd(T)are all negative values,both have a low10000Ga/Al value,and both lose Ba,Nb,Sr,P and Ti.SiO₂and Ti O₂,Fe₂O₃^T,CaO,Nb has a negative correlation.The biotite in Yunkai Group Miscite and Yunlougang granodiorite are rebalanced native biotite,with almost the same temperature,pressure and depth.It shows that after diagenesis,the two rocks were modified under almost the same conditions.The three types of rocks are different.The REE distribution curve of Yunkai Group mixed rocks is generally similar to the REE distribution curve of Yunkai Group meta-sedimentary rocks.The Yunlougang pluton has a lower(⁸⁷Sr/⁸⁶Sr)_iratio and a higher?_Nd(T)than the Yunkai Group mixed rock and metasedimentary rock.The Sr-Nd isotopic characteristics of the Yunkai Group mixed rock and the Yunkai Group metasedimentary rock are similar.The Nd model ages of Yunkai Group mixed rocks and Yunkai Group metasedimentary rocks are almost the same,while the Nd model ages of Yunlougang granite bodies are significantly smaller than the former two.The Rb/Sr ratio of the Yunlougang pluton is 1.4?1.6,which is significantly lower than the 2.7?9.2 of the mixed rock.On the whole,the geochemical characteristics of Yunkai Group's mixed rocks are more similar to those of Yunkai Group's metasedimentary rocks.Therefore,the Yunkai Group mixed rocks may be the products of in-situ melting of metasedimentary rocks.(3)Yunlougang granodiorite may be derived from lower crustal anatism and mixed with mixed magma formed by a small amount of young mantle components,while Yunkai Group mixed rocks are in-situ melting products of metasedimentary rocks.Therefore,the Yunlougang granodiorite is not homologous to the adjacent Yunkai Group migmatite,and the former is not the final product of the latter.The formation time of Yunlougang pluton and Yunkai Group mixed rock may represent the peak and end of collision between the South China plate and the Indosinian plate,respectively.