Petrological And Geochemical Characteristics And Its Geodynamic Significance Of Huangling Granite Batholith In Western Hubei Province

The Huangling granite batholith is located in Yichang City,western Hubei Province,on the northern margin of the Yangtze Block,with an area of about 970km².It is one of the few intraplate Neoproterozoic granites in the Yangtze Block.It is a product of the island arc and orogenic environment formed by the southward subduction of the"Qinling Ocean"oceanic crust on the northern side of the Yangtze block in Jinning period.The Huangling granite batholith,formed between 820Ma and 800Ma,can be divided into three super-units:Sandouping super-unit,Huanglingmiao super-unit and Dalaoling super-unit from early to late.Sandouping superunit was formed in the pre-collision subtraction stage.Its lithology is mainly coarse-grained amphibole-bearing biotite diorite,medium-coarse-grained biotite amphibole diorite and medium-coarse-grained quartz diorite,which can be divided into six units.Huanglingmiao superunit and Dalaoling superunit are mainly formed in the collision stage of plate,and Huanglingmiao superunit is mainly medium-coarse-grained amphibole biotite-augite granite.Rocks,medium-grained porphyritic biotite-like orthoclase granite and medium-grained amphibole-biotite granodiorite can be divided into three units.The Dalaoling surperunit is mainly composed of medium-coarse-grained biotite monzodiorite,porphyritic amphibolite-like quartz monzodiorite and medium-coarse-grained biotite monzogranite,which can be divided into four units.The lithology of the three superunits in Huangling granite batholith is mainly type I granite.There may be type A granite in Huanglingmiao and Dalaoling superunits.Sandouping superunit granite is mainly calc-alkaline rock,Huanglingmiao superunit granite and Dalaoling superunit granite are mainly calc-alkaline-high potassium calc-alkaline rock.According to the aluminium saturation index,Sandouping superunit granite is mainly metaaluminous rock,Huanglingmiao superunit granite and Dalaoling superunit granite are mainly peraluminous rock.As for trace elements,Huangling granite batholith is rich in large ion lithophile elements and depleted in high field strength elements.There are generally positive Delta Eu anomalies in the rocks,which are characterized by TTG rock association.The distribution pattern of rare earth elements in Huangling granite batholith is consistent as a whole,showing that light rare earth elements are relatively enriched and heavy rare earth elements are relatively deficient,which has the potential to discover light rare earth deposits.Among them,the LREE/HREE and?La/Yb?_N values of Sandouping superunit are generally small,indicating a small degree of differentiation of light and heavy rare earth elements;the LREE/HREE and?La/Yb?_N values of Huanglingmiao superunit and Dalaoling superunit are larger,indicating a greater degree of differentiation of light and heavy rare earth elements.This paper summarizes the calculation results of?Nd?t?,(⁸⁷Sr/⁸⁶Sr)_i of Huangling granite batholith by predecessors.Combined with the determination of zircon core age,the results indicate that the source rocks of Huangling granite batholith may be Archean basaltic crystalline basement.According to the tectonic environment and evolution process of the superunit rocks,the three superunits constituting the Huangling granite batholith can be divided into two successive and non-repetitive magmatic evolution sequences:quartz diorite-granodiorite evolution sequence and quartz monzonitic diorite-monzonitic granite evolution sequence.It indicates that Huangling granite batholith is a multi-stage complex with three superunits changing from early to late lithology,chemical composition changing from neutral to acidic,and alkalinity rising slowly,forming two continuous series.Combined with DI analysis,among the three superunits of Huangling granite batholith,the Sandouping superunit is formed by deep differentiation,the Huanglingmiao superunit is formed by in-situ differentiation,and the Dalaoling superunit is formed by deep differentiation and in-situ differentiation.The structural characteristics of different superunits and the content of dark minerals in Huangling granite batholith have different changing trends.By analyzing the grain size change of each superunit,the degree of crystal self-shape,the variety and content change of dark minerals in Huangling granite batholith,the forming order and emplacement environment of each superunit can be roughly analyzed,and then the formation environment change can be obtained.Huangling granite batholith has poor ore-bearing property,which is mainly characterized by small-scale mineralization related to Au and Mo.The metallogenic control is mainly influenced by fracture structure.The main ore deposits are of medium-low temperature and medium-high temperature hydrothermal type,contact metasomatic?skarn?type gold deposits and molybdenum deposits related to magmatic hydrothermal fluid.Gold deposits and molybdenum deposits have the characteristics of Au,Cu,Pb,Zn Cu?Mo,Au?Cu?Mo,W,Au?metallogenic series related to island arc,continental arc,continental collision granitoids and post-orogeny,and Pb,Zn,Mo,Cu,Ag Mo,W?Cu?metallogenic series related to island arc,continental arc,continental collision granitoids and post-orogeny.Based on the analysis of the lithology and tectonic environment of the three superunits of Huangling granite batholith and the geochemical characteristics of the rocks,it is considered that Huangling granite batholith may have the potential to form light rare earth,tungsten,tin,niobium,tantalum,molybdenum,bismuth and beryllium deposits,and has a certain prospecting prospect.At the same time,Huangling granite batholith has the characteristics of U enrichment.It is found that the mineral content,lithological characteristics and geochemistry of biotite granite and biotite monzonite in Huanglingmiao and Dalaoling superunits have many similarities with uranium-producing rocks,such as high acidity,high alkalinity,over-saturation of aluminium and low dark components.These characteristics indicate that uranium-producing rocks are rich in uranium.Biotite granite or mica granite are the main uranium-producing rocks,and these rocks are abundant in Huanglingmiao and Dalaoling superunits of Huangling granite batholith.At the same time,U elements in these two superunits are relatively enriched,so Huangling granite batholith may have the potential to form uranium mineralization.