Analysis Of The Characteristics And Genesis Of Mafic Rock Mass In Yueyawan,Hami City,Xinjiang

The Yueyawan mafic rocks are located in the Karatag region on the southern margin of the East Tianshan Mountains in Xinjiang.The tectonic units are part of the northern belt of the Tusuquan-Danan Lake Paleozoic island arc belt on the southern margin of the Tuha Basin and are located in the East Tianshan metallogenic belt.The geological conditions in the study area are complex and affected by tectonic movements and magmatic activities.It is a favorable area for mineralization in this area.This article takes mafic rock as the research object,conducts systematic sampling through field regional geological survey,adopts petrology,mineralogy,rock geochemistry and isotope chronology and other research methods when conditions permit,and then combines predecessors Data,systematically study the magmatic activity in this area,discuss the source of magma,the evolution of tectonic environment and the age of formation,so as to draw conclusions related to the origin of Yueyawan mafic rock mass.The Yueyawan mafic rock mass intrudes into the second lithologic section(D₁d²)of the Lower Devonian Dananhu Formation,and the formation of the rock mass is closely related to the structure.The rock assemblages in the rock mass are mainly olivine gabbro,olivine,gabbro,plagioclase,pale gabbro,and a small amount of syenite,and the horizontal direction shows a unidirectional evolution trend with low basicity to the northeast;The upward trend of increasing basicity.According to the contact relationship between the lithofacies in the rock body,the intrusion order of each lithofacies from early to late is judged as:peridotite facies,gabbro facies?olivine gabbro facies?plagioclase facies?Suchang facies.It is preliminarily judged that Yueyawan has the characteristics of continuous evolution and emplacement of the same source,multiple stages and multiple stages,and it is believed that there are at least three stages of sub-mafic magmatic activity in the area of the mafic complex of Yueyawan:The first phase is dominated by mafic magmatic eruption activities;the second phase is dominated by mafic magmatic intrusion and dissociation and differentiation activities;the third phase is formed by fine-grained plagioclase and sulvinite.The main elements of the Yueyawan mafic complex show that the Si O2 content of all samples is 42.98%?53.66%,which belongs to ultrabasic-medium basic rock.The trace element characteristics of the rocks in the Y1 and Y2 rock masses show that all kinds of rocks have the same elemental distribution curve and significant negative anomalies of Th,Nb,and Ta.However,the original mantle normalization values of the high-field-strength elements of the two complex rocks are significantly different,which means that the two have suffered from different levels of assimilation and contamination during magma evolution.The total amount of rare earth elements in the Y1 rock mass is relatively low,generally with different degrees of positive europium anomalies;the total amount of rock rare earth elements in the Y2 rock mass is relatively high,the europium anomalies are not obvious,and the Y1 and Y2rock masses show light-heavy The fractionation between rare earth elements is obvious,while the fractionation between light rare earth elements and heavy rare earth elements is weak.The sources of magma in Y1 and Y2 mafic rocks in Yueyawan are the same,all from the upper mantle,and are fluidized by the dehydration of subducted slabs in the source region of the mantle.The evolution of magma is mainly contaminated by the assimilation of lower crustal materials There is also the separation and crystallization of pyroxene,olivine and plagioclase.However,the magma of Y1 and Y2 mafic rock masses suffers from different levels of assimilation and contamination.The zircon in the peridot gabbro in the Y1 rock body of the Crescent Bay was selected for U-Pb zircon dating.The 206Pb/238U age weighted average was 288±2.5Ma(MSWD=0.85),which represents the crystallization of the rock body The age is Permian(early).It is consistent with the formation background of the East Tianshan mafic rock mass in the same period,indicating that the rock mass was formed in the collisional intracontinental extension environment after the Early Permian.