云南香格里拉可麦洛新生代碱性侵入岩地球化学特征及意义

分布于扬子地台西缘、哀牢山-红河断裂带的新生代碱性侵入岩为研究板内岩浆系统中的壳幔作用及地球化学循环提供了理想的研究窗口。研究选择对香格里拉地区可麦洛碱性侵入岩的元素地球化学特征进行测试分析,结果显示该岩体具有高铝(w_Al2O_313.50%～15.50%,平均14.63%)、碱值(w_Na2O+K_2O为6.79%～9.95%,平均8.74%)的特征;w(MgO)为1.74%～5.25%,平均为3.21%;w(Ni)为25.17×10^-6～127.16×10^-6,平均54.47×10^-6;w(Cr)为12.86×10^-6～48.23×10^-6,平均26.76×10^-6,与滇西新生代碱性岩相比富含亲稀土元素(644.55×10^-6～402.09×10^-6),Eu异常不明显(Eu/Eu~*=0.89～1.09)。微量元素蛛网图显示出较强的负K,Ti(Ti/Ti~*=0.38～0.45)异常,Nb异常变化较大(Nb/Nb~*=1.29～0.47)。综合分析该侵入岩可能起源于壳幔过渡带的部分熔融,其源区残留有石榴石、角闪石和金云母。软流圈上涌及下地壳拆沉很可能导致扬子地台西缘下伏岩石圈地幔与下地壳形成物质能量交换,而长期的壳幔反应会造成岩石圈地幔弱化,局部出现低强度的弱化岩石圈地幔,形成壳幔过渡带。

GEOCHEMICAL CHARACTERISTICS AND SIGNIFICANCE OF THE CENOZOIC ALKALINE INTRUSIONS IN KEMAILUO AREA OF SHANGRI-LA,WESTERN YUNNAN PROVINCE,CHINA

Cenozoic alkaline intrusions occurred on the east side of the Ailaoshan-Red River shear zone in the western Yangtze craton provide an opportunity for understanding of the crust-mantle interaction and geochemical cycling in the intra-plate magmatic system.The analyzed ten samples from the Kemailuo alkaline intrusions,Shangri-La County are characterized by high contents of w(Al2O3)(13.50%~15.50%),alkaline(6.79%~9.95%),w(MgO)(1.74%~5.25%),w(Ni)(25.17×10^-6~127.16×10^-6) and w(Cr)(12.86×10^-6~48.23×10^-6).Light rare earth element(644.55×10^-6~402.09×10^-6) in these samples are higher than other Cenozoic alkaline rocks in Western Yunnan.In addition,these samples show nearly flat heavy rare earth element(HREE) patterns and insignificant Eu anomalies(Eu/Eu^*=0.89~1.09).Trace element spider diagram displays strong negative K,Ti(Ti/Ti^*=0.38~0.45) anomalies and variable Nb anomalies(Nb/Nb^*=1.29~0.47).Trace element modeling indicates that garnet,amphibole and phlogopite may be present in the residua during source partial melting.Through comprehensive analysis,it is considered that the crust-mantle transition zone might be the source of Kemailuo alkaline intrusions,and the upwelling of the asthenosphere and delamination of lower crust lead to the exchange of material energy between the lower lithosphere mantle and the lower crust in the west margin of Yangtze craton.