闽西南红山含黄玉浅色花岗岩地球化学特征和成因  

Geochemistry and origin of the Hongshan topaz-bearing leucogranites in southw estern Fujian Province

作　　者：赵蕾[1] 于津海[1] 谢磊[1] 

机构地区：[1]南京大学地球科学系内生金属矿床成矿机制研究国家重点实验室,江苏南京210093

出　　处：《地球化学》2004年第4期372-386,共15页Geochimica

基　　金：国家自然科学基金(40132010;40372087);南京大学开放测试基金项目

摘　　要：红山花岗岩体主要由钾长石、石英和自形的钠长石组成,次要矿物包括原生铁锂云母、黑云母和黄玉等;岩石具有高SiO2、K2O、Rb、Nb、Ta、Th、U含量,低CaO、P、Ba、Sr、Zr、Hf含量以及富A1(ACNK>1.1)和强烈Eu亏损(Eu/Eu<0.15)等地球化学特征,属于富F低P花岗岩亚类。但是,相对高的TiO2、MgO含量,K2O/Na2O比值以及成分偏离低共熔点表明红山花岗岩不是强烈演化的产物;而相对低的F含量(<0.56%)、K/Rb>50、Nb/Ta>5、低的REE四分组效应以及Y/Ho比值仍处于球粒陨石范围也指示,尽管在演化晚期岩浆富集了一定的流体,但红山花岗岩没有进入典型的流体分离阶段。分离结晶模拟显示从早期到晚期红山花岗岩发生了20%～30%以钾长石+斜长石为主和黑云母次之的分离结晶作用,同时伴随锆石、独居石和磷钇矿等的分离。红山花岗岩具有高的(87Sr/86Sr)i(0.723)和低的εNd(t)(-9.8～-12.5),Nd模式年龄介于1.64～1.92Ga之间,不同于中元古界桃溪岩组和震旦纪变质围岩的同位素组成。结合部分熔融模拟,认为中、新元古代的变质围岩可能不是红山花岗岩的源岩。同位素和地球化学的特征暗示红山花岗岩的源岩很可能是类似于古元古代麻源群的变质岩。花岗岩的原始岩浆是在850℃以上由泥质变质岩为主的岩石经30%以上的部分熔融产牛;The Hongshan topaz-bearing leucogranites, consisting mainly of K-feldspar, quartz and euhedral albite, with subordinate zinnwaldite, biotite and topaz, are characterized by high SiO2, K2O, Rb, Nb, Ta, Th and U, low CaO, P, Sr, Ba, Zr and Hf as well as high ACNK (> 1.1) and strong Eu depletion (Eu/Eu *< 0.15), and belong to low-P, F-rich granite subtype. However, relati vely high TiO2, MgO contents and K2O/ Na2O ratios, and deviation of compositio n from the minimum melt strongly document that the Hongshan granites are not the products of highly evolved residual melt, but crystallized from relatively pri mary melt generated by partial inching. Moreover, relative to typical F-rich granites all over the worhl, low F content (< 0.56%) and REE tetrad effect (T E1,3 = 1.06～1.19), high K/Rb (> 50) and Nb/Ya (> 5) ratios and similar Y/Ho ra tio to chondritic one suggest that the evolution of the Hongshan granitic magma did not reach the typical fluid fractionation stage, even though fluids were in creasingly enriched in late phase. Fractional crystallization modeling indicate s that the Hongshan granites underwent only 20%～30%mineral fractionation , involving K-feldspar, quartz and plagioclase, and subordinate biotite and t race zircon, monazite, xenotime. The Hongshan leucogranites have high initial 87 Sr/86Sr ratios (0.723 0) and low ?Nd(t) (-9.8～-12.5), their Nd model age s vary from 1.64 to 1.93 Ga, different from Mesoproterozoic and Sinian metamorp hic wall-rocks. Coupled with partial inching modeling, it is suggested that the Meso-and Neo-Proterozoic metamorphic wall-rocks are unlikely the sour ce rocks of the Hongshan granites. Whilst their source rocks are probably those analogous to the metamorphic rocks of Paleoproterozoic Mayuan Group, based on t heir resemblance in isotopic and chemical compositions. The primary melt of the Hongshan granite was generated by more than 30%partial melting of pelitic m etamorphic rocks at higher than 850℃; and the granites were mostly formed at t emperature from 780℃to

关 键 词：含黄玉钠长花岗岩 地球化学 岩石成因论 南岭东段 福建省 

分 类 号：P594[天文地球—地球化学] P588.12[天文地球—地质学]