南沙地块花岗质岩石矿物学特征及其成因信息  

Mineralogical Characteristics of Granitic Rocks from the Nansha Block(South China Sea) and Its Implications for Magmatic Process

作　　者：鄢全树[1] 石学法[1] 高晶晶[1] 苏天赟[1] 

机构地区：[1]海洋沉积与环境地质国家海洋局重点实验室国家海洋局第一海洋研究所,山东青岛266061

出　　处：《矿物学报》2012年第1期131-138,共8页Acta Mineralogica Sinica

基　　金：国家自然科学基金(批准号:40609034);中国博士后科学基金(编号:200904501348;201104616);山东省博士后创新项目专项资金(编号:200802007);国家海洋局第一海洋研究所基本科研业务费专项资金(编号:GY02-2008G38;GY02-2010G20)

摘　　要：样品来自南沙地块北缘、洋陆过渡带附近2个拖网站位,主要为代表陆壳基底的中-酸性侵入岩,如花岗闪长岩(中性组)和二长花岗岩(酸性组)等。分析了这些中-酸性侵入岩的长石、黑云母和角闪石等矿物的主量元素成分。中性组的斜长石的牌号(An为13～38)明显高于酸性组的斜长石的牌号(An值为9～12),岩石主要组成部分的斜长石成分与岩石类型一致。两组岩石的黑云母均为富镁黑云母,黑云母成分反映其岩浆物质来源为幔源或壳幔混源,且酸性组的黑云母成分反映其寄主岩石受到地幔物质的影响要大于中性组,角闪石只出现在中性岩石内,为壳幔混合成因,反映其寄主岩石为典型的I型花岗岩。矿物共生组合温压条件计算表明,中性组岩石的结晶温度和深度分别为544～630℃(平均为573℃)和18～19 km,而酸性组岩石的结晶温度和深度总体上都低于中性组岩石,分别为416～538℃(平均为494℃)和9～10 km。本研究所揭示的矿物化学特征与所计算的温压条件为基于全岩元素地球化学特征提出的岩石成因模型提供证据。Two dredged samples from near ocean-continent transition zone in the northern margin of Nansha micro- block （SCS） are mainly intermediateacid intrusive rocks representing continental basement, i. e. , granodiorite （ intermediate end-member） and monzonite granite （acidic end-member） . This study analyzed mineral composition （including feldspar, biotite and hornblede） of four representative rock samples by using electron microprobe technique. Values （13 -38） of plagioclase in the intermediate end-member are obviously higher than those （9 - 12） in the acidic end-member. Biotites in these two group rocks are magnesium-rich biotite, whose compositions reflect that the magma origin is mantle-derived or mixed source between crust and mantle, implying that the acidic end-member rocks received greater influences from mantle material than the intermediate end-member rocks. Hornblendes only appea- ring in the intermediate end-member rocks are produced from crust-mantle mixing, reflecting that its host rocks are typical I-type granite. Using mineral compositions and appropriate geothermobarometers, this study calculated the crystallization temperature and depth of intermediate end-member rocks, being 544 - 630 ℃ with average of 573 ℃ and 17 km, respectively, and those of acidic end-member is 416 -538 ℃ with average of 494 ℃ and 9 -10 km, respectively. Mineral chemicial characteristics and calculated value of temperatures and pressures support the petrogenetic model which have been supposed based on whole-rock geochemistry.

关 键 词：南沙地块 花岗质岩石 中生代 矿物化学 南海 

分 类 号：P571[天文地球—矿物学] P581[天文地球—地质学]