摘要
出露于广东省从化市南的腊圃角闪黑云二长花岗岩占地面积约500km2,由钙质角闪石(0.5%),黑云母(11%~13%),斜长石(An35~41,29%~31%),隐纹长石(24%~31%)和石英(36%~37%)组成,含富Ca,Ti副矿物褐帘石和榍石等。根据颗粒锆石U-Pb定年,其定位时间为163±2Ma(中侏罗世)。化学成分上为弱过铝质(平均A/NKC=1.043),富K2O(平均4.72%),属高钾钙碱性系列。稀土总量较高,ΣREE=(180~460)×10-6,轻稀土明显富集,重稀土明显亏损,具有大的(La/Yb)N值(平均19),说明熔融作用是在下地壳深度进行(p>108Pa),石榴子石是主要的残留相矿物。多种源岩示踪方法指出,形成腊圃岩体岩浆的源岩是变硬砂岩或变角闪岩(包括变火成岩)。模拟计算显示,下地壳深度的该类源岩55%部分熔融形成的熔体,与腊圃花岗岩岩浆有极为相似的地球化学性质。Sr,Nd同位素成分测定表明,岩石具有较高的ISr值(0.7124~0.7155)和较低的εNd(t)值(-11.18^-11.54),模拟计算显示,这显然是一种下地壳部分熔融的产物。
Exposed at the south of Conghua city, Guangdong province, the Lapu amphibole- and biotite-bearing monzonitic granite occupies an area of about 500 km2. The rock is composed of calcic amphibole （0.5%）, biotite （ 11 - 13% ）, plagioclase （An35 -41,29 -31% ）, cryptoperthite （24 -31% ） and quartz （36 -37% ）, carrying some amounts of Ca-, Ti-rich minor minerals such as allanite and titanite. Based on zircon U-Pb isotopic dating, the rock emplaced at 163 ±2 Ma （mid-Jurassic）. Petrochemically, the Lapu granite is weakly peraluminous （A/ NKC = 1. 043 in average） and with higher K20 content （4.72% in average）, belonging to the high-K calcic-alkaline series. The rock has high EREE contents （（ 180 -460） × 10-6）, showing an evident LREE-enriched and HREE-depleted tendency, and with higher （La/Yb）N values （19 in average）. These features indicate that partial melting of source materials for forming Lapu magma occurred at a deeper （ lower crust） level （p 〉 10 × l0s Pa） and that garnet would be a main residual phase, which resulted in HREE depletion in the melt. According to many trac- ers for source rocks （Patino Douce, 1999）, it is suggested that the source rocks for forming Lapu magma were metagreywakes or meta-amphibolites. Analyses for Sr, Nd, Pb isotopic compositions of the Lapu granite yielded a feebly high Isr （0.7124 - 0.7155 ） and lower εNd （t） values （ - 11. 18 - - 11. 54 ）. Model calculation shows that the melt formed by 55% partial melting of the lower crust rocks would have the similar geochemical features as those of real Lapu granite magma.
出处
《高校地质学报》
CAS
CSCD
北大核心
2005年第3期343-357,共15页
Geological Journal of China Universities
基金
国家自然科学基金项目(40132010)
