粤东地区早白垩世花岗质岩浆作用及其成因演化

The Magmatic and Genetic Evolution of Early Cretaceous Granitoids in Eastern Guangdong Province

粤东地区出露有大埔黑云母花岗岩、大埔黑云母钾长花岗岩和揭西黑云母钾长花岗岩3种岩石类型,大埔黑云母花岗岩和揭西黑云母钾长花岗岩的LA-ICP-MS锆石U-Pb年龄分别为136.3±0.6Ma和134.9±0.4Ma,属于晚中生代早白垩世,而非前人认为的晚侏罗世;3种岩石在主量元素上总体具有富硅、铝,碱含量中等,贫铁、镁、钙、钛、磷的特征,属于高钾钙碱性的弱过铝质岩石;大埔黑云母花岗岩的δEu负异常中等,具略向右倾的轻稀土富集模式,可能是由时代相当于元古宙的富砂屑岩部分熔融形成的;大埔黑云母钾长花岗岩、揭西黑云母钾长花岗岩具有中等——强的δEu负异常,稀土配分模式为海鸥型,二者在野外分布上紧密共生,时间上比较接近,在地球化学上表示出连续变化的趋势,具有相似的同位素组成,可能是由时代相当于元古宙的陆壳富泥质变质沉积岩部分熔融形成的,是同一岩浆演化到不同阶段的产物。

Granitoids in the Eastern Guangdong encompass three main rock types： the Dapu biotite-granites, the Dapu bitite-K-spar granites and the Jiexi bitite-K-spar granites. Zircon LA-ICP-MS U-Pb dating of the Dapu biotite-granites and the Jiexi bitite-K-spar granites indicates similar ages of emplacement of 136.3 ± 0.6Ma and 134.9 ±0.4Ma ,respectively, which belongs to Early Cretaceous but not Late Jurassic; All of these three types of rocks are rich in Si,A1, medium in alkali content, but poor in Fe, Mg, Ca,Ti and P, belong to a high-K calcalkaline series, as well as a weakly peraluminous granite series. The Dapu biotite-granites hasSEu mid-negative anomaly, slightly right-inclined REE distribution pattern, forming by the partial-melting of Proterozoic arenitic metasediments. The Dapu bitite-K-spar granites and the Jiexi bitite-K-spar granites have strongly BEu negative anomaly, seagull-like REE pattern. The Dapu bitite-K-spar granites and the Jiexi bitite-K-spar granites are coexist closely, forming in the same time, and shows continuous variation trend in geochemistry, have similar isotopic composition, may be formed by partial mehing of Proterozoic pelitic metamorphic sedimentary rocks, are the results of different evolution stage of the same magma.