岚皋早古生代碱质煌斑杂岩地球化学特征及成因探讨

摘要

The alkali lamprophyre complex from Langao County, whose chondrite-normalized REE patterns all incline to the right and whose major elements vary regularly, has abundant incompatible elements. Studies on major and trace elements indicate that there existed two parallel fractional crystallization trends during the evolution of primary magma which suffered insignificant contamination of crustal material. The enrichment of LREE and incompatible elements with the change of Zr/Nb, Ce/Y, Dy/Yb, La/Yb and Zr/Sm ratios show that the lamprophyre magma couldn't have been derived from partial melting of spinel-, garnet-lherzolite mantle source or amphibole-bearing spinel or garnet lherzolite mantle source. Sr-Nd-Pb isotope variations indicate that the source of lamprophyre magma was mainly composed of HIMU mantle. The mantle plume not only played an important role in the formation of lamporphyre, but also controlled the metasomatism that occurred in the source of the alkali lamprophyre complex.%岚皋碱质煌斑杂岩主量元素呈规律性演化，REE球粒陨石标准化配分型式呈强右倾型, 富集不相容元素。岩石主元素和微量元素地球化学特征表明，煌斑岩浆在演化过程中存在2个平行的结晶分异演化趋势，岩浆演化过程中受地壳混染的程度很小。LREE、不相容元素的强烈富集及Dy/Yb、La/Yb、Zr/Sm、Ce/Y等微量元素的质量分数比值变化表明，煌斑杂岩不可能由尖晶石或石榴石二辉橄榄岩、含角闪石的尖晶石或石榴石二辉橄榄岩的部分熔融形成，它的源区应为含金云母和单斜辉石的交代地幔。Sr-Nd-Pb同位素结果显示，煌斑岩浆源区的地幔主要为HIMU端元组分。地幔柱的活动与煌斑岩浆的起源密切相关，并制约了其源区的地幔交代作用。