贵州赫章地区玄武岩地质地球化学特征及其对峨眉山玄武岩的响应

Geological and geochemical characteristics of Hezhang basalt in Guizhou and its response to Emeishan basalt

赫章地区玄武岩以气孔-杏仁玄武岩、无斑-少斑玄武岩为主,含少量的微晶和隐晶质玄武岩,出露玄武岩熔岩阶地和柱状节理。4件样品的LA-ICP-MS锆石U-Pb年龄最年轻为253~255 Ma,代表赫章玄武岩的形成时代,与峨眉山玄武岩的高峰喷发时限一致。赫章玄武岩为亚碱性系列拉斑玄武岩,为典型的高钛玄武岩;具有右倾平滑型的稀土配分模式,负铕异常不明显(δEu 0.88~0.95);富集Rb、Ba、Th、U等大离子亲石元素(LILE),相对亏损Nb、Y、Yb等高场强元素(HFSE)。野外地质产状、主微量元素特征以及构造环境判别图解均表明,赫章玄武岩应属于大陆板内玄武岩,属于峨眉山玄武岩东岩区的一部分。

In Hezhang basalt,stomata-almond basalts and non-spot-less spot basalts are the principal deposits with a little microcrystal and vryptocrystal basalts,and the shape of leva terraces and columnar joints of basalt.The age of the youngest LA-ICP-MS zircon U-Pb by the four age samples is(252-255)Ma,marking the eruption time of Hezhang basalt,which is consistent with the eruption time of Emeishan basalt.Belonging to the sub-alkaline tholeiite series,Hezhang basalt is a kind of typical high titanium basalt.It has a right smooth type of REE distribution pattern with distinct negative europium abnormality(δEu 0.88-0.95).It is enriched in Rb,Ba,Th,U and other large ion lithophile elements(LILE),and lacked of Nb,Y,Yb and other high field strength element(HFSE).Due to the contamination of crustal or lithospheric mantle,Hezhang basalt has a certain degree of fractional crystallization.The ratios of its incompatible elements(Zr/Nb,La/Nb,Ba/Nb,Ba/Th,Th/La,Th/Nb,Ba/La,Rb/Nb)have more similarities with OIB.Field geological occurrence condition,the characters of major and trace elements and tectonic environment discrimination diagram indicate that Hezhang basalt should belong to the continental intraplate basalt and a part of the eastern rock area of Emeishan basalt.