【摘要】 鲁西地区下常庄岩体是由新发现的一种岩石类型—磁铁角闪岩组成。磁铁角闪岩主要由角闪石(40%~45%)、磁铁矿(35%~45%)、斜长石(10%~15%)和次要的单斜辉石及副矿物锆石、磷灰石组成。该岩体中锆石的阴极发光图像显示出锆石大多数呈自形半自形的晶形,具有典型的岩浆生长环带,其Th/U均大于0.25,表明具有岩浆成因。对锆石进行的LA-ICP-MSU-Pb定年结果表明,多数锆石构成了上交点为(2396±110)Ma、下交点为(264±170)Ma的不一致年龄线。(242±10)Ma代表了该岩体的侵位结晶年龄;(476±62)Ma与华北克拉通东部古生代金伯利岩的形成时代相吻合;(758±28)Ma所代表的岩浆事件与扬子克拉通及其与华北克拉通相接触部位出现的新元古代岩浆事件相一致;(1855±8)Ma、(2014±8)Ma和(2394±9)Ma年龄则代表了华北克拉通基底物质的存在。更多还原

【Abstract】 The Xiachangzhuang intrusion is composed of magnetite-amphibolite discoved newly in western Shandong. The magnetite-amphibolite consists of amphibole (40%～45%), magnetite (35%～45%), plagioclase (10%～15%), and minor clinopyroxene and accessory minerals such as zircon and apatite. Most of zircons show the euhedral-subhedral shapes and typical magmatic growth zone on cathodoluminesence (CL) images, some of them are round with strong absorption cores and light absorption rims. ThU ratios for zircons are more than 0.25, implying their magmatic origin. The LA-ICP-MS U-Pb dating results for different shape and absorption of zircons indicate that most zircons constitute a discordia line with the upper intercept age of (2 396±110)Ma and a lower intercept age of (264±170)Ma.The age of(242±10)Ma for zircons represents the crystalline age of the intrusion.(476±62)Ma is consistent with the formation time of the Paleozoic kimberlite from eastern North China Craton,(758±28)Ma coincides with the Neoproterozoic magmatic event occurred in the Yangtze Craton and its neighboring North China Craton, and(1 855±8)Ma,(2 014±8)Ma and(2 394±9)Ma imply the existence of the North China Craton basement.更多还原