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天水地区百花变质岩浆杂岩主要由辉石岩-辉长(闪长)岩-闪长岩-石英闪长岩组成,构成较完整的同源岩浆演化序列.基性-中基性岩浆岩的地球化学特征表明,属于拉斑玄武岩系列,稀土元素分布型式呈REE近平坦型-LREE轻微富集型,微量元素原始地幔标准化的蛛网图和MORB标准化蛛网图上的分布型式总体很相似,富集大离子亲石元素(LILE)Cs,Ba,Sr,Th,U而相对亏损Rb,K和高场强元素(HFSE)Nb,P,Zr,Sm,Ti和Y,显示同源岩浆演化成因特征.微量元素构造环境判别显示其形成于岛弧构造环境.百花变质基性岩浆杂岩的LA-ICP-MS锆石U-Pb同位素年龄为(434.6±1.5)Ma(MSWD=1.3),证明西秦岭北带岛弧型岩浆岩的形成时代为晚奥陶世末或早志留世初,同时也揭示出以关子镇蛇绿岩为代表的古洋盆的俯冲作用及产生岛弧型岩浆活动的时限可能为中晚奥陶世-早志留世.
The Baihuai magmatic complexes in Tianshui area are mainly composed of pyroxene-gabbro (diorite) -diorite-quartz diorite, and constitute a complete sequence of homologous magmatic evolution. The basic-mafic magmatic The geochemical characteristics show that the distribution patterns of rare earth elements are slightly enriched in REE near-flat-LREE and belong to the area of tholeiite basalts. The trace patterns normalized by trace elements in the original mantle are generally similar to those distributed by MORB standardized spidergrams. Relative loss of Rb, K and HFSE Nb, P, Zr, Sm, Ti and Y due to LILE Cs, Ba, Sr, Th, U, The trace element tectonism shows that it was formed in the island arc tectonic environment.The LA-ICP-MS zircon U-Pb isotopic ages of the Baihuai metamorphic magmatic complexes are (434.6 ± 1.5) Ma (MSWD = 1.3) The formation of arc-shaped magmatic rocks in the northern belt of the Qinling Mountains was Late Ordovician or early Early Silurian. At the same time, the subduction of the paleo-oceanic basin represented by Guanzizhen ophiolite and the generation of island arc-type magmatic activity The time limit may be middle-late Ordovician - Early Hollow.