鲁西潘店铁矿成矿岩体成因:锆石U-Pb年代学和地球化学证据

Ore-forming Origin of Rock Mass Zircon U - Pb Chronology and Geochemical Evidence of Pandian Iron Deposit in Luxi Area

潘店岩体为近年山东省齐河—禹城地区新发现的潘店铁矿的成矿岩体,主要由辉石闪长岩组成。对郭店地区潘店岩体辉石闪长岩进行了SHRIMP锆石U-Pb定年,其结果为(124.4±1.4)Ma,表明该岩体形成于早白垩世。潘店岩体SiO_(2)、K_(2)O和Na_(2)O含量分别介于59.68%~62.71%、0.13%~3.30%和6.57%~8.42%,Mg^(#)值为54.23~78.17,A/CNK为0.52~0.71,具有轻稀土富集,重稀土亏损的右倾型稀土配分模式,轻、重稀土分馏明显,具中—弱Eu负异常。富集大离子亲石元素Ba、Sr和高场强元素U、Pb、Zr,与相邻元素相比大离子亲石元素Rb、K和高场强元素Nb、Ce、P、Ti明显亏损。Nb/Ta、Zr/Hf比值及Nb、Ta的亏损等特征暗示原始岩浆可能来源于岩石圈地幔的部分熔融,并在岩浆上升侵位的过程中有地壳物质的同化混染。潘店岩体形成于岩石圈大规模快速减薄期,与燕山晚期太平洋板块俯冲作用密切相关。

Pandian rock mass is a newly discovered ore-forming body of Pandian iron deposit in Qihe-Yucheng area in Shandong province.It is mainly composed of pyroxene diorite.SHRIMP zircon U-Pb dating of pyroxene diorite in Pandian pluton has been carried out.The result is(124.4±1.4)Ma,indicating that the pluton was formed in the early Cretaceous.The contents of SiO_(2),K_(2)O and Na_(2)O in Pandian rock mass are 59.68%~62.71%,0.13%~3.30%and 6.57%~8.42%respectively.The Mg^(#)value is 54.23~78.17,and the A/CNK value is 0.52~0.71,It has a right-dip rare earth distribution pattern of light rare earth enrichment and heavy rare earth depletion.Comparing the light and heavy rare earth fractionation is obvious,with a medium-weak Eu negative anomaly.Enrichment of large ion lithophile elements Ba,Sr and high field strong elements U,Pb,Zr with adjacent elements,large ion lithophile elements Rb,K and high field strong elements Nb,Ce,P,Ti are obviously depleted.The characteristics of Nb/Ta,Zr/Hf ratios and Nb/Ta depletion indicate that the original magma may come from the partial melting of lithospheric mantle,and there is assimilation and contamination of crustal materials in the process of magma ascending and emplacement.The Pandian intrusion was formed during the large scale and rapid thinning of the lithosphere,which is closely related to the subduction of Paleo-Pacific plate in late Yanshan period.