徐宿地区新元古代辉绿岩床的地球化学特征

同位素测年数据显示，徐宿地区的辉绿岩床是震旦纪早期和震旦纪晚期两次侵入的 产物。岩床多呈板状或楔状，为超浅成—浅成侵入体，其化学成分以高SiO2、CaO和低Al 2O3、MgO及(K2O+Na2O)为特征，属大陆拉斑玄武岩系列。稀土元素配分模式为轻 稀土富集型，但稀土元素分馏并不强烈。Rb、K、La等不相容元素富集，而Nb、Sr亏损明显 。δ18O值在6.63‰～9.93‰之间，多数>8‰。研究表明，该区基性岩浆来源于过 渡型地幔，主要通过部分熔融方式形成，在岩浆上侵过程中遭到陆壳或花岗质岩石的混染。

Geochemical Features of NeoProterozoic Diabase Sills in Xuzhou-Suzhou Area

The studied diabase sills are found in Xuzhou Suzhou area of the southeastern part of North China Plate.They intruded into the NeoProterozoic strata and might be the products of two stages Isotopic ages of the two stage diabase sills are 706-723 Ma and 604-654 Ma, respectively,corresponding to the early and late Sinian period The sills are tabular and wedge shaped,with a thickness from tens to more than hundred metres The emplacement depth of the diabase sills ranges from 0 05km to 2km They are hypabyssal to subsurface intrusives and were folded during the Mesozoic time together with their surrounding rocks The sills are composed of diabase and quartz diabase A lithological change occurred in some thick sills The olivine (hyalosiderite) bearing diabase, amygdaloidal diabase and medium to coarse grained diabase (sometimes alkali gabbro) occur at the bottom, top and middle parts of the sills, respectively Chemical compositions of the sills are enriched in SiO 2, CaO and depleted in Al 2O 3, MgO, (K 2O Na 2O) In the K 2O-TiO 2-P 2O 5 plot, all sample points almost fall into the field of continental tholeiite It is therefore deduced that the diabases might belong to the tholeiite series occurring within the North China Plate The chondrite normalized REE patterns of diabases show a Eu smooth type, an enrichment in light REE and a small separation between LREE and HREE The rocks are enriched in K, Rb, La and depleted in Nb, Sr The depletion of Nb is almost a common feature for all continental tholeiite series rocks Spidergram of Nb normalized ratios and Nb-Zr, Y-Zr related diagrams show that the basaltic magma, from which the diabase was crystallized, might be generated from the transitional mantle An excellent distribution of positive slope line for all sample points in the La/Sm vs La diagram suggests that the rocks were mainly generated by partial melting The spidergram of Yb normalized ratios,the Thompson diagrams of trace elements and the Nb * anomaly values calculated from chondrite normalized Nb, K, La values show that the basic magma was contaminated by the crustal or granitic materials during its upwelling