内蒙古镶黄旗哈达庙地区晚古生代中酸性侵入岩的年代学、地球化学、Sr-Nd同位素组成及其地质意义

SHRIMP zircon U-Pb dating,geochemistry,Sr-Nd isotopic analysis of the Late Paleozoic intermediate-acidic intrusive rocks in the Hadamiao area,Xianghuang Banner,Inner Mongolia and its geological significances

内蒙古哈达庙地区位于华北板块北缘,本文对区内花岗斑岩和闪长岩进行了锆石SHRIMP U-Pb定年,其形成年龄分别为271±3Ma和267±3Ma。花岗斑岩具有高的SiO2含量(均值75.11%)、较高的K2O含量(均值5.06%)、低的MgO含量(均值0.43%)及低的Cr(均值6.70×10-6)、Ni(均值5.15×10-6)和V(均值26.86×10-6)含量,闪长岩与花岗斑岩相比具有更低的SiO2(均值57.28%)和K2O含量(均值1.23%),更高的MgO(均值5.31%)、Cr(均值195.18×10-6)、Ni(均值59.11×10-6)和V(均值148.13×10-6)含量。从闪长岩到花岗斑岩,稀土元素总量增加,铕负异常更明显,轻重稀土分馏程度增大。两者均富集大离子亲石元素、贫高场强元素、强烈亏损Nb、Ta、P和Ti等元素,具有较高的锶初始比值(ISr:0.704803～0.707025)、较低的钕初始比值(εNd(t):-3.92～1.03)和相对年轻的Nd模式年龄(898～1322Ma)。哈达庙地区花岗斑岩和闪长岩形成于中二叠世古亚洲洋的俯冲过程,高镁闪长岩是受俯冲板片流体交代的地幔楔部分熔融形成的熔体上升过程中受到地壳物质混染的产物,而花岗斑岩很可能是闪长质岩浆结晶分异的产物。

The Hadamiao area is located in the northern margin of the North China plate. The SHRIMP U-Pb dating of zircons from granite porphyry and diorite of the Hadamiao area yields ages of 271 ± 3Ma and 267 ± 3Ma. Granite porphyry is characterized by its high SiO 2（ averaging 75. 11%） and K 2 O contents（ averaging 5. 06%）,low MgO（ averaging 0. 43%）,Cr（ averaging 6. 70 × 10- 6）, Ni（ averaging 5. 15 × 10- 6） and V contents（ averaging 26. 86 × 10- 6）,but diorite is characterized by its lower SiO 2（ averaging 57. 28%） and K 2 O contents（ averaging 1. 23%）,higher MgO（ averaging 5. 31%）,Cr（ averaging 195. 18 × 10- 6）,Ni（ averaging 59. 11 × 10- 6） and V contents（ averaging 148. 13 ×10- 6）,respectively. The rare earth elements（ REE） contents have an obvious increase from diorite to granite porphyry,but granite porphyry has more strongly negative Eu anomalies and fractional degree of heavy REE（ HREE） and light REE（ LREE）. These rocks are enriched in large ion lithophile elements（ LILE）,but depleted in high field strength elements（ HFSE）. Both granite porphyry and diorite share the common features of relative high I Sr valeus（ I Sr ： 0. 704803 ～ 0. 707025）,low ε Nd（ t） values（ ε Nd（ t） ：- 3. 92 ～ 1. 03） and young Nd-model age（ 898 ～ 1322Ma）. We suggest that granite porphyry and diorite of the Hadamiao area were formed during a middle Permian subduction of paleo-Asian ocean slab. The high Mg diorite was a product of partial melting of mantle wedge replaced by slab-derived fluid and mixed by crustal materials,and granite porphyry was probable a product of crystallization differentiation of dioritic magma.