Geochemical characteristics and zircon U-Pb isotopic ages of island-arc basic igneous complexes from the Tianshui area in West Qinling
  • 【摘要】

    The Liushuigou intermediate-basic meta-igneous complex at Guanzizhen, Tianshui area, is mainly composed of metagabbro, metagabbro diorite and metadiorite, while the Baihua basic meta-igneous complex c... 展开>>The Liushuigou intermediate-basic meta-igneous complex at Guanzizhen, Tianshui area, is mainly composed of metagabbro, metagabbro diorite and metadiorite, while the Baihua basic meta-igneous complex consists mainly of pyroxenite, gabbro (gabbro diorite), diorite and quartz diorite.They form a relatively complete comagmatic evolutionary series. The geochemical characteristics of intermediate-basic igneous rocks indicate that they belong to a tholeiite suite.Their chondrite-normalized REE patterns are nearly flat and are LREE-slightly enriched type, and their primitive mantle-normalized and MORB-normalized trace element spider-grams are generally similar; the LILEs Cs, Ba, Sr, Th and U are enriched, while Rb and K and the HFSEs Nb, P, Zr,Sm, Ti and Y are depleted. All these show comagmatic evolu-tionary and genetic characteristics. The tectonic environment discrimination by trace element reveals that these igneous complexes formed in an island-arc setting. The Thermal Ionization Mass Spectrometry (TIMS) single-grain zircon U-Pb age for the Liushuigou intermediate-basic meta-igneous rocks in the Guanzizhen area is (507.5 ± 3.0) Ma, represent-ing the age of these igneous complexes, which indicates that island-arc-type magmatite rocks in the northern zone of West Qinling are Late Cambrian and also reveals that the timing of subduction of the paleo-ocean basin represented by the Guanzizhen ophiolite and resulting island-arc-type magrnaticactivity are probably Late Cambrian to Early Ordovician. 收起<<

  • 【作者】

  • 【作者单位】

    Faculty of Earth Sciences and Land Resources

  • 【刊期】

    地球科学前沿 2007年1期

  • 【关键词】

    basic igneous complex  geochemistry  island-arc setting  zircons U-Pb isotopic ages  Early Paleozoic,Tianshui area  West Qinling 

  • 【基金项目】

    This study was supported by the National Natural Science Foundation of China the Ministry of Education, China China Geological Survey