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首页> 外文期刊>Journal of Volcanology and Geothermal Research >Petrochemistry of a xenolith-bearing Neogene alkali olivine basalt from northeastern Iran
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Petrochemistry of a xenolith-bearing Neogene alkali olivine basalt from northeastern Iran

机译：伊朗东北部含异种岩的新近纪碱性橄榄石玄武岩的石油化学

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A small isolated Neogene, possibly Quaternary, monogenetic alkali olivine basalt cone in northeastern Iran contains both mantle peridotite and crustal gabbroic xenoliths, as well as plagioclase megacrysts. The basaltic magma rose to the surface along pathways associated with local extension at the junction between the N-S right-lateral and E-W left-lateral strike slip faults that form the northeastern boundary of the Lut microcon-tinental block. This basalt is enriched in LREE relative to HREE, and has trace-element ratios similar to that of oceanic island basalts (OIB). Its ~87Sr/~86 Sr (0.705013 to 0.705252), ~143Nd/~144 Nd (0.512735 to 0.512738), and Pb isotopic compositions all fall in the field of OIB derived from enriched (EM-2) mantle. It formed by mixing of small melt fractions from both garnet-bearing asthenospheric and spinel-facies lithospheric mantle. Plagioclase (An_(26-32)) megacrysts, up to 4 cm in length, have euhedral crystal faces and show no evidence of reaction with the host basalt Their trace-element concentrations suggest that these megacrysts are co-genetic with the basalt host, although their ~87Sr/~86 Sr (0.704796) and ~143Nd/~144 Nd (0.512687) ratios are different than this basalt. Round to angular, medium-grained granoblastic meta-igneous gabbroic xenoliths, ranging from ～1 to 6 cm in dimension, are derived from the lower continental crust Spinel-peridotite xenoliths equilibrated in the subcontinental lithosphere at depths of 30 to 60 km and temperatures of 965 °C to 1065 °C. These xenoliths do not preserve evidence of extensive metasomatic enrichment as has been inferred for the mantle below the Damavand volcano further to the west in north-central Iran, and clinopyroxenes separated from two different mantle xenoliths have ~87Sr/~86 Sr (0.704309 and 0.704593) and ~143 Nd/~144 Nd (0.512798) ratios which are less radiogenic than either their host alkali basalt or Damavand basalts, implying significant regional variations in the composition and extent of metasomatism in the sub-Iranian mantle.
机译：伊朗东北部的一个小的孤立的新近纪，可能是第四纪的单生碱性橄榄石玄武岩锥，包含地幔橄榄岩和地壳辉长岩异岩，以及斜长石巨晶。玄武岩浆沿与形成卢特微大陆块东北边界的南北向右走向和西向左走向走滑断层之间的交界处的局部扩展相关的路径上升到地表。该玄武岩相对于HREE富含LREE，其痕量元素比率与大洋洲玄武岩（OIB）相似。其〜87Sr /〜86 Sr（0.705013至0.705252），〜143Nd /〜144 Nd（0.512735至0.512738）和Pb同位素组成均属于由富集（EM-2）地幔衍生的OIB领域。它由石榴石软流圈和尖晶石相岩石圈地幔中的少量熔体组分混合而成。斜长石（An_（26-32））巨晶长达4厘米，具有正方晶面，没有显示出与主体玄武岩反应的证据。它们的痕量元素浓度表明，这些巨晶与玄武岩主体共生，尽管它们的〜87Sr /〜86 Sr（0.704796）和〜143Nd /〜144 Nd（0.512687）之比与该玄武岩不同。圆形至成角的中粒粒状火成岩辉长岩异岩，尺寸约在1至6 cm之间，来自在30至60 km深度和30摄氏度温度下在大陆下岩石圈平衡的下部大陆壳尖晶石-橄榄岩异岩。 965°C至1065°C。这些异岩体没有保留广泛的交代富集的证据，正如伊朗中北部更西部的达马万德火山下方的地幔所推断的那样，从两种不同的地幔异岩体中分离出的斜辉石具有〜87Sr /〜86 Sr（0.704309和0.704593 ）和〜143 Nd /〜144 Nd（0.512798）之比，其放射源性低于其宿主碱玄武岩或Damavand玄武岩，这意味着伊朗亚幔中交代作用的组成和程度存在明显的区域差异。

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