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本文通过对塔西南达木斯剖面中玄武岩进行 K-Ar 同位素定年,获得年龄为289.6Ma,并结合 Ar-Ar 坪年龄结果(290.1Ma)和古生物以及沉积特征,认为290Ma 的年龄代表了塔西南玄武岩形成于早二叠世,对应于盆地内下二叠统库普库兹满组下段层位的年龄。地球化学特征显示塔西南熔岩为分异的碱性玄武岩并含45%SiO_2和4%MgO 含量。塔西南玄武岩与盆地内柯坪玄武岩具有相近的主量元素含量和稀土配分与微量元素蜘蛛网图型、无 Eu 异常、富集轻稀土元素、较高的其它不相容元素(如高场强元素)。但塔西南玄武岩比柯坪玄武岩具有较高的 Al_2O_3和 CaO 含量及稀土总量(288×10~(-6)～358×10~(-6)),偏低的 Na,O,P_2O_5和 FeO 含量。K、Rb 和 Cs 丰度的无系统性变化主要受这些元素丰度本身变化的影响。对其它不活动组分,塔西南玄武岩具有高 Ti(Ti/Y=522～624)和 Nb 含量(30×10~(-6)～40×10~(-6))及低 Zr/Nb 比值,暗示其来自富集的地幔源区。其 Nb 含量相对 La 含量无显著变化以及相对低的 Nb/U(近30)和 Ce/Pb 比值(近15),指示塔西南玄武熔岩来自大陆岩石圈或受一定程度的地壳混染。塔里木盆地大规模的火山喷发以及富集不相容元素的地球化学特征支持这样一种假设,即塔西南玄武岩来自地幔柱火山作用,或由于地幔柱的供热和上升导致富集的岩石圈地幔部分熔融而形成。且岩浆作用过程以部分熔融为主,结晶分异作用较弱。基于塔西南玄武岩和柯坪玄武岩相近的时代、源区成分和/或岩浆作用过程以及处于陆内稳定构造环境,笔者认为塔里木二叠纪玄武岩的分布范围可以从塔里木盆地内的塔中、柯坪一带一直延伸到塔西南地区。
In this paper, the K-Ar isotope dating of basalts in the Darmus section of the southwestern Tarim basin was used to obtain the age of 289.6Ma. Combined with the Ar-Ar plateau age (290.1Ma) and paleontology and sedimentary characteristics, the age of 290Ma is considered to represent the southwest of the tower Basalts were formed in the Early Permian, corresponding to the age of the lower member of the Lower Kupuqi Formation in the basin. Geochemical characteristics show that the southwest of the lava is a differentiated alkaline basaltic and contains 45% SiO 2 and 4% MgO. The basalt in the southwestern Tarim Basin has the similar major and minor elemental cobblestone patterns with the main elements and the cobweb pattern without Eu anomalies, enriched in LREE and higher in other incompatible elements (such as high field strength element). However, the southwestern Tarim basin basalts have a higher content of Al 2 O 3 and CaO and a total amount of rare earths (288 × 10 -6 ~ 358 × 10 -6) than Kejiaping basalts, and low Na, O, P 2 O 5 and FeO content. The unsystematic changes in abundance of K, Rb and Cs are mainly affected by the abundance of these elements themselves. For other inactive components, the basalt in the southwestern Tarim basin has high Ti (Ti / Y = 522 ~ 624) and Nb contents (30 × 10 -6 ~ 40 × 10 -6) and low Zr / Nb ratio , Suggesting that it comes from the enriched mantle source area. There is no significant change of Nb content relative to La content and relatively low Nb / U (nearly 30) and Ce / Pb ratio (nearly 15), indicating that the southwestern basaltic lavas of southwestern China are from the continental lithosphere or are contaminated by some crustal contamination. Large-scale volcanic eruptions in the Tarim Basin and geochemical features enriched in incompatible elements support the hypothesis that the southwestern Tarim basin is derived from mantle plume volcanoes or enriched in lithospheric mantle due to mantle plume heating and ascent Partially melted and formed. And the magmatic process is mainly partial melting, crystallization differentiation is weak. Based on the similar epoch, provenance composition and / or magmatism of Tarim Bashan and Keping basalts as well as their stable tectonic setting in the interior, the authors believe that the distribution of Permian basalts in the Tarim Basin can range from the towers in Tarim Basin to Keping The area stretches to the southwest of the tower.