塔什库尔干碱性杂岩体形成时代及其地质意义

AGES OF TAXKORGAN ALKALINE INTRUSIVE COMPLEX AND THEIR GEOLOGICAL IMPLICATIONS

帕米尔构造结是青藏高原变形最强烈的地区之一,区内新生代岩浆侵入活动发育,既有壳源岩浆侵位,也有幔源岩浆广泛分布.根据岩石学和地球化学研究,侵人岩可分为幔源碱性正长岩和壳源花岗岩2个系列.幔源碱性正长岩总体上由暗色正长岩、浅色正长岩和碱性花岗岩组成,其成因为岩浆不混溶作用.壳源花岗岩类成分单一,具有低共熔岩浆属性,其成因可能与幔源岩浆对地壳加热有关.利用碱性正长岩的钾长石进行40Ar-39Ar法获得3个分别为大约23Ma、13 Ma和8 Ma坪年龄数据,结合岩体地质特征,认为它们分别代表了碱性正长岩和花岗岩的侵位时间以及后期构造热事件.研究结果表明,岩浆活动是帕米尔构造结形成和帕米尔强烈变形的主要因素之一.

The Pamir syntaxis is one of the strongly deformatted areas in Tibetan Plateau. It underwent complex processes of formation and evolution. Meanwhile, it is one of the most developed regions with Cenozoic magma intrusions. There are extensive emplacements of magmas from both crust and mantle sources. Based on petrology and geochemistry, the intrusive rocks are divided into two series: alkaline syenitoid and granitoid respectively. Overall, the alkaline syenite massif consists of melanosyenitoid, leucosyenitoid and alkaline granite. Magma immiscibility is a very important process for the magma evolution to generate rock variations. The granitoid has a small composition variation indicating its syntexis origin related to heating crust resource by mantle-derived magma. From 40Ar/39Ar dating of potassium feldspar in alkaline syenitoid, we have got three plateau ages: 23 Ma, 13Ma and 8Ma. Considering the geological characteristics of massif, it is believed that the ages represent the time of emplacement of alkaline syenitoid and granitoid and a later tectonic heating event. Compared with former researches, this study believes that the magmatism is very important for the formation of Pamir syntaxis. The magmatism is one of the main factors leading to stronger deformation in Parmir region than in other areas of Tibetan plateau.