Contrasting origin of post-collisional high-K calc-alkaline and shoshonitic versus alkaline and peralkaline granitoids. The use of sliding normalization
Contrasting origin of post-collisional high-K calc-alkaline and shoshonitic versus alkaline and peralkaline granitoids. The use of sliding normalization
复制标题
DOI：
10.1016/s0024-4937(98)00023-1
复制
发表时间：
1998-12
期刊：
影响因子：
3.5
通讯作者：
J. Liégeois;J. Navez;J. Hertogen;R. Black
中科院分区：
文献类型：
--
作者：
J. Liégeois;J. Navez;J. Hertogen;R. Black
丰富的高钾钙碱性（HKCA）岩浆活动似乎是后碰撞，并经常转移到钾玄岩或碱性-过碱性成分在造山运动的最后阶段。本文根据图阿雷格地盾（马里的Adrar des Iforas和尼日尔的Auberkur）泛非花岗岩类的308个主量元素和86个未发表的微量元素（包括REE）分析结果，研究了这种转变的性质和原因。该数据库涵盖了从俯冲相关到板内类型的各种岩浆，包括丰富的HKCA岩基。还包括来自地球动力学良好约束情况的文献数据。除了常规的地球化学方法研究岩浆作用，滑动归一化方法提出。该工具的目的是比较岩浆系列：每种研究的岩石都被归一化为具有与样品相同的SiO2含量的参考系列的内插成分。这种方法放大了来源和分馏过程的差异，并允许从基本到酸性组成的岩石进行比较。两个不同的少年来源提出：一个以前丰富的金云母钾里希特轴承岩石圈地幔或较低的青年地壳相当于HKCA钾玄质岩浆，和最低的岩石圈上软流圈OIB型地幔的碱性过碱性岩浆。第一个来源是熔融后不久，它的生成时，岩石圈仍然是热的，这限制了HKCA岩浆活动主要是碰撞后的设置。第二个软流圈/最低岩石圈源根据定义接近其熔融温度，可以在空间和时间上产生无处不在的岩浆。主要的熔融触发因素是岩石圈主要结构，这些结构不仅在碰撞后环境中起作用，而且在其他环境中（如板内环境）也起作用。因此，地球化学提供了关于源的性质和大地构造背景的指示。然而，后者是二级信息，其部分依赖于模型。后碰撞时期与其他环境不同的是倾向于产生大量的各种岩浆，其中HKCA岩浆活动在体积上是最突出的。
Abundant high-K calc-alkaline (HKCA) magmatism appears to be post-collisional and often shifts to shoshonitic or alkaline–peralkaline compositions in the final stages of orogeny. The nature and the causes of this transition are studied on the basis of 308 major element and of 86 unpublished trace element (including REE) analyses of the Pan-African granitoids from the Tuareg shield (Adrar des Iforas, Mali and Aı̈r, Niger). This database covers a wide variety of magmas from subduction-related to intraplate-type including abundant HKCA batholiths. Literature data from geodynamically well-constrained cases are also included. In addition to a conventional geochemical approach of the studied magmatism, the sliding normalization method is proposed. This tool aims at comparing magmatic series: each studied rock is normalized to the interpolated composition of the reference series that has the same SiO2content as the sample. This method amplifies differences in sources and in fractionation processes and allows comparison of rocks from basic to acid composition. Two distinct juvenile sources are proposed: a previously enriched phlogopite-K richterite bearing lithospheric mantle or a lower juvenile crustal equivalent for HKCA-shoshonitic magmas, and a lowest lithospheric-upper asthenospheric OIB-type mantle for alkaline-peralkaline magmatism. The first source is melted only shortly after its generation when the lithosphere was still hot, which restricts HKCA magmatism mainly to post-collisional settings. The second asthenospheric/lowest lithosphere source is by definition close to its melting temperature and can generate magma ubiquitously both in space and time. The main melting triggers are lithospheric major structures which are not only operative in a post-collisional setting but also in other environments such as intraplate setting. Geochemistry thus gives indications about the nature of the source and on geotectonic settings. However, the latter is a second rank information, which is partly model-dependant. The post-collisional period differs from other settings by a propensity to generate large amounts of magma of various kinds, among which HKCA magmatism is volumetrically the most prominent.