RETROLOGICAL STUDY OF THE BILIBILI ALKALI LAYERED INTRUSION

本项目对印度尼西亚苏拉威西岛南部BiliBili碱层状岩体的发生情况进行了调查，并对层状构造的成因进行了考察，得出以下结论：(1)在侵入体与周围中新世昌巴组接触的120 m范围内，有197层。层的厚度向侵入体内部有系统地增加。该系统遵循与列色冈环相似的间距规律。(2)层由富含Na2O的硬层和富含K20的软层组成。(3)基于随机采集的24个样品的整体岩石化学特征，岩体的整体化学变化与单层内岩体的整体化学特征基本相似。因此，化学分异发生在均质岩浆凝固形成地层的过程中。(4)提出了层形成的物理模型，使层代表一个共晶糊状层，其中层锋（层的高温侧）和凝固锋（低温侧）的相互作用导致层的周期性生长和凝固。层内的化学分化是由与热传递相关的传质引起的。间距定律可以用凝固部分的生长来解释，凝固部分的生长阻止了影响层厚的侵入所产生的有效热损失。

This project carried out the investigation of the occurrence of the BiliBili alkali layered intrusion in the south of Sulawesi island, Indonesia, and examines the origin of the layered structures, leading to the following conclusions.(1) There are 197 layers within 120 meters from the contact between the intrusion and the surrounding Chamba Formation of the Miocene. The thickness of the layer increases systematically towards the interior of the intrusion. The systematics obeys the Spacing Law similar to that of the Liesegang Rings.(2) A layer consists of a hard part rich in Na2O and a soft part rich in K20.(3) Overall chemical variation of the intrusion based on the bulk rock chemistries of randomlly collected 24 samples is almost similar to that within a single layer. Thus chemical differentiation occurred during the layer formation by solidification of a homogeneous magma.(4) A physical model is proposed for the layer formation such that the layer represent a eutectic mushy layer where the interplay of the layer front (high temperature side of the layer) and the solidification front (low temperature side) casuses a periodical growth and solidification of the layer. Chemical differentiation within a layer was caused by mass transfer associated with heat transfer. The Spacing Law can be explained by the growth of solidified part which prevents an efficient heat loss from the intrusion that influences the thickness of the layer.