山西恒山—河北宣化—内蒙古兴和地区的“基性岩墙”是赞岐岩吗？

发布时间：2018-07-10 18:23

  本文选题：赞岐岩 + 基性岩墙　； 参考：《中国地质大学(北京)》2017年硕士论文

【摘要】：在以往的研究中,华北地区的恒山、河北宣化、内蒙古兴和地区的“基性岩墙”所代表的为一种裂解伸展构造背景,但近来,有研究提出这些“基性岩墙”可能为赞岐岩,代表了俯冲汇聚构造背景。因此,广泛出露于恒山—河北宣化—内蒙古兴和地区的大量古中元古代“基性岩墙”是否为赞岐岩,对于明确该地区在古元古代是汇聚还是伸展构造背景,具有重要的科学意义。本文对恒山—河北宣化—内蒙古兴和古元古代的基性岩墙进行了详细的岩相学、矿物化学及地球化学研究。恒山—张家口宣化—内蒙古兴和地区的岩石手标本可见典型的岩浆结构—辉绿结构,其中恒山地区岩墙岩石主要是由具角闪石后成合晶的辉石、自形的斜长石和石榴石组成,其中斜长石主要为中长石、有成分环带,辉石主要为火成钙辉石及少量紫苏辉石。河北宣化样品岩石薄片光学显微镜下无明显的辉绿结构,由石榴石、斜长石、单斜辉石、斜方辉石,角闪石组成。内蒙古兴和地区岩墙岩石主要由角闪石和中性斜长石组成,角闪石填充在斜长石组成的三角架中。恒山、宣化主量元素SiO2=50~51.3 wt.%、K2O=0.51~0.87wt.%、Na2O/K2O=2.8~4.7、MgO=5.8-6.7wt.%、Mg#=41.3~48.3,略富集相容元素(Ni=42.5~63.9μg/g,Cr=82~143μg/g,Co=48.7~58.6,V=349~395μg/g)和不相容元素(Sr=164~220μg/g,Ba=194~317μg/g,Rb=11.8~19.3μg/g),且轻稀土较重稀土富集(3.1LREE/HREE8.5),这与已发表的赞岐岩数据相似,但不相容元素和相容元素含量与赞岐岩相比都偏低,Mg#也不算很高;兴和地区的Mg#(32.2~32.6)则更偏低,更富集不相容元素(Sr=373~375μg/g,Ba=1092~1097μg/g,Rb=50.1~52.6μg/g),相容元素则未见明显富集(Ni=9.98~11.6μg/g,Cr=5.58~11μg/g),与赞岐岩的特征相差较大。此外,研究区的样品普遍都存在富铁和富钛的特征。通过分析讨论,可得出以下结论:(1)恒山、宣化、兴和地区的基性岩墙不是典型的赞岐岩;(2)研究区这些岩墙为高铁玄武质岩石;(3)这些基性岩墙经历了一定程度的结晶分离作用和地壳混染作用。(4)这些基性岩墙很可能属于板内裂解的产物。
[Abstract]:In previous studies, the "basic rock walls" of Hengshan in North China, Xuanhua in Hebei and Xinghe in Inner Mongolia represent a kind of pyrolysis and extensional tectonic setting. But recently, some studies have suggested that these "basic rock walls" may be Zhanqi rocks. It represents the tectonic background of subduction convergence. Therefore, whether a large number of Paleoproterozoic "basic rock dikes" widely exposed in Hengshan-Xuanhua-Xinghe area, Inner Mongolia, are Zhanqi rocks, in order to determine whether the paleoproterozoic convergence or extension of the tectonic background in this area, It has important scientific significance. In this paper, the paleofacies, mineralogical chemistry and geochemistry of the basic rock wall of Heng Shan Xuanhua and Xinghe Gu Yuan in Inner Mongolia are studied in detail. Typical magmatic structure-pyrophyllite structure can be seen in the hand specimens of Hengshan Zhangjiakou Xuanhua area, Inner Mongolia. The rocks of the rock wall in Hengshan area are mainly composed of pyroxene with amphibole, plagioclase and garnet. The plagioclase is mainly meso-feldspar with compositional annulus and pyroxene is mainly pyrocalopyroxene and a small amount of perilla pyroxene. There is no obvious structure of phosphorescence in the thin slice optical microscope of Xuanhua sample in Hebei Province, which consists of garnet, plagioclase, clinopyroxene, clinopyroxene and hornblende. The rock wall rocks in Xinghe area, Inner Mongolia are mainly composed of amphibole and neutral plagioclase, and amphibole is filled in a tripod composed of plagioclase. 鎭掑北,瀹ｅ寲涓婚噺鍏冪礌SiO2=50~51.3 wt.%,K2O=0.51~0.87wt.%,Na2O/K2O=2.8~4.7,MgO=5.8-6.7wt.%,Mg#=41.3~48.3,鐣ュ瘜闆嗙浉瀹瑰厓绱，

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