湖北黄陵球状花岗闪长岩的发现及其岩相学特征

在扬子陆块核部黄陵地区发现具球状构造的花岗闪长岩。岩石产于新元古代斑状花岗闪长岩与石英闪长岩之间,出露面积极小。球状花岗闪长岩岩体由主岩、球状体及球间基质三部分组成,球状体呈圆形、椭圆形及不规则状,由球核和同心球壳组成,球体大小多为5~12cm。依据球壳及球核的差异,可大致分为具有多壳层同心结构、具单壳层结构、无明显壳层结构3种类型的球状体。单壳层球壳由角闪石、黑云母等暗色矿物含量高的暗色层组成,具放射状构造;多壳层球壳由含角闪石、黑云母等暗色矿物的暗色层和基本不含或含少量暗色矿物、以斜长石为主的浅色层组成韵律层,具梳状、放射状构造;球核成分可以是同源岩浆组分,也可以是异源捕虏体。单壳层球体,球核、球壳、基质的斜长石牌号依次为36、32、26,酸性程度不断增加,内部呈放射状生长,反映其可能由内向外经岩浆结晶作用形成。初步认为多壳层球体球壳富韵律的变化为富含气水热液的岩浆在动荡的环境下结晶形成,球壳中矿物结晶顺序可能由外向内,核部结晶时间相对更长。

The discovery of orbicular granodiorite and its petrographic characteristics in Huangling, Hubei

The orbicular granodiorite outcropped between Neoproterozoic phyric granodiorite and quartz diorite in an extremely small place of Huangling area, the Yangtze continental nucleus, was discovered for the first time. This kind of orbicular granodiorite is composed of host rock, orbs and matrix among orbs. Though the orbs are round, oval or irregular in shape, they are all composed of nuclear bulges and concentric shells. Based on the discrepancies of their nuclear bulges and spherical shells, the authors divide the orbs into three types, i.e., orbs with multiple shell layers and concentric structure, orbs with single shell layer structure, and orbs with no obvious structure of shell layers. Composed of dark layers with dark minerals like amphibole and biotite, the single shell layer exhibits radial structure. However, the shell of multiple shell layers is composed of rhythmites comprising layers of dark minerals like amphibole and biotite as well as light-color layers comprising dominantly plagilclase with no or very few dark minerals, exhibiting comb or radial structure. The composition of nuclear bulge might have come from comagma or heterogeneous xenolith, amphibolite and enclaves rich in mica. In the orbs with single shell layer, the acidity increases constantly from nuclear bulge through shell to matrix, and the inner part grows in radial patterns, indicating the growth of magmatic crystallization from the inner part to the outer part. As for the rhythmites in the orbs with multiple shell layers, the authors preliminarily hold that they might have resulted from the crystallization of magma rich in hydrothermal solution in a turbulent environment, the minerals in the shell might have crystallized from the inner part to the outer part, and the crystallization of nuclear bulges lasted relatively longer time.