灵山断褶带地质构造基本特征及其大地构造性质的探讨

灵山断褶带地处桂东南灵山、钦州和东兴等县,东北和西南两侧分别受六万大山和十万大山所夹峙,北端截于浦北县寨圩北西向断裂,南段延出国境以外,在我国长约240公里,宽约30公里。断褶带北东-南西向,主要由古生代、中生代和新生代地层以及酸性岩浆岩构成,断裂与褶皱发育,具明显的多期性和继承性。

ON THE GEOLOGICAL STRUCTURAL CHARACTERISTICS OF LINGSHAN FOLDING BLOCK ZONE

The Lingshan folding block zone bordered the Beibu Bay and is a NE-SW trending structural zone roughly in the "S" form. In Late Silurian with the exception of the Lingshan troughlike ocean basin Caledonian movement involved nearly all South China leading to the recycling of geosyncline. In Silurian and Devonian periods due to the continuous succession of sedimentation a flysch formation was formed with a distinct rhythm and being rich in graptolit, such as Pristiograptus tumes-cens (S3) and Monograptus uniformis (D1). At the end of Early Permian Dongwu orogeny had made the rock strata intensively folded and thus ended the geosynclinal nature of this zone. In the Alpine cycle three main marginal faults around the Lingshan folding block zone were formed and thus converted the once marine basin of Paleozoic sedimentation into an uplifted continental territory. The folds are chiefly of the transitional-extensive type, while the fractures are mainly of NE-NW trending "X" shaped conjugate fractures. The frequent intrusion by acid magma is clearly controlled by fractured structures. There exist four intrusions of median-depth biotite granite and shallow granite-porphyry which contain a lot of metalliferous deposits, such as Sb, Pb, Zn, Cu and Fe. In general, the metamorphism caused here by faulting is remarkably developed and zones of brecciazation and mylomitization are widely distributed. The intensity of the Mesozoic tectonic activities of these zones is comparable more or less to those in the geosynclinal zone, and it marks the arrival of a fault block tectonic period for the earth’s crust.This tectonic zone belongs to the second Neocathaysian subsidence zone of Li Siguang which was formed in the Indo-Chinese epoch and finished in the Yanshanian age.