摘要
核杂岩顶部代表深处韧性变形的长英质糜棱岩,其实是温度敏感型的,在异常高的古地温梯度或同构造岩浆活动的情况下,不一定代表中地壳变形的产物。伸展的剥离断层造成相当厚的地壳柱的切失,但在长期受剥蚀的古老岩系出露处,年轻岩层(如白垩系或第三系)直接覆盖于太古宇之上,究竟是沉积缺失还是构造切失,必须加以具体分析。核杂岩隆升至地面,难以单纯用地壳变薄的重力均衡作用来解释。与变质核杂岩密切相关的局部的古地热异常、同构造岩浆岩的强力侵位等,揭示出热隆和岩浆作用在核杂岩隆升中的重要作用,以及变质核杂岩和岩浆核杂岩的密切相关;二者可能只是表现形式不同而已。晚造山的伸展不一定是变质核杂岩所反映的伸展作用的唯一起因。一个地区可以有多次伸缩交替的构造运动。
The felsic mylonite just at the top of extensional metamorphic core complexes(MCC)as a mark of ductile shear deformation at the deep level is actually temperature-sensitive.In the case of an extraordi-narily high paleogeothermal gradient or under the influence of intrusion of syntectonic magma ,mylonite is not necessarily the result of deformation in the middle crust.The extensional detachment fault may cause excisement of a thick crustal column ,but in areas where a large quantity of older rocks are exposed ow-ing to long-continued erosion,it is necessary to determine carefully whether the resting of younger rocks(e.g.Cretaceous or Tertiary rocks)directly on the Archean basement rocks is the result of structural excise-ment or sedimentary hiatus.It is difficult to explain the rise of the MCC onto the surface by the isostatic adjustment of the extensional thinned crust.The local paleogeothermal anomaly and forceful emplacement of syntectonic magma closely related to the MCC suggest the important role of magmatism and thermal uplift in the rise of the core complexes,and the close relationship between the MCC and magmatic core com-plex which may be a different type of outcrop.The late-orogenic extension is not necessarily the only cause for the extension of the MCC.Extension and contraction may alternate several times in one area.
出处
《地质通报》
CAS
CSCD
北大核心
2002年第4期193-197,共5页
Geological Bulletin of China
