Palaeomagnetism of Sukinda chromites and their geological implications
Palaeomagnetism of Sukinda chromites and their geological implications
复制标题
苏金达铬铁矿的古地磁学及其地质意义
DOI：
--
复制
发表时间：
1984
期刊：
影响因子：
--
通讯作者：
M. Bhalla
中科院分区：
文献类型：
--
作者：
Anil Kumar;M. Bhalla
概括
从前寒武纪苏金达铬铁矿矿石（东经 85°43′；北纬 21°01′和北纬 85°50′；北纬 21°03′）的 7 个地点采集了 38 个定向样品，该矿石呈倾倒向斜形式。在隔离磁化的主要成分并影响必要的构造校正时，发现四个地点（A、B、C、F）具有反磁极性（D = 210°，I = + 22°，K = 122 和 α95 = 6°），并且发现一个地点（E）具有正常极性（D = 49°，I = -16°，K = 474 和 α95 = 2°）。其余两个位点 D 和 G 被拒绝，前者是因为方向上的分散，后者是由于红土化引起的主导二次磁化的叠印。通过对这些铬铁矿矿床评估的 VGP 与年龄几乎相似的其他前寒武纪岩石的 VGP 进行比较，可以看出这些铬铁矿可能比 Gwalior Traps 的年龄为 1830 ± 200 Ma 更古老。来自岩石 磁力和显微检查推断，苏金达山谷的块状铬铁矿并未受到蛇纹石化作用的很大程度的磁性影响，尽管它们的主岩是蛇纹石化的超镁铁质岩石。一致的剩磁方向表明这些矿床在相当稳定的条件下结晶，这是铬铁矿矿床层状类型的特征，因此，使我们推断出苏金达铬铁矿 成为那种类型。这些古地磁数据在进行褶皱测试时，显示了早于构造扰动的主要剩磁，从而证明这些铬铁矿在该地区的区域构造活动之前就已固结。
Summary
Thirty-eight oriented samples were collected from seven sites over the Precambrian Sukinda chromite ore (between 85°43′E; 21°01′N and 85°50′E; 21°03′N), which is in the form of a plunging syncline. On isolating the primary component of magnetization and affecting the necessary tectonic correction, four sites (A, B, C, F) were found to possess a reverse magnetic polarity (D= 210°, I=+22°, with K= 122 and α95= 6° and one site (E) was found to bear a normal polarity (D= 49°, I= -16° with K= 474 and α95= 2°). The remaining two sites D and G were rejected, the former because of scatter in directions and the latter due to overprinting by a dominant secondary magnetization, induced by lateritization. On comparison of VGPs evaluated for these chromite deposits, with those of other Precambrian rocks almost of a similar age, it is seen that these chromites are probably older than the Gwalior Traps whose age is 1830 ± 200 Ma. From the rock magnetic and microscopic examination it is deduced that the massive chromites of the Sukinda valley have not been affected magnetically to any great extent by serpentinization, though their host rocks are serpentinized ultramafics. Consistent directions of remanent magnetism point to the fact that these deposits crystallized in fairly stable conditions, characteristic of the stratiform type of chromite deposits, therefore, leading us to infer the Sukinda chromites to be of that type. These palaeomagnetic data, when subjected to the fold test, show the primary remanence to pre-date the tectonic disturbance and hence prove these chromites to have consolidated prior to the regional tectonic activity of the area.