摘要
在基性—超基性岩中,特别是那些含矿岩体,常常发育有原生的侧向分带,传统的重力分异理论无法用原地分异机制对这一现象进行合理解释;新的硫化物成矿模型同样不能令人信服。我们在对重力结晶分异的研究中发现,对流干扰下的重力结晶分异可以形成侧向分带。研究采用动力学分析的方法,深入了解对流干扰下岩浆重力分异作用中的颗粒行为。在动力学分析中,考虑了前人研究中普遍忽略的伯努利效应。研究表明,伴随着快速对流干扰的岩浆重力结晶分异可以产生侧向分离效应,使颗粒趋于在侧壁附近快速堆积。侧分离效应和侧壁冷却效应一起迫使循环向热流上升中心方向后退,形成侧向分带岩石。由于对流通常只发生在岩浆侵位后结晶分异的早期高温阶段,与铜镍硫化物熔离的阶段相吻合,因此,铜镍硫化物的矿化通常与对流干扰下的重力分异密切相关。最后以一个实例解释侧向分带和成矿作用的形成机制。研究成果突破了传统关于重力分异的认识,为深入认识岩浆演化及指导找矿提供新的思路。
In mafic—ultramafic intrusions, especially those ore bearing intrusions, primitive lateral zoning are common. Traditional gravitational separation theory failed to account for the mechanism to the formation of these occurrences. New patterns of sulfide deposits cannot provide a convincing explanation, too. In the study of magmatic gravitational separation, we found that a gravitational separation accompanied with interference of rapid convection can produce lateral zoning. Based on dynamics analysis, we studied the movement of crystals during the gravitational separation disturbed by rapid convection. Bernoulli Effect was taken into account in our dynamic analysis, which had been generally neglected in previous studies. The paper shows that, a magmatic gravitational separation accompanied with rapid convection can produce a lateral separating effect, causing rapid burial of crystals near the wall. Influenced by lateral separating effect and the cooling near the wall, convection will retreat toward the center of the rising heat flow，and a lateral series of igneous rocks may form，in which the compositions of phases may show progressive changes from wall to center. Since the convection commonly occurred at the early high temperature stage of the magmatic differentiation in a magma chamber, corresponded to the stage of liquid immiscibility of sulfide，the mineralization of Ni—Cu sulfide is usually closely related to the gravitational separation accompanied with interference of convection. Finally, an example is given to explain the formation mechanism of lateral zoning and mineralization. The study result breaks through the traditional knowledge about the gravitational separation, and would be greatly help to deeply understand the evolution of magma and to guide the prospecting for deposits.
作者
梁磊
张玲
LIANG Lei ZHANG Ling(China Nonferrous Metals （Guilin） Geology and Mining Company Limited, Guilin, Guangxi, 541004 Institute of Karst Geology, Chinese Academy of Geological Sciences~Key Laboratory of Karst Dynamics, Ministry of Land and Resources ＆ Guangxi Zhuang Autonomous Region, Guilin, Guangxi, 541004)
出处
《地质论评》
CAS
CSCD
北大核心
2017年第4期869-880,共12页
Geological Review
基金
广西区大规模地质找矿项目“广西恭城县五福锡钽铌矿普查”(编号:[2010]604)的资助~~
关键词
基性—超基性岩
侧向分带
重力分异
对流
伯努利效应
铜镍硫化物
成矿机制
mafic—ultramafic intrusion
lateral zoning
gravitational separation
Bernoulli Effect
convection
Ni—Cu sulfide
mechanism of mineralization
