The upper critical zone of the Bushveld Complex and the origin of merensky-type ores
The upper critical zone of the Bushveld Complex and the origin of merensky-type ores
复制标题
DOI：
10.2113/gsecongeo.81.5.1105
复制
发表时间：
1986-08
期刊：
影响因子：
5.8
通讯作者：
A. J. Naldrett;E. Gasparrini;S. Barnes;G. Gruenewaldt;M. R. Sharpe
中科院分区：
文献类型：
--
作者：
A. J. Naldrett;E. Gasparrini;S. Barnes;G. Gruenewaldt;M. R. Sharpe
在布什维尔德杂岩临界区顶端的每个单元中，黄铜矿的“镁数”[镁/(镁+铁)原子比]呈向上递减的趋势，这与分离结晶的方式一致。每个单元的底部都以镁离子数的增加为标志，表明新鲜岩浆的结晶作用是该单元形成的原因。Merensky生物礁的块体遗迹和主量元素含量与中粒长石铜质岩类相似，它们本身构成了一系列旋回单元之一的基础部分。每个单元的底部也有口袋或一层硫化物，其镍/铜和铂/铜比值比单元其余部分的硫化物高得多。因此，铂的男高音在三个单元中从高到低交替三次。这些数据有力地表明，铂基调是根据岩石的地层建立的，与呼吁热液或岩浆流体向上迁移以富含铂族元素中的硫化物的模型不一致。岩石中没有任何特征表明，流体可能被引导到被连续的梅伦斯基珊瑚礁占据的数十到数百公里的横向流动。一个模型，基于Campbell等人的模型。(1983)，其中少量硫化物在注入新鲜岩浆时形成一股湍动的羽流，然后在与大量岩浆完全混合后沉淀，这很好地解释了我们所有的观察结果和临界区上部的许多其他特征。
The "Mg number" [Mg/(Mg + Fe) atomic ratio] of bronzite in each unit at the top of the critical zone of the Bushveld Complex decreases upward in a manner consistent with fractional crystallization. The base of each unit is marked by an increase in the Mg number, suggesting that crystallization of fresh magma is responsible for the initiation of the unit. Bulk trace and major element concentrations in pegmatoids of the Merensky reef, which itself forms the basal part of one of a series of these cyclic units, are similar to those in medium-grained feldspathic bronzitite.The base of each unit is also marked by pockets or a layer of sulfide with a higher Ni/Cu and much higher Pt/Cu ratio than the sulfides of the remainder of the unit. Thus the Pt tenor alternates from high to low three times upward through the three units. These data indicate strongly that the Pt tenor was established with the stratigraphy of the rocks and are inconsistent with models calling upon upward migration of hydrothermal or magmatic fluids to enrich the sulfides in platinum-group elements. There are no features in the rocks to indicate that fluids could have been channeled to flow laterally for the tens to hundreds of kilometers occupied by continuous Merensky reef. A model, based on that of Campbell et al. (1983), in which small amounts of sulfides form during injection of fresh magma as a turbulent plume and then settle after becoming thoroughly mixed with a large mass of magma, accounts well for all of our observations and many other features of the upper part of the critical zone.