Pegmatite genesis: state of the art
Pegmatite genesis: state of the art
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DOI：
10.1127/0935-1221/2008/0020-1833
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发表时间：
2008-08
影响因子：
2.1
通讯作者：
W. B. Simmons;K. Webber
中科院分区：
文献类型：
--
作者：
W. B. Simmons;K. Webber
目前还没有一种普遍接受的伟晶岩成因模型能够令人满意地解释花岗质伟晶岩的所有不同特征。花岗质岩体结晶产生的残余熔体成因受到大多数研究者的青睐。不相容组分、助熔剂、挥发物和稀有元素在残余熔体中富集。助熔剂和挥发物的存在降低了结晶温度，降低了成核速率、熔体聚合和粘度，增加了扩散速率和溶解度，被认为是形成大晶体的关键。一些新的概念阐明了伟晶岩成因的有关问题。根据热冷却模型计算的冷却速率表明，浅层伟晶岩的冷却速度比以前认为的要快得多。伟晶岩的快速冷却速度代表了一种广泛持有的观点的量子转变，即在伟晶岩中发现的大晶体是非常缓慢的冷却和晶体生长速度的结果。实验和现场证据都表明，过冷和不平衡结晶是伟晶岩结晶的主要原因。伦敦的伟晶岩演化的构造带精炼模型涉及过冷、含通量的花岗岩熔体的不平衡结晶。熔体不一定是富通量的，该模型也不要求存在水蒸汽相。对富含挥发物和熔剂的熔体以及流体包裹体的实验研究表明，富含挥发物的硅酸盐熔体可以在远低于500℃甚至低至350℃的温度下持续存在。对熔体包裹体和流体包裹体的研究使一些研究人员提出，在任何有关伟晶岩成因的模型中都必须考虑非混溶流体的作用。流体饱和被认为发生在伟晶岩结晶史的早期。在伟晶岩矿物中发现了两种熔融包裹体和原生流体包裹体共存。peter Cerný在伟晶岩分类方面的进展被广泛应用，Nb、Ta等HFSE和K、Rb、Cs、Li、Ga和Tl的分选趋势得到了很好的了解。伟晶岩熔体是如何产生的，所涉及的烃源岩类型以及熔体的产生与板块构造模式的关系是未来研究的挑战性领域。区域分带作用、深熔作用和化学淬灭作用在伟晶岩成因中的作用是未来伟晶岩研究的方向。
No one universally accepted model of pegmatite genesis has yet emerged that satisfactorily explains all the diverse features of granitic pegmatites. Genesis from residual melts derived from the crystallization of granitic plutons is favoured by most researchers. Incompatible components, fluxes, volatiles and rare elements, are enriched in the residual melts. The presence of fluxes and volatiles, which lower the crystallization temperature, decrease nucleation rates, melt polymerization and viscosity, and increase diffusion rates and solubility, are considered to be critical to the development of large crystals. A number of new concepts have shed light on problems related to pegmatite genesis. Cooling rates calculated from thermal cooling models demonstrate that shallow-level pegmatites cool radically more rapidly than previously believed. Rapid cooling rates for pegmatites represent a quantum shift from the widely held view that the large crystals found in pegmatites are the result of very slow rates of cooling and crystal growth. Experimental and field evidence both suggest that undercooling and disequilibrium crystallization dominate pegmatite crystallization. London’s constitutional zone refining model of pegmatite evolution involves disequilibrium crystallization from an undercooled, flux-bearing granitic melt. The melt is not necessarily flux–rich and the model does not require the presence of an aqueous vapor phase. Experimental studies of volatile- and flux-rich melts and fluid inclusion studies suggest that volatile-rich silicate melts may persist to temperatures well below 500 °C and even down to 350 °C. Studies of melt inclusions and fluid inclusions have led some researchers to suggest that the role of immiscible fluids must be considered in any model regarding pegmatite genesis. Fluid saturation is thought to occur early in the crystallization history of pegmatites. Two types of melt inclusions along with primary fluid inclusions have been found coexisting in pegmatite minerals. Advances by Petr Cerný in pegmatite classification are in wide use and the fractionation trends of Nb, Ta and other HFSE and K, Rb, Cs, Li, Ga and Tl are now well understood. How pegmatitic melts are produced, the types of source rocks involved and how melt generation relates to plate tectonic models are challenging areas for future investigations. Also, the roles of regional zoning, anatexis, and chemical quenching in pegmatite genesis are areas for future pegmatite research.