Petrogenetic implications of Ti, Zr, Y, and Nb variations in volcanic rocks
Petrogenetic implications of Ti, Zr, Y, and Nb variations in volcanic rocks
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DOI：
10.1007/bf00375192
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发表时间：
1979-05
影响因子：
3.5
通讯作者：
J. Pearce;M. Norry
中科院分区：
文献类型：
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作者：
J. Pearce;M. Norry
实验数据、超镁铁质岩石中的共存相和火山岩中的斑晶-基质对被用于编制碱性、中间和酸性熔体成分中Ti、Zr、Y和Nb的矿物-液体分布系数表。这些值随后被用来解释这些元素的变化，首先是在玄武岩中，其次是在碱性岩浆到酸性岩浆的分步结晶过程中。玄武岩的Zr/Y、Zr/Ti和Zr/Nb比值的岩石成因模型，结合稀土元素、铬元素和同位素变化，表明：(1)洋中脊向板块内的Zr/Y比值升高和碱性玄武岩的低Zr/Nb比值是由于（流体控制的）源非均质性所致；(2)火山弧玄武岩的低Zr和Zr/Y比值是由于贫源部分熔融程度高所致；(3)快扩张脊与慢扩张脊中玄武岩的高Zr和相似的Zr/Y比值是开放体系分异结晶的结果。利用Y-Zr、Ti-Zr和Nb-Zr图对更进化的岩石分选趋势进行建模，特别突出了从岛弧（斜辉石岩为主）到安第斯型弧（角闪洞±黑云母为主）结晶基性相的变化。这些方法可以应用于未知亲缘的蚀变熔岩，以提供有关其成因和喷发环境的额外信息。
Data from experimental runs, coexisting phases in ultramafic rocks and phenocryst-matrix pairs in volcanic rocks have been used to compile a table of mineral-liquid distribution coefficients for Ti, Zr, Y, and Nb for basic, intermediate and acid melt compositions. These values have then been used to interpret variations of these elements, first in basalts and second, during fractional crystallization from basic to acid magmas. For basalts, petrogenetic modelling of Zr/Y, Zr/Ti, and Zr/Nb ratios, when used in conjunction with REE, Cr and isotopic variations, suggests that: (1) the increase in Zr/Y ratio from mid-ocean ridge to within plate basalts and the low Zr/Nb ratios of alkalic basalts are due to (fluid controlled) source heterogeneities; (2) the low Zr and Zr/Y ratio of volcanic arc basalts results from high degree of partial melting of a depleted source; and (3) the high Zr and similar Zr/Y ratio of basalts from fast spreading relative to slow spreading ridges results from open-system fractional crystallization. Modelling of fractionation trends in more evolved rocks using Y-Zr, Ti-Zr and Nb-Zr diagrams highlights in particular the change in crystallizing mafic phases from island arcs (clinopyroxene-dominated) to Andean-type arcs (amphibole±biotite-dominated). These methods can be applied to altered lavas of unknown affinities to provide additional information on their genesis and eruptive environment.