Apatites from the Kaiserstuhl Volcanic Complex, Germany: new constraints on the relationship between carbonatite and associated silicate rocks
Apatites from the Kaiserstuhl Volcanic Complex, Germany: new constraints on the relationship between carbonatite and associated silicate rocks
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DOI：
10.1127/0935-1221/2014/0026-2377
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发表时间：
2014-06
影响因子：
2.1
通讯作者：
Lianxun Wang;M. Marks;T. Wenzel;A. Handt;J. Keller;Holger Teiber;G. Markl
中科院分区：
文献类型：
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作者：
Lianxun Wang;M. Marks;T. Wenzel;A. Handt;J. Keller;Holger Teiber;G. Markl
来自碳酸岩的磷灰石、相关的碱性硅酸盐岩石、含碳酸盐的黄长岩脉岩（辉石岩）以及德国西南部中新世凯撒斯图尔火山杂岩的角砾岩（包含碳酸盐和硅酸盐碎片）被用来重建这些岩石之间的岩石成因关系。磷灰石从碳酸岩达到较高的Sr和Nb的含量，但一般较低的Fe，Mn，Th，U，Si，S，Cl和Br相比，磷灰石从相关的硅酸盐岩石，而钠，稀土元素和F的含量是重叠的。磷灰石从斜方岩显示出系统的和不连续的核-环环带，与核心成分相似的磷灰石从硅酸盐岩石和边缘对应的碳酸磷灰石。这些观察结果意味着，bergalite磷灰石成核硅酸盐熔体，并继续从不断发展的CO2-富熔体结晶可能与碳酸盐亲和力。角砾岩中的磷灰石包括三个种群：（1）类似于硅酸盐岩石中的磷灰石，（2）类似于碳酸盐磷灰石，（3）类似于磷灰石种群（1）部分被磷灰石（2）取代。我们推断，磷灰石（1）来自硅酸盐岩石碎片，磷灰石（2）从后来侵入的碳酸盐熔体中结晶出来，交代了硅酸盐岩石碎片，并造成了磷灰石种群（3）中观察到的置换结构。我们的结论是磷灰石从Kaiserstuhl复杂的碳酸盐和硅酸盐熔体之间的成岩关系的重要信息。Kaiserstuhl杂岩中的碳酸质熔体可能是富CO2霞岩熔体长期分馏的产物。
Apatites from carbonatites, related alkaline silicate rocks, a carbonate-bearing melilititic dyke rock (bergalite), and a diatreme breccia (containing both carbonate and silicate fragments) of the Miocene Kaiserstuhl Volcanic Complex, SW Germany, are used to reconstruct the petrogenetic relationship among these rocks. Apatites from carbonatites reach higher Sr and Nb contents but are generally lower in Fe, Mn, Th, U, Si, S, Cl and Br compared to apatites from associated silicate rocks, whilst Na, REE and F contents are overlapping. Apatites from bergalite show a systematic and discontinuous core-rim zonation, with the core being compositionally similar to apatites from silicate rocks and the rim corresponding to carbonatitic apatites. These observations imply that the bergalite apatites nucleated in a silicate melt and continued to crystallize from an evolving CO 2 -enriched melt probably with carbonatitic affinity. Apatites from a diatreme breccia comprise three populations: (1) similar to the apatites from silicate rocks, (2) similar to the carbonatitic apatites, and (3) resembling apatite population (1) partially replaced by apatite (2). We infer that apatite (1) was derived from silicate-rock fragments and apatite (2) crystallized from a later intruding carbonatitic melt, which metasomatized the silicate-rock fragments and caused the replacement textures as observed in apatite population (3). We conclude that apatites from the Kaiserstuhl complex preserve important information on the petrogenetic relationship between carbonatitic and silicate melts. The carbonatitic melts at the Kaiserstuhl complex are probably the products of protracted fractionation of a CO 2 -rich nephelinitic melt.