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首页> 外文期刊>Contributions to Mineralogy and Petrology >Experimental constraints on ultrapotassic magmatism from the Bohemian Massif (durbachite series, Czech Republic)
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Experimental constraints on ultrapotassic magmatism from the Bohemian Massif (durbachite series, Czech Republic)

机译：波西米亚地块超钾质岩浆作用的实验约束（捷克德意志人系列）

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摘要

The equilibrium phase relations of a mafic durbachite (53 wt. percent SiO_2) from the Trebic pluton, repre-sentative of the Variscan ultrapotassic magmatism of the Bohemian Massif (338-335 Ma), have been determined as a function of temperature (900-1,100 deg C), pressure (100-200 MPa), and H_2O activity (1.1-6.1 wt. percent H_2O in the melt). Two oxygen fugacity ranges were investigated: close to the Ni-NiO (NNO) buffer and 2.6 log unit above NNO buffer (DELTA NNO + 2.6). At 1,100 deg C, olivine is the liquidus phase and co-crystallized with phlogopite and augite at 1,000 deg C for the whole range of investigated pressure and water content in the melt. At 900 deg C, the mineral assemblage consists of augite and phlogopite, whereas olivine is not stable. The stability field of both alkali feldspar and pla-gioclase is restricted to low pressure (100 MPa) at nearly water-saturated conditions (<3-4 wt. percent H_2O) and T < 900 deg C. A comparison between experimental products and natural minerals indicates that mafic durbachites have a near-liquidus assemblage of olivine, augite, Ti-rich phlogo-pite, apatite and zircon, followed by alkali feldspar and plagioclase, similar to the mineral assemblage of minette magma. Natural amphibole, diopside and orthopyroxene were not reproduced experimentally and probably result from sub-solidus reactions, whereas biotite re-equilibrated at low temperature. The crystallization sequence olivine followed by phlogopite and augite reproduces the sequence inferred in many mica-lamprophyre rocks. The similar fractionation trends observed for durbachites and minettes indicate that mafic durbachites are probably the plutonic equivalents of minettes and that K- and Mg-rich magmas in the Bohemian Massif may have been generated from partial melting of a phlogopite-clinopyroxene-bearing metasoma-tized peridotite. Experimental melt compositions also sug-gest that felsic durbachites can be generated by simple fractionation of a more mafic parent and mixing with mantle-derived components at mid crustal pressures.
机译：确定了波西米亚断层块的瓦里斯坎超钾化岩浆岩（338-335 Ma）代表的特里比克岩体的镁铁质辉铁矿（53 wt。％SiO_2）的平衡相关系是温度的函数（900- 1100℃），压力（100-200 MPa）和H_2O活性（熔融物中H_2O的含量为1.1-6.1 wt。％）。研究了两个氧逸度范围：接近Ni-NiO（NNO）缓冲液和在NNO缓冲液上方2.6 log单位（DELTA NNO + 2.6）。在1100摄氏度下，橄榄石是液相线，并与金云母和a石在1000摄氏度下共结晶，用于研究的整个熔体压力和水含量范围。在900摄氏度时，矿物组合由辉石和金云母组成，而橄榄石则不稳定。在接近水饱和的条件下（<3-4 wt％H_2O）和T <900℃，碱金属长石和斜长石蜡酶的稳定性场都限于低压（100 MPa）。实验产品与天然产品的比较矿物表明，镁铁质德巴基岩具有橄榄石，辉石，富含钛的金云母，磷灰石和锆石的近液相线组合，其次是碱长石和斜长石，类似于小礼帽岩浆的矿物组合。天然闪石，透辉石和邻苯二酚未进行实验性复制，可能是亚固相线反应导致的，而黑云母在低温下重新平衡。橄榄石的结晶顺序，接着是金云母和a石，其重现了许多云母-兰斑岩岩石中推测的顺序。观察到的榴辉石和min的类似分馏趋势表明，镁铁质榴辉石可能是min的矿物学等价物，并且波西米亚地块中富含K和Mg的岩浆可能是由于部分金云母-含斜辉石的变质岩融化而产生的。橄榄岩。实验性熔体组合物还暗示，可以通过简单地分馏出更多的镁铁矿母体，并在地壳中等压力下与地幔衍生的组分混合，来生成长英质辉石。

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