The Alpe Arami story: Triumph of data over prejudice
The Alpe Arami story: Triumph of data over prejudice
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Alpe Arami 的故事：数据战胜偏见
DOI：
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发表时间：
2010
期刊：
影响因子：
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通讯作者：
K. Bozhilov
中科院分区：
文献类型：
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作者：
H. Green;L. Dobrzhinetskaya;K. Bozhilov
瑞士阿尔卑斯山南部的阿尔卑阿拉米石榴石橄榄岩与榴辉岩共生，产于石英长石片麻岩中。自20世纪70年代以来，围绕该地块的起源深度一直存在争议，当时新开发的温度气压测量技术的应用表明，该地块的最后平衡深度超过120公里。这种争论在1996年加速，当时我们报道了从橄榄石中广泛沉淀钛铁矿和尖晶石的显微结构证据，并提出了更深的成因深度。随后的实验表明，可以将观测到的数量的二氧化钛溶解在橄榄石中，但只有在超过300公里的深度才能溶解，这与早先的提议一致。1999年，我们增加了新的、独立的证据，证明高压斜辉石从透辉石中逸出，本身需要超过250公里的起源深度。随后，我们还补充了来自周围极高压力榴辉岩的证据和实验证据，表明该岩石的变形石榴石中的辉石在可能更大的压力下从主要母体中析出。为了反驳前两种观察结果，有意见认为：(I)我们对橄榄石中含有多少钛铁矿(因此有多少二氧化钛已溶解在橄榄石中)的估计存在严重错误；(Ii)该钛铁矿并未从橄榄石中析出，而是存在并分解生成钛铁矿；(Iii)从透辉石中析出的辉石是高温斜辉铜矿。在所有这三个案例中，提供的替代方案都声称是在低压力下提供的。在这里，我们回顾了这场争议的实质，并表明，唯一可以解释所有数据的情景是我们最初提出的情景；事实上，最近的数据有力地支持了这一解释，并将地块的最低起源推向接近400公里的深度。
The Alpe Arami garnet peridotite of the Southern Swiss Alps is associated with eclogites and included within quartzofeldspathic gneisses. Controversy has swirled around the depth of origin of this massif since the 1970s when application of the newly-developed technique of thermobarometry suggested a depth of last equilibration of greater than 120 km. Such controversy accelerated in 1996 when we reported microstructural evidence of extensive precipitation of ilmenite and spinel from olivine and proposed a much greater depth of origin. Subsequent experiments showed that it was possible to dissolve the observed amount of TiO2 in olivine, but only at depths in excess of 300 km, agreeing with the earlier proposal. In 1999 we added new, independent, evidence concerning exsolution of high-pressure clinoenstatite from diopside that in-and-of-itself required a depth of origin in excess of 250 km. Subsequently, we also added evidence from the surrounding eclogites of very high pressures and experimental evidence that the pyroxenes included in the amoeboid garnets of this rock had exsolved from a majoritic parent at perhaps even greater pressures. In refutation of the first two of these observations, suggestions were made that (i) we had made a serious error in our estimate of how much ilmenite was present in olivine (and therefore how much TiO2 had been dissolved in olivine); (ii) the ilmenite had not been exsolved from olivine but former titanian clinohumite had been present and broke down to yield the ilmenite; (iii) the pyroxene exsolved from diopside had been high-temperature clinoenstatite. In all three of these cases, the alternatives offered were claimed to be accommodated at low pressures. Here we review the essence of this controversy and show that the only scenario that can explain all of the data is the one that we originally proposed; indeed, the more recent data have strongly supported that interpretation and pushed the minimum origin of the massif to depths approaching 400 km.