Garnet–omphacite–phengite thermobarometry of eclogites from the coesite-bearing unit of the southern Dora-Maira Massif, Western Alps
Garnet–omphacite–phengite thermobarometry of eclogites from the coesite-bearing unit of the southern Dora-Maira Massif, Western Alps
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DOI：
10.1016/s0024-4937(99)00091-2
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发表时间：
2000-04
期刊：
影响因子：
3.5
通讯作者：
Elke Ursula Nowlan;H. Schertl;W. Schreyer
中科院分区：
文献类型：
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作者：
Elke Ursula Nowlan;H. Schertl;W. Schreyer
利用相关的地温测量方法，收集了34个榴辉岩样品的p - t数据，重建了这些样品的变质演化过程。这些榴辉岩样品来自于多拉-迈拉地块超高压（UHP）变质碳酸盐岩Brossasco-Isasca单元（BIU）内的小透镜体和岩块。根据仔细的岩石学研究，所使用的矿物阶段（斜辉石、石榴石、云母）或其生长带被确定为在变质作用的不同阶段共存。在几个已发表的地温计中，Powell的石榴石斜辉石温度计[Powell， R., 1985]。地温计/地压计校准中的回归诊断和稳健回归：重新审视石榴石斜辉石地温计。j . Metamorph。青烟。， 3，第231-243页。在Waters和Martin之后，结合了石榴石-斜辉石-白云石晴雨表[Waters， D, Martin， H.N, 1993]。石榴石-斜辉石-白云石气压表。Terra Abstr。， 5，页410-411。]在这里被选择，因为它提供了最可靠的结果。然而，榴辉岩的顺变质（第I阶段）、峰变质（第II阶段）和逆行（第III阶段）发育的p - t数据点的离散性仍然相当大。在讨论这种不一致的许多可能原因中，一些榴辉岩在其变质历史中部分缺乏平衡应该被考虑在内。尽管数据分散，但可以估计平均p - t路径，其中包括以下坐标：阶段I: 15 kbar/500°C；25千巴/ 570°C;32千巴/ 650°C;阶段II: 36kbar /720℃；阶段III: 24kbar /680°C和14kbar /620°C。这与先前根据其他地温压计得出的BIU其他岩石类型的p - t路径相当一致。
Using relevant geothermobarometric methods, P–T-data were collected for the reconstruction of the metamorphic evolution of 34 eclogite samples taken from small lenses and boudins within the ultrahigh-pressure (UHP) metamorphic coesite-bearing Brossasco-Isasca Unit (BIU) of the Dora-Maira Massif. The mineral phases used (clinopyroxene, garnet, phengite), or growth zones thereof, were identified as being coexistent for different stages of metamorphism on the basis of careful petrographic studies. Of several published geothermobarometers, the garnet–clinopyroxene thermometer of Powell [Powell, R., 1985. Regression diagnostics and robust regression in geothermometer/geobarometer calibration: the garnet–clinopyroxene geothermometer revisited. J. Metamorph. Geol., 3, pp. 231–243.] combined with the garnet–clinopyroxene–phengite barometer after Waters and Martin [Waters, D., Martin, H.N., 1993. The garnet–clinopyroxene–phengite barometer. Terra Abstr., 5, pp. 410–411.] was chosen here, because it provided the most reliable results. Nevertheless, the scatter of P–T-data points for the prograde (stage I), peak metamorphic (stage II), and retrograde (stage III) development of the eclogites is still considerable. Among the many possible reasons for this inconsistency discussed, a partial lack of equilibration of some of the eclogites during their metamorphic history should be taken into account. Despite the data scatter, an average P–T-path could be estimated, which includes the following coordinates: for stage I: 15 kbar/500°C; 25 kbar/570°C; 32 kbar/650°C; for stage II: 36 kbar/720°C; and for stage III: 24 kbar/680°C and 14 kbar/620°C. This is in fair agreement with P–T-paths derived earlier for other rock types of the BIU on the basis of other geothermobarometers.