Reaction overstepping and re-evaluation of peak P‒T conditions of the blueschist unit Sifnos, Greece: implications for the Cyclades subduction zone
Reaction overstepping and re-evaluation of peak P‒T conditions of the blueschist unit Sifnos, Greece: implications for the Cyclades subduction zone
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希腊锡弗诺斯岛蓝片岩单元的反应超越和峰值 P-T 条件的重新评估：对基克拉泽斯俯冲带的影响
DOI：
10.1080/00206814.2016.1200499
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发表时间：
2017
影响因子：
2.6
通讯作者：
Spear, Frank S.
中科院分区：
文献类型：
--
作者：
Castro, Adrian E.;Spear, Frank S.
平衡热力学模型，石英石榴石（QuiG）拉曼地质压力计，并在超越条件下的石榴石成核建模应用于三个石榴石蓝片岩从一个1.5公里长的横断面横跨榴辉岩蓝片岩单位在锡夫诺斯，希腊，为了评估的准确性PSTT条件通过平衡热力学计算。QuiG气压计利用石榴石中石英包裹体的拉曼位移来估计石榴石成核的压力，并且与化学平衡无关。石榴石成核温度进行了估计，通过确定的稳定场推断的古组合石榴石包裹体套件矿物组合图计算MnNCKFMASH系统和从锆在金红石测温温度。这些条件进行了比较，在平衡石榴石等值线，相交等值线的方法计算的P PART条件。用交叉石榴石等值线计算的PSTT条件分别超过和低估了样品SPH 99 -1a和SPH 99 -7的成核温度，而它们显著低估了SPH 99 -5的成核压力。在12 kbar和~484°C下，SPH 99 -1a中石榴石的成核需要超过~6 kbar和2.2 kJ mol·1 O的反应亲和力。SPH 99 -5要求在15 kbar和~520°C下超过~8 kbar，石榴石反应亲和力至少为2.0 kJ mol·1 O。SPH 99 -7要求在~23 kbar和~530°C下超过约15 kbar，亲和力约为2.0-2.4 kJ mol·1 O。根据SPH 99 -7（~6.7°C km-1）和SPH 99 -5（9.8°C km-1）计算的地热与以前的研究一致。然而，SPH 99 -1a计算出的地温要高一些（11.3°C km ²），这可能反映了俯冲速率的变化或下行板块内构造位置的差异。SPH 99 -7和SPH 99 -1a之间10 kbar的压力差可以解释为板片回滚和重力塌陷促进了板下楔材料薄片的逆冲和加积。
Equilibrium thermodynamic modelling, quartz in garnet (QuiG) Raman geobarometry, and modelling of garnet nucleation at overstepped conditions were applied to three garnet-bearing blueschists from a 1.5 km-long transect across the eclogite-blueschist unit in Sifnos, Greece, in order to evaluate the accuracy of P‒T conditions calculated via equilibrium thermodynamics. QuiG barometry uses the Raman shift of quartz inclusions in garnet to estimate the pressure of garnet nucleation and is independent of chemical equilibrium. Garnet nucleation temperatures were estimated by determining the stability field of the palaeo-assemblage inferred from garnet inclusion suites on mineral assemblage diagrams calculated in the MnNCKFMASH system and on temperatures obtained from Zr in rutile thermometry. These conditions were then compared to P‒T conditions calculated at the equilibrium garnet isograd, and the method of intersecting isopleths. The P‒T conditions calculated with intersecting garnet isopleths over- and underestimated the temperature of nucleation in samples SPH99-1a and SPH99-7, respectively, whereas they significantly underestimated nucleation pressure in SPH99-5. Nucleation of garnet in SPH99-1a at 12 kbar and ~484°C requires overstepping of ~6 kbar and a reaction affinity of 2.2 kJ mol‒1O. SPH99-5 requires overstepping of ~8 kbar with garnet reaction affinities of at least 2.0 kJ mol‒1O at 15 kbar and ~520°C. SPH99-7 requires overstepping of approximately 15 kbar and affinities of about 2.0–2.4 kJ mol‒1O at ~23 kbar and ~530°C. The geotherms calculated from SPH99-7 (~6.7°C km‒1) and SPH99-5 (9.8°C km‒1) are in accordance with previous studies. The geotherm calculated from SPH99-1a, however, is warmer (11.3°C km‒1), and could reflect changes in the rate of subduction or differences in structural position within the down-going slab. The 10 kbar pressure difference between SPH99-7 and SPH99-1a can be explained by thrusting and accretion of thin slices of underplated wedge material facilitated by slab rollback and gravitational collapse.
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DOI：
--
发表时间：
1984
期刊：
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