P–T–t evolution of spinel–cordierite–garnet gneisses from the Sauwald Zone (Southern Bohemian Massif, Upper Austria): is there evidence for two independent late-Variscan low-P/high-T events in the Moldanubian Unit?
P–T–t evolution of spinel–cordierite–garnet gneisses from the Sauwald Zone (Southern Bohemian Massif, Upper Austria): is there evidence for two independent late-Variscan low-P/high-T events in the Moldanubian Unit?
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Sauwald 地带（上奥地利州南波希米亚地块）尖晶石-堇青石-石榴石片麻岩的 P-T-t 演化：是否有证据表明摩尔达努比亚单元有两次独立的晚瓦里斯期低 P/高 T 事件？
DOI：
10.1007/s00531-006-0082-x
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发表时间：
2006
影响因子：
2.3
通讯作者：
R. Kaindl
中科院分区：
文献类型：
--
作者：
P. Tropper;I. Deibl;F. Finger;R. Kaindl
索瓦尔德区位于上奥地利州波西米亚山脉的南缘，属于摩尔多瓦单元。暴露出Variscan造山运动碰撞后高/低阶段形成的均匀黑云母+斜长石±堇青石副长岩。稀有的变质长石嵌层矿物组合为石榴石+堇青石+绿尖晶石+硅线石+钾长石+斜长石+黑云母+石英。矿物化学和结构数据表明矿物生长分为四个阶段：(1)石榴石包裹体的峰值组合（第1阶段）：石榴石芯+堇青石+绿尖晶石+硅线石+斜长石（An35-65）；(2)峰后组合（第2、3阶段）：堇青石+尖晶石（棕绿色和褐色）±硅线石±石榴石边缘+斜长石（An10-45）；(3)第4期纤维岩、白云母和钠长石（An0-15）的晚期生长。峰值组合（阶段1）的p - t条件计算得到750-840°C， 0.29-0.53 GPa；阶段2的基体组合石榴石+堇青石+绿尖晶石+硅线石+斜长石620-730°C， 0.27-0.36 GPa。所观察到的相位关系显示出顺时针的ep - tpath，终止于0.38 GPa以下。索瓦尔德带和单调单元的p - evolution非常相似，但前者的独居石年龄更年轻（321±9 Ma比334±1 Ma）。这表明索瓦尔德带的高温/低温变质作用要么持续时间较长，要么在摩尔多瑙河单元存在两期独立的晚瓦力斯晚期低温/高温变质作用。
The Sauwald Zone, located at the southern rim of the Bohemian Massif in Upper Austria, belongs to the Moldanubian Unit. It exposes uniform biotite + plagioclase ± cordierite paragneisses that formed during the post-collisional high-T/low-Pstage of the Variscan orogeny. Rare metapelitic inlayers contain the mineral assemblage garnet + cordierite + green spinel + sillimanite + K-feldspar + plagioclase + biotite + quartz. Mineral chemical and textural data indicate four stages of mineral growth: (1) peak assemblage as inclusions in garnet (stage 1): garnet core + cordierite + green spinel + sillimanite + plagioclase (An35–65); (2) post-peak assemblages in the matrix (stages 2, 3): cordierite + spinel (brown-green and brown) ± sillimanite ± garnet rim + plagioclase (An10–45); and (3) late-stage growth of fibrolite, muscovite and albite (An0–15) during stage 4. Calculation of theP–Tconditions of the peak assemblage (stage 1) yields 750–840°C, 0.29–0.53 GPa and for the stage 2 matrix assemblage garnet + cordierite + green spinel + sillimanite + plagioclase 620–730°C, 0.27–0.36 GPa. The observed phase relations indicate a clockwiseP–Tpath, which terminates below 0.38 GPa. TheP–Tevolution of the Sauwald Zone and the Monotonous Unit are very similar, however, monazite ages of the former are younger (321 ± 9 Ma vs. 334 ± 1 Ma). This indicates that high-T/low-Pmetamorphism in the Sauwald Zone was either of longer duration or there were two independent phases of late-Variscan low-P/high-Tmetamorphism in the Moldanubian Unit.