Time-scale of deformation and intertectonic phases revealed by P-T-D-t relationships in the orogenic middle crust of the Orlica-Snieznik Dome, Polish/Czech Central Sudetes
Time-scale of deformation and intertectonic phases revealed by P-T-D-t relationships in the orogenic middle crust of the Orlica-Snieznik Dome, Polish/Czech Central Sudetes
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波兰/捷克苏台德中部奥尔利卡-斯涅兹尼克圆顶造山中地壳的 P-T-D-t 关系揭示的变形和构造间阶段的时间尺度
DOI：
10.1111/jmg.12103
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发表时间：
2014
影响因子：
3.4
通讯作者：
KRONER A. and BIALEK D.
中科院分区：
文献类型：
--
作者：
SKRZYPEK E.;LEHMANN J.;SZCZEPANSKI J.;ANCZKIEWICZ R.;STIPSKA P.;SCHULMANN K.;KRONER A. and BIALEK D.
研究了造山中地壳的一个剖面（Orlica‐ Benniebannik Dome，波兰/捷克中苏台德），以限制变形（D）和构造间（I）阶段的持续时间和意义。在所研究的变沉积岩向斜中，三次变形事件产生了初始的近水平面理S1（D1），随后的近垂直面理S2（D2）和晚期的近水平轴面劈理S3（D3）。该构造受D2期前、同、后花岗岩片侵入。云母片岩样品中的结晶-变形关系记录了I1- 2石榴子石-十字石生长、正-D2十字石分解为石榴子石-黑云母-硅线石/红柱石、I2- 3堇青石变晶和后期-D3堇青石生长。石榴子石成斑晶显示出从核心到内缘Mn-Ca线性降低，内缘中交替的富Ca-Y-和P-环带，以及贫Ca-外缘。富Ca-Y环带可能反映了十字石等梯度条件下褐帘石向独居石转变的发生，而贫Ca外缘则归因于十字石消亡。通过对共生体和石榴石分带的稳定性进行建模而获得的重建P-Tpath记录了I1-2期间从~4 kbar/485 °C到~4.75 kbar/575 °C的近等压加热。随后在D2过程中进行到4-5 kbar/580-625 °C，随后压力降低到3-4 kbar。低于3 kbar的压力降低归因于I2-3，而低于约500 °C的冷却发生在D3期间。在测年的云母片岩样品中，石榴子石边缘显示出强烈的Lu富集，Lu振荡环带和轻微的Ca增加。这些特征也与褐帘石的分解和十字石的出现有关。由于富Lu石榴石边缘在Lu-Hf预算中占主导地位，因此344 ± 3 Ma等时线年龄归因于十字石级的石榴石结晶，接近I1-2的末端。对角闪-黑云母花岗岩片的测年样品，其Pb-Pb单颗粒锆石蒸发年龄为353 ± 1 Ma，与深成活动的开始有关。结果表明，D1可能是泥盆纪，中地壳岩石中的石炭纪埋藏-折返循环与D2期间邻近HP岩石的折返大致相同。根据已发表的年代，提出了一系列的时间跨度从c.建议10至2-3 Ma。最初较长的构造平静期（I1- 2期，c. 10 Ma）与深部同期变形形成对比，表明造山楔内部的P-T-D历史是不一致的。约30 °C km− 1的升高梯度和假定的高加热速率。20 °C Ma− 1的地壳垂直运动是由花岗岩片的长期侵入（有或没有变形）所解释的，而地壳中的快速垂直运动（2-3 Ma，D2阶段）则需要变形阶段的活动。
A section of the orogenic middle crust (Orlica‐Śnieżnik Dome, Polish/Czech Central Sudetes) was examined to constrain the duration and significance of deformation (D) and intertectonic (I) phases. In the studied metasedimentary synform, three deformation events produced an initial subhorizontal foliation S1 (D1), a subsequent subvertical foliation S2 (D2) and a late subhorizontal axial planar cleavage S3 (D3). The synform was intruded by pre‐, syn‐ and post‐D2granitoid sheets. Crystallization–deformation relationships in mica schist samples document I1–2garnet–staurolite growth, syn‐D2staurolite breakdown to garnet–biotite–sillimanite/andalusite, I2–3cordierite blastesis and late‐D3chlorite growth. Garnet porphyroblasts show a linear Mn–Ca decrease from the core to the inner rim, a zone of alternating Ca–Y‐ and P‐rich annuli in the inner rim, and a Ca‐poor outer rim. The Ca–Y‐rich annuli probably reflect the occurrence of the allanite‐to‐monazite transition at conditions of the staurolite isograd, whereas the Ca‐poor outer rim is ascribed to staurolite demise. The reconstructedP–Tpath, obtained by modelling the stability of parageneses and garnet zoning, documents near‐isobaric heating from ~4 kbar/485 °C to ~4.75 kbar/575 °C during I1–2. This was followed by a progression to 4–5 kbar/580–625 °C and a subsequent pressure decrease to 3–4 kbar during D2. Pressure decrease below 3 kbar is ascribed to I2–3, whereas cooling below ~500 °C occurred during D3. In the dated mica schist sample, garnet rims show strong Lu enrichment, oscillatory Lu zoning and a slight Ca increase. These features are also related to allanite breakdown coeval with staurolite appearance. As Lu‐rich garnet rims dominate the Lu–Hf budget, the 344 ± 3 Ma isochron age is ascribed to garnet crystallization at staurolite grade, near the end of I1–2. For the dated sample of amphibole–biotite granitoid sheet, a Pb–Pb single zircon evaporation age of 353 ± 1 Ma is related to the onset of plutonic activity. The results suggest a possible Devonian age for D1, and a Carboniferous burial‐exhumation cycle in mid‐crustal rocks that is broadly coeval with the exhumation of neighbouring HP rocks during D2. In the light of published ages, a succession of telescoping stages with time spans decreasing fromc. 10 to 2–3 Ma is proposed. The initially long period of tectonic quiescence (I1–2phase,c. 10 Ma) inferred in the middle crust contrasts with contemporaneous deformation at deeper levels and points to decoupledP–T–Dhistories within the orogenic wedge. An elevated gradient of ~30 °C km−1and assumed high heating rates ofc. 20 °C Ma−1are explained by the protracted intrusion of granitoid sheets, with or without deformation, whereas fast vertical movements (2–3 Ma, D2phase) in the crust require the activity of deformation phases.