Transient, synobduction exhumation of Zagros blueschists inferred from P‐T, deformation, time, and kinematic constraints: Implications for Neotethyan wedge dynamics
Transient, synobduction exhumation of Zagros blueschists inferred from P‐T, deformation, time, and kinematic constraints: Implications for Neotethyan wedge dynamics
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DOI：
10.1029/2005jb004103
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发表时间：
2006-11
影响因子：
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通讯作者：
P. Agard;P. Monié;W. Gerber;J. Omrani;M. Molinaro;B. Meyer;L. Labrousse;B. Vrielynck;L. Jolivet;P. Yamato
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文献类型：
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作者：
P. Agard;P. Monié;W. Gerber;J. Omrani;M. Molinaro;B. Meyer;L. Labrousse;B. Vrielynck;L. Jolivet;P. Yamato
我们首次对Zagros （Hajiabad地区）唯一已知的蓝片岩相岩（BS）进行了P-T、变形时间和运动学约束。BS位于sanandaji - sirjan带下方，并在广泛的彩色混杂岩单元中作为千米尺度的体出现，不连续地标志着新特提斯缝合带。P-T估计指向高压/低温（HP-LT）条件下，大多数BS在约11 kbar和520-530°C的条件下，沿着~ 15°C km - 1梯度。在~ 500°C时，基体蛇纹石中的一些外来块体达到17-18 kbar。原位激光探测40Ar-39Ar辐射年龄限制在85 ~ 95 Ma之间，表明(1)Zagros BS从35 ~ 50 km到深度<15 ~ 20 km的同辐合发掘是在80 Ma之前完成的，(2)相对于伊朗地下长期俯冲（~ 150 ~ 35 Ma）， BS发掘是一个短暂的过程。(3) Zagros BS的年龄限制比附近的阿曼HP-LT岩石的年龄限制要早5-10迈，并且与该地区的逆冲过程大致吻合（约95-70 Ma）。我们认为，伊朗下的新特提斯俯冲带（NSZ）的力学耦合被伴随逆冲的大规模板块重排所改变，从而导致了Zagros BS的短暂发掘。当阿拉伯大陆边缘的俯冲停止时，在逆冲结束时，挖掘工作停止了。运动学计算表明，在118-85 Ma期间，NSZ的辐合速度可能翻了一番（达到~ 5-6 cm yr - 1），因此，BS的发掘可能是由逆冲运动和辐合速度的增加共同促进的。
[1] We present the first P-T, deformation time, and kinematic constraints on the only known blueschist facies rocks (BS) present in the Zagros (Hajiabad area). The BS were underplated below the Sanandaj-Sirjan zone and crop out as kilometer-scale bodies within extensive colored melange units marking discontinuously the Neotethyan suture zone. P-T estimates point to high-pressure/low-temperature (HP-LT) conditions around 11 kbar and 520–530°C for the majority of BS, along a ∼15°C km−1 gradient. Some exotic blocks in matrix serpentinite reached 17–18 kbar at ∼500°C. In situ laser probe 40Ar-39Ar radiometric age constraints on phengite cluster between 85 and 95 Ma and suggest that (1) synconvergence exhumation of Zagros BS from 35–50 km to depths <15–20 km was accomplished before 80 Ma, (2) BS exhumation corresponded to a transient process with respect to the long-lived subduction beneath Iran (∼150–35 Ma), and (3) age constraints for Zagros BS are 5–10 Myr older than for the nearby Oman HP-LT rocks and broadly coincide with obduction processes in the region (circa 95–70 Ma). We propose that the mechanical coupling across the Neotethyan subduction zone (NSZ) beneath Iran was modified by the large-scale plate rearrangement accompanying obduction, allowing for a short-lived exhumation of Zagros BS. Exhumation ceased at the end of obduction, when subduction of the Arabian continental margin stopped. Kinematic calculations suggest that convergence velocities across the NSZ likely doubled (to ∼5–6 cm yr−1) during the period 118–85 Ma, so that BS exhumation may have been promoted by a combination of obduction movements and increased convergence velocities.