Transient, synobduction exhumation of Zagros blueschists inferred from P-T, deformation, time, and kinematic constraints:: Implications for Neotethyan wedge dynamics

被引:176
作者
Agard, P.
Monie, P.
Gerber, W.
Omrani, J.
Molinaro, M.
Meyer, B.
Labrousse, L.
Vrielynck, B.
Jolivet, L.
Yamato, P.
机构
[1] Univ Paris 06, Lab Tecton, CNRS, UMR 7072, F-75252 Paris 05, France
[2] Univ Montpellier 2, Lab Dynam Lithosphere, CNRS, UMR 5573, F-34095 Montpellier 05, France
[3] Geol Survey Iran, Tehran, Iran
[4] Univ Cergy Pontoise, Lab Tecton, F-95031 Neuville Sur Oise, Cergy, France
关键词
D O I
10.1029/2005JB004103
中图分类号
P3 [地球物理学]; P59 [地球化学];
学科分类号
0708 [地球物理学]; 070902 [地球化学];
摘要
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 degrees C for the majority of BS, along a similar to 15 degrees C km(-1) gradient. Some exotic blocks in matrix serpentinite reached 17-18 kbar at similar to 500 degrees 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 (similar to 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 similar 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.
引用
收藏
页数:28
相关论文
共 135 条
[1]
Discovery of paleozoic Fe-Mg carpholite in Motalafjella, Svalbard Caledonides: A milestone for subduction-zone gradients [J].
Agard, P ;
Labrousse, L ;
Elvevold, S ;
Lepvrier, C .
GEOLOGY, 2005, 33 (10) :761-764
[2]
Convergence history across Zagros (Iran): constraints from collisional and earlier deformation [J].
Agard, P ;
Omrani, J ;
Jolivet, L ;
Mouthereau, F .
INTERNATIONAL JOURNAL OF EARTH SCIENCES, 2005, 94 (03) :401-419
[3]
Exhumation of the Schistes Lustres complex:: in situ laser probe 40Ar/39Ar constraints and implications for the Western Alps [J].
Agard, P ;
Monié, P ;
Jolivet, L ;
Goffé, B .
JOURNAL OF METAMORPHIC GEOLOGY, 2002, 20 (06) :599-618
[4]
Tectonometamorphic evolution of the Schistes Lustre's complex:: implications for the exhumation of HP and UHP rocks in the western Alps [J].
Agard, P ;
Jolivet, L ;
Goffé, B .
BULLETIN DE LA SOCIETE GEOLOGIQUE DE FRANCE, 2001, 172 (05) :617-636
[5]
TECTONICS OF THE ZAGROS OROGENIC BELT OF IRAN - NEW DATA AND INTERPRETATIONS [J].
ALAVI, M .
TECTONOPHYSICS, 1994, 229 (3-4) :211-238
[6]
Late Cenozoic reorganization of the Arabia-Eurasia collision and the comparison of short-term and long-term deformation rates [J].
Allen, M ;
Jackson, J ;
Walker, R .
TECTONICS, 2004, 23 (02) :TC20081-16
[7]
Late Cretaceous blueschist metamorphism in the Indus Suture Zone, Shangla region, Pakistan Himalaya [J].
Anczkiewicz, R ;
Burg, JP ;
Villa, IM ;
Meier, M .
TECTONOPHYSICS, 2000, 324 (1-2) :111-134
[8]
[Anonymous], 1944, ESSAI STRUCTURE LIRA
[9]
[Anonymous], 1972, GEOLOGY PETROGRAPHY
[10]
EVIDENCE FOR EXCESS ARGON DURING HIGH-PRESSURE METAMORPHISM IN THE DORA-MAIRA MASSIF (WESTERN ALPS, ITALY), USING AN ULTRA-VIOLET LASER-ABLATION MICROPROBE 40AR-39AR TECHNIQUE [J].
ARNAUD, NO ;
KELLEY, SP .
CONTRIBUTIONS TO MINERALOGY AND PETROLOGY, 1995, 121 (01) :1-11