تكتونيك لبه شرقي پهنه لوت در منطقه نهبندان؛ موردي از معماري يك حاشيه همگراي قديمي

Tectonics of the eastern edge of the Lut Zone in Nehbandan area; example of an ancient convergent plate margin architecture

حاشيه شرقي پهنه لوت در منطقه نهبندان با توالي ضخيمي از سنگ هاي سيليسي - كلاستيكي ريزدانه منتسب به ترياس فوقاني- ژوراسيك مشخص مي شود. مطالعات صحرايي و آزمايشگاهي چهار واحد تكتونو - استراتيگرافي را براي منطقه مذكور پيشنهاد مي كنند كه به ترتيب از غرب به شرق با راستاي تقريبي شمالي - جنوبي كشيده شده اند. اين واحدها عبارتند

The eastern edge of the Lut Zone in the Nehbandan area is characterized by the fine - grained sequence of the Late Triassic - Jurassic siliciclastic rocks. Field and satellite investigations as well as laboratory studies the whole region along with Satellite image investigations, resulted into the identification of the four tectono - stratigraphic units extending along the N - S direction, developed from west to east as follows; (1) the Triassic-Jurassic the shale - sandstone unit; this unit was intruded by the late Jurassic intrusions and covered by the volcano - clastic rock remnants with the same age. There, the pelagic layers which are accompanied the basalts yield the late Triassic radiolarites. (2) An olistolitic unit; a chaotic olistostrome assemblage including sandstone olistolites and a cleaved matrix. Pillow basalts and pelagic limestone slices were sporadically observed. (3) The green belt; it's a narrow and lengthy belt of basalts younger than Jurassic times underwent the green – schist - facies metamorphism. Geochemistry of the basalts reveals significant similarities with those of the mafic rocks in the supra - subduction zone and/or the MOR. Moreover, the presence of large recumbent fold documents an eastward regional transport direction of thrust sheets from Lut to the Sistan suture zone side. (4) The easternmost unit is dominated by phyllitic rocks with a pelitic source. The Paleodictyon trace fossils were found led us to conclude about its Eocene protolith age. The nature and arrangement of the units are supposing presence of an accretionary complex along the Lut Zone documenting the existence of a long - standing subduction zone under the Lut Zone for the Triassic - Eocene times.