نوع مقاله : مقاله پژوهشی

نویسندگان

1 تکتونیک، گروه زمین شناسی، دانشکده علوم، دانشگاه بیرجند

2 تکتونیک، پژوهشکده علوم زمین، سازمان زمین شناسی و اکتشافات معدنی کشور

3 دپارتمان علوم زمین دانشگاه ETH زوریخ، سوئیس

چکیده

گسل گیلاتو-سیه­چشمه-خوی، با سازوکار جنبشی راستالغز راست­بر و با راستای NW-SE در بخش میانی پهنه برخوردی صفحه­های قاره­ای عربی-اوراسیا و هم روند با گسل­های شمال تبریز، چالدارن، نخجوان و پامبک-سوان-سونیک، در شمال­باختر ایران قرار گرفته است. در این مطالعه، جایگاه زمین­ساختی گسل گیلاتو-سیه­چشمه-خوی، آهنگ لغزش و نیز جنبه­های ارتباطی آن با گسل­های شمال­تبریز و چالدران به عنوان جنباترین گسل­های منطقه که به ترتیب در پایانه­های جنوب­خاوری و شمال باختری این گسل قرار دارند، مورد بررسی قرار گرفته است. در پاره گسلی گیلاتو-سیه­چشمه (پاره شمال­باختری گسل گیلاتو-سیه­چشمه-خوی)، با استفاده از جابجایی راست­بر در روانه­های بازالتی و با استناد به سن تعیین شده برای این بازالت به روش­های Pb206/U238 و Ar40/Ar39، کمینه آهنگ لغزش mm yr-1  1/0±65/1 تعیین شده است. همچنین در پاره گسلی سیه­چشمه-خوی (پاره جنوب­خاوری گسل گیلاتو-سیه­چشمه-خوی) با تعیین سن رادیوکربن از جوان­ترین نهشته رودخانه­ای جابجا شده در دیواره آبراهه، کمینه آهنگ لغزش mm yr-1 2/0±8/4 بدست آمد. نتایج آهنگ لغزش در امتداد گسل گیلاتو-سیه­چشمه-خوی، اتصال ساختاری پاره گسلی سیه­چشمه-خوی را به ترتیب با ادامه باختری و خاوری گسل­های شمال­تبریز و چالدران نشان می­دهد.

کلیدواژه‌ها

موضوعات

عنوان مقاله [English]

Active tectonics and slip rate variation along the Gailatu-Siah Cheshmeh-Khoy fault

نویسندگان [English]

  • Syrous Esmaeili 1
  • Mohammad Mahdi Khatib 1
  • Hamid Nazari 2
  • Jean-Pierre Bourg 3
  • Ebrahim Gholami 1

1 Tectonics, Department of Geology, Faculty of Science, Birjand University

2 Tectonics, Research Institute of Earth Sciences,, Geological Survey of Iran

3 Department of Geosciences, ETH Zurich, Switzerland

چکیده [English]

Summary:
Introduction:
The 200 km long Gailatu-Siah Cheshmeh-Khoy (GSK) fault, with the same trend as the North Tabriz, Chaldiran, Nakhichevan and Pambak-Sevan-Syunik faults, is regarded as a part of the strike-slip fault system in the middle of Arabian and Eurasian collision zone, which extends from 42˚ E to 48˚ E with the Tutak and North-Tabriz faults in the west and east, respectively. This system includes a series of right-lateral strike-slip faults between the southern front of the Lesser Caucasus in the northeast and Bitlis-Zagros suture zone in the southwest. Tchalenko (1977), Apart and Iz (1977) and Baraka and Kadinsky-Cade (1988) was studied different segments of GSK fault and Berberian (1997) and Karakhanian et al. (1998, 2002 & 2004) describe them as a unified active strike-slip fault. Different sections of GSK fault was named by previous authors as the Northwestern Fault System (Tchalenko, 1977) and Balikgölü fault (Baraka and Kadinsky-Cade, 1988), as well as, considering this fault as the western continuation of the North-Tabriz and Chaldiran faults by some authors has been called, North Tabriz-Gailatu fault system (Krakhanian et al., 1998) Balikghel-North-Tabriz fault (Karakhanian et al., 2002), Guilato–Siahcheshmeh–Khoy– Tabriz (Solaymani Azad et al., 2015) and Chaldiran-Khoy fault (Berberian, 1977).
Seismicity:
 During historical times, some destructive earthquakes especially on the northwestern parts of GSK fault have been occurred. The disastrous M=7.4 earthquake of 1840 A. D., reported as a strongest historical earthquake along GSK fault, destroyed the region along the NW part of this fault and more than 1000 people were killed in the towns of Maku, Dogubayazit, Avajigh (Kelissa-kandi) and many villages around NW part GSK fault (Ambraseys and Melville, 1982). About 72 km surface rupture along this and eruption of Ararat volcano is presumably was related to this event (Ambraseys and Melville, 1982; Karakhanian et al., 2002). After 3 years, an earthquake in 1843 A. D. devastate khoy city and killed between 500 and 1000 people (Berberian. 1977). Maku, Avajikh, Siahcheshmeh and its surrounding area, in 1968 A.D. damaged by Bedavli earthquake, considered to be related to activity of GSK fault (Berberian. 1977). Earthquakes of 363 A.D., 1319 A.D. (Qara Kelisa earthquake), 1808 A.D., 1834 A.D (Pambukh earthquake), 1900 A.D. and 1970 A.D. (khoy and Badalan earthquakes) are the other moderate historical and instrumental earthquakes of GSK fault (Ambraseys and Melville, 1982; Berberian. 1977).  Outlines of this fault is very obvious and display a series of well-developed and preserved morphologic evidence indicating recent activity of the fault, same as, fault scarps and horizontal deflection in the Quaternary features, pull-apart basins, hot water springs and uplifted terrace deposits. The available literature, fault plane solutions, offsets of various geomorphological, man-made features and basaltic lavas indicate the right-lateral strike-slip nature of the GSK fault. Debate on the eastern and the northwestern terminations of the Chaldiran and North-Tabriz faults, respectively, have been raised in the few recent decades.  In this paper, we investigated linkage of the North-Tabriz and Chaldiran faults, to the southeast and northwest of GSK fault, respectively.
Methods and discussion:
 This paper also provides critical data for the Quaternary slip rate and kinematic behavior of the GSK fault. One of the remarkable structural features is the Siah Cheshmeh pull-apart basin at a right step-over of the GSK fault. Two remarkable offsets along the strike of GSK fault define its horizontal slip rate. To determine long-term slip rates, Copley and Jackson (2006) studied two morphological features that have been displaced along the GSK fault up to 13-km, SPAB and Agchay river. By using these displacements, they estimated an average horizontal slip rate of 2-4 mmyr-1 since late Miocene along GSK fault. Along the SK,  Quaternary basaltic lavas, known as Maku basalts, form a few ridges that are elongated parallel to the strike of the fault and displaced by ~ 725±50. Using the about 400 kyr published age of these basalts (Pb206/U238 and Ar40/Ar39 dating methods, Allen et al., 2011; Lechmann et al., 2018), a mean slip rate is 1/65 ± 0.1 mmyr-1. On the SK segment, we excavated a trench to determine the fault geometry and its rake, and assessment of offsets which conditioned by the fault activity. In the trench, faults are shallow dipping with thrusting components that resemble foreberg structures in pressure ridges along strike-slip faults. Radiocarbon dating of the youngest deposits in the stream wall which displaced by 42±4 m, yield 6764±283 calBC, indicate the horizontal slip rate of 4.6±0.3 mmyr-1. Also, ourOur field observations have not identified any step along the SK segment, where more than four releasing and restraining bends have been reported by some authors along the GS segment. The existence of multiple bends along the GS segment relative to SK fault indicates lower geological offset of GS fault relative to SK fault, in accordance with theoretical consideration of Wesnousky (1988) for strike-slip faults. Based on this theory, the number of steps per unit length along the trace of strike-slip fault zones is a decreasing function of cumulative geological offset. In addition, published geodetic results show that the largest displacements occur along the North-Tabriz and Chaldiran faults, in the northwestern Iran and Eastern Turkey.
Conclusion:
 Our results indicate that, SK segment of the GSK  fault, due to its greater activity relative to its GS segment, can be considered as the western and eastern continuation of north Tabriz and Chaldiran faults, with a high slip rate.

کلیدواژه‌ها [English]

  • Gailatu-Siah Cheshmeh-Khoy fault
  • stike-slip fault
  • active tectonics
  • North Tabriz fault
  • Chaldiran fault