بررسی بالاآمدگی تکتونیکی در کوه های شکراب واقع در شمال بیرجند (خراسان جنوبی) با استفاده از شواهد ریخت زمین ساختی

نوع مقاله: مقاله پژوهشی

نویسندگان

چکیده

ویژگی­های ژئومورفیکی ساختارهایی که در نتیجه­ی بالاآمدگی تکتونیکی ایجاد می­شوند اطلاعات باارزشی در رابطه با نیروهای تکتونیکی به وجود آورنده­ی آن­ها را فراهم می­کنند. منطقه­ی مورد مطالعه یکی از سرشاخه­های انتهایی گسل نهبندان می­باشد که درشرق ایران و شمال بیرجند قرار دارد. هدف از این پژوهش تفکیک مناطق با بالاآمدگی متفاوت در طول کوه­های شکراب می­باشد، برای رسیدن به هدف پژوهش از داده­های صحرایی، داده­های توپوگرافی و شاخص­های ژئومورفیک استفاده گردید. با استفاده از عملیات صحرایی گسل­ها که یکی از مهم­ترین ساختارها در منطقه­ی مورد مطالعه هستند شناسایی گردید. شاخص­های ژئومورفیک که در این پژوهش استفاده گردید شامل: نسبت عرض کف دره به ارتفاع دره (Vf)، انتگرال هیپسومتریک (Hi)، منحنی هیپسومتریک (Hc)، شکل حوضه(Bs)  و زمین ساخت فعال نسبی  (Iat)می­باشد. محاسبه­ی شاخص Vf در کوه­های شکراب نشان می­دهد کمترین مقدار شاخص Vf و بیشترین مقدار نرخ بالاآمدگی تکتونیکی مربوط به قسمت غربی و شمال­شرقی کوه­های شکراب می­باشد. بیشترین مقدار شاخص­های Hi و Hc مربوط بخش­های غربی و شمال­شرقی منطقه­ی مورد مطالعه می­باشد. محاسبه­ی شاخص  Bsنشان می­دهد بیشترین مقدار شاخص Bs مربوط به بخش غربی کوه­­های شکراب است، افزایش شاخص Bs و وجود حوضه­های کشیده در قسمت­های غربی و شمال­شرقی کوه­های شکراب نشان می­دهد که بیشترین بالاآمدگی مربوط به قسمت غربی منطقه­ی مورد مطالعه است. نتایج این پژوهش نشان می­دهد در مناطقی از کوه­های شکراب که شاهد بیشترین تراکم گسل­های تراستی هستیم، تحت تاثیر عملکرد مولفه­ی فشارشی گسل­های تراستی بالاآمدگی تکتونیکی نیز افزایش یافته است. وجود گسل­های تراستی در قسمت­های غربی و شمال­شرقی منطقه­ی مورد مطالعه باعث فشارش، بالاآمدگی تکتونیکی و ایجاد دره­های V شکل گردیده است.

کلیدواژه‌ها


عنوان مقاله [English]

Investigation of tectonic uplift in Shekarab Mountain located in North of Birjand (Southern Khorasan) using morphotectonic evidence

نویسندگان [English]

  • Maryam Ezati
  • Ebrahim Gholami
  • Seyed Morteza Moussav
چکیده [English]

 
Introduction
Landscape evolution represents a morphotopographic balance resulting from interactive competition between tectonics and climate. The development of geomorphic features in response to tectonic uplift provides important information regarding nature, spatial and temporal distributions of tectonic forces in contractional and extensional tectonic regimes. The distribution of tectonic activities in regions experiencing tectonic uplift can be mapped through geomorphic proxie. Commonly, geomorphic indices are useful to classify areas as being very active, moderately active, or inactive. Aim of this research is separating of areas with differental tectonic uplift. Study area (Shekarab Mountain) is located in the East of Iran. In this research, for identifying rate of tectonic uplift geomorphic indices such as valley floor width–valley height ratio (Vf), hypsometric curve (Hc) and hypsometric integral (Hi), drainage basin shape (Bs) and Relative tectonic activity (Iat) were calculated.
 
Methodology
For reaching to the aim of this research field work and Geomorphic indices were used. Indices of active tectonics may detect anomalies in the fluvial system or along mountain fronts. These anomalies may be produced by local changes from tectonic activity resulting from uplift or subsidence. The research design is to analyze several different indices in Shekarab Mountain.
Ratio of Valley Floor Width to Valley Height (Vf):
Vf is defined as the ratio of the width of the valley floor to its average height (Bull and McFadden, 1977; Bull, 1978) and is computed by
Vf=2Vfw/[(Eld–Esc)]+(Erd–Esc)]                                                                                      (1)                                                             
Hypsometric Integral (Hi):
The hypsometric integral is an index that describes the distribution of elevation of a given area of a landscape. The index is defined as the area below the hypsometric curve and thus expresses the volume of a basin that has not been eroded. The simple equation that may be used to calculate the index is
Hi = (average elevation – min. elevation) / (max. elevation – min. elevation).                    (2)
Index of Drainage Basin Shape (Bs):
Bs (Ramirez-Herrera, 1998) expressed by the equation
Bs=Bl/Bw                                                                                                                          (3)                                     
Where Bl is the length of the basin measured from the headwaters to the mouth, and Bw is the width of the basin measured at its widest point.
Relative tectonic activity (Iat):
Several index combined to provide information of relative degree of tectonic activity. To provide Iat index is obtained by averaging of different classes of geomorphic indices (S/n) and divided in to four classes. Class 1 is very high tectonic activity with values of S/n between 1 and 1.5; class 2 is high tectonic activity with values of 2>S/n>1.5; class 3 is moderately active tectonics with 2.5>S/n >2; and class 4 is low active tectonics with values of S/n>2.5 (El Hamdouni et al., 2008).
 
Result and Discussion
In this study, we have used 1: 25,000 topographic maps with 50 m contour intervals. This projection was the UTM zone 40 N. Values of Vf vary from a low of 0.3 for the west part of Shekarab Mountain where it is deeply incised into hard bedrock, to a high of 3.4 at east part of Shekarab Mountain. Hi index computed for each subbasin, ranges from 0.8 (Subbasin 1) to 0.3 (Subbasin 51). Computing of hypsometric integral (Hi) shows that actives part of Shekarab Mountain is west and north eastern part of Shekarab Mountain (subbasins 1, 24). Calculating hypsometric integral shows that in west and north eastern side of study area (subbasins 1, 24), rate of uplift are faster than rate of erosion. Bs was calculated for Shekarab Mountain, The highest value of Bs index is related to western basins of Shekarab Mountain. The highest class values for Iat mainly occur in the west and north eastern of Shekarab Mountain, while the rest of study area has classes of Iat suggesting moderate to low tectonic uplift. The distribution of indices defines areas associated with different rates of tectonic activity. Within the study area tow subbasin (subbasin 1 and 24) is about class 1 (very high relative tectonic activity). Result of this research shows that highest amount of tectonic uplift is about the west and north east side of study area, and in the areas of Shekarab Mountain that thrust fault were more concentrated  tectonic uplift increased.
 
Conclusion
The values of morphometric indices valley floor width–valley height ratio (Vf), hypsometric curve (Hc), hypsometric integral (Hi), drainage basin shape (Bs) and Relative tectonic activity (Iat) compared with lineament and geological map. Calculating Af and T indices shows that most streams of study area is tilted toward the South. Computing of Hi index show that main basin is in youthful stage. Computing of SL index shows that highest amount of SL index is related to fault 3. Calculating of Vf index indicate that lowest value of Vf index is related to fault 3.  Computing of geomorphic indices shows that fault 3 are more tectonically active than other faults of study area. Existing of thrust faults caused to pressure, tectonic uplift and V shape valleys in western and north eastern part of study area.

کلیدواژه‌ها [English]

  • Tectonic uplift
  • morphotectonic analysis
  • Geomorphic indices
  • Shekarab Mountain
  • East Of Iran
  • اشتوکلین، ی. افتخارنژاد، ج. هوشمندزاده، ع. 1352. بررسی مقدماتی زمین­شناسی در لوت مرکزی، شرق ایران. سازمان زمین­شناسی و اکتشافات معدنی کشور، گزارش شماره 22. 86.
  • اوهانیان، ت. طاوسیان، ش. و افتخارنژاد، ج.، 1366. نقشه زمین­شناسی 100000/1 بیرجند، سازمان زمین­شناسی و اکتشافات معدنی کشور.
  • بربریان، م.، 1362. دگرریختی قاره­ای در فلات ایران زمین. سازمان زمین­شناسی و اکتشافات معدنی، گزارش شماره 52. 352-307. 
  • روشن­روان، ج. شجاعی کاوه، ن. بهره­مند، م. 1386 . نقشه زمین­شناسی 100000/1 موسویه، سازمان زمین­شناسی و اکتشافات معدنی کشور.
  • وحدتی­دانشمند، ف. و خلقی، م. ح. 1365 . نقشه زمین­شناسی 100000/1 خوسف، سازمان زمین­شناسی و اکتشافات معدنی کشور.
  • مددی، عقیل. رضایی مقدم، محمد حسین. رجایی، عبدالحمید. 1383. تحلیل فعالیت­های تکتونیک با استفاده از روش­های ژئومورفولوژی در دامنه­های شمال غربی تالش (باغروداغ). پژوهش­های جغرافیایی. دانشگاه تهران. شماره 48. صص 123-138.
    • Benabdellouahed, M. Klingelhoefer, F. Gutscher, M.A. Rabineau, M. Biari,Y. Hafid, M. Duarte, J.C. Baltzer, A. Pedoja, K. LeRoy, P. Reichert, C. Recent uplift of the Atlantic Atlas (offshore West Morocco): Tectonic arch and submarine terraces, Tectonophysics706-707. pp. 46-58.
    • Burbank, D.W. and Anderson, R.S., 2001. Tectonic Geomorphology. Malden.
    • EL Hamdouni R., Irigaray C., Fernandez T., Chacon J., and Keller E. A., 2008. Assessment of relative active tectonics, southwest border of Sierra Nevada (southern spain), Geomorphology, No. 969, pp. 150-173.
    • Figueiredo, P.M. Rockwell, T.K. Cabral, J. Ponte Lira, C., 2018. Morphotectonics in a low tectonic rate area: Analysis of the southern Portuguese Atlantic coastal region, Geomorphology, pp. 1- 51.
    • Gaidzik, K. and Ramirez-Herrera, M.T., 2016. Geomorphic indices and relative tectonic uplift in the Guerrero of the Mexican forearc, Geoscience frontiers, pp. 1-54.
    • Keller, E.A. and Pinter N. 2002, Active tectonic, Earthquickes, Uplift and Landscape, Prentice Hall, P. 362.
  • Kirby, E. Whipple, K.X., 2012. Expression of active tectonics in erosional and scapes, J. Struct. Geol. 44, pp. 54-75.
  • Lewis, C.J. Sancho, C. McDonald, E.V. Pena-Monne, J.L. Rhodes, E. Calle, M. Soto. R., 2017. Post-tectonic landscape evolution in NE Iberia using staircase terraces: combined effects of uplift and climate,Geomorphology 292, pp. 85-103.
 

  • Li, Q. Pan, B. Geo, H. Wen, Z. Hu, X., 2018, Differential rock uplift along the northeastern margin of the Tibetan Plateau inferred from bedrock channel longitudinal, Journal of Asian Earth Science, pp. 1-73.
    • Samimi, S. and Gholami, E. 2017. Geometric and Kinematic Analysis of Structural along North Front of Bagharan Kuh Mountain, NE Iran, Geotectonics 51 (2), pp. 192-208.
    • Tirrul, R., Bell, I.R., Griffis, R.J., and Camp, V.E., 1983, The sistan suture zone of eastern Iran. Geological Society of American Bulletin, 94, 134-156. 
  • Whipple, K.X., 2004. Bedrock rivers and the geomorphology of active orogens. Annu. Rev. Earth Planet. Sci. 32, pp. 151-185.
    • Walker, R. Jackson, J., 2002. Offset and evolution of the Gowk fault, SE Iran: a major intra- continental strike- slip system, Journal of Structural Geology, v.24, p 1677-1698.
    • Walker, R. Jackson, J., 2004. Active tectonics and late cenozoic strain distribution in central and eastern Iran, Tectonics, v.23, 1-24.
  • Xue, L. Alemu, T. Gani, N.D. Abdelsalam, M.G., 2018, Spatial and temporal variation of tectonic uplift in the southeastern Ethiopian Plateau from morphotectonic analysis, Geomorphology 309, pp. 98-111.