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生长断层

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生长断层和周遭结构的关系

生长断层(英语:growth fault)是在大陆板块边缘形成的一种同沉积的伸展构造[1]. 通常平行于并具有大量沉积物供应的被动边缘[2]. 它们的断层面向盆地方向倾斜,属于铲形断层一种。故其断层面倾角,浅処陡近乎垂直,深処逐渐变缓。在底部其断层面可能达到与地层面平行,形成滑脱面

生长断层上下两盘,沉积物厚度及倾角不一样,断层上盘沉积物较薄并向盆地方向倾斜,下盘沉积物较厚并向陆地方向倾斜。在下盘,同层沉积物也向断层面方向增厚,故称生长断层。在下盘地层增厚原因,是断层活动使水底向断层面方向加深,导致沉积空间增大。容纳较多沉积物[3]。通常沉积层面向盆地方向倾斜,但因为生长断层在断层面附近向反方向倾斜,就导致背斜,造成滚动背斜。属于石油构造圈闭之一种[3]

形成机制

被提出的生长断层形成机制有多种,包括基底构造、深层盐或页岩移动、坍塌等。但在德克萨斯州南部和中部沿海地区,这些生长断层大多数是由沉积物不同加载而引起的不同压实和重力滑动[4]

流动岩体移动

如果沉积盆地底层有厚曾蒸发岩或高压泥岩,当其上方沉积物达到一定厚度时,蒸发岩或高压泥岩不能再支持上覆地层重力,而产生移动。由厚层上覆地层(高压)向薄层上覆地层(低压)方向移动。因而导致在上覆地层产生断层。由于底层蒸发岩或高压泥岩继续移动。深部断层面倾角也随之减缓。最后形成滑脱面。浅部断层面近垂直倾角则不变。因为断层面倾角深浅処不同,导致断层上下盘落差浅処大,深处小。地层厚度也在下盘,随深度变薄[5][6]。事实上,上覆沉积物横向厚度差异所需不多,就能导致深层流动岩体移动[7]

差异压实

生长断层是同沉积断层一种,在墨西哥湾,分析同沉积断层在沉积中心的分布,表明相邻沉积物由于厚度或岩相不同,就能产生差异压实, 而导致生长断层[8]. 生长断层的特征之一是在下降盘的地层厚度往断层增加。在研究尼日尔三角洲一个主要生长断层时。证实这种地层增厚结构受三种因素控制:1)地层的差异压实,2)断层运动导致的沉降横向变化 3) 由深层页岩移动引起的局部沉降。而同沉积断层压实本身就能造成25% 至 35%容积空间[9]

重力滑动

生长断层是伸展构造的一种,在前积型大陆棚的前缘,由于沉积物的堆积引发重力滑动。而造成伸展断层。伸展断层能导致下降盘横向平移和纵向下沉。造成的沉积空间大于上升盘。加上充裕的沉积物的供应。其地层厚度比上升盘同层厚。岩相亦不同。因而形成生长断层[10] [11]

参考文献

  1. ^ Cazes, C. A.; 2004. "Overlap Zones, Growth Faults, and Sedimentation: Using High Resolution Gravity Data, Livingston Parish, LA.". Faculty of the Louisiana State University and Agricultural and Mechanical College in partial fulfillment of the requirements for the degree of Master of Science in The Department of Geology and Geophysics; Louisiana State University, Thesis": 147.
  2. ^ Schlische, R.W.; Anders, M.H. (1996). "Stratigraphic effects and tectonic implications of the growth of normal faults and extensional basins. In: Berata, K. (Ed.), Reconstructing the History of the Basin and Range Extension using Sedimentology and Stratigraphy". Geological Society of America. 303: 183–203 doi:10.1130/0-8137-2303-5.183
  3. ^ 3.0 3.1 Doglioni, C.; D’Agostino, N.; Mariotti, G. (1998). "Normal faulting versus regional subsidence and sedimentation rate". Marine and Petroleum Geology. 15: 737–750. doi:10.1016/s0264-8172(98)00052-x
  4. ^ C.H. Bruce (1983). "Shale Tectonics, Texas Coastal Area Growth Faults", Seismic Expression of Structural Styles: A Picture and Work Atlas. Volume 1–The Layered Earth, Volume 2–Tectonics Of Extensional Provinces, & Volume 3–Tectonics Of Compressional Provinces, A. W. Bally
  5. ^ Yuill, B.; Lavoie, D.; Reed, D.J. (2009). "Understanding subsidence processes in coastal Louisiana". Journal of Coastal Research. 10054: 23–36. doi:10.2112/si54-012.1
  6. ^ Joel S. Watkins (1994)Growth-Fault Evolution in Offshore Texas Gulf Coast Association of Geological Societies Transactions Vol. 44 (1994), Pages 103-110
  7. ^ Michael Warsitzka,Jonas Kley and Nina Kukowski(2013)Salt diapirism driven by differential loading — Some insights from analogue modelling Tectonophysics,Volume 591,Pages 83-97
  8. ^ Robert E. Carver; Differential Compaction as a Cause of Regional Contemporaneous Faults. AAPG Bulletin 1968;; 52 (3): 414–419. doi: https://doi.org/10.1306/5D25C2E3-16C1-11D7-8645000102C1865D
  9. ^ Amed Fazli Khani and Stefan Back (2015),The influence of differential sedimentary loading and compaction on the development of a deltaic rollover,Marine and Petroleum Geology,Volume 59,2015,Pages 136-149, ISSN 0264-8172, https://doi.org/10.1016/j.marpetgeo.2014.08.005. (https://www.sciencedirect.com/science/article/pii/S026481721400261X)。
  10. ^ William E. Galloway (1986)Growth Faults and Fault-Related Structures of Prograding Terrigenous Clastic Continental Margins。Gulf Coast Association of Geological Societies Transactions,Vol.36, Pages 121-128.
  11. ^ Martin P. A. Jackson and William E. Galloway(1984), Thin-skinned Gravity Sliding as a Mechanism for Growth Faulting, in Structural and Depositional Styles of Gulf Coast Tertiary Continental Margins: Application to Hydrocarbon Exploration. P37-45 AAPG Special Volumes.