Structural Geology and Kinematics of Rock Deformation

Here we show that fault-vein growth and transient changes in fault-vein kinematics are an important component of the evolution of epithermal vein systems. The Toguraci deposit, in the Gosowong goldfield, Halmahera, exposes a spectacular system of segmented veins, subsidiary vein networks linking between each segment (step-over zones), and wall rock margins comprising clay-rich fault rock. Different structural components were distinguished on the basis of their mineralogy, orientations and kinematics. Using an approach based on combinatorial mathematics we demonstrate that veins with very different orientations, consistently overprint one another in the wall rock and step-over zones. The different vein populations occur across the goldfield and not just the Toguraci Pit. This result implies a cyclic deformation history. Transient changes in stress state and kinematics occurred in the system, and fluid pathways likely changed dramatically between individual fracture events.

Course name: Earth Systems I: Solid Earth

Saint Louis University, Madrid Campus, Faculty: Science and Engineering

Semester:  Spring 2005.

Course description: On the structure of our planet and the forming processes: plate tectonics, crustal evolution, rocks, surface and groundwater hydrology, and so on. Focus on volcanic activity in the Canary Islands, where students will carry out field studies during a long-weekend visit.
Mandatory trip: Lanzarote (Canary Islands); unpaid fees result in automatic removal from class.

Course Objectives: 
By end of the course the student should:
• Know the basic types of rocks and understand the basic principles of the rock cycle.
• Know and understand the basic principles of plate tectonics and volcanism.
• Know and understand the most important processes on the earth´s surface.
• Achieve a foundation on the basic principles underlying the patterns and dynamics of the earth´s surface and interior.

Textbook: Following textbook is absolutely necessary for the course:
PRESS, Frank, & SIEVER, Raymond (2001): Understanding Earth. 3rd edition. – New York (W. H. Freeman and Company).

Supplementary reading: Following books may be interesting or helpful for some aspects of the course, but they are not necessary:
ANDEL, T. H. van, (1994): New views on an old planet. A history of global change. 439 pp.; Cambridge (Cambridge University Press).
ARAÑA, V., & CARRACEDO, J. C. (1979): Los volcanes de las islas Canarias. – Vol. I: Tenerife; Vol. II: Lanzarote y Fuerteventura.
BOLT, Bruce A. (1999): Earthquakes. – 366 p.; New York (W. H. Freeman and Company).
CUNNINGHAM, W.P., & SAIGO, B. Woodworth (1992): Environmental Science – A Global Concern. 2nd edition. – 622 p., Dubuque (Wm. C. Brown Publishers).
CUNNINGHAM, W.P., & CUNNINGHAM, M.A., & SAIGO, B. Woodworth (2002): Environmental Science – A Global Concern. 7th edition. – 646 p., Boston.
DECKER, Robrt & Barbara: Volcanoes. – 321 p.; New York (W. H. Freeman and Company).
MERRITTS, D., & WET, A. DE, & MENKING, K. (1998): Environmental geology. 452 pp.; New York (Freeman a. Co.).
SCARTH, Alwyn & TANGUY, Jean-Claude (2000): Volcanoes of Europe. – Oxford.
YARZA, Esperanza (1988): Volcanes de Iberoamerica. – 128 p.; Madrid (Anaya).

Course Calendar:
Tuesday, Jan. 18th: Introduction – Building a planet (Textbook chapter 1)
Thursday, Jan. 20th: Minerals (Textbook chapter 2)
Tuesday, Jan. 25 & Thursday, Jan. 27: Rocks (Textbook chapter 3)
Thursday, Jan. 27: End of DROP/ADD period
Tuesday, Feb. 1 & Thursday, Feb. 3: Igneous Rocks (Textbook chapter 4)
Tuesday, Feb. 8 & Thursday, Feb. 10: Volcanism (I) (Textbook chapter 5)
Tuesday, Feb. 15: Review & Preparation of first mid-term exam
Tuesday, Feb. 15: Deadline for the submission of the title of the paper
Thursday, Feb. 17: First mid-term exam
Tuesday, Feb. 22 & Thursday, Feb. 24: Volcanism (II) (Textbook chapter 5)
Tuesday, Mar. 1 & Thursday, Mar. 3: Volcanism (III) (Textbook chapter 5)
Saturday, Mar. 5, to Sunday, Mar. 13: SPRING BREAK
Tuesday, Mar. 15: Weathering and Erosion (Textbook chapter 6)
Thursday, Mar. 17, to Sunday, Mar.20: Field trip to the Canary Islands
Tuesday, Mar. 22: Sediments and Sedimentary Rocks (I) (Chapter 7)
Thursday, Mar. 24, to Sunday, Mar.27: Easter
Tuesday, Mar. 29: Review & Preparation of second mid-term exam
Thursday, Mar. 31: Second mid-term exam
Tuesday, Apr. 5: Deadline for the submission of papers and PowerPoint presentations
Tuesday, Apr. 5: Sediments and Sedimentary Rocks (II) (Chapter 7)
Thursday, Apr. 7: Metamorphic Rocks (Textbook chapter 8)
Thursday, Apr. 7: Deadline for the submission of the exercise
Friday, Apr. 8: Last day to drop a class and receive a grade of "W"
Tuesday, Apr. 12: The Rock Record and the Geologic Time Scale (Textbook chapter 9)
Thursday, Apr. 14: Rock Deformation (Textbook chapter 10)
Tuesday, Apr. 19 & Thursday, Apr. 21: The Hydrologic Cycle and Groundwater (Chapter 12)

Jackson et al. (2015) used 3D seismic reflection data to describe intrasalt deformation in salt walls in the Santos Basin. They focused on the origin of enigmatic allochthonous salt sheets of older evaporites (A1 unit) emplaced above overlying stratified evaporites (A2eA4 units). Their kinematic model incorporates: (i) initial inward flow and thickening of A1 salt within the rising wall, and arching of A2eA4 overburden; (ii) breaching of the arched overburden, ascent of mobile A1 evaporites along single or multiple feeders, and emplacement of upper-wall sheets or canopies; and (iii) a component of regional shortening within the salt. This companion paper uses physical modelling to explain how and why these structures occur and proposes a mechanical basis for the kinematic model. Our first two models simulated salt having uniform internal density, with walls growing by (i) initially symmetric differential loading and (ii) initially symmetric differential loading plus shortening. These models reproduced anticlines and injection folds seen in the simpler deformed walls in the Santos Basin. However, neither model reproduced the most complex structures within the Santos evaporites, which are: (i) allochthonous intrusions, (ii) steep feeders, and (iii) recumbent synclines. Thus, differential loading and shortening alone are insufficient to generate these complex structures. In our third model, a less-dense lower evaporite (A1) was overlain by denser upper evaporites (A2eA4), similar to the density structure found by Santos Basin wellbores. The wall rose solely by differential loading. In this model, A1 breached the overlying evaporites to form vertical diapirs feeding salt sheets and salt wings in the upper part of the salt wall. Breakthrough of A1 folded A2eA4 evaporites into recumbent synclines. Model sections closely resemble Santos seismic examples, suggesting that the key to forming these complex intrasalt structures is a density inversion within the evaporite sequence that creates a RayleigheTaylor instability.