This chapter is concerned with the orientations of lines and planes. The structural elements that we measure in the field are mostly lines and planes, and manipulating these elements on paper or on a computer screen helps us visualize and analyze geologic structures in three dimensions. In this chapter we will examine several graphical and mathematical techniques for solving apparent-dip problems. Each technique is appropriate in certain circumstances. The examination of various approaches to solving such problems serves as a good introduction to the techniques of solving structural problems in general. Finally, many of these problems are designed to help you visualize structural relations in three dimensions, a critical skill for the structural geologist. <...>

In 1930 Bruno Sander, in his now classic Gefiigekunde der Gesteine, presented a comprehensive account of the fabric of deformed rocks, new geometric methods for its analysis, and a broad philosophy for its kine¬ matic interpretation. Since then, and especially since the Second World War, Sander’s methods have been applied with varying degrees of success in attempts to elucidate the structure of metamorphic rocks in many countries. Outstandingly successful among such attempts are studies, still in progress, on the nature and geometry of repeated folding in the Highlands of Scotland.

The mechanism of continental growth of Central Asia is currently debated between models invoking continuous subduction–accretion, or punctuated accretion due to closure of multiple ocean basins. Ophiolites in Central Asia may represent offscraped fragments in an accretionary complex or true collisional sutures. The Bayankhongor ophiolite, a NW–SE-striking sublinear belt 300 km long and 20 km wide, is the largest ophiolite in Mongolia and possibly Central Asia. We present results of the first detailed structural and lithological study of the ophiolite. The study area is divided into four zones: Baidrag complex, Burd Gol, Bayankhongor, and Dzag zones. The Archaean Baidrag complex comprises tonalitic granulites and metasediments. The Burd Gol zone is a metamorphosed sedimentary and igneous me´lange. The Bayankhongor zone contains the dismembered ophiolite forming a serpentinite me´lange. The Dzag zone consists of asymmetrically folded chlorite–mica schists resembling meta-turbidites. The structure is dominated by steeply dipping, NE directed thrusts and NE-vergent folds. We suggest the Bayankhongor ophiolite marks the closure of an ocean separating two microcontinents: the Baidrag complex with the Burd Gol accretionary complex to the south, and a northern continent that forms the basement for the Hangai region. Subduction was towards the SW with NE-directed ophiolite obduction onto a passive margin represented by the Dzag zone.

PLAN:

1. INTRODUCTION

2. OBJECTIVES

3. HISTORY AND PREVIOUS WORK

4. METHODS

5. GEOLOGY AT DEEP POST MINE

6. Stratigraphy

7. Structures

8. HYDROTHERMAL ALTERATION

9. MINERALIZATION

10. MODEL AND CONCLUSIONS