18-Geol-A1 Mineralogy and Petrology · December 2016
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
EGBC National Exam — Geological Engineering, 04-Geol-A1 Mineralogy and Petrology, 2016-Dec. Closed book; no calculator permitted. Part 1 requires all six 10-mark short-answer questions (60 marks); Part 2 instructs "answer 4 of the 7 ten-mark questions" (40 marks).
Reference texts: Klein & Dutrow, Manual of Mineral Science, 23rd ed. (mineral/silicate structural classification, ore mineralogy); Winter, Principles of Igneous and Metamorphic Petrology, 2nd ed. (magmatic differentiation, phase diagrams, metamorphic reactions and facies, AFM projections, volcanic processes, ophiolites and oceanic crust, subduction-zone/rift/hotspot melting); Nesse, Introduction to Optical Mineralogy, 4th ed. (index-mineral optics).
Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.
| Agent | What it does | Geological example |
|---|---|---|
| Heat (temperature) | Drives mineral reactions and recrystallization toward assemblages stable at higher T; the primary control on metamorphic grade. | The thermal aureole surrounding a shallow granitic pluton, producing a zoned sequence of hornfels grades outward from the contact. |
| Pressure (confining/lithostatic) | Uniform, all-sided pressure from the weight of overlying rock; increases density and favours mineral assemblages with smaller molar volume, without imposing a preferred orientation. | Burial metamorphism of a thick sedimentary basin pile (e.g. zeolite-facies burial metamorphism at the base of a deep sedimentary basin). |
| Differential stress (directed pressure) | Unequal stress in different directions; drives dynamic recrystallization, grain flattening/elongation and preferred mineral alignment, producing foliation and lineation. | Development of schistosity/mylonitic fabric in a ductile shear zone or at a convergent-margin fold-and-thrust belt (regional dynamothermal metamorphism). |
| Chemically active fluids | Aqueous/carbonic fluids transport heat and dissolved species, catalyzing reactions and enabling metasomatic (allochemical) mass transfer that dry solid-state diffusion could not achieve on a human timescale. | Skarn formation (metasomatism) at the contact between an intrusion and a limestone country rock, where fluid-borne Si, Fe, Al and Mg are exchanged for country-rock Ca. |
