18-Geol-A1 Mineralogy and Petrology · Undated paper
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
Paper format. National Exam — 18-Geol-A1 Mineralogy and Petrology. 3 hours, closed book, no calculator permitted. Two parts, twelve ten-mark short-answer questions in total: Part 1 (Q1–5) requires all five questions (50 marks); Part 2 (Q6–12) is printed as "answer 5 of the 7" on one page and "answer 5 of the 5" on another (the paper's own instructions disagree on the count) — every question in both parts is solved in full below so this set also serves as a complete study reference. This sitting is treated as undated because the paper is internally inconsistent about its own date: the first-page footer reads "May 2018" (matching the 18-Geol-A1 code, in use from December 2018 onward) while a later page's footer reads "19-Geol-A1 / May 2019". No exam date is asserted.
Reference texts: Klein & Dutrow, Manual of Mineral Science, 23rd ed. (silicate/oxide structural classification, mineral chemistry, solid solution and exsolution, crystal systems); Winter, Principles of Igneous and Metamorphic Petrology, 2nd ed. (magmatic differentiation, Bowen's reaction series, tectonic settings of magmatism and melting, ophiolites, LIPs, anatexis, contact/thermal metamorphism).
There is no numeric given data anywhere in this qualitative/descriptive paper.
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.
LIPs (Large Igneous Provinces) are massive volcanic and intrusive complexes of predominantly mafic (basaltic/picritic) composition, emplaced in a geologically very short interval (typically well under 1–5 Myr for the main pulse), covering enormous areas (>0.1 million km²) and volumes (>0.1 million km³), and generated by processes unrelated to normal, steady-state plate-boundary volcanism (i.e. not ordinary mid-ocean-ridge or arc magmatism). Continental examples include the Siberian Traps, the Deccan Traps and the Columbia River Basalt Group (flood basalts); the Ontong Java Plateau is the type example of an oceanic LIP.
LIPs are generally attributed to a buoyant, anomalously hot mantle plume head rising from deep in the mantle (potentially as deep as the core–mantle boundary) and impinging on the base of the lithosphere. Because the plume material carries an elevated mantle potential temperature $T_p$ well above ambient upwelling mantle, it crosses its solidus over a much thicker vertical interval during decompression than ordinary ridge-source mantle does — generating a far larger degree and volume of partial melting in a geologically brief pulse. Where this occurs beneath continental lithosphere, the result is a continental flood-basalt province, often closely associated in time with continental rifting and breakup (e.g. the Deccan Traps erupting close to the India–Seychelles separation); where it occurs beneath oceanic lithosphere, the result is an oceanic plateau (e.g. Ontong Java).
LIPs are of more than academic interest: several of the largest, best-dated LIP eruptions correlate closely in age with major mass-extinction boundaries — the Siberian Traps with the end-Permian extinction and the Deccan Traps with the end-Cretaceous extinction — on the hypothesis that the enormous, rapid release of volcanic $\text{CO}_2$ and $\text{SO}_2$ from a LIP-scale eruption can drive severe, geologically abrupt climate perturbation independent of (in the Deccan case, possibly in addition to) any bolide impact.
