Igneous Petrology Lesson 1:Types of magmas & Variation diagram

In this introductory lesson, we explore the foundational concepts of igneous petrology, focusing on the origins and evolution of magmas. We begin by defining primary magmas, which form through partial melting of mantle or crustal rocks and rise without significant modification. These magmas are the starting point for understanding magma evolution. Parental magmas, derived from primary magmas, act as the initial melts from which more evolved compositions develop through processes like fractional crystallization, assimilation, and magma mixing. Special attention is given to basaltic magmas — the most common primary magmas — as they offer crucial insights into mantle processes and tectonic settings.

We also dive into variation diagrams, which are powerful tools for visualizing chemical trends in evolving magmatic systems. These diagrams, such as Harker plots and AFM ternary diagrams, illustrate how key oxides or element ratios change as magma crystallizes and differentiates. By interpreting these trends, we can distinguish between tholeiitic and calc-alkaline series, track crystallization pathways, and infer the processes driving magma evolution. Understanding these concepts is essential for deciphering the complex history of igneous rocks and linking their chemical signatures to tectonic environments.

This lesson provides a solid framework for interpreting magmatic processes and sets the stage for more advanced discussions on phase equilibria, mineral stability, and magma genesis in various geological contexts.