Do you think that you would be likely to find a broad region (hundreds of kilometers across and hundreds of kilometers long) in which the outcrops consist of highgrade hornfels? Why or why not? (Hint: Think about the causes of metamorphism and the conditions under which a hornfels forms.) (B, E)

High-grade hornfels are metamorphic rocks that are produced through the process of metamorphism, specifically due to contact metamorphism. Contact metamorphism occurs when a pre-existing rock (the parent rock) is subjected to high temperatures from an intrusive igneous body (such as a magma chamber or a pluton). The heat from this intrusive body causes the minerals in the parent rock to recrystallize, resulting in the formation of a hornfels.

The spatial distribution and size of hornfels formations depend on several factors, such as: 1. The size and shape of the intrusive igneous body: A larger intrusive body will affect a broader area and potentially create larger regions of hornfels. 2. The temperature gradient around the intrusive body: Higher temperature gradients will produce a more pronounced effect on the metamorphism and contribute to the formation of high-grade hornfels, which require high temperatures. 3. The thickness and composition of the parent rock: Thicker layers of the susceptible host rock may promote the formation of a larger region of hornfels. 4. The extent of erosion and deformation processes: Both erosional and tectonic processes can expose hornfels outcrops at the surface over time.

Considering the factors mentioned in Step 2, it is improbable to find a broad region (hundreds of kilometers across and long) consisting of high-grade hornfels outcrops due to the following reasons: 1. Intrusive igneous bodies are typically not large enough to affect such a large area. 2. The temperature gradient and the contact metamorphic aureole (the zone of metamorphism surrounding an intrusive body) are limited in extent. 3. The conditions required for the formation of high-grade hornfels are relatively extreme compared to other metamorphic rocks, making them less common. 4. Erosion and deformation processes can also reduce the exposure of existing hornfels outcrops, making it even more unlikely to find such a large continuous region of high-grade hornfels. In conclusion, while it is possible to find hornfels outcrops, it is highly unlikely to find a broad region as described in the exercise, primarily due to the nature of the processes that form high-grade hornfels and the limited extent of their formation conditions.