Geometry and Structural Controls on the Magmatic Emplacement and Geo-spatial Distribution of the San Feliciano Plutonic System, Northern Zacatecas, Mexico: Insights from Integrated Aeromagnetic Modelling and Geological Constraints
By integrating aeromagnetic modeling with geological constraints, this study reconstructs the three-dimensional geometry and structural controls of the Late Cretaceous San Feliciano Plutonic System in Northern Zacatecas, revealing a large, irregularly shaped intrusive body emplaced along a NE–SW trend and subsequently deformed by NW–SE tectonic forces associated with the Mexican Orogen.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer
Deep beneath the earth's surface, where rock is hot and pressure is immense, magma sometimes forces its way upward to cool and solidify into massive underground chambers known as plutons. These hidden giants shape the landscape over millions of years, often remaining invisible until erosion or human excavation reveals them. However, in many parts of the world, these bodies are buried under thick layers of sediment, making them impossible to see from the ground. To find them, scientists turn to the Earth's magnetic field. Just as a compass needle points north, every rock has a unique magnetic signature based on the minerals it contains. By measuring tiny variations in the magnetic field from the air, researchers can map the shape and depth of these buried intrusions without ever digging a hole, effectively seeing through the ground to understand how the planet's crust has moved and changed.
In northern Zacatecas, Mexico, a team of researchers set out to uncover the hidden architecture of the San Feliciano Plutonic System, a large body of rock formed during the Late Cretaceous period. This system is part of a larger volcanic arc created when one tectonic plate slid beneath another, a process that squeezed and folded the Earth's crust. While geologists had seen pieces of this rock system on the surface, the full extent of the underground structure remained a mystery. The researchers wanted to know exactly how big this hidden body was, what shape it took, and how the forces of the Earth's crust had distorted it over time. To solve this, they combined detailed geological maps with high-resolution magnetic data collected by aircraft flying over the region.
The team analyzed the magnetic signals to create a clear picture of the subsurface. They found that the San Feliciano system is not a single, round blob of rock, but a massive, elongated structure stretching approximately 35 kilometers in length and between 12 and 15 kilometers wide. Imagine a long, irregular loaf of bread that has been pushed and twisted; this is the shape of the pluton. The magnetic data revealed that the body has a complex roof with multiple peaks and valleys, rather than a smooth top. Some parts of this roof rise close to the surface, creating the rock outcrops visible today, while other sections remain buried deep underground, hidden beneath layers of sediment. The study suggests the entire structure extends down to a depth of about 10 kilometers, with its center sitting roughly 4 kilometers below the surface.
A key discovery was that the shape of this underground rock body was heavily influenced by the movement of the Earth's crust. The magma originally rose and spread in a northeast-to-southwest direction, following a natural path of least resistance. However, as the rock cooled, powerful tectonic forces pushed from the northwest and southeast, deforming the body and bending its shape. This compression created a distinct break or fault line running through the middle of the system, effectively splitting it into two main sections. The researchers identified this fracture as the Tanquesillos Fault, a structure that acts as a boundary between two large magnetic cores within the pluton. This fault, along with other regional cracks, controlled not only the final shape of the rock but also where the magma was able to rise and where it was blocked.
The study also clarified the relationship between the main pluton and smaller, surrounding rock formations. While the San Feliciano system is the dominant feature, the magnetic maps showed several smaller, isolated bodies nearby. Some of these are likely satellite intrusions connected to the main system, while others belong to a completely different, younger volcanic event. By distinguishing between these different magnetic signatures, the team could separate the ancient, deep-seated pluton from more recent volcanic activity that occurred on the surface. This level of detail helps geologists understand the complex history of the region, showing how a single magmatic event can be reshaped by multiple phases of tectonic stress.
Ultimately, the research provides a three-dimensional model of a hidden geological feature that was previously only partially understood. The findings confirm that the San Feliciano Plutonic System is a vast, deformed structure whose geometry was dictated by the collision of tectonic plates. The work demonstrates how combining magnetic modeling with surface geology can reveal the hidden architecture of the Earth's crust, offering a clear view of how magma moves, settles, and is subsequently warped by the immense forces that shape our planet.
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