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- Title
Wall Fracturing Versus Mechanical Instability as Competing Intrusion Mechanisms of Dikes: Insights From Laboratory Experiments.
- Authors
Biswas, Uddalak; Mitra, Atin Kumar; Mandal, Nibir
- Abstract
Igneous dike intrusion is a primary crust‐forming process at the Earth's plate boundaries. Understanding its mechanism is thus crucially important in lithospheric studies. Our present article combines experimental and field observations to investigate the problem of dike emplacement from a mechanical perspective. Scaled laboratory experiments were conducted by injecting immiscible liquids into visco‐elastic and visco‐elasto‐plastic host materials at varying volumetric flow rates (VFR = 0.100 to 1.670 ml s−1). Another set of experiments used different injecting liquid–host combinations to set their viscosity ratios (η*) at low (105), moderate (106), and high (109) values. These two lines of experiments allow us to recognize three principal mechanisms of liquid pathways: tensile fracturing of the host, wave instability at the liquid‐host interface, and coupled fracturing‐wave instability process. The three mechanisms give rise to a wide variation in intrusion geometry, ranging from planar structures with elliptical outlines to typical bulbous geometry, with intermediate patterns characterized by in‐plane and off‐plane wavy interfaces with the host. This study uses the experimental data to constrain the VFR conditions that determine the fracturing versus wave instability‐controlled mechanisms. It is also shown from the experiments that η* can significantly influence the evolution of three‐dimensional intrusive geometry. The Chotonagpur Granite Gneiss Complex in eastern India is chosen as a field study area to validate our laboratory findings using a 2D shape analysis of the intrusive boundaries in terms of their fractal dimensions (D) and skewness‐kurtosis estimates. Plain Language Summary: Magmas generated deep inside the Earth flow through solid rock strata both in horizontal and vertical directions. However, how they create passages for their flow is not yet fully understood, and it needs a systematic study of this problem, which is the primary goal of our article. We mechanically reproduced magma flows in rock analog materials under laboratory conditions and studied the mechanisms of passage generation by magma to intrude into the host material. The experimental results show three primary mechanisms: (a) opening mode of host fracturing, (b) wave formation at the liquid–host interface, and (c) fracturing, coupled wave formation at the fracture walls. It is shown that these mechanisms are related to the volumetric magma influx rate and the viscosity ratio of host materials to magma. Each mechanism gives rise to characteristic geometry of magma intrusions, such as straight tabular, lobate geometry, or complex network patterns. To validate the laboratory findings, this study provides field examples from the Chotonagpur Granite Gneiss Complex of Shingbhum Craton, Eastern India. A two‐dimensional shape analysis of intrusion boundaries presented in this article uses a set of geometrical parameters to show their geometry quantitatively as an indicator of the emplacement mechanisms. Key Points: Magmatic intrusions into host rocks can occur by host fracturing, interface instability, or a combination of fracturing and instabilityEach intrusion mechanism gives rise to characteristic geometry of the dike‐host boundaries and the spatial patterns of dikesThe magma influx rate and the host‐to‐magma viscosity ratio are the two crucial factors in controlling the intrusion processes
- Subjects
INDIA; IGNEOUS intrusions; EARTHFLOWS; FRACTAL dimensions; ROCK deformation; MAGMAS; FRACTAL analysis
- Publication
Journal of Geophysical Research. Solid Earth, 2023, Vol 128, Issue 9, p1
- ISSN
2169-9313
- Publication type
Article
- DOI
10.1029/2023JB026921