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High-Resolution Igneous Stratigraphy of On- and Off-Axis Sills at a Nascent Spreading Center, Guaymas Basin, Gulf of California
Abstract
Guaymas Basin in the Gulf of California is a young spreading center with complex magmatic sill-sediment interactions, giving rise to interesting and complex chemical stratigraphy. X-ray fluorescence core scanning is employed here as a semiquantitative method of elemental analysis to shed light on magma differentiation and evolution using petrogenetically significant elements. An important aspect of this work is to demonstrate the successful application of elemental ratios to show compositional change with depth of sill, forming when magma is emplaced in wet sediments. Most significant are crystallization and alteration of minerals, leading to variation in maficity and trace element content.
The results on the igneous rock scans of off- and on-axis sills drilled by International Ocean Discovery Program (IODP) Expedition 385 and Deep-Sea Drilling Project (DSDP) Leg 64 show the complexity of the magma-sediment interaction in that region. The variations in elemental peak area ratios illustrate changes in magmatic composition, pointing to the presence of distinct magma batches that intruded over time across Guaymas Basin to form a system of sills with varying levels of magmatic evolution, particularly at an intricate off-axis hydrothermal mound structure called Ringvent (Sites U1547 and U1548) that reveals a stack of distinct intrusion bodies. They likely indicate two distinct generations of magmatic pulses. Further investigations of all IODP and DSDP sites that contain mafic hypabyssal rocks in the Guaymas Basin provided deeper insights into not only the geological interactions between wet sediment and sills but also the magmatic off- and on-axis architecture at an actively rifting sedimented spreading center, which is going to aid in further understanding of the magmatic structure by way of propagation mode and tectonic setting of this region.
Subject
IODPExpedition 385
Leg 64
Guaymas Basin
Mid-Ocean ridge
XRF-CS
Igneous rocks
Sills
Crystal fractionation
Magma groups
Magma generations
Magma evolution
Magma genesis
Collections
Citation
Yeon, Jesse Jehe (2023). High-Resolution Igneous Stratigraphy of On- and Off-Axis Sills at a Nascent Spreading Center, Guaymas Basin, Gulf of California. Master's thesis, Texas A&M University. Available electronically from https : / /hdl .handle .net /1969 .1 /203056.