Study on the Link Between Crustal “Bobbing” and Lithospheric Foundering in the Central Andean Plateau

Academic Background

The Andean Plateau is one of the most active orogenic belts on Earth, and its formation and evolution have long been a focus of geologists. Lithospheric foundering is an important mechanism for crustal deformation, basin subsidence, and surface uplift in orogenic systems. However, the details, timing, and specific role of the crust in this process remain poorly quantified. Particularly in the Puna region of the central Andean Plateau, the thinner lithosphere and crust suggest the possibility of lithospheric foundering. The Arizaro Basin, a typical basin in the Puna region, is considered a product of late Miocene lithospheric foundering, but the history of crustal thickness changes has not been fully constrained.

This study aims to reconstruct the history of crustal thickness changes in the Arizaro Basin and its surrounding magmatic source regions using a novel approach—exploiting the geochemistry of detrital zircons from volcanic ashes—thereby revealing the impact of lithospheric foundering on crustal thickness and surface deformation.

Source of the Paper

This paper was co-authored by B. Carrapa, G. Jepson, P.G. DeCelles, and others, with the team hailing from multiple research institutions, including the University of Arizona, University of Oklahoma, University of Bucharest, and University of Massachusetts–Amherst. The paper was published online on October 18, 2024, in the journal Geology, titled Crustal Bobbing in Response to Lithospheric Foundering Recorded by Detrital Proxy Records from the Central Andean Plateau.

Research Process and Results

1. Research Objectives and Methods

The primary objective of this study is to reconstruct the history of crustal thickness changes in the Arizaro Basin and its surrounding regions during the Cenozoic by analyzing detrital zircons from volcanic ashes. To achieve this, the research team employed the following methods:

• Zircon U-Pb Geochronology and Trace Element Analysis: High-resolution laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) was used to determine the ages and geochemical characteristics of zircons.
• Lu/Hf Isotope Analysis: Multi-collector LA-ICP-MS was used to analyze the Lu/Hf isotopic composition of zircons to characterize the magmatic source.
• Crustal Thickness Estimation: Using La/Yb ratios and Eu anomalies from zircons, combined with existing crustal thickness estimation models, the team reconstructed the history of crustal thickness changes in the Arizaro Basin and surrounding areas.

2. Sample Collection and Processing

The research team collected 10 volcanic ash samples and one detrital sample from the Vizcachera and Batín formations in the Arizaro Basin. These samples ranged in age from approximately 36 million years (Ma) to 11 Ma. Through analysis of zircons from these samples, the team obtained extensive U-Pb ages, trace element data, and Lu/Hf isotope data.

3. Data Analysis and Results

• History of Crustal Thickness Changes: The results show that the magmatic source region of the Arizaro Basin had a crustal thickness of about 53 km at around 36 Ma, indicating significant crustal thickening during the early Cenozoic. Between approximately 20 Ma and 13 Ma, the crust thickened further, followed by thinning after 13 Ma. This change is consistent with the formation and subsequent removal of a crustal root due to lithospheric foundering.
• Characteristics of the Magmatic Source: Lu/Hf isotope data show significant variations in εHf values, indicating contributions from both crustal and mantle sources. This result aligns with the geochemical characteristics of late Miocene volcanic rocks in the Puna region, suggesting a close relationship between magmatic activity and lithospheric foundering.

4. Model Validation and Interpretation

The research team validated their findings through numerical and analog models. The models show that as a lithospheric root forms, the surface subsides due to viscous stresses, followed by isostatic rebound and uplift as the root is removed. This process closely matches the subsidence and uplift history of the Arizaro Basin.

Conclusions and Significance

This study, through geochemical analysis of detrital zircons, quantitatively reconstructs the history of crustal thickness changes in the Arizaro Basin and its surrounding regions for the first time. The results indicate that lithospheric foundering is the primary mechanism driving changes in crustal thickness and surface deformation in this region. This finding not only deepens our understanding of the formation mechanisms of the Andean Plateau but also provides new insights and methods for studying other orogenic belts.

Research Highlights

• Novel Research Method: This study is the first to use the geochemical characteristics of detrital zircons to reconstruct the history of crustal thickness changes, providing a new tool for similar research.
• Significant Scientific Discovery: The study reveals the specific impact of lithospheric foundering on crustal thickness and surface deformation, filling a knowledge gap in the field.
• Broad Application Value: The research is not only significant for understanding the formation mechanisms of the Andean Plateau but also applicable to studies of other orogenic belts, offering broad geological applications.

Additional Valuable Information

The research team also noted that changes in crustal thickness in the Arizaro Basin may be related to local variations in magmatic activity. Future research could further explore the specific relationship between magmatic activity and lithospheric foundering to provide a more comprehensive understanding of orogenic belt evolution.

This study provides important scientific evidence for understanding the formation mechanisms of the Andean Plateau and demonstrates the great potential of detrital zircon geochemical analysis in geological research.