A red bole zircon record of cryptic silicic volcanism in the Deccan Traps, India

Abstract

Silicic magmas within large igneous provinces (LIPs) are understudied relative to volumetrically dominant mafic magmas despite their prevalence and possible contribution to LIP-induced environmental degradation. In the 66 Ma Deccan LIP (India), evolved magmatism is documented, but its geographic distribution, duration, and significance remain poorly understood. Zircons deposited in weathered Deccan lava flow tops (“red boles”) offer a means of indirectly studying potentially widespread, silicic, explosive volcanism spanning the entire period of flood basalt eruptions. We explored this record through analysis of trace elements and Hf isotopes in zircon crystals previously dated by U–Pb geochronology. Our results show that zircon populations within individual red boles fingerprint distinct volcanic sources that likely developed in an intraplate setting on cratonic Indian lithosphere. However, our red bole zircon geochemical and isotopic characteristics do not match those from previously studied silicic magmatic centers, indicating that they must derive from yet undiscovered or understudied volcanic centers associated with the Deccan LIP.

Methodologies for 176Lu–176Hf Analysis of Zircon Grains from the Moon and Beyond

“…Correction for the decay of 176 Lu into 176 Hf after zircon crystallization is done by combining TIMS high-precision U–Pb crystallization ages and measured Lu/Hf ratios. TIMS U–Pb dating was done at Princeton University using established procedures. , The U–Pb age was calculated for each leachate and trace elements (including Lu/Hf ratio) were analyzed on an aliquot of each solution using a Thermo iCAP single collector quadrupole ICP-MS following the methodology in O’Connor et al Measurements were calibrated using a matrix-matched external calibration solution with Lu, Hf, and other trace elements proportional to those in natural zircon. Instrument drift and data reproducibility were monitored by the measurement of four independent standard solutions: MUNZirc 1–2c, MUNZirc 3–2c, Plesovice, , and an in-house Zr–Hf standard.…”

High-precision U-Pb zircon dating identifies a major magmatic event on the Moon at 4.338 Ga

“…The trace element analyses (TEA) ( 88 ) were performed at Princeton University with methods similar to those applied in O’Connor et al ( 89 ), reproduced here with minimal adjustments. All results are available in data S1.…”

Supplemental Material: Recommendations for the reporting and interpretation of isotope dilution U-Pb geochronological information

“…In addition, for ID-TIMS U-Pb geochronology, minerals are dissolved and U and Pb are isolated from other elements using ion exchange chemistry. Now it is becoming more common to measure the chemical (e.g., rare earth element) or isotopic (e.g., Hf, Sr, and Nd) composition of other elements in the sample by ICP-MS to add another layer of information to help with U-Pb date interpretation (Amelin et al, 1999;O'Connor et al, 2022;Schaltegger et al, 2002;Schoene et al, 2010b). Each of these tools can be used to both formulate and evaluate hypotheses regarding progressive growth of dated minerals and can even be used to argue in favor of protracted crystal growth or Pb-loss as the viable mechanism for creating age dispersion in a sample (Schoene and Baxter, 2017; Schoene Szymanowski et al, 2017;Wotzlaw et al, 2013).…”