ORCID Profile
0000-0002-0859-7900
Current Organisation
Monash University
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Publisher: Geological Society of London
Date: 13-03-2023
Abstract: Continental arcs are key sites of granitic magmatism, yet details of the origins of these magmas, including the role and contribution of mafic magma, the timing and location of initial zircon formation and how zircon isotopic signatures relate to granite formation, remain as challenges. Here we use U–Pb dating, trace elements and Hf isotopic systematics of zircon in mafic microgranular enclaves (MMEs), from the convergent plate margin Satkatbong diorite (SKD) in Korea to understand lower arc magmatism and zircon production. The host granitic body and MMEs display similar major element evolutionary trends and similar ranges of Sr, Nd and Hf isotopes, implying a cognatic relationship. Zircons show a large variability in ε Hf ( t ) ( c. 6 units) and age ( Ma). We propose that the SKD and MMEs originated from the same, long-lasting, lower crustal mush reservoir, enabling long and variable residence times for zircons. Prolonged zircon ages, combined with the Hf isotope variability within a single pluton (SKD and its MME), indicate that not all zircons were instantaneously crystallized in a rapidly cooling shallow magma chamber but were continuously formed in a long-lasting hot source. A low-melt-fraction mush type reservoir in a deep crustal hot zone provides a viable model for the source setting. Continuous replenishment of mafic magmas acts as the main re-activator of the reservoir, and provide a critical role in spawning zircons that record a long age span, because (1) the magma adds Zr into the reservoir, enabling it to reach zircon saturation and (2) the generated zircon grains are transported upward as antecrysts by flow inside of the reservoir. This means that antecrysts with different ages may mix with each other in the ascending magma body. The significance of this model is that a conclusive time of intrusion cannot be constrained by such zircon ages, as these antecrysts constitute inherited grains.
Publisher: Elsevier BV
Date: 03-2019
Publisher: Mineralogical Society of America
Date: 06-2022
DOI: 10.2138/AM-2022-8045
Abstract: The origin of celadonite still remains enigmatic and fragmentary. Exceptional celadonite mineralization was discovered in the Miocene lacustrine Janggi Basin in the southeastern Korean Peninsula. This Janggi celadonite is a greenish, earthy/vitreous material filling east-west trending fault zones in basaltic flows. The scale of the celadonite body is up to a meter thick and laterally extends ~10 m. These occurrences are markedly in contrast with celadonite as vesicle-filling or mineral-replacing types in the literature. The Janggi celadonite allows exploring the puzzling genesis of celadonite and comparing its characteristics with global cases for a better understanding of celadonite formation. X-ray diffraction and microprobe analyses demonstrate that the Janggi celadonite ranges from ferroceladonite through celadonite to ferroaluminoceladonite and is mixed with opal at a ratio of up to ~3:7. Detailed fieldwork and whole-rock major, trace, and oxygen isotope analyses indicate that celadonite is formed in an open system at ~120 °C by the interaction of hybridized fluid (a mixture of & % magmatic and & % other origins) and basalts during the physicochemical fault brecciation of the host rock. The cations needed for celadonite formation were supplied from the smectitization/zeolitization of rhyolitic mesostasis (for Al and part of K) and pyroxene microlites (for Fe and Mg) in the basaltic breccias during the associated oxidation of micro-nanoparticles by circulating fluids (for most of K). A comparison of the Janggi celadonite with global cases highlights that celadonite genesis is neither limited to the seawater alteration of basalt nor do hosts and reactive fluids control celadonite compositions. A contextualized perspective on celadonite genesis alludes that a potassic alteration of rock that is rich in ferromagnesian components in a shallow crustal environment (& ~200 MPa at & ~450 °C) produces celadonite. Because of the relative availability of the necessary components for celadonite precipitation, our model predicts celadonite mineralization in many volcanic environments, where magmatic fluid and particle size reduction could contribute. These insights emphasize celadonite’s potential applications for tracing geothermal history.
Publisher: Springer Science and Business Media LLC
Date: 08-2022
Publisher: Elsevier BV
Date: 04-2018
Publisher: Geological Society of London
Date: 29-09-2023
Abstract: Different mineral clocks in granite can provide age information reflecting various aspects of rock formation, including cooling or post-emplacement fluid-rock interaction. However, the dating tool chosen can yield inconclusive age information due to differences in closure temperatures and susceptibility to fluid alteration among chronometers. This has led to an inferred superiority of U-Pb in zircon over U-Pb in monazites or Rb-Sr in micas. Here, we investigate age systematics using Rb-Sr biotite grains, U-Pb in monazite and zircons in a Devonian granite from Australia. Single-grain laser ablation ICP-MS/MS biotite analyses are combined with zircon-monazite U-Pb ages and trace element systematics. Textural and trace element evidence combined with age systematics reveals a Rb-Sr closure age of ∼360-330 Ma relative to a putative 364 Ma emplacement age, suggesting hydrothermal alteration of the granite. Trace element systematics and magnetic susceptibility in biotites reflect their partial chemical reset and fluid overprint in the granite. Similar systematics are, however, also observed for zircon and monazite. Our multiple chronometer dating approach, studied with modern laser-ablation methods, highlights the need for detailed investigation of isotope and trace element systematics in single grains and that in idual ages should be used cautiously when dating altered granitoids. Supplementary material at 0.6084/m9.figshare.c.6758747
No related grants have been discovered for Hoseong Lim.