DSpace Collection:

Mineralogical and isotopic constraints on early, high-temperature events and reservoirs recorded in the interior of a Type B Ca-Al-rich inclusion from the reduced CV3 chondrite Vigarano

Tue, 01 Jul 2025 00:00:00 GMT

Title: Mineralogical and isotopic constraints on early, high-temperature events and reservoirs recorded in the interior of a Type B Ca-Al-rich inclusion from the reduced CV3 chondrite Vigarano Authors: Han Jangmi; Park, Changkun; Liu Ming-Chang; Matsuda Nozomi; Simon Justin I.; Keller Lindsay P. Abstract: A coordinated mineralogical and oxygen and Al-Mg isotopic study of a Type B Ca-Al-rich inclusion (CAI) from the reduced CV3 chondrite Vigarano was carried out using electron microprobe analysis, transmission electron microscopy, and secondary ion mass spectrometry. This CAI, a once molten igneous object, shows heterogeneous oxygen isotopic compositions among its constituent mineral phases. Spinel is uniformly 16O-rich with Q17O <-23 %o. The Q17O values of Al,Ti-diopside in the CAI core range from-11 %o to-18 %o, which are positively correlated with its TiO2 contents, whereas diopside in the Wark-Lovering (WL) rim is 16O-rich with Q17O =-23 %o. Melilite in the CAI mantle shows Q17O values <-10 %o only when & Aring;k<15 but becomes more 16O-poor (Q17O =-3 %o to-9 %o) when & Aring;k>15. These correlated chemical and oxygen isotopic variations were likely established during crystallization of melilite and Al,Ti-diopside from a partial melt, while spinel preserves the original 16O-rich composition of the CAI precursor. We infer that a partial melt was isotopically evolving from 16O-rich to 16O-poor during melilite crystallization, then back to 16O-rich during Al,Ti-diopside crystallization via exchange with different gas reservoirs of 16O-poor and 16O-rich compositions during heating event(s). Our Al-Mg isotopic measurements of the CAI core and mantle define a single isochron with an inferred initial 26Al/27Al ratio of (4.93 f 0.18) x 10-5, indistinguishable from that of the WL rim. This indicates that multiple high-temperature events and oxygen isotope exchange with isotopically distinct gas reservoirs occurred rapidly during the CAI formation.

Upper mantle scale enrichment of Cenozoic intraplate magmatism in Northeast Asia: He-Sr-Nd-Pb-O isotope geochemistry of the basalts around the Korean peninsula

Wed, 01 Jan 2025 00:00:00 GMT

Title: Upper mantle scale enrichment of Cenozoic intraplate magmatism in Northeast Asia: He-Sr-Nd-Pb-O isotope geochemistry of the basalts around the Korean peninsula Authors: Kim D.; Lee H.; Lee, Mi Jung; Park, Changkun; Rizzo A.L. Abstract: The Earth's mantle is considered to be geochemically heterogeneous, which is reflected by the diverse compositions of oceanic island basalts (OIB). The mantle enrichment resulting in this is primarily attributed to the influx of recycled crustal materials into the mantle through subduction. Additionally, the sub-continental lithospheric mantle (SCLM) complicates the elucidation of mantle heterogeneity. From this perspective, Northeast Asia, where the Pacific stagnant slab in the mantle transition zone and the SCLM distribution are presented, is the suitable site for examining the upper mantle scale enrichment. Here we report He-Sr-Nd-Pb-O isotope compositions of Cenozoic basalts found around the Korean Peninsula to illustrate the source lithology and components that caused mantle heterogeneity. Our measured helium isotope ratios ranging from 5.7 to 7.3 Ra (3He/4He ratio of air, Ra = 1.39 x 10-6) are mostly within the SCLM range (6.1 ± 0.9 Ra) but lower than the mid-ocean ridge basalt range (MORB; 8 ± 1 Ra). The Sr-Nd-Pb isotope compositions of the basalts generally display a mixture of depleted MORB mantle (DMM), enriched mantle 1 (EM1), and enriched mantle 2 (EM2) components. In addition, the basalts have δ18Oolivine (vs. V-SMOW) values ranging from 4.7 to 5.7 ‰ that deviate from the DMM range (δ18Oolivine = 5.1 ± 0.2 ‰). Our isotopic analysis results highlight the role of a pyroxenite source in the metasomatized SCLM in the genesis of basalts, and the low 3He/4He ratios of the basalts indicates a significant contribution of SCLM. Moreover, the delaminated cratonic SCLM and asthenosphere-lithosphere interaction are scenarios for the low 3He/4He ratios. Therefore, we propose that mixing of DMM (high 3He/4He ratio; 7 to 9 Ra) and the metasomatized SCLM (low 3He/4He ratio; 5 to 7 Ra) allowed enrichment within the upper mantle scale for the Cenozoic intraplate magmatism in Northeast Asia. ⓒ 2024 International Association for Gondwana Research

Sedimentary protolith and high-P metamorphism of oxidized manganiferous quartzite from the Lanterman Range, northern Victoria Land, Antarctica

Fri, 01 Mar 2024 00:00:00 GMT

Title: Sedimentary protolith and high-P metamorphism of oxidized manganiferous quartzite from the Lanterman Range, northern Victoria Land, Antarctica Authors: Kim, Taehwan; Kim Yoonsup; Tumiati Simone; Kim, Daeyeong; Yi Keewook; Lee, Mi Jung Abstract: We investigated the mineral assemblage, mineral and bulk-rock chemistry, and zircon U-Pb age of a manganiferous quartzite layer in the Lanterman Range, northern Victoria Land, Antarctica. The mineral assemblage consists primarily of phengite and quartz, along with spessartine-rich garnet, Mn3+ and rare earth element-yttrium (REY)-zoned epidote-group minerals, and titanohematite. Mineral inclusions such as tephroite, rutile and pyrophanite are hosted in porphyroblasts of the latter three minerals and suggest prograde blueschist-facies to low-T eclogite-facies metamorphism (M-1). Epidote-group minerals commonly exhibit multiple growth zones of piemontite and/or epidote (M-1), REY-rich piemontite (M-2), REY-rich epidote (M-3), and epidote (M-4) from core to rim. Pseudobinary fO(2)-X diagrams at constant P-T support the stability of an epidote-group mineral-bearing assemblage under highly oxidized conditions during prograde M-2 to peak M-3 metamorphism. In marked contrast, tephroite-bearing assemblages (M-1) are limited to relatively reduced environments and Mn-rich, silica-deficient bulk-rock compositions. Mn nodules have such characteristics, and the contribution of this hydrogenous component is inferred from bulk-rock chemical features such as a strong positive Ce anomaly. The major-element composition of the manganiferous quartzite suggests a protolith primarily consisting of a mixture of chert and pelagic clay. The presence of rare detrital zircons supports terrigenous input from a craton and constrains the maximum time of deposition to be ca. 546 Ma. The lack of arc-derived detrital zircons in the quartzite and the predominance of siliciclastic metasedimentary rocks among the surrounding rocks suggest that the deep-sea protolith was most likely deposited in an arc/back-arc setting at a continental margin. High-P metamorphism associated with terrane accretion during the Ross orogeny took place in the middle Cambrian (ca. 506 Ma), broadly coeval with the metamorphic peak recorded in the associated high-P rocks such as mafic eclogites. Finally, it is noteworthy that the high-P manganiferous quartzite was amenable to exhumation because the paleo-position of the protolith was likely distal from the leading edge of the downgoing slab.

Virtual taphonomy of trilobite heads: understanding compressive deformation using 3D modeling and rigid body simulation

Mon, 01 Jan 2024 00:00:00 GMT

Title: Virtual taphonomy of trilobite heads: understanding compressive deformation using 3D modeling and rigid body simulation Authors: Jung, Jikhan; Park, Tae-Yoon S.; Hughes Nigel C. Abstract: Shape deformation during fossilization can prevent accurate reconstruction of an organism's form during life, hampering areas of paleontology ranging from functional morphology to systematics. Retrodeformation attempts to restore the original shape of deformed fossil specimens and requires an adequate knowledge of the deformation process. Although tectonic processes and retrodeformation are relatively well understood, research on quantifying the effect of compressive deformation on fossil morphology is scant. Here we investigate the factors that can cause changes in the shape of fossil specimens during compressive deformation. Three-dimensional (3D) models of trilobite cranidia/cephala are subjected to simulated deposition and compaction using rigid body simulation and scaling features of the open-source 3D software Blender. The variation in pitch and roll angle is lowest on flat surfaces, intermediate on tilted surfaces, and highest on irregular surfaces. These trends are reflected in the morphological differences captured by principal component scores in geometric morphometric analyses using landmarks. In addition, the different shapes of trilobite cranidia/cephala according to their systematic affinity influence the degree of angular variation, which in turn affects their posture-normal or inverted. Inverted cranidia/cephala show greater morphological variability than those with normal postures.