Abstract Textural and compositional variations in titanite constrain the roles of magma mixing and hydrothermal alteration in two plutons in central Utah: the Jurassic Notch Peak and the Oligocene Little Cottonwood stocks. In the Notch Peak intrusion, magmatic titanite grains usually have oscillatory zones combined with BSE-bright sector zones, in some cases surrounding simple unzoned cores. These grains are frequently overprinted by hydrothermal titanite with low concentrations of high field strength elements (HFSE). Magmatic titanite has an average δ18O of 6.0‰ and post-magmatic titanite is 6.2‰, as analyzed by SIMS. Average Zr-in-titanite temperatures are also similar, with 718 °C for magmatic and 711 °C for hydrothermal titanite. These observations indicate simple magmatic growth, followed by hydrothermal alteration by magmatic fluids. Titanite in aplite dikes and sills has lower concentrations of all trace elements except F. Many titanite grains in the aplites have late overgrowths of high-Fe titanite. This high-Fe titanite has δ18O of 6‰ and an average Zr-in-titanite temperature of 718 °C and likely precipitated from a last flush of exsolved magmatic water enriched in Cl and Fe. Titanite in the Little Cottonwood stock typically has distinct patchy cores with rounded and embayed ilmenite inclusions. Mafic enclaves have abundant titanite that is similar in texture and δ18O (5.1‰) to titanite in the host (δ18O = 4.9‰), but it has a slightly higher average Zr-in-titanite temperature (731 vs. 717 °C). The patchy cores in the enclaves have the highest average Zr-in-titanite temperature (759 °C) and distinctive REE patterns. The textural and compositional data indicate that a hotter, more reduced, ilmenite-bearing mafic magma mixed into an oxidized felsic magma, destabilizing existing ilmenite and allowing crystallization of titanite. In the granodiorite and in the enclaves, hydrothermal growth of titanite is evidenced by distinct narrow rims as well as anhedral titanite that grew between sheets of chloritized biotite. Secondary hydrothermal titanite typically has lower concentrations of most HFSE, but is relatively enriched in F, Mg, Mo, and U, and it has higher Nb/Ta and lower Th/U ratios. Post-magmatic titanite also has strikingly different REE patterns than magmatic titanite, including the absence of pronounced Eu anomalies and lower REE abundances. These chemical features are controlled by element solubilities in aqueous fluids. In most cases, hydrothermal titanite has δ18O values similar to magmatic titanite, indicating alteration and recrystallization from exsolved magmatic fluids. The involvement of meteoric water with low δ18O is evident locally; individual spots have δ18O as low as 1.7‰ in the Little Cottonwood stock. Titanite compositions and textures provide important insights into the origins of granitic rocks and can be used to distinguish separate batches of magma, gauge the evolution of magmatic rocks, assess mixing processes, and infer compositions of mixing components. Because titanite also forms hydrothermally, it retains hints about the composition, temperature, and oxygen fugacity of the hydrothermal fluids and reveals details about titanite-forming reactions. However, the Al-in-titanite geobarometer does not yield realistic pressures of crystallization and the use of titanite as a geochronometer is compromised by the development of U-rich hydrothermal titanite.
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Molecular tests support the viability of rare earth elements as proxies for fossil biomolecule preservation
The rare earth element (REE) composition of a fossil bone reflects its chemical alteration during diagenesis. Consequently, fossils presenting low REE concentrations and/or REE profiles indicative of simple diffusion, signifying minimal alteration, have been proposed as ideal candidates for paleomolecular investigation. We directly tested this prediction by conducting multiple biomolecular assays on a well-preserved fibula of the dinosaur
- NSF-PAR ID:
- 10193640
- Publisher / Repository:
- Nature Publishing Group
- Date Published:
- Journal Name:
- Scientific Reports
- Volume:
- 10
- Issue:
- 1
- ISSN:
- 2045-2322
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Dreadnoughtus schrani based on observations of osteological correlates and Extant Phylogenetic Bracket comparisons. Recovered fossils ofDreadnoughtus exhibit remarkably well‐preserved, well‐developed, and extensive muscle scars. Furthermore, this taxon is significantly larger bodied than any titanosaurian for which a myological reconstruction has previously been performed, rendering this contribution highly informative for the group. All 20 of the muscles investigated in this study are sufficiently well supported to enable reconstruction of at least one division, including reconstruction of the M. ischiocaudalis for the first time in a sauropod dinosaur. In total, 34 osteological correlates were identified on the pelvic girdle and hind limb remains ofDreadnoughtus , allowing the reconstruction of 14 muscles on the basis of Level I or Level II inferences (i.e., not Level I' or Level II' inferences). Comparisons among titanosaurians suggest widespread myological variation, yet potential phylogenetic and other paleobiologic patterns are often obscured by fragmentary preservation, infrequent myological studies, and lack of consensus on the phylogenetic placement of many taxa. However, a ventrolateral accessory process is present on the preacetabular lobe of the ilium in all of the largest titanosauriforms that preserve this skeletal element, suggesting that the presence of this process (representing the origin of the M. puboischiofemoralis internus part II) may be associated with extreme body size. By identifying such myological patterns among titanosauriforms, we can begin to address specific evolutionary and biomechanical questions related to their skeletal anatomy, how they were capable of leaving wide‐gauge trackways, and resulting locomotor attributes unique to this clade. -
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