Compositional Data Analysis (CoDA) of Clinopyroxene From Abyssal Peridotites

Abstract We analyze a large database of abyssal peridotite clinopyroxene compositions using log‐ratio transformation, principal component analysis (PCA) and k‐means clustering, to better understand clinopyroxene compositional systematics in abyssal peridotites. We combine this analysis with open‐system melting models to investigate the potential sources of compositional variation. PCA shows that 84% of the variation in clinopyroxene compositions can be represented using only 2‐dimensional information. We use k‐means clustering to classify clinopyroxene compositions into four clusters. Clusters 1–3, representing 85% of the data, show progressive depletions in LREE/HREE, and are associated with decreases in Na2O in clinopyroxene, and general increases in Cr# of spinel. We interpret peridotites with clinopyroxene compositions from clusters 1–3 to represent residues of partial melt extraction. The degree of melt extraction increases from cluster 1 to 3, and exerts a primary control on compositional variations. The presence or absence of garnet‐field melting prior to spinel‐field melting and the retained melt fraction during partial melting exert secondary controls on clinopyroxene compositions. Cluster 4 clinopyroxenes, representing show less fractionated LREE/HREE with low‐HREE abundances, elevated Sr, and depleted signatures in their host peridotites. Clinopyroxene compositions in cluster 4 cannot be modeled by melt depletion alone. Instead, they are only reconstructed in our models where melt‐rock interaction, suggesting that peridotites with cluster 4 clinopyroxenes have experienced both of these processes. Clusters 1–4 are observed in most ridges, reflecting compositional heterogeneity on each ridge. This variability reflects variations in the degree of partial melting, amount of garnet‐field melting, retained melt fractions, and melt‐rock interaction

Qualifying and Quantifying Interestingness in Dramatic Situations

Dramatic situations have long been studied in Drama Studies since they characterize tension and interestingness in a plot. In the field of Interactive Digital Storytelling (IDS), integrating knowledge about dramatic situations is of great relevance in order to design improved systems that dynamically generate more narratively-relevant events. However, current approaches to dramatic situations are descriptive and not directly applicable to the field of IDS. We introduce a computational model that fills that gap by both describing dramatic situations visually and providing a quantitative measure for the interestingness of a plot. Using a corpus of 20 Aesop's fables, we compared the calculations resulting of the model with the assessments provided by 101 participants. Results suggest that our model works appropriately at least for stories characterized by a strong plot structure rather than their semantic content

Tight bounds on missing late veneer in early Archean peridotite from triple oxygen isotopes

Oxygen isotopes provide a unique possibility to study Earth's late accretion phase from a lithophile element perspective, because most carbonaceous chondrites - meteorites that likely resemble the composition of the terrestrial late veneer - have markedly different Delta O-'17 values than the silicate Earth. Ultramafic rocks in the early Archean assemblage of southwest Greenland have not incorporated the full amount of late accreted materials, and therefore possibly record the Delta O-'17 of the mantle before late accretion. We measured O-17/O-16 and O-18/O-16 ratios of olivine from these ultramafic rocks and compared them with olivine from post-Archean mantle petidolite. A missing late veneer component was not resolved. The missing component from the early Archean mantle is therefore restricted to <= 0.12 % of Earth's mass (M-circle plus) for most carbonaceous chondrite-like materials, unless the missing component resembles CI chondrites - the only car- bonaceous chondrites with Delta O-'17 values similar to those of the silicate Earth. If the early Archean mantle had incorporated 60 % late veneer, the overall late accreted mass would be restricted to <= 0.3% M-circle plus for most types of carbonaceous chondrites, with a more massive late veneer only possible for CI-like chondrites