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Abstract We analyze how interdependencies in financial networks can lead to self-fulfilling insolvencies and multiple possible equilibrium outcomes. Multiplicity arises if a certain type of dependency cycle exists in the network. We show that finding the cheapest bailout policy that prevents self-fulfilling insolvencies is computationally hard, but that the optimal policy has intuitive features in some typical network structures. Leveraging indirect benefits ensures systemic solvency at a cost that never exceeds half of the overall shortfall. In core-periphery networks, it is optimal to bail out peripheral banks first as opposed to core banks. 

Abstract Age-progressive seamount tracks generated by lithospheric motion over a stationary mantle plume have long been used to reconstruct absolute plate motion (APM) models. However, the basis of these models requires the plumes to move significantly slower than the overriding lithosphere. When a plume interacts with a convergent or divergent plate boundary, it is often deflected within the strong local mantle flow fields associated with such regimes. Here, we examined the age progression and geometry of the Samoa hotspot track, focusing on lava flow samples dredged from the deep flanks of seamounts in order to best reconstruct when a given seamount was overlying the mantle plume (i.e., during the shield-building stage). The Samoan seamounts display an apparent local plate velocity of 7.8 cm/yr from 0 to 9 Ma, 11.1 cm/yr from 9 to 14 Ma, and 5.6 cm/yr from 14 to 24 Ma. Current fixed and mobile hotspot Pacific APM models cannot reproduce the geometry of the Samoa seamount track if a long-term fixed hotspot location, currently beneath the active Vailulu’u Seamount, is assumed. Rather, reconstruction of the eruptive locations of the Samoan seamounts using APM models indicates that the surface expression of the plume migrated ~2° northward in the Pliocene. Large-scale mantle flow beneath the Pacific Ocean Basin cannot explain this plume migration. Instead, the best explanation is that toroidal flow fields—generated by westward migration of the Tonga Trench and associated slab rollback—have deflected the conduit northward over the past 2–3 m.y. These observations provide novel constraints on the ways in which plume-trench interactions can alter hotspot track geometries. 

Abstract We show that the entry of formal financial institutions can have far-reaching and long-lasting impacts on informal lending and social networks more generally. We first study the introduction of microfinance in 75 villages in Karnataka, India, 43 of which were exposed to microfinance. Using difference-in-differences, we show that networks shrank more in exposed villages. Moreover, links between households that were both unlikely to borrow from microfinance were at least as likely to disappear as links involving likely borrowers. We replicate these surprising findings in the context of a randomised controlled trial (RCT) in Hyderabad, where a microfinance institution randomly selected 52 of 104 neighbourhoods to enter first. Four years after all neighbourhoods were treated, households in early-entry neighbourhoods had credit access longer and had larger loans. We again find fewer social relationships between households in these neighbourhoods, even among those ex-ante unlikely to borrow. Because the results suggest global spillovers, atypical in usual models of network formation, we develop a new dynamic model of network formation that emphasizes chance meetings, where efforts to socialize generate a global network-level externality. Finally, we analyse informal borrowing and the sensitivity of consumption to income fluctuations. Households unlikely to take up microcredit suffer the greatest loss of informal borrowing and risk sharing, underscoring the global nature of the externality. 

Major and trace element abundances, including highly siderophile elements, and 187Os and 182W isotopic compositions were determined for ca. 89 Ma mafic and ultramafic rocks from the islands of Gorgona (Colombia) and Curaçao (Dutch Caribbean). The volcanic systems of both islands were likely associated with a mantle plume that generated the Caribbean Large Igneous Provence. The major and lithophile trace element characteristics of the rocks examined are consistent with the results of prior studies, and indicate derivation from both a chemically highly-depleted mantle component, and an enriched, or less highly-depleted mantle component. Highly siderophile element abundances for these rocks are generally similar to rocks with comparable MgO globally, indicating that the major source components were not substantially enriched or depleted in these elements. Rhenium-Os isotopic systematics of most rocks of both islands indicate derivation from a mantle source with an initial 187Os/188Os ratio between that of the contemporaneous average depleted mid-ocean ridge mantle and bulk silicate Earth. The composition may reflect either an average lower mantle signature, or global-scale Os isotopic heterogeneity in the upper mantle. Some of the basalts, as well as two of the komatiites, are characterized by calculated initial 187Os/188Os ratios 10-15% higher than the chondritic reference. These more radiogenic Os isotopic compositions do not correlate with major or trace element systematics, and indicate a mantle source component that was most likely produced by either sulfide metasomatism or ancient Re/Os fractionation. Tungsten-182 isotopic compositions measured for rocks from both islands are characterized by variable 182W values ranging from modern bulk silicate Earth-like to strongly negative values. The 182W values do not correlate with major/trace element abundances or initial 187Os/188Os compositions. As with some modern ocean island basalt systems, however, the lowest 182W value (-53) measured, for a Gorgona olivine gabbro, corresponds with the highest 3He/4He previously measured from the suite (15.8 R/RA). Given the lack of correlation with other chemical/isotopic compositions, the mantle component characterized by negative 182W and possibly high 3He/4He is most parsimoniously explained to have formed as a result of isotopic equilibration between the mantle and core at the core-mantle boundary.