Evidence from accreted seamounts for a depleted component in the early Galapagos plume

The existence of an intrinsic depleted component in mantle plumes has previously been proposed for several hotspots in the Pacific, Atlantic, and Indian Oceans. However, formation of these depleted basalts is often associated with unusual tectonomagmatic processes such as plume-ridge interaction or multistage melting at plume initiation, where depleted basalts could reflect entrainment and melting of depleted upper mantle. Late Cretaceous to middle Eocene seamounts that accreted in Costa Rica and are part of the early Galapagos hotspot track provide new insights into the occurrence and nature of intrinsic depleted components. The Paleocene (ca. 62 Ma) seamounts include unusually depleted basalts that erupted on the Farallon plate far from a mid-ocean ridge. These basalts closely resemble Gorgona komatiites in terms of trace element and radiogenic isotope composition, suggesting formation from a similar, refractory mantle source. We suggest that this source may be common to plumes, but is only rarely sampled due to excessive extents of melting required to extract melts from the most refractory parts of a heterogeneous mantle plume

Non-Hawaiian lithostratigraphy of Louisville seamounts and the formation of high-latitude oceanic islands and guyots

Guyots are large seamounts with a flat summit that is generally believed to form due to constructional biogenic and/or erosional processes during the formation of volcanic islands. However, despite their large abundance in the oceans, there are still very few direct constraints on the nature and formation of guyots, in particular those formed at high latitude that lack a thick cap of shallow-marine carbonate rocks. It is largely accepted based on geophysical constraints and surficial observations/sampling that the summit platform of these guyots is shaped by wave abrasion during post-volcanic subsidence of volcanic islands. Here we provide novel constraints on this hypothesis and the summit geology of guyots with a lithostratigraphic analysis of cores from three Louisville seamounts (South Pacific) collected during Expedition 330 of the Integrated Ocean Drilling Program (IODP). Thirteen lithofacies of sedimentary and volcanic deposits are described, which include facies not previously recognized on the top of guyots, and offer a new insight into the formation of high-latitude oceanic islands on a fast-moving plate. Our results reveal that the lithostratigraphy of Louisville seamounts preserves a very consistent record of the formation and drowning of volcanic islands, with from bottom to top: (i) volcaniclastic sequences with abundant lava-fed delta deposits, (ii) submarine to subaerial shield lava flows, (iii) post-volcanic shallow to deeper marine sedimentary rocks lacking thick reef deposits, (iv) post-erosional rejuvenated volcanic rocks, and (v) pelagic sediments. Recognition of erosional boundaries between subaerial lava flows and shallow-marine sedimentary rocks provides novel support for post-volcanic wave planation of guyots. However, the summit geology of Louisville seamounts is dissimilar to that of high-latitude Hawaiian-Emperor guyots that have emplaced in a similar tectonic and environmental setting and that include thicker lava stacks with apparently little lava-fed delta deposits. To explain observed lithostratigraphic discrepancy we propose that Louisville seamounts represent a distinct type of intraplate ocean volcano characterized by formation of a smaller island, with a central shield volcano surrounded by extended shallow-marine shelves formed by lava-fed deltas. In this interpretation the summit platform of Louisville-type guyots results from early (syn-volcanic) subaerial to shallow-marine constructional volcanic processes and marine erosion, enhanced by later (post-volcanic) wave planation. This contrasts with larger Hawaiian edifices that are capped by thicker shield volcanoes, and that develop an extended wave planation surface during post-volcanic subsidence (in the absence of efficient coral growth). The difference between Hawaiian- and Louisville-type volcanic islands and guyots can be explained by contrasted dynamic disequilibrium between magmatic growth, erosion, and subsidence during the island-building stage. Unlike Hawaiian-type volcanoes, Louisville seamounts are characterized by alkaline magmatism that extends from the late seamount to island stages. This supports more limited magmatic growth during the formation of Louisville islands, and we hypothesize that this promotes the formation of ephemeral shallow-marine platforms and extended lava-fed deltas. Hawaiian-type volcanoes and guyots are unusually large in the population of intraplate ocean volcanoes. Louisville-type guyots as defined in this study could therefore represent a very common but yet poorly documented mode of oceanic island formation in the Pacific Ocean and other similar fast-moving plate settings

Non-Hawaiian lithostratigraphy of Louisville seamounts and the formation of high-latitude oceanic islands and guyots

Guyots are large seamounts with a flat summit that is generally believed to form due to constructional biogenic and/or erosional processes during the formation of volcanic islands. However, despite their large abundance in the oceans, there are still very few direct constraints on the nature and formation of guyots, in particular those formed at high latitude that lack a thick cap of shallow-marine carbonate rocks. It is largely accepted based on geophysical constraints and surficial observations/sampling that the summit platform of these guyots is shaped by wave abrasion during post-volcanic subsidence of volcanic islands. Here we provide novel constraints on this hypothesis and the summit geology of guyots with a lithostratigraphic analysis of cores from three Louisville seamounts (South Pacific) collected during Expedition 330 of the Integrated Ocean Drilling Program (IODP). Thirteen lithofacies of sedimentary and volcanic deposits are described, which include facies not previously recognized on the top of guyots, and offer a new insight into the formation of high-latitude oceanic islands on a fast-moving plate. Our results reveal that the lithostratigraphy of Louisville seamounts preserves a very consistent record of the formation and drowning of volcanic islands, with from bottom to top: (i) volcaniclastic sequences with abundant lava-fed delta deposits, (ii) submarine to subaerial shield lava flows, (iii) post-volcanic shallow to deeper marine sedimentary rocks lacking thick reef deposits, (iv) post-erosional rejuvenated volcanic rocks, and (v) pelagic sediments. Recognition of erosional boundaries between subaerial lava flows and shallow-marine sedimentary rocks provides novel support for post-volcanic wave planation of guyots. However, the summit geology of Louisville seamounts is dissimilar to that of high-latitude Hawaiian-Emperor guyots that have emplaced in a similar tectonic and environmental setting and that include thicker lava stacks with apparently little lava-fed delta deposits. To explain observed lithostratigraphic discrepancy we propose that Louisville seamounts represent a distinct type of intraplate ocean volcano characterized by formation of a smaller island, with a central shield volcano surrounded by extended shallow-marine shelves formed by lava-fed deltas. In this interpretation the summit platform of Louisville-type guyots results from early (syn-volcanic) subaerial to shallow-marine constructional volcanic processes and marine erosion, enhanced by later (post-volcanic) wave planation. This contrasts with larger Hawaiian edifices that are capped by thicker shield volcanoes, and that develop an extended wave planation surface during post-volcanic subsidence (in the absence of efficient coral growth). The difference between Hawaiian- and Louisville-type volcanic islands and guyots can be explained by contrasted dynamic disequilibrium between magmatic growth, erosion, and subsidence during the island-building stage. Unlike Hawaiian-type volcanoes, Louisville seamounts are characterized by alkaline magmatism that extends from the late seamount to island stages. This supports more limited magmatic growth during the formation of Louisville islands, and we hypothesize that this promotes the formation of ephemeral shallow-marine platforms and extended lava-fed deltas. Hawaiian-type volcanoes and guyots are unusually large in the population of intraplate ocean volcanoes. Louisville-type guyots as defined in this study could therefore represent a very common but yet poorly documented mode of oceanic island formation in the Pacific Ocean and other similar fast-moving plate settings

Long-term non-erosive nature of the south Costa Rican margin supported by arc-derived sediments accreted in the Osa Mélange

Understanding the erosive and accretionary nature of convergent margins is significant to understand tectonics and the crustal mass balance at subduction zones. The Costa Rican margin is commonly regarded as an archetypal example of an erosive margin, where subduction of sediments and basal removal of the upper plate in the subduction zone have occurred for most of the Cainozoic. This view is supported by structural constraints from 3D seismic reflection data in the outer forearc, as well as periods of forearc subsidence at ODP/DSDP/IODP drill sites. However, determining the origin of the Upper Eocene-Miocene Osa Mélange that is exposed in south Costa Rica only 10–30 km from today's trench offers another opportunity to constrain the long-term erosive, accretionary, and/or non-erosive evolution of the margin. Existing models for formation of the mélange propose that it resulted from (i) accretion of arc-derived trench-fill sediments, (ii) punctual accretion of the clastic apron of an ocean islands system, (iii) local dismemberment of the margin due to tectonic erosion, or (iv) in-situ deformation of a forearc sedimentary cover. To test the validity of these models and provide new constraints on the accretionary and/or erosive nature of the margin we studied the provenance of volcaniclastic material in the Upper Eocene San Pedrillo Unit of the Osa Mélange using geochemical analysis of detrital pyroxenes, amphiboles and igneous rocks. This innovative approach to determine the origin(s) of dismembered sedimentary sequences reveals that the volcaniclastic fraction of the mélange is, without ambiguity, predominantly composed of forearc material that preserves an assemblage of arc basement, proto-arc and arc sequences of the pre-Oligocene Costa Rican margin. This result and previous geological constraints show that the Osa Mélange formed through accretion of arc-derived trench-fill deposits in the Late Eocene to Miocene, with possibly minor tectonic incorporation of intra-oceanic material (ocean floor and seamount sequences). Therefore, consistently with recent seismic observations in south Costa Rica that document a phase of accretion within the past ∼5 m.yr., preservation of arc-derived sediments in the Osa Mélange shows that the margin was predominantly non-erosive over the past ∼35 m.yr. Cycles of subsidence and uplift in the south Costa Rican forearc during this period could represent a tectonic response to episodic subduction of seamounts formed at the Galapagos Hotspot, without causal link to short-term subduction erosion or accretion. Fundamentally, new results from the Osa Mélange show that large (10 km-thick) accretionary complexes can form durably due to local sedimentary recycling of the forearc in seamount collisional settings. The recycled component of the NW Osa Mélange exemplifies that quantifying the extent of local recycling vs net crustal addition through accretion of intra-oceanic sequences or net crustal loss due to tectonic erosion poses a serious challenge to determine the crustal mass balance at subduction zones

Modelling a Secure, Mobile, and Transactional System with CO-OPN

Modelling complex concurrent systems is often difficult and error-prone, in particular when new concepts coming from advanced practical applications are considered. These new application domains include dynamicity, mobility, security, and localization dependent computing. In order to fully model and prototype such systems we propose to use several concepts introduced in our specification language CO-OPN, like context, dynamicity, mobility, subtyping and inheritance. CO-OPN (Concurrent Object Oriented Petri Net) is a formal specification language for modelling distributed systems; it is based on coordinated algebraic Petri nets. This paper focuses on the use of several basic mechanisms of CO-OPN for modelling mobile systems and the generation of corresponding Java code. A significant example of distributors accessible through mobile devices (for example, PDA with Bluetooth) is fully modelled and implemented with our technique