Extremely thin crust in the Indian Ocean possibly resulting from Plume–Ridge Interaction

International audienceThe thickness of the crust created at ocean spreading centres depends on the spreading rate and melt production in the mantle. It is ~5–8 km for a crust formed at slow and fast spreading centres and 2–4 km at ultra-slow spreading centres away from hotspots and mantle anomalies. The crust is generally thin at the fracture zones and thick beneath hotspots and large igneous provinces. Here we present results for the crust generated at the fast Wharton spreading centre 55–58 Ma ago using seismic reflection and refraction data. We find that the crust over a 200 km segment of the Wharton Basin is only 3.5–4.5 km thick, the thinnest crust ever observed in a fast spreading environment. A thin crust could be produced by the presence of depleted and/or cold mantle. Numerical simulations and recent laboratory experiments studying the impact of a hot plume under a lithosphere show that a curtain of weak cold downwellings of depleted mantle material is likely to develop around the edges of the hot plume pond. Because of a strongly temperature-dependent viscosity of lithospheric material, the hotter, therefore less viscous, bottom of the lithosphere can be mobilized by an impinging plume. If sampled by a spreading centre, the locally cold and depleted mantle should result in low production of melt. We suggest that the observed thin crust in the Wharton Basin is likely to have been formed by the interaction between the Kerguelen mantle plume and the Wharton spreading centre ~55 Ma ago

Extremely thin crust in the Indian Ocean possibly resulting from Plume–Ridge Interaction

The thickness of the crust created at ocean spreading centres depends on the spreading rate and melt production in the mantle. It is ∼5–8 km for a crust formed at slow and fast spreading centres and 2–4 km at ultra-slow spreading centres away from hotspots and mantle anomalies. The crust is generally thin at the fracture zones and thick beneath hotspots and large igneous provinces. Here we present results for the crust generated at the fast Wharton spreading centre 55–58 Ma ago using seismic reflection and refraction data. We find that the crust over a 200 km segment of the Wharton Basin is only 3.5–4.5 km thick, the thinnest crust ever observed in a fast spreading environment. A thin crust could be produced by the presence of depleted and/or cold mantle. Numerical simulations and recent laboratory experiments studying the impact of a hot plume under a lithosphere show that a curtain of weak cold downwellings of depleted mantle material is likely to develop around the edges of the hot plume pond. Because of a strongly temperature-dependent viscosity of lithospheric material, the hotter, therefore less viscous, bottom of the lithosphere can be mobilized by an impinging plume. If sampled by a spreading centre, the locally cold and depleted mantle should result in low production of melt. We suggest that the observed thin crust in the Wharton Basin is likely to have been formed by the interaction between the Kerguelen mantle plume and the Wharton spreading centre ∼55 Ma ago

Manifestações fonoaudiológicas relatadas por pais de crianças com hipotireoidismo congênito Speech-language pathology manifestations reported by parents of children with congenital hypothyroidism

OBJETIVO: Identificar manifestações fonoaudiológicas apresentadas por crianças com hipotireoidismo congênito e investigar a associação de tais manifestações com a época do diagnóstico e o início do tratamento. MÉTODOS: Responsáveis por 15 crianças diagnosticadas com hipotireoidismo congênito e atendidas pelo Serviço de Referência em Triagem Neonatal dos estados de Rondônia e Acre responderam a um questionário no qual deveriam relatar principalmente queixas fonoaudiológicas. A idade das crianças variou de 2 a 7 anos, 67% de meninos e 33% de meninas. A média de idade da época do diagnóstico foi de 1 mês e 3 dias e o tratamento iniciou-se, em média, com 1 mês e 6 dias. A dosagem do medicamento variou entre 5 mg/dia e 100 mg/dia. RESULTADOS: As queixas relatadas foram: atraso para início da linguagem oral, trocas na fala, fala ininteligível, comportamento agitado e comportamento nervoso. Alguns responsáveis não referiram queixas. Verificou-se que a maioria dos sujeitos apresentou problemas na fala (80%) e a menor parte (7,7%), alteração auditiva. Para aqueles que referiram queixa, a média da época do diagnóstico e do início do tratamento foi mais tardia quando comparado àqueles que não as relataram. CONCLUSÃO: Foram relatadas manifestações fonoaudiológicas, principalmente relacionadas à fala. Além disso, houve associação entre a presença de queixa e problema de fala com a época do diagnóstico e o início do tratamento. Sugere-se a inserção do fonoaudiólogo no acompanhamento das crianças com hipotireoidismo congênito.<br>PURPOSE: To identify speech-language pathology manifestations presented by children with congenital hypothyroidism, and to investigate the association of such manifestations with the time of diagnosis and beginning of treatment. METHODS: Caregivers of 15 children diagnosed with congenital hypothyroidism who attended the Reference Service on Neonatal Screening of the states of Rondônia and Acre answered a questionnaire in which they should report mainly speech-language pathology complaints. Children's age ranged from 2 to 7 years, 67% of boys and 33% of girls. The average age at the time of diagnosis was 1 month and 3 days, and treatment started, in average, at 1 month and 6 days. The dosage of the drug varied from 5 mg/day to 100 mg/day. RESULTS: The complaints reported were: delay in the onset of oral language, speech alterations, unintelligible speech, agitated and nervous behavior. Some caregivers did not report any complaints. It was found that most subjects had problems with speech (80%), and a few had hearing impairment (7.7%). For those who reported complaints, mean time of diagnosis and beginning of treatment was delayed when compared to those who did not report. CONCLUSION: Speech-language pathology manifestations were reported, especially regarding speech. Moreover, there was association between the presence of complaints and speech disorders with the time of diagnosis and beginning of treatment. It is suggested the inclusion of the speech-language pathologist and audiologist in the team monitoring the development of children with congenital hypothyroidism