Semiconductors exposed to oils in pressure-tolerant electronic systems

The present study indicates that most semiconductor components are fabricated such that they are not affected by operation in a dielectric oil environment. A quantitative estimate of the conditions under which oil-soluble ions will invert semiconductor surfaces and interfere with proper device operation is developed. The results are discussed in terms of pressure-tolerant electronic systems—solid-state components operated immersed in chemically inert dielectric oils when these components are subject to, and experience, ambient hydrostatic pressures of the ocean depths. The feasibility of pressure-tolerant electronic systems is demonstrated.     

Precise U-Pb Zircon Constraints on the Earliest Magmatic History of the Carolina Terrane

The early magmatic and tectonic history of the Carolina terrane and its possible affinities with other Neoproterozoic circum-Atlantic arc terranes have been poorly understood, in large part because of a lack of reliable geochronological data. Precise U-Pb zircon dates for the Virgilina sequence, the oldest exposed part, constrain the timing of the earliest known stage of magmatism in the terrane and of the Virgilina orogeny. A flow-banded rhyolite sampled from a metavolcanic sequence near Chapel Hill, North Carolina, yielded a U-Pb zircon date of 632.9 +2.6/-1.9 Ma. A granitic unit of the Chapel Hill pluton, which intrudes the metavolcanic sequence, yielded a nearly identical U-Pb zircon date of 633 +2/-1.5 Ma, interpreted as its crystallization age. A felsic gneiss and a dacitic tuff from the Hyco Formation yielded U-Pb zircon dates of 619.9 +4.5/-3 Ma and 615.7 +3.7/-1.9 Ma, respectively. Diorite and granite of the Flat River complex have indistinguishable U-Pb upper-intercept dates of 613.9 +1.6/-1.5 Ma and 613.4 +2.8/-2 Ma. The Osmond biotite-granite gneiss, which intruded the Hyco Formation before the Virgilina orogeny, crystallized at 612.4 +5.2/-1.7 Ma. Granite of the Roxboro pluton, an intrusion that postdated the Virgilina orogeny, yielded a U-Pb upper intercept date of 546.5 +3.0/-2.4 Ma, interpreted as the time of its crystallization. These new dates both provide the first reliable estimates of the age of the Virgilina sequence and document that the earliest known stage of magmatism in the Carolina terrane had begun by 633 +2/-1.5 Ma and continued at least until 612.4 +5.2/-1.7 Ma, an interval of approximately 25 m.yr. Timing of the Virgilina orogeny is bracketed between 612.4 +5.2/-1.7 Ma and 586+/-10 Ma (reported age of the upper Uwharrie Formation). The U-Pb systematics of all units studied in the Virgilina sequence are simple and lack any evidence of an older xenocrystic zircon component, which would indicate the presence of a continental-type basement. This observation, together with the juvenile Nd isotopic character of the Virgilina volcanic arc sequence, suggests that the oldest part of the Carolina terrane was built on oceanic crust away from a continental crustal influence.     

Nd isotopic evidence for juvenile crust in the Carolina terrane,southern Appalachians

 Nd isotopic analyses of whole-rock samples from the older portion of the Carolina terrane, one of the largest terranes in the Appalachian orogen, demonstrate that part of this terrane is composed of juvenile, mantle-derived crust. These data suggest that the terrane may not have originally been built upon old, evolved basement material but rather may have been built upon oceanic crust. A recent study by other workers demonstrates a more crustally evolved Nd isotopic signature for younger components of the Carolina terrane. These data may indicate that the terrane interacted with evolved crust at a later time, possibly by amalgamation with a more evolved crustal fragment before final accretion to Laurentia, rather than indicating a primary old basement. A juvenile nature for the older portion of the terrane contrasts with models that suggest it is an evolved crustal fragment that formed in a continental margin setting — a scenario proposed to explain the high proportion of felsic volcanic rocks within the terrane. It is herein suggested that Carolina is a chemically evolved but isotopically juvenile crustal fragment, because it remained in an oceanic setting for an unusually long time. In this regard the Carolina terrane is similar to some of the large accreted terranes in the Canadian Cordillera, such as Wrangellia and Alexander. The presence of juvenile crust in the Carolina terrane documents that at least part of the southern Appalachian orogen is not composed solely of reactivated pre-existing continental crust. The importance of this part of the orogen in terms of the volume of juvenile Phanerozoic crustal material in North America may be larger than previously thought. However, until additional major Appalachian terranes have been isotopically characterized the volume of juvenile crust in the whole orogen remains unknown. The isotopic make-up of a terrane can be an important aspect of terrane analysis as different terranes may have significantly different isotopic compositions, while even widespread pieces of a single terrane should have very similar isotopic characteristics. The Nd isotopic data for the Carolina terrane form the beginning of an isotope database for terranes in the southern Appalachians. Received: 15 June 1994/Accepted: 31 January 1995     

‘They are stealing my island’: Residents’ opinions on foreign investment in the residential tourism industry in Tamarin,Mauritius

The small nation of Mauritius in the Indian Ocean, once a poor sugar plantation island, has successfully diversified and expanded its economy since independence, by attracting foreign investment in manufacturing and modern service industries. Tourism is a major part of the ‘Mauritian Miracle’; in recent years residential tourism—attracting wealthy foreigners to take up semi‐permanent residence—has become a growth industry transforming coastal areas like Tamarin. Based on in‐depth interviews among 17 residents of Tamarin, this paper looks at how local people perceive the changes residential tourism is causing in the local area. It appears that while the majority is positive about economic changes like more jobs and income opportunities, and to some extent about improvements in infrastructure and services, there are growing misgivings about some of the social impacts. Notably, the increasing scarcity of land and rising house prices are making it impossible for growing numbers of local people to afford a place to live, resulting in growing squatter settlements in the area. Such growing social disparities challenge the Mauritian development model and may undermine its stability. These undesirable effects call for careful management of tourism development, incorporation of sustainability standards and attention to the position of major stakeholder groups, such as local residents.     

U-Pb Geochronologic, Nd Isotopic, and Geochemical Evidence for the Correlation of the Chopawamsic and Milton Terranes, Piedmont Zone, Southern Appalachian Orogen

We report U-Pb crystallization ages from four metavolcanic rocks and two granitic gneiss samples as well as whole-rock chemical analyses and Sm-Nd isotopic ratios from 25 metaigneous and metasedimentary rocks from the Chopawamsic and Milton terranes, southern Appalachian Orogen. A metarhyolite sample from the Chopawamsic Formation and a metabasalt sample from the Ta River Formation in the Chopawamsic terrane have indistinguishable U-Pb crystallization ages of 471.4+/-1.3 Ma and 470.0+1.3/-1.5 Ma, respectively. A sample from the Prospect granite that intruded metavolcanic rocks of the Ta River Formation yields a younger U-Pb date of 458.0+/-1 Ma. Metarhyolite and granitic gneiss samples from the northern part of the Milton terrane yield U-Pb dates of 458.5+3.8/-1.0 Ma and 450+/-1.8 Ma, respectively. Metavolcanic and metaplutonic rocks from both terranes span a range in major element composition from basalt to rhyolite. Trace element concentrations in these samples show enrichment in large-ion lithophile elements K, Ba, and Rb and depletion in high field strength elements Ti and Nb, similar to those from island arc volcanic rocks. Initial epsilon(Nd) values and T(DM) ages of the metaigneous and metasedimentary samples range from 0.2 to -7.2 and from 1200 to 1700 Ma for the Chopawamsic terrane and from 3.7 to -7.2 and from 850 to 1650 Ma for the Milton terrane. The crystallization ages for the metavolcanic and metaplutonic samples from both terranes indicate that Ordovician magmatism occurred in both. Similar epsilon(Nd) values from representative samples from both terranes suggest that both were generated from an isotopically similar source. Xenocrystic zircons from metavolcanic rocks in the Chopawamsic terrane have predominately Mesoproterozoic (207)Pb/(206)Pb ages (600-1300 Ma), but a single Archean (2.56 Ga) core was also present. The xenocrystic zircons and the generally negative epsilon(Nd) values indicate that both terranes are composed of isotopically evolved continental crust.