Parce que c’était lui; parce que c’était moi: Sharing Baudelaire’s music

My first meeting with Baudelaire was through a Flammarion paperback edition of Les Fleurs du mal. Baudelaire was a ‘set author’ on the first-year syllabus of the French undergraduate degree programme I was embarking on. I had never encountered the poet’s work before, though I had read some Hugo and Verlaine. At first, I hardly knew what to make of Baudelaire’s writing. I found myself having to look up a lot of words in the dictionary – le chemin bourbeux, le feston et l’ourlet, un grand reposoir, un siècle vaurien – and started to build a picture of a poetic world that was strangely enticing. I still own that same paperback, which is filled with pencil scribbles, underlining ideas and concepts that inspired or confused, annotating unfamiliar meanings and connotations, and sketching out links between poems

Archaean plate tectonics revisited 2. Paleo-sea level changes, continental area, oceanic heat loss and the area-age distribution of the ocean basins

In a previous paper, we derived plate tectonic models for continental accretion from the early Archaean (3800 m.y. B.P.) until the present. The models are dependent upon the number of continental masses, the seafloor creation rate and the continental surface area. The models can be tested by examining their predictions for three key geological indicators: sea level changes, stable isotopic evolution (e.g., continental surface area), and oceanic heat loss. Models of paleo-sea level changes produced by the accretion of the continents reproduce the following features of earth history: (1) greater continental emergence (lower sea level) during the Archaean than the Proterozoic; (2) maximum continental emergence about 3000 m.y. B.P.; and (3) maximum continental submergence (high sea level) from 30 to 125 m.y. B.P. The high sea level stand between 380–525 m.y. B.P. is only weakly reproduced, probably due to the simplified nature of the model. Changes in the number of continental masses can result in tectonic erosion or accretion of the continents, with resulting changes in sea level. The two major transgressions in the Phanerozoic, although still requiring some increase in the total terrestrial heat loss, can be sucessfully explained by a combination of increases in continental surface area and in seafloor creation rate. Changes in the total heat loss of the ocean basins predicted by our plate tectonic models closely parallel the changes in terrestrial heat production predicted by Wasserburg et al. (1964). This result is consistent with thermal history models which assume whole mantle convection. The history of changes in continental surface area predicted by our best continental accretion models lies within the ranges of estimated continental surface area derived from independent geochemical models of isotope evolution

The case for accretion of the tectosphere by buoyant subduction

This paper tests three hypotheses for the origin of the tectosphere. Continental collision cannot explain the low metamorphic grade of crust that predates the tectosphere. Halfspace cooling and buoyant underlating can both fit the diamond age data, although underplating by buoyant subduction is the favored model. Thermal models provide a further test. If half space cooling formed the tectosphere, diamonds from 150km depth will be at least 200 m.y. younger than diamonds from 190km. If buoyant subduction formed the tectosphere, diamonds from 150km depth will be the same age or older than diamonds from 190km

A statistical correlation between Ridge Crest offsets and spreading rate

Ridge crest offsets follow the statistical distribution, N = A exp [−B ln (L/Lo)], where N is the cumulative number of ridge crest offsets with lengths greater than L, Lo is the cutoff length, and A and B are constants. We measured A and B for the slow spreading mid-Atlantic ridge, the intermediate spreading Juan de Fuca Ridge, and the fast spreading east Pacific Rise. The predicted mean distances between offsets greater than 4 km long are 30, 32, and 74 km on the slow, intermediate and fast spreading ridge crests. These distances are in agreement with observations of other workers and calculations of modal ridge lengths

Tectonically controlled origin of three unusual rock suites in the Woodlark Basin

We propose alternative mechanisms for the origin of three unusual rock suites, high-Mg andesites, NaTi basalts, and arclike rocks, that have been dredged from the Woodlark basin, southwest Pacific Ocean. We show that the high-Mg andesites and NaTi basalts are associated with an unusually cool ridge environment. The cooling is due to increased hydrothermal circulation, stimulated by an unusually high crustal permeability. The high permeability is mainly due to cracking of the Woodlark basin lithosphere as it passes over the flexural bulge in front of the subduction zone, although local processes, such as faulting in fracture zones, may also make some contribution. This increased convective cooling affects magma dynamics and chemistry at the ridge crest. The high-Mg andesites occur where the hydrothermal circulation lowers the temperatures in the upper oceanic crust, causing the magma chamber to sit in the mantle rather than in the crust and promoting the interaction of basalt magma with harzburgite. The NaTi basalts are also the indirect result of increased crustal cooling, which causes anomalously low degrees of partial melting of their depleted mantle source. The arclike rocks are caused by interaction with volatiles from lithosphere that was emplaced beneath the edge of the basin less than 6 m.y. ago by a now inactive subduction zone to the north of the currently active one. Simple thermal models indicate that this formerly subducting plate is still cold enough to retain volatiles and to remain seismically active. As the old plate loses volatiles, they rise into the mantle convection cell which feeds the Woodlark basin ridge crest. Because ridge subduction increases the likelihood of ophiolite obduction, these observations and explanations of Woodlark basin tectonics are potentially important for ophiolites

Increased mantle convection during the mid-Cretaceous: A comparative study of mantle potential temperature

Mantle convection patterns of the past are not well known, yet an understanding of changing mantle convection characteristics is fundamental to understanding the evolution of plate tectonics. There are very few ways to examine mantle characteristics of the past. Changes in spreading rate and volcanic activity with time have been used to draw conclusions about historic changes in mantle activity. Mantle temperature has been found to be related to crustal thickness. With this relationship, crustal thicknesses may now yield new conclusions about historic changes in mantle characteristics. We have inferred changes in mantle convection patterns throughout the last 180 m.y. by examining variations in assumed crustal thickness within the Pacific basin. Crustal thicknesses were calculated from residual depth anomalies by assuming that residual depth anomalies are the result of isostatic compensation of variations in crustal thickness. Crustal thickness is determined at the time of crustal formation and is dependent upon the temperature of the mantle source material. Intraplate hot spot volcanism effects on crustal thickness were not ignored. Examination of variations in crustal thickness of crust of different ages can reveal information about changing temperatures of the mantle at the ridge through time. We have learned that mantle temperatures at the ridge during the mid-Cretaceous were more variable than those temperatures at the ridge after the mid-Cretaceous. Furthermore, we have inferred from the data that mantle temperatures at hot spots were higher during the mid-Cretaceous than those at hot spots existing after the mid-Cretaceous. We suggest that mantle convection at the ridge was more rapid during the mid-Cretaceous causing a higher variability of temperatures at the ridge. We also note that this period of increased mantle convection is concurrent with the increased mantle temperatures at hot spots within the Pacific basin

New historical records and relationships among 14C production rates, abundance and color of low latitude auroras and sunspot abundance

Incursions of high-energy particles from space, specifically solar energetic particles and galactic cosmic rays, have significant effects on the Earth, including disruption of the Earth’s magnetic field, generation of electric fields strong enough to damage electronic devices as well as the production of auroras at low-latitudes, within 45° of the magnetic equator. We examine the relationships among 14C production, auroral abundance, auroral color and sunspot abundance using existing data supplemented by a new dataset. The new dataset, based on Chinese and Korean records from A.D. 1100–1700, includes 46 new or revised records of sunspots and 279 records of low-latitude auroras. Low-latitude auroras are predominantly red (66%, 835 events) with lesser proportions of white (20%, 253 events) and black auroras (6%, 67 events). All other auroral colors (green, yellow, multicolored, blue and purple) aggregate to a total of 100 events (8%). Overall, white auroras are more frequent during times of higher 14C production. We use two empirical methods of evaluating the flux of high-energy particles: modeled peaks and lows in 14C production and peaks and lows in the 14C calibration curve. We find that comparison to modeled 14C production gives significant results. White auroras are significantly more abundant (98% probability) at times of high production of 14C. Red auroras are somewhat more abundant (88% probability) at times of low production of 14C. The abundances of black, multicolored, green, yellow, and blue auroras between times of low and high 14C production are not significantly different. Violet/purple auroras are significantly more abundant (98% probability) at times of low 14C production. The positive correlation of violet/purple auroras with times of low14C production rate and the lack of correlation of blue auroras with times of high14C production is surprising, for this portion of the visible spectrum contains strong emission lines and some lines with high energies of excitation. Observations of emissions in the blue to violet part of the spectrum may be biased towards time periods when the atmosphere is exceptionally clear, as these colors are more difficult for the human eye to perceive

Age of oceanic plates at subduction and volatile recycling

The age of the subducting plate as it enters the trench controls the maximum depth of volatile transport by the downgoing plate. As the slab descends and heats up, decarbonation and dehydration reactions cause alteration minerals and sediments to release volatiles. Our calculations show that subducting oceanic plates <11 m.y. old in oceanic arcs and <34 m.y. old in continental arcs heat up so rapidly that no H2O or CO2 can return to the asthenosphere. Instead, these volatiles rise into the over-riding lithospheric plate. CO2 and H2O are released differently during subduction. A thickly-sedimented plate subducting beneath an oceanic arc will return H2O to the asthenosphere only if the subducting plate is older than 11 m.y. and CO2 only if it is older than 25 m.y. If Archaean oceanic lithosphere had a maximum age of 30-50 m.y. and an average age of 10-18 m.y., then the amount of volatile recycling to the asthenosphere could have been much lower than at present, despite a greater total consumption rate

Plume-related mafic volcanism and the deposition of banded iron formation

We have compiled a record of the geochronology of mantle plume activity between 3.8 and 1.6 Ga. Over this time period, the ages of komatiites, and those of global plumes, correlate strongly, at the 99% confidence level, with the ages of banded iron formations (BIFs). The ages of continental plumes correlate more weakly, at an overall 85% confidence level. Using the geochronological records of these events, we can define four periods characterized by mantle superplume activity. Three of these periods are also times of enhanced BIF deposition. The fourth mantle plume period may similarly be coeval with increased BIF accumulation, but the BIF chronostratigraphic resolution is not accurate enough to test this rigorously. Mantle superplume volcanism may promote BIF deposition by increasing the Fe flux to the global oceans through continental weathering and/or through submarine hydrothermal processes. It may also be enhanced by increasing the number of paleotectonic environments appropriate for BIF deposition (particularly plume-induced ocean plateaus, seamounts, and intracratonic rifts) and by promoting global anoxic, Fe-rich hydrothermal plumes in the shallow to intermediate marine water column