Biogenic Sediments and Their Paleoceanographic Implication in West Pacific Warm Pool during the Pleistocene

Primary productivity has played an important role in the global carbon cycle during the Quaternary. The average Corg/N ratio was 7.0 from the core MD97-2140 in the West Pacific Warm Pool (WPWP) over the last 1 755 ka, which indicates a main contribution of marine organic carbon to the organic matter in the sediments. Large fluctuations in mass accumulation rates (MARs) of biogenics and lithogenics from this core since the marine isotope stage (MIS) 6 reflected the moderate variability in oceanographic condi...     

Chemistry and genesis of garnets in metamorphic rocks

250 analyses of garnets in metamorphic pelitic, arkosic, and pyroclastic rocks from the Stavanger area have been made by means of a microprobe (ARL-EMX). The relations between chemistry and metamorphic grade are discussed. The dependence of the Mn content upon temperature, pressure, chemistry of the parent rocks and oxygen fugacity is a very sophisticated one.It is shown that the Mn content of the garnets depends on the oxygen fugacity of the system and that the oxygen fugacity is strongly linked to the behaviour of graphite during increasing metamorphism.Examples described by Miyashiro (1953) and Engel and Engel (1960) are in agreement with the model presented here.Some observations show an influence of primary sedimentary enrichments of manganese upon the first occurrence of garnets in the course of metamorphism.     

Chemical composition and stable carbon isotopic ratios of crude oils from Southern Germany

Thirty crude oils were sampled in the South German Molasse Basin. The crude oils were chemically separated into five component groups and their stable carbon isotopic ratios were determined by mass spectrometry. A distinct differentiation of four regionally connected groups can be inferred from the results of the δ¹³C values and chemical analyses. This grouping is in accordance with the present geologic information on the origin of crude oils in the Molasse Basin.The chemistry of crude oils seems to have been influenced by secondary processes in the eastern part of the Molasse Basin.     

A reconnaissance geochemical study of La Primavera geothermal area, Jalisco, Mexico

The Sierra La Primavera, a late Pleistocene rhyolitic caldera complex in Jalisco, México, contains fumaroles and large-discharge 65°C hot springs that are associated with faults related to caldera collapse and to later magma insurgence. The nearly-neutral, sodium bicarbonate, hot springs occur at low elevations at the margins of the complex, whereas the water-rich fumaroles are high and central.The Comisión Federal de Electricidad de México (CFE) has recently drilled two deep holes at the center of the Sierra (PR-1 and Pr-2) and one deep hole at the western margin. Temperatures as high as 285°C were encountered at 1160 m in PR-1, which produced fluids with 820 to 865 mg/kg chloride after flashing to one atmosphere. Nearby, PR-2 encountered temperatures to 307°C at 2000 m and yielded fluids with chloride contents fluctuating between 1100 and 1560 mg/kg after flashing. Neither of the high-temperature wells produced steam in commercial quantities. The well at the western margin of the Sierra produced fluids similar to those from the hot springs. The temperature reached a maximum of 100°C near the surface and decreased to 80°C at 2000 m.Various geothermometers (quartz conductive, Na/K, Na-K-Ca, δ¹⁸O(SO₄-H₂O) and D/H (steam-water) all yield temperatures of 170 ± 20°C when applied to the hot spring waters, suggesting that these spring waters flow from a large shallow reservoir at this temperature. Because the hot springs are much less saline than the fluids recovered in PR-1 and PR-2, the mixed fluid in the shallow reservoir can contain no more than 10–20% deep fluid. This requires that most of the heat is transferred by steam. There is probably a thin vapor-dominated zone in the central part of the Sierra, through which steam and gases are transferred to the overlying shallow reservoir. Fluids from this reservoir cool from 170°C to 65°C by conduction during the 5–7 km of lateral flow to the hot springs.     

Gases and water isotopes in a geochemical section across the Larderello,Italy, geothermal field

Steam samples from six wells (Colombaia, Pineta, Larderello 57, Larderello 155, Gabbro 6, and Gabbro 1) in a south to north section across the Larderello geothermal field have been analyzed for inorganic and hydrocarbon gases and for oxygen-18 and deuterium of steam. The wells generally decrease in depth and increase in age toward the south. The steam samples are generally characterized by

1. Total gas contents increasing south to north from 0.003 to 0.05 mole fraction;
2. Constant CO₂ (95±2 percent); near constant H₂S (1.6±0.8), N₂ (1.2±0.8), H₂ (2±1), CH₄ (1.2±1), and no O₂ in the dry gas;
3. Presence of numerous, straight chain and branched C₂ to C₆ hydrocarbons plus benzene in amounts independent of CH₄ contents with highest concentrations in the deeper wells;
4. Oxygen-18 contents of steam increasing south to north from ?5.0‰ to ?0.4‰ with little change in deuterium (?42±2‰).

These observations are interpreted as showing:

1. Decreasing gas contents with amount of production because the proportion of steam boiled from liquid water increases with production;
2. Synthesis of CH₄ from H₂ and CO₂ with CO₂ and H₂ produced by thermal metamorphism and rock-water reactions;
3. Extraction of C₂ to C₆ hydrocarbons from rock organic matter;
4. Either oxygen isotope exchange followed by distillation of steam from the north toward the south (2 plates at ～220°C) or mixture of deeper more-exchange waters from the north with shallow, less-exchanged recharging waters from the south.

     

Die Bimodalität des Vulkanismus und die Herkunft der Magmen

Zusammenfassung Häufigkeitsdiagramme der Explosivitätsindiees der tätigen Vulkane und einiger Komponenten der Magmen (Abb. 1–5) beweisen die Bimodalität des Vulkanismus, die nur durch eine Herkunft der Magmen aus zwei voneinander unabhängigen Quellen (oberer Mantel und Kontinentalkruste) erklärt werden kann.Gegen die Hypothesen, die die Bildung von basisdien Magmen durch Einschmelzung von kristallinen Mantelgesteinen zu erklären versuchen, werden physikalisch und geochemisch begründete Einwände erhoben. Dagegen wird der low velocity layer als teilweise geschmolzene Zone aufgefaßt, aus der die simatischen Magmen stammen. Die sialischen Magmen entstehen dagegen in der Hauptsache durch eine teilweise oder völlige Einschmelzung von Krustenmaterial in Orogenen (Regionalanatexis) und lokal in Kratonen (Kontaktanatexis). Die relativ große Variationsbreite der sialischen Magmen wird durch die Verschiedenheit des Ausgangsmaterials (metamorphe Differentiation), durch Hybridismus und durch Differentiationsprozesse erklärt.Geologische Tatsachen beweisen, daß die sialische Erdkruste schon vor niemals 3 1/2 Milliarden Jahren vorhanden war. Andererseits zeigen die Mohorovii-Diskontinuität und die Bimodalität des Vulkanismus, daß das Sial nicht ein Differentiat des simatischen Mantelmaterials sein kann. Es wird gezeigt, daß weder die Entstehung des Sials noch der Vulkanismus im Rahmen der Planetesimalhypothese erklärt werden können. Im Dilemma zwischen der Emföhrrmg einer unbegründbaren ad hoc Hypothese von sialischen Riesenmeteoriten und der Hypothese einer heliogenen Erde, wird die letztere vorgezogen, da sie eine ungezwungene Erklärung der Entstehung der Sialkruste und der Bimodalität des Vulkanismus ermöglicht.

---

The frequency diagrams of the index of volcanic explosivity and of some chemical components of the magmas (Fig. 1–5) prove the bimodality of volcanism, which can be explained only by admitting two independent sources of magma, the mantle and the crust. On the basis of physical and chemical facts objections are made against the hypotheses which try to explain the formation of basaltic magmas by partial or total melting of crystalline mantle rocks. It is much more probable that these magmas derive from the low velocity layer which is considered to consist of already, at least partially, molten material. The sialic magmas are produced chiefly by melting of crustal material in orogenic belts (regional anatexis) or, occasionally, in cratonic regions (contact anatexis). The relatively wide variation of sialic magmas is explained by different composition of the original material (metamorphic differentiation), by hybridism and by various types of magmatic differentiation.Geological facts demonstrate the sialic crust to have existed already over 3 1/2 b. y. ago. The Moho-discontinuity and the bimodality of volcanism show that the sialic crust cannot be a product of differentiation of the upper mantle material. It is shown that neither the origin of Sial nor the volcanism can be reasonably explained by the hypothesis of planetesimals. Having the choice between the ad hoc hypothesis of the impact of giant meteorites of about sialic composition, capable to create at once a continent, and the old hypothesis of a solar origin of the earth, the author prefers the latter one.

---

Résumé La bimodalité du volcanisme est démontrée par la fréquence des indices d'explosivité des volcans actifs et par celle de certains constituants chimiques des magmas. Cette bimodalité s'explique par l'existence de deux sources de magmas indépendants: le manteau supérieur et la croûte sialique. Pour des raisons physiques et géochimiques, l'auteur s'oppose aux hypothèses qui cherchent à expliquer l'origine des magmas basaltiques par une fusion partielle ou totale de matériel cristallisé du manteau supérieur. Il considère le « low velocity layer » comme au moins partiellement fondu et étant la source des magmas basiques. Par contre les magmas sialiques prennent origine dans l'anatexie régionale (zones orogéniques) ou, localement, dans l'anatexie de contact (zones cratoniques étirées). La variation relativement grande, des magmas sialiques peut être expliquée par la différence des roches préexistantes (differentiation métamorphique) et aussi par l'hybridisme et par des divers processus de différentiation magmatique.Des faits géologiques démontrent que la croûte sialique a existé déjà il y a plus de 3 1/2 milliards d'années. La discontinuité de Mohorovii ainsi que la bimodalité du volcanisme ne peuvent pas être produites par une différentiation quelconque du matériel du manteau supérieur. Ni l'origine du Sial, ni le volcanisme ne peuvent être expliqués raisonnablement dans le cadre classique de l'hypothèse planétésimale. Ayant le choix entre une hypothèse ad hoc qui veut expliquer l'origine des continents par la chute de météorites gigantesques de composition à peu près sialique et l'hypothèse d'une origine solaire de la terre, l'auteur préfère la dernière.

---

. , . .