Zusammenfassung
Die chemische Veränderung der oberen ozeanischen Kruste durch Gestein/Meerwasser-Interaktionen produziert verschiedene und unterscheidbare Alterationszonen die von der Krustentiefe abhängig sind. Diese Zonierung zeigt weltweit vergleichbare Muster.
Das oberste Basement wird von einer niedrig temperierten oxidativen Meerwasseralteration beeinflußt. Mit zunehmender Krustentiefe steigen die Reaktionstemperaturen an, die Redox- und pH-Werte werden kleiner, d.h. nichtoxidative Alterationsvorgänge dominieren. Unterhalb dieser Zonen wird die ozeanische Kruste überwiegend von reduzierenden und sauren Hydrothermallösungen alteriert.
Im Verlauf der Seewasser/Basalt-Reaktionen werden die Gesteine mineralogisch und chemisch verändert, indem verschiedene Elemente aus den Basalten herausgelöst und wiederum andere aufgenommen werden. Diese Vorgänge haben auch für die Zusammensetzung des Meerwassers drastische Konsequenzen.
Mit Hilfe publizierter aber vor allem mit eigenen Daten werden die mineralogischen und geochemischen Charakteristika der unterschiedlichen Alterationsprozesse zusammengefaßt dargestellt.
Abstract
The alteration of the upper oceanic crust through sea water-basement rock interaction produces different and distinct alteration zones with increasing depth. The zonation generally shows a consistent worldwide pattern.
The uppermost basement is influenced by oxidative sea water-basalt alteration at low temperatures and high water/rock ratios. With increasing crustal depth or even in a single pillow the temperatures rise, the water/rock ratios become lower, the redox and pH values normally decrease, and the oxidative zone is followed by a non-oxidative one. Below these zones the basement has suffered high-temperature alteration under reducing and acidic conditions.
This results in chemical modifications of the rocks by the addition or leaching of certain elements, and has also consequences for the composition of sea water.
From our own data and data presently available in the literature I summarize the mineralogical and geochemical characteristica of sea water alteration processes affecting the oceanic crust.
Résumé
L'altération de la partie supérieure de la croûte océanique sous l'action de l'eau de mer engendre plusieurs zones distinctes qui se succèdent de haut en bas. Ce zonage présente d'ordinaire une extension mondiale.
La partie supérieure de la croûte est affectée d'une altération oxydante de basse température du basalte. Vers le bas, parfois même au sein d'un même pillow, la température s'élève, la quantité d'eau décroît, le potentiel redox et le pH diminuent, de sorte que la zone d'oxydation est suivie d'une zone non oxydante. En-dessous de ces deux zones, les roches ont subi une altération de haute température dans des conditions acides et réductrices.
Il en résulte des changements de la composition chimique des roches par apport ou par lessivage de certains élements, ainsi qu'une modification de la composition de l'eau de mer.
A partir des données de la littérature et surtout de mes propres observations, je présente une synthèse des caractères minéralogiques et géochimiques des divers processus de l'altération sous-marine.
Краткое содержание
Химические изменени я верхней океаническ ой коры в результате взаимод ействия породы и морс кой воды приводят к появлению в ней различных зон, за висящих от глубины их залеган ия. Такая зональность имеет большое распростран ение на Земном шаре. По д воздействием морской воды верхние горизонты фундамент а окисляются при низко й температуре. С глуби ной залегания горизонто в коры возрастает и те мпература реакции окисления, а р едокспотенциал и pH понижаются, т.е. начина ют доминировать проц ессы, протекающие без дост упа кислорода. В этой з оне океаническая кора изменяется под в лиянием восстановит ельных и кислых гидротермал ьных растворов.
В процессе реакций ме жду морской водой и ба зальтами изменяется, как минер алогический, так и хим ический состав пород, т. к. одни элементы вымываются из базальтов, а другие абсорбируются ими. Эт и процессы влияют на химический состав морской воды.
На основании ранне из вестных и собственны х данных составили минералог ические и геохимичес кие характеристики разл ичных процессов, прои сходящих в морской воде.
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Erzinger, J. Chemical alteration of the oceanic crust. Geol Rundsch 78, 731–740 (1989). https://doi.org/10.1007/BF01829318
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DOI: https://doi.org/10.1007/BF01829318