. Collected reprints / Atlantic Oceanographic and Meteorological Laboratories [and] Pacific Oceanographic Laboratories. Oceanography Figure 10. Diagrammatic sketch of a sub-sea-floor hydrothermal con- vection system like that hypothesized to exist at the TAG Hydrothermal Field (drawn from profile F, Fig. 6; vertical exaggeration is about x2). Arrows indicate directions of hydrothermal flow. Slant lines indicate direc- tions of maximum permeability controlled by structural grain, including fractures, faults, and dikes. Hydrothermal deposits are forming adjacent to the rift valley,
. Collected reprints / Atlantic Oceanographic and Meteorological Laboratories [and] Pacific Oceanographic Laboratories. Oceanography Figure 10. Diagrammatic sketch of a sub-sea-floor hydrothermal con- vection system like that hypothesized to exist at the TAG Hydrothermal Field (drawn from profile F, Fig. 6; vertical exaggeration is about x2). Arrows indicate directions of hydrothermal flow. Slant lines indicate direc- tions of maximum permeability controlled by structural grain, including fractures, faults, and dikes. Hydrothermal deposits are forming adjacent to the rift valley, and relict deposits are present away from the rift valley as a consequence of sea-floor spreading. Actually, relict deposits may be covered by off-axis volcanism. Symbols: +, zone of recharge; -, zone of discharge; x, zone of igneous intrusion. sea-floor spreading southeast of the active site at the wall of the rift valley (Table 2; station TO 75AK61-1A) indicates the per- sistence of the special structural and ther- mal conditions that maintain subâsea-floor hydrothermal convection for at least 1 Off-axis extrusive volcanism may act both to suppress hydrothermal activity and to cover hydrothermal deposits. Consequent- ly, the actual extent of hydrothermal de- posits along flow lines of sea-floor spread- ing may be difficult to determine. Relative to magnetic measurements, the model (Fig. 11) is consistent with the ob- served general parallelism between rema- nent magnetic lineations and the rift valley (Fig. 8). Because remanent magnetization resides in the rocks of the fault blocks, the inferred parallelism between the long axes of these blocks and the rift valley ensures that the gross pattern of linear residual anomalies remains parallel to the axis of the rift valley in spite of the asymmetric tec- tonic fabric. The 3-km southeastward offset of the center of the axial (Brunhes) mag- netic anomaly from the rift valley that re- mains after removal of the magnetic fiel
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