Evidence of Mesozoic multiple hydrothermal activity in the basement at Nonnenmattweiher (southern Schwarzwald), Germany

• Published in: Mineralium deposita Vol. 32; no. 2; pp. 197 - 200
• Main Authors: Wernicke, R. S., Lippolt, H. J.
• Format: Journal Article
• Language: English
• Published: Heidelberg Springer Nature B.V 01.02.1997
• Subjects: Geological time; Geology; Mineralogy
• ISSN: 0026-4598; 1432-1866
• DOI: 10.1007/s001260050085

Two botryoidal hematites from the qtz-fl-hem veins at the Nonnenmattweiher cirque (zone of Badenweiler-Lenzkirch, Südschwarzwald) were dated using the (U+Th)-He method. One hematite gives an Early Triassic age (234±5 Ma) and the second straddles the Cretaceous/Jurassic time boundary (126±4 Ma). The ages bracket the entire age spectrum reported to date for Mesozoic vein-type mineralizations in the Schwarzwald. The maximum sedimentary overburden and associated palaeo-temperatures (>130°C) in the basement of the southern Schwarzwald during the Jurassic did not cause severe age-resetting of the hematites. This implies that both ages probably are formation ages rather than ages of cooling, provided that the ^sup 4^He retentivities of both hematites are similar. The fact that two hematites from the veins at Nonnenmattweiher yield highly discordant Mesozoic ages suggests multiple hydrothermal activity during the Mesozoic. A previously published age of two adularia (155 Ma), intermediate between the hematite ages, supports this view.[PUBLICATION ABSTRACT]