Lawsonite geochemistry and stability – implication for trace element and water cycles in subduction zones
Access Status
Authors
Date
2014Type
Metadata
Show full item recordCitation
Source Title
ISSN
School
Collection
Abstract
This contribution reviews the existing data on lawsonite stability and trace element geochemistry, and provides new data for metabasaltic and metasedimentary (quartzite) rocks from New Caledonia, Turkey and California. Lawsonite is a major host of REE, Sr, U, Th and Pb in basaltic compositions. Trace element-rich lawsonite also occurs in metasedimentary rocks, in which comparatively fewer phases compete for trace elements than in metabasaltic rocks. Trace element patterns in lawsonite are influenced by the coexistence or breakdown of allanite, titanite, apatite and garnet that compete for these elements in high-P metamorphic rocks. Lawsonite is restricted to cool geotherms and therefore is an indicator mineral for subduction-zone metamorphism. The lawsonite stability field shows a strong dependence on temperature and composition and it is largest in rocks with a high normative anorthite content and, in basaltic systems, carbon content. Along cold geotherms, lawsonite can transport water and trace elements to great depths, providing a source for these elements in the deep mantle. Along warmer geotherms, lawsonite disappears on a continuous reaction, gradually releasing water over a temperature interval of several tens of degrees. During lawsonite breakdown in complex systems, Th and LREE remain trapped in newly formed accessory allanite. However, owing to extreme LREE content, allanite has lower Pb/Ce and Sr/Nd than lawsonite, resulting in a relative enrichment of Sr and Pb compared with Ce and Nd in the fluids produced during lawsonite breakdown. Existing experimental data on the solidus of altered oceanic crust suggest that the lawsonite-breakdown reaction is within 50 °C of the solidus at sub-arc pressures of 3–4 GPa.
Related items
Showing items related by title, author, creator and subject.
-
Maslen, Ercin (2010)Petroleum geochemistry is an important scientific discipline used in the exploration and production of hydrocarbons. Petroleum geochemistry involves the applications of organic geochemistry to the study of origin, formation, ...
-
Li, C.; Wang, X.; Wilde, Simon; Li, X.; Wang, Y.; Li, Z. (2017)© 2017 Elsevier B.V. The Archean Anshan Complex in the northeastern part of the North China Craton is one of the few areas on Earth where rocks older than 3.8 Ga have been identified, and thus it provides a rare opportunity ...
-
Wang, S.; Wang, L.; Brown, M.; Piccoli, P.; Johnson, Tim; Feng, P.; Deng, H.; Kitajima, K.; Huang, Y. (2017)Composite granite-quartz veins occur in retrogressed ultrahigh pressure (UHP) eclogite enclosed in gneiss at General's Hill in the central Sulu belt, eastern China. The granite in the veins has a high-pressure (HP) mineral ...