TY - JOUR

T1 - Trace element evidence for anatexis at oceanic magma chamber roofs and the role of partial melts for contamination of fresh MORB

AU - Fischer, Lennart A.

AU - Erdmann, Martin

AU - France, Lydéric

AU - Wolff, Paul E.

AU - Deloule, Etienne

AU - Zhang, Chao

AU - Godard, Marguerite

AU - Koepke, Jürgen

N1 - Funding Information: This research used samples and/or data provided by the International Ocean Discovery Program (IODP) expeditions 312, and 335. Funding for this research was provided by grants from the Deutsche Forschungsgemeinschaft ( KO 1723/13 ). We would like to thank Julian Feige and Otto Dietrich for the sample preparation, Tim Müller for the EPMA assistance and André Stechern for the IHPV support. The manuscript has been substantially improved after thorough reviews by H. Rollinson and an anonymous reviewer. This is CRPG contribution no. 2427. Appendix A

PY - 2016/9/1

Y1 - 2016/9/1

N2 - At oceanic spreading centers, interactions between magma and hydrothermal convecting systems trigger major physical, thermal, and chemical exchanges. The two-pyroxene hornfels recovered from the base of the sheeted dike sequence at Integrated Ocean Drilling Program (IODP) Site 1256 (equatorial Eastern Pacific) are interpreted as a conducting boundary layer between the underlying axial melt lens and the hydrothermally cooled sheeted dikes. They are cut by numerous small, felsic veins, which were recently interpreted as a product of hydrous partial melting of sheeted dikes. Here, we present trace element compositions of products (melts and residues) of hydrous partial melting experiments using basalts and hornfels from IODP Site 1256 as starting material. The experimental products generated between 910 °C and 970 °C match the natural lithologies from Site 1256 in terms of major and trace element compositions. The compositions of the anatectic melts correspond to the compositions of the felsic veins, while the residual minerals match the compositions of the two-pyroxene hornfels, evidencing that hydrous partial melting is an important magmatic process in the gabbro/dike transition of fast-spreading mid-oceanic ridges. Our results complement previous experimental studies on anatectic processes occurring at the roof of the magma chambers from fast-spreading mid-ocean ridges. Moreover, calculations of mixing and assimilation fractional crystallization using the experimental partial melts as contaminant/assimilant showed that anatectic melts can only be a minor contributor to the contamination process.

AB - At oceanic spreading centers, interactions between magma and hydrothermal convecting systems trigger major physical, thermal, and chemical exchanges. The two-pyroxene hornfels recovered from the base of the sheeted dike sequence at Integrated Ocean Drilling Program (IODP) Site 1256 (equatorial Eastern Pacific) are interpreted as a conducting boundary layer between the underlying axial melt lens and the hydrothermally cooled sheeted dikes. They are cut by numerous small, felsic veins, which were recently interpreted as a product of hydrous partial melting of sheeted dikes. Here, we present trace element compositions of products (melts and residues) of hydrous partial melting experiments using basalts and hornfels from IODP Site 1256 as starting material. The experimental products generated between 910 °C and 970 °C match the natural lithologies from Site 1256 in terms of major and trace element compositions. The compositions of the anatectic melts correspond to the compositions of the felsic veins, while the residual minerals match the compositions of the two-pyroxene hornfels, evidencing that hydrous partial melting is an important magmatic process in the gabbro/dike transition of fast-spreading mid-oceanic ridges. Our results complement previous experimental studies on anatectic processes occurring at the roof of the magma chambers from fast-spreading mid-ocean ridges. Moreover, calculations of mixing and assimilation fractional crystallization using the experimental partial melts as contaminant/assimilant showed that anatectic melts can only be a minor contributor to the contamination process.

KW - Conductive boundary layer

KW - Fast-spreading mid-ocean ridge

KW - Granoblastic hornfels

KW - MORB contamination

KW - Oceanic plagiogranite

KW - Partial melting

UR - http://www.scopus.com/inward/record.url?scp=84969780773&partnerID=8YFLogxK

U2 - 10.1016/j.lithos.2016.05.001

DO - 10.1016/j.lithos.2016.05.001

M3 - Article

AN - SCOPUS:84969780773

VL - 260

SP - 1

EP - 8

JO - LITHOS

JF - LITHOS

SN - 0024-4937

ER -