TY - JOUR

T1 - Trace elements in anatectic products at the roof of mid-ocean ridge magma chambers

T2 - An experimental study

AU - Erdmann, Martin

AU - France, Lydéric

AU - Fischer, Lennart A.

AU - Koepke, Jürgen

AU - Deloule, Etienne

N1 - Funding information: We thank Otto Dietrich and Julian Feige for their careful sample preparation. The manuscript has been substantially improved after a thorough review by Froukje M. van der Zwan. This research used samples and/or data provided by the International Ocean Drilling Program (IODP). IODP is sponsored by the U.S. National Science Foundation (NSF) and participating countries under management of the Consortium for Ocean Leadership (COL). Funding for this research was provided by grants from the Deutsche Forschungsgemeinschaft (KO 1723/13). This is CRPG contribution number 2500.

PY - 2017/5/5

Y1 - 2017/5/5

N2 - At fast-spreading mid-ocean ridges (MORs), the horizon between the axial melt lens (AML) and the overlying sheeted dikes is characterized by extensive anatectic processes. The heat flux of the AML in combination with hydrothermal fluids from above causes high-grade contact metamorphism, which may result in anatexis of the roof rocks above the AML. The products of this process are silica-rich anatectic melts that have the potential to contaminate MOR basalts and residual hornfels. Here, we simulate the complex igneous and metamorphic processes occurring at the AML roof by hydrous partial melting experiments and provide corresponding trace element partition coefficients between melt and residues, which are useful to quantify those processes. We present trace element patterns from experimental anatectic felsic melts and the related residue produced by hydrous partial melting of various types of AML roof rocks. The starting materials used are sheeted dikes and hornfelses from Hole 1256D drilled by the Integrated Ocean Drilling Program. Results are compared with directly-related natural lithologies (i.e., felsic veins and granoblastic hornfels) from the same site. The trace element contents generally overlap with natural examples and experimental melts produced at low water activity (aH2O < 0.5) can be highly enriched in trace elements despite relatively low SiO2 contents (58.9 to 65.7 wt%). A low aH2O is required to reproduce the low Al2O3 contents observed in natural silica-rich rocks. However, low aH2O implies that the presence of residual amphibole is not required for anatectic processes Even though residual amphibole is often used as an important phase for explaining trace element characteristics in relevant felsic rocks formed at MORs when modeling anatexis. Because amphibole is lacking in any experimental residue, which is in agreement with natural hornfelses from the dike/gabbro transition at Site 1256, we assume that partial melting within the AML roof rocks proceeds without the participation of amphibole as residual phase. We present a comprehensive set of trace element compositions as well as bulk and mineral/melt trace element partition coefficients obtained from our amphibole-free experimental results for different potential protoliths over a large range of temperature and at different aH2Os.

AB - At fast-spreading mid-ocean ridges (MORs), the horizon between the axial melt lens (AML) and the overlying sheeted dikes is characterized by extensive anatectic processes. The heat flux of the AML in combination with hydrothermal fluids from above causes high-grade contact metamorphism, which may result in anatexis of the roof rocks above the AML. The products of this process are silica-rich anatectic melts that have the potential to contaminate MOR basalts and residual hornfels. Here, we simulate the complex igneous and metamorphic processes occurring at the AML roof by hydrous partial melting experiments and provide corresponding trace element partition coefficients between melt and residues, which are useful to quantify those processes. We present trace element patterns from experimental anatectic felsic melts and the related residue produced by hydrous partial melting of various types of AML roof rocks. The starting materials used are sheeted dikes and hornfelses from Hole 1256D drilled by the Integrated Ocean Drilling Program. Results are compared with directly-related natural lithologies (i.e., felsic veins and granoblastic hornfels) from the same site. The trace element contents generally overlap with natural examples and experimental melts produced at low water activity (aH2O < 0.5) can be highly enriched in trace elements despite relatively low SiO2 contents (58.9 to 65.7 wt%). A low aH2O is required to reproduce the low Al2O3 contents observed in natural silica-rich rocks. However, low aH2O implies that the presence of residual amphibole is not required for anatectic processes Even though residual amphibole is often used as an important phase for explaining trace element characteristics in relevant felsic rocks formed at MORs when modeling anatexis. Because amphibole is lacking in any experimental residue, which is in agreement with natural hornfelses from the dike/gabbro transition at Site 1256, we assume that partial melting within the AML roof rocks proceeds without the participation of amphibole as residual phase. We present a comprehensive set of trace element compositions as well as bulk and mineral/melt trace element partition coefficients obtained from our amphibole-free experimental results for different potential protoliths over a large range of temperature and at different aH2Os.

KW - Fast spreading mid-ocean ridge

KW - Granoblastic hornfels

KW - Hydrous partial melting

KW - Oceanic plagiogranites

KW - Partition coefficients

KW - Trace elements

UR - http://www.scopus.com/inward/record.url?scp=85015419829&partnerID=8YFLogxK

U2 - 10.1016/j.chemgeo.2017.03.004

DO - 10.1016/j.chemgeo.2017.03.004

M3 - Article

AN - SCOPUS:85015419829

VL - 456

SP - 43

EP - 57

JO - Chemical Geology

JF - Chemical Geology

SN - 0009-2541

ER -