Trace elements in anatectic products at the roof of mid-ocean ridge magma chambers: An experimental study

Erdmann, M.; Fischer, Lennart A.; Deloule, Étienne; Koepke, Jürgen

doi:10.1016/j.chemgeo.2017.03.004

Cited by 11 publications

(10 citation statements)

References 44 publications

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“…The origin of melts forming felsic rocks in oceanic crust is diverse and is still debated. The felsic rocks are generally interpreted to have formed either from highly evolved fractionated melts in the late stage of crystallization of the gabbroic sequences, or by partial melting of pre-existing hydrothermally altered crustal rocks [6][7][8][9][10][11][12][13][14][15][16][17]. The intimate association of felsic rocks and oxide gabbros in slow-spreading ridge samples suggests another mechanism for the formation of the felsic melt, such as liquid immiscibility, as discussed and experimentally proved in References [18][19][20][21] and references therein.…”

Section: Introductionmentioning

confidence: 90%

Occurrence of Felsic Rocks in Oceanic Gabbros from IODP Hole U1473A: Implications for Evolved Melt Migration in the Lower Oceanic Crust

Nguyen¹,

Morishita

Soda³

et al. 2018

Minerals

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Felsic rocks are minor in abundance but occur ubiquitously in International Ocean Discovery Program Hole U1473A, Southwest Indian Ridge. The trace element abundances of high-Ti brown amphibole, plagioclase, and zircon in veins, as well as the presence of myrmekitic texture in the studied felsic rocks support crystallization origin from highly-evolved melts, probably controlled by fractional crystallization. Based on geochemical criteria and texture of the mineral assemblage in felsic rocks and their relationship with host gabbros, they can be divided into three types: (1) Felsic rock with sharp boundaries is formed when felsic melt intrudes into fractures of host gabbros, resulting in minimal interaction between the melt and the wall minerals. (2) Replacive felsic rock, which is characterized by a pseudomorphic replacement of minerals in the host gabbro. This vein type is caused by the replacement of the host mineralogy by minerals in equilibrium with the felsic melts. (3) Felsic rock with diffused boundaries is formed either by infiltration of felsic melt into the solidifying gabbro body or crystallization of interstitial melts. Infiltration modes of felsic melts are likely controlled by the temperature condition of the cooling host gabbros.

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Section: Introductionmentioning

confidence: 90%

Occurrence of Felsic Rocks in Oceanic Gabbros from IODP Hole U1473A: Implications for Evolved Melt Migration in the Lower Oceanic Crust

Nguyen¹,

Morishita

Soda³

et al. 2018

Minerals

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“…Stage 2, t = t 1 . The rising of the AML stops in a high position, transforming the overlying previous hydrothermally altered sheeted dikes to granoblastic hornfelses by intense contact metamorphism (formation of a conductive boundary layer), with local partial melting of the roof rocks leading to felsic veins (Erdmann et al, 2017). At this stage, stoped parts of the AML roof representing granoblastic hornfelses sink into the melt and form those relics, which can be observed in the GT3A gabbros as microgranular domains.…”

Section: Magmatic Processes At the Roof Of An Aml -A Formation Scenar...mentioning

confidence: 99%

ICDP Oman Drilling Project: varitextured gabbros from the dike–gabbro transition within drill core GT3A

Engelhardt

Koepke²,

Zhang³

et al. 2022

Eur. J. Mineral.

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Abstract. The Oman ophiolite (Samail massif, Sultanate of Oman) is the largest sub-aerial exposure of oceanic lithosphere on Earth and provides the opportunity to study the accretion and alteration of oceanic lithosphere formed under fast-spreading conditions. Drill hole GT3A (23∘06′50.7′′ N, 58∘12′42.2′′ E) of the ICDP (International Continental Scientific Drilling Program) Oman Drilling Project with a length of 400 m aimed at penetrating the dike–gabbro transition of the Samail ophiolite paleocrust in order to shed light on the role of the axial melt lens (AML) during accretion of the lower plutonic crust. AMLs beneath fast-spreading mid-ocean ridges are sandwiched between the sheeted dike complex and the uppermost gabbros and are believed to feed the upper crust and, at least partially, the underlying crystal mush. Typical gabbroic rocks from dike–gabbro transitions of fast-spreading systems are the so-called “varitextured gabbros”, often showing considerable variations in mineral mode, texture and grain size, which are regarded as the frozen fillings of axial melt lenses. Here, we present a detailed petrographic, microanalytical and bulk-chemical investigation of 36 mafic rocks from the drill hole GT3A, which represent mostly varitextured gabbros, revealing a complex formation with several evolution stages. Poikilitic domains formed first, corresponding to an early crystallization stage, where only plagioclase and clinopyroxene of more primitive composition crystallized. Later, domains of granular textures containing also interstitial amphibole and Fe–Ti oxide were formed. This stage is characterized by a magma evolution that underwent crystal fractionation established by lower temperatures due to more efficient hydrothermal cooling at the margin of the AML. A last stage is characterized by pervasive hydrothermal alteration, where all primary minerals have been altered under temperature conditions, varying from the magmatic regime down to greenschist facies. A highlight of this stage is amphiboles showing noticeable compositional zoning. The observation of peculiar microgranular domains, representing relics of stoped exogenic material from the sheeted dike complex, documents the upward migration of an AML in a replenishment event, forcing the AML to burn through previously altered sheeted dikes. This process is responsible for significant assimilation of hydrothermally altered components, indicated by a marked Cl enrichment in the outer zones of magmatic amphiboles. Petrological modeling involving gabbros and basalts revealed that the GT3A rock suite followed a fractional crystallization evolution trend, with a primitive MORB as parental melt with an estimated water content of 0.2 wt % to 0.8 wt %. The modeled liquid lines of descent suggest a magmatic evolution via fractional crystallization, where the basalts correspond to frozen liquids, while the gabbros, especially the more primitive ones, show a significant cumulate component.

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“…GT3A main objective was to have a detailed knowledge of the Coleman &Peterman, 1975, andKoepke et al, 2007 for a discussion on the use of the term oceanic plagiogranite that includes all oceanic felsic rocks). If not crystallized as oceanic plagiogranites, the corresponding anatectic melts can mix within the AML contaminating MORB melts at crustal levels (Nehlig, 1993;Michael & Cornell, 1998;Coogan, 2003;Coogan et al, 2003;Gillis et al, 2003;France et al, 2009;Wanless et al, 2010Wanless et al, , 2011Koepke et al, 2011;Fischer et al, 2016;Erdmann et al, 2017). The base of the SDC has been identified to be texturally and chemically different (over tens of meters) of the overlying SDC section; it is recrystallized to hornfels-like granoblastic assemblages as a consequence of a re-heating event due to contact metamorphism likely triggered by magma intrusion(s) in the SDC root (Gillis & Roberts, 1999;Gillis, 2002Gillis, , 2008Koepke et al, 2008;France et al, , 2010aFrance et al, , 2014Gillis & Coogan, 2019).…”

Section: Introductionmentioning

confidence: 99%

“…The reheating event has the potential to trigger hydrous anatexis of the SDC root (hydrous solidus < 850°C; France, Ildefonse, et al., 2010; France, Koepke, et al., 2010), and to produce melts similar to the bulk composition of most of the oceanic plagiogranites that are observed close to the SDC root (Erdmann et al., 2015, 2017; France et al., 2014; France, Koepke, et al., 2010; Gillis & Coogan, 2002; Grimes et al., 2013; see Coleman & Peterman, 1975, and Koepke et al., 2007 for a discussion on the use of the term oceanic plagiogranite that includes all oceanic felsic rocks). If not crystallized as oceanic plagiogranites, the corresponding anatectic melts can mix within the AML contaminating MORB melts at crustal levels (Coogan, 2003; Coogan et al., 2003; Erdmann et al., 2017; Fischer et al., 2016; France et al., 2009, 2014; Gillis et al., 2003; Koepke et al., 2011; Michael & Cornell, 1998; Nehlig, 1993; Wanless et al., 2010, 2011). The base of the SDC has been identified to be texturally and chemically different (over tens of meters) of the overlying SDC section; it is recrystallized to hornfels‐like granoblastic assemblages as a consequence of a re‐heating event due to contact metamorphism likely triggered by magma intrusion(s) in the SDC root (France et al., 2009, 2014; France, Koepke, et al., 2010; Gillis, 2002, 2008; Gillis & Coogan, 2019; Gillis & Roberts, 1999; Koepke et al., 2008).…”

Section: Introductionmentioning

confidence: 99%

“…Granoblastic assemblages can be both recrystallized dehydrated rocks, or igneous residue resulting from a hydrous anatexis stage associated with oceanic plagiogranite formation (e.g., Coogan et al., 2003; Gillis & Coogan, 2002; Erdmann et al., 2015, 2017; France et al., 2014; France, Koepke, et al., 2010). Strong constraints based on experimental petrology, and related to the reheating of the SDC root are now available, test protoliths with various alteration and recrystallization grades, and document recrystallization under both metamorphic and anatectic conditions (Erdmann et al., 2015, 2017; Fischer et al., 2016; France et al., 2014; France, Koepke, et al., 2010). Below the SDC/gabbro transition, the upper isotropic gabbros (or varitextured gabbros) represent a highly heterogeneous plutonic interval that is mainly composed of fine‐grained isotropic gabbros with subordinated coarse‐grained gabbros, microgranular enclaves or domains that are remnants of partially digested granoblastic dikes, felsic (or plagiogranitic) and Fe‐Ti gabbroic patches or veins (e.g., France et al., 2009; Koepke et al., 2011; MacLeod & Yaouancq, 2000; T. Müller et al., 2017; Wilson et al., 2006).…”

Section: Introductionmentioning

confidence: 99%

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Quantifying the Axial Magma Lens Dynamics at the Roof of Oceanic Magma Reservoirs (Dike/Gabbro Transition): Oman Drilling Project GT3 Site Survey

et al. 2021

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At oceanic spreading centers, the interactions between the igneous system that builds the crust, and the hydrothermal system that cools it govern the plumbing system architecture and its thermokinetic evolution. At fast-spreading centers, most of those interactions occur around the axial magma lens (AML) that feeds the upper crust, and possibly part of the underlying mushy igneous reservoir. Heat extracted from crystallizing AML is transferred through a conductive boundary layer to the overlying hydrothermal system. Quantifying the AML physical and thermal evolutions and its interactions with hydrothermal system is therefore essential to understand oceanic accretion. Those general issues were the rationale of drilling ICDP OmanDP Hole GT3A, and we present herein the geological, structural, and petrological data that were used as a site survey to select its location. GT3 area enables observations in three dimensions of fossilized AMLs and overlying dikes. The new field data and corresponding mineral compositions are used together with thermokinetic and thermodynamic models to deliver an integrated dynamic model for the AML / hydrothermal system interactions.Results attest that the isotropic gabbro interval is composite, with gabbro bodies intruding and reheating both gabbros and dikes (up to 1040°C). We show that AMLs should be considered as transient igneous bodies that likely crystallize from primitive MORBs in decades, releasing heat to the intruded hosts, and feeding high temperature vents on the seafloor. We show for the first time that the thermal gradient recorded in AML roof is consistent with the heat fluxes reported at active hydrothermal vents.

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Trace elements in anatectic products at the roof of mid-ocean ridge magma chambers: An experimental study

Cited by 11 publications

References 44 publications

Occurrence of Felsic Rocks in Oceanic Gabbros from IODP Hole U1473A: Implications for Evolved Melt Migration in the Lower Oceanic Crust

Occurrence of Felsic Rocks in Oceanic Gabbros from IODP Hole U1473A: Implications for Evolved Melt Migration in the Lower Oceanic Crust

ICDP Oman Drilling Project: varitextured gabbros from the dike–gabbro transition within drill core GT3A

Quantifying the Axial Magma Lens Dynamics at the Roof of Oceanic Magma Reservoirs (Dike/Gabbro Transition): Oman Drilling Project GT3 Site Survey

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