Juergen Koepke

Juergen Koepke
Leibniz Universität Hannover · Institute of Mineralogy

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176
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Introduction

Publications

Publications (176)
Conference Paper
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The drillholes CM1A and CM2B of the ICDP Oman Drilling Project provide an unprecedented opportunity to study the behavior of metals Crust-Mantle boundary of an ancient fast-spreading mid-ocean ridge system (Oman ophiolite), where arriving primitive MORB melts extensively react with the mantle. The layered gabbro sequence (#Mg=58-68) is underlain by...
Article
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Due to its inaccessibility, no complete and coherent data set exists for the composition of modern fast‐spreading oceanic crust. We sampled outcrops through 6,500 m of fossil oceanic crust in the Oman Ophiolite (Wadi Gideah Transect) that is regarded as best analogue of fast‐spreading crust on land. Here we report a complete set of whole‐rock major...
Article
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Reactive porous or focused melt flows are common in crystal mushes of mid-ocean ridge magma reservoirs. Although they exert significant control on mid-ocean ridge magmatic differentiation, their role in metal transport between the mantle and the ocean floor remains poorly constrained. Here we aim to improve such knowledge for oceanic crust formed a...
Article
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Oceanic gabbros are the most abundant rocks close to Earth's surface. Here we present new data from a consistent profile through the paleocrust of the Samail Ophiolite (Oman), which is thought to provide the best analog for modern fast‐spreading oceanic crust. Incompatible trace elements of co‐existing plagioclase and clinopyroxene fractionate from...
Article
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An outcrop in the layered gabbro section from the Wadi Wariyah of the Oman ophiolite has been investigated to provide new insights into the hydrothermal activities that cover a large temperature range in the lower crust at fast-spreading mid-ocean ridges. Our observations reveal a complex veining system composed of gabbroic dikes, hydrous mineral (...
Article
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We established a 5,000 m thick profile through the paleo lower oceanic crust of the Samail ophiolite (Sultanate of Oman, Wadi Gideah), in order to investigate accretion processes beneath fast‐spreading mid‐ocean ridges. The Samail ophiolite is regarded as best on‐land analog for fast‐spread oceanic crust, and Wadi Gideah allows sampling of the enti...
Article
Full-text available
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 par...
Article
Full-text available
The combined Fe-Ti oxide geothermometry and oxygen barometry is an important tool in petrology and volcanology. However, its appropriate application to natural magmatic systems is still challenged by poorly constrained kinetics of the re-equilibration processes between magnetite, ilmenite, melt and other magmatic phases. In this study, we experimen...
Article
Full-text available
The combined Fe-Ti oxide geothermometry and oxygen barometry is an important tool in petrology and volcanology. However, its appropriate application to natural magmatic systems is still challenged by poorly constrained kinetics of the re-equilibration processes between magnetite, ilmenite, melt and other magmatic phases. In this study, we experimen...
Article
Multichannel seismic studies performed at fast‐spreading mid‐ocean ridges revealed the presence of a thin (tens to hundreds of meters high), narrow (< 1–2 km wide) axial melt lens (AML) in the mid‐crust, which is underlain by crystal/melt mush that is in turn laterally surrounded by a transition zone of mostly solidified material. In order to shed...
Conference Paper
Full-text available
Hole GT3A of the Oman Drilling Project located near Aswad in the Samail block, intersected the dike-gabbro transition of the Samail Ophiolite. It crossed 301.6 m of the sheeted dike complex (diabase, basalt), 87.14 m of high-level gabbros and 14.82 m of evolved lithologies (diorite, tonalite, trondjhemite). Igneous contacts mostly consist of dikes...
Conference Paper
Full-text available
Magma evolution in the lower oceanic crust affects the metal contents in the derivative magmas and the formation of seafloor massive sulfides. At spreading segments with low magma supply, sulfide differentiate primarily by melt-mantle reaction, with subordinate role of fractional crystallization 1,2. At spreading segments with high magma supply, di...
Conference Paper
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IODP Expedition 360 drilled the 810-m-deep U1473A hole into the lower crust of the Atlantis Bank ocean core complex at the Southwest Indian Ridge (33.7°S, 57.3°E). Gabbro from a depth of 615-730 mbsf contain up to 8 mm large igneous sulfides (Ciążela et al., 2016). Igneous sulfides of this size are unusual in the lower oceanic crust and rare elsewh...
Article
Hydrothermal circulation is a key process for chemical and isotopic exchange between the solid Earth and oceans, and for the extraction of heat from newly accreted crust at mid-ocean ridges. However, due to a dearth of samples from intact oceanic crust, or continuous sample suites from ophiolites, there remain major shortcomings in our understandin...
Article
Natural occurrences of Cl-bearing amphibole indicate crystallization in the presence of a highly saline fluid. Amphibole with varying Cl contents (0.1 to 5 wt% Cl) found in lower oceanic crustal rocks demonstrates the activity of saline hydrothermal fluids at depth. Here we present an experimental study done in cold seal pressure vessels (CSPV) and...
Article
Hydrothermal veins and dykelets that cross-cut layered olivine gabbros deep in the plutonic section of the Samail Ophiolite, Sultanate of Oman, point towards the occurrence of hydrothermal circulation in the deep oceanic crust, and these features record interactions between rock and high temperature seawater-derived fluids or brines. Deep penetrati...
Article
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We present a new calibration for the determination of the iron oxidation state in silicate glasses by electron probe micro-analysis (EPMA) with the “flank method”. This method is based on the changes in both intensity and wavelength of the FeLα and FeLβ X-ray emission lines with iron oxidation state. The flank method utilizes the maximum difference...
Article
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The Kane Megamullion oceanic core complex located along the Mid-Atlantic Ridge (23°30′N, 45°20′W) exposes lower crust and upper mantle directly on the ocean floor. We studied chalcophile elements and sulfides in the ultramafic and mafic rocks of the crust-mantle transition and the mantle underneath. We determined mineralogical and elemental composi...
Conference Paper
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The JEOL JSX3600CA1 energy dispersive Xray fluorescence core logger (XRFCL) on the D/V Chikyu provides quantitative element concentrations of scanned cores. Scans of selected intervals are made on an xy grid with point spacing of 5 mm. Element concentrations for Si, Al, Ti, Ca, Mg, Mn, Fe, Na, K, Cr, Ni, S and Zn are collected for each point on the...
Conference Paper
Full-text available
IODP expedition 360 drilled 810-m-long Hole U1473A into the gabbroic lower crust of the Atlantis Bank oceanic core complex at the Southwest Indian Ridge (SWIR, 32°42'S, 57°17'E; Ciążela et al., 2016). All the investigated samples contain pyrrhotite-chalcopyrite-pentlandite grains exsolved from former monosulfides and show mantle-derived δ 34 S sign...
Conference Paper
Full-text available
Primary and secondary transport of chalcophile metals through the oceanic lithosphere control the formation of seafloor massive sulfide deposits. Although, chalcophile elements have been investigated in the upper oceanic crust, little work has thoroughly examined their migration through the lower oceanic crust due to the scarcity of drilled materia...
Article
Although the axial melt lens (AML) beneath fast-spreading mid-ocean ridges has been detected by seismic reflection for decades, its nature and role in the accretion of lower oceanic crust and the evolution and eruption of mid-ocean ridge basalts (MORB) are still poorly constrained. Plutonic rocks consisting of quartz-bearing gabbros, diorites and t...
Conference Paper
Full-text available
Cooled lithosphere that occurs near fracture zones at the slow-spreading ridges is known to trigger subcrustal crystallization of silicate minerals from a MORB-like melt. Although cooler lithosphere may also affect the sulfide crystallization and the metal budget of the lower and upper crust, the related sulfide behavior is poorly understood.
Article
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The Kuluncak (Malatya) ophiolite in the Eastern Tauride, Turkey, consists of mantle tectonites, ultramafic-mafic cumulates, isotropic gabbros, a sheeted dike complex, plagiogranites, and a volcanic complex. The best exposure of the mafic cumulate rocks of the Kuluncak ophiolite is in the Hekimhan region, where they are represented by olivine gabbro...
Article
Full-text available
Gabbroic veins enclosed in mantle peridotite from oceanic core complexes next to oceanic transform faults demonstrate sub-crustal crystallization of silicate minerals from a mid-oceanic ridge basalt (MORB)-like melt. Cooler lithosphere there may also affect sulfide crystallization and the metal budget of the lower and upper crust, but the related s...
Article
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We present textures and halogen and trace-element compositions of apatites in intrusive rocks from the dike-gabbro transition zone of a fast-spreading mid-ocean ridge, which was formed at the East Pacific Rise and recently drilled by IODP Hole 1256D. These data are used to discuss the properties of parental magmas and seawater-derived hydrothermal...
Article
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....
Article
At fast-spreading mid-ocean ridges, axial melt lenses (AMLs) sandwiched between the sheeted dyke section and the uppermost gabbros are assumed to be the major magma source of crust formation. Here, we present our results from a field study based on a single outcrop of a frozen AML in the Samail ophiolite in the Sultanate of Oman which presents a wh...
Article
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We experimentally investigated phase relations and phase compositions as well as the influence of water activity (aH2O) and redox conditions on the equilibrium crystallization path within an oceanic dacitic potassium-depleted system at shallow pressure (200 MPa). Moreover, we measured the partitioning of trace elements between melt and plagioclase...
Article
Fluorine plays an important role in magmatic and hydrothermal processes, but due to its low abundance in geological samples determining F is difficult by electron probe microanalysis. By using a W-Si multi-layered pseudocrystal as the diffraction crystal instead of thallium acid phthalate (TAP), count rates were considerably higher, which however i...
Conference Paper
Full-text available
Copper sulfide deposits at oceanic crust-mantle transition zones are known from the Oman ophiolite. The corresponding sulfides are seen as late secondary formations. Whether or not primary Cu and S enrichment occurred is unclear due to the ophiolite’s complex history. The crust-mantle transition zone exposed in the southern part of the Kane Megamul...
Article
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) is interpreted as a conducting boundar...
Article
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We present major and trace element as well as Sr, Nd, and Hf isotope data on a suite of 87 plutonic rock samples from 27 felsic crustal intrusions in seven blocks of the Oman ophiolite. The rock compositions of the sample suite including associated more mafic rocks range from 48 to 79 wt% SiO2, i.e. from gabbros to tonalites. The samples are groupe...
Article
Experiments in high silica systems at temperatures close to the solidus often produce crystals and melt pools that are too small for in situ analysis. Oscillating the temperature during an experimental run speeds up recrystallization of magma by dissolving small and increasing the size of larger crystals, dramatically changing the crystal size dist...
Conference Paper
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Expedition 360, Atlantis Bank, started at 30.11.2015 in Colombo (Sri Lanka) and ended at 30.01.2015 in Port Louis (Mauritius). Expedition 360 was Leg 1 of the SloMo Project, a Multi-Phase Drilling Program to drill through the Moho at a slow-spreading ocean ridge. The primary objective of the SloMo Project is to test competing hypotheses on the natu...
Data
In-situ Fe isotope measurements have been carried out to estimate the impact of the hydrothermal metamorphic overprint on the Fe isotopic composition of Fe-Ti-oxides and Fe-sulfides of the different lithologies of the drilled rocks from IODP Hole 1256D (eastern equatorial Pacific; 15 Ma crust formed at the East Pacific Rise). Most igneous rocks nor...
Article
Full-text available
The mantle is the most voluminous part of the Earth. However, mantle petrologists usually have to rely on indirect geophysical methods or on material found ex situ. In this review paper, we point out the in-situ existence of oceanic core complexes (OCCs), which provide large exposures of mantle and lower crustal rocks on the seafloor on detachment...
Presentation
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The oxydation state of Earth’s upper mantle (OSEUM) is a key thermodynamic parameter as it influences, among other variables, the depth of melting initiation, the liquidus/solidus temperatures and the composition of mantle melts, the speciation of numerous species (e.g., Fe, S, V…), the phase relations, the trace element partitionning, the volcanic...
Conference Paper
Full-text available
Highly increased chalcophile element concentrations in harzburgites which underwent interaction with MORB melts in comparison to normal abyssal harzburgites have been observed from the Kane Megamullian oceanic core complex (OCC; Mid-Atlantic Ridge, 23°30' N; Ciazela et al. 2014). Ciazela et al. 2015 quantified the Cu enrichment based on the bulk ro...
Conference Paper
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Primitive mantle is depleted in many elements by partial melting processes, but it can be subsequently refertilized by impregnation with percolating melts. It is known that Cu can be enriched in primitive melts, depleting mantle residue, due to the former process (Patten et al. 2013). However, the behavior of Cu in the processes of mantle-melt inte...
Article
Replenished axial melt lenses at fast-spreading mid-oceanic ridges may move upward and intrude into the overlying hydrothermally altered sheeted dikes, resulting in high-grade contact metamorphism with the potential to trigger anatexis in the roof rocks. Assumed products of this process are anatectic melts of felsic composition and granoblastic, tw...
Article
Full-text available
The rocks forming the crustal section of the Oman ophiolite show an increasing input of a subduction component with time, most likely reflecting the generation of the ophiolite above a subducting slab. Field relations, new geochemical and Nd-Hf isotope data of felsic to mafic intrusive rocks in the mantle harzburgite from the Haylayn block in the O...
Conference Paper
Full-text available
The chalcophile elements, as associated with sulfides, are believed mainly from the study of ophiolites to be generally enriched in the upper mantle, but depleted by magmatic processes in the lower and upper ocean crust. However, studies of some orogenic lherzolites suggest a copper depletion of peridotites in relation to the primitive mantle, sugg...
Article
Full-text available
Axial melt lenses sandwiched between the lower oceanic crust and the sheeted dike sequences at fast-spreading mid-ocean ridges are assumed to be the major magma source of oceanic crust accretion. According to the widely discussed "gabbro glacier" model, the formation of the lower oceanic crust requires efficient cooling of the axial melt lens, lead...
Article
The voluminous diatexites in the Dabie orogen of eastern China indicate spectacular anatexis in the orogen basement before exhumation to shallow depths, but determination of the pressure–temperature (P–T) conditions for anatexis in the core complex is problematic because of the lack of suitable mineral assemblages in the diatexite and of re-equilib...
Data
Mid-ocean ridge basalts (MORBs) are the most abundant magmas produced on Earth. They are widely studied to infer mantle compositions and melting processes. However, MORB liquids are also the complex end-product of a variety of intra-crustal processes such as partial or fractional crystallization, melt–rock interaction, and contamination. Decipherin...
Conference Paper
Full-text available
The chalcophile element copper is believed mainly from the study of ophiolites to be generally enriched in the upper mantle, but depleted by magmatic processes in the lower and upper ocean crust. It is then locally enriched in the latter by hydrothermal processes, leading to the formation of large Cu deposits. Oceanic core complexes (OCC's) provide...
Conference Paper
Full-text available
The regionally important Kuluncak (Malatya) Ophiolite in the Eastern Tauride, are composed of mantle tectonites, ultramafic-mafic cumulates, isotropic gabbros, a sheeted dike complex, plagiogranite, extrusives and pelagic cover sediments. The best exposure of the mafic cumulate rocks of the Kuluncak ophiolite are located in the Hekimhan region. Maf...
Article
Detailed backscattered electron (BSE) and cathodoluminescence (CL) observations in an olivine gabbro from the Wadi Rajmi of the Fizh block of the Oman Ophiolite revealed that this gabbro represents a perfect example of a partial melting reaction. The observed micro textures imply that water-rich fluids migrated on grain boundaries in a ductile regi...
Article
Full-text available
Our newly obtained data on the geochemistry and age of plagiogranite-gabbronorite association in the oceanic core complex of the Mid-Atlantic Ridge (MAR) at 5°10′S suggest close genetic relations between these rocks in this segment of the ridge. The U/Pb zircon age of an oceanic plagiogranite (OPG) sample is 1.059 ± 0.055 Ma and is in good agreemen...
Article
Full-text available
The late Palaeoproterozoic (1.72-1.70 Ga) ferroan granites of the Khetri complex, northern Aravalli orogen, NW India, were extensively metasomatised ~900 Ma after their emplacement, at around 850-830 Ma by low-temperature (ca. 400 °C) meteoric fluids that attained metamorphic character after exchanging oxygen with the surrounding metamorphic rocks....
Article
Mid-ocean ridge basalts (MORB) are the most abundant magmas produced on Earth. They are widely studied to infer mantle compositions and melting processes. However, MORB liquids are also the complex end-product of a variety of intra-crustal processes such as partial or fractional crystallization, melt-rock interaction, and contamination. Deciphering...