Michael Bröcker

Michael Bröcker
University of Münster | WWU · Institut für Mineralogie

About

122
Publications
52,905
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3,481
Citations
Citations since 2016
32 Research Items
1553 Citations
2016201720182019202020212022050100150200250
2016201720182019202020212022050100150200250
2016201720182019202020212022050100150200250
2016201720182019202020212022050100150200250
Introduction
Michael Bröcker currently works at the Institut für Mineralogie, University of Münster. Michael does research in geology, mineralogy and petrology with emphasis on the geochronology of metamorphic rocks from subduction zone settings. Current projects focus on such rocks from Greece, Iran and Indonesia.

Publications

Publications (122)
Article
The Sistan suture zone, eastern Iran, exposes a well-preserved accretionary complex that formed by the closure of a Neotethyan ocean basin between the Central Iranian Lut block and the Afghan microcontinent. Mélange sequences include tectonic slices of adakitic plagiogranitic rocks and rare jadeitite. Adakitic whole rock characteristics, compositio...
Article
Full-text available
This study corroborates interpretations suggesting that the Makrotantalon Unit on Andros represents a tectonic slice with Pelagonian affinity in the nappe stack of the Cycladic Blueschist Unit. Previously reported Cretaceous ⁴⁰ Ar– ³⁹ Ar dates of a garnet-glaucophane schist from the Makrotantalon Unit could not be reproduced by Rb–Sr geochronology,...
Article
Full-text available
This study aims at clarifying the relationship between the Cape Steno mélange, southern Andros, and the main tectonic units of the Attic-Cycladic Crystalline Belt. Jurassic protolith ages and geochemical characteristics indicate a Pelagonian affinity and point to a correlative relationship with the Tsiknias Ophiolite on Tinos Island. However, jadei...
Article
In this study we establish a time frame for metamorphic processes affecting Neotethyan suture zones at the northern (Sabzevar) and southern (Makran) margin of the Central Iranian Microcontinent. For this purpose, we have applied Rb–Sr and U–Pb geochronology to blueschist‐ and amphibolite facies rocks from these occurrences. So far, no isotopic ages...
Article
We report new petrological and geochronological data for eclogitic rocks of the Pouébo Eclogite Mélange (PEM) in the New Caledonian high-pressure/low-temperature (HP/LT) belt. Pseudosections were calculated to link newly determined LuHf dates with P-T conditions corresponding to garnet growth, which started on the prograde path and continued into t...
Article
Metamorphic rocks of the Central Indonesian Accretionary Collision Complex are exposed in widely scattered occurrences on the islands of Java, Sulawesi, and Kalimantan. Their relationship to one or more subduction zones is controversial which can partly be explained by insufficient geochronological investigation. Using RbSr geochronology we have da...
Article
Ophicalcites exposed on the island of Tinos, Greece, occur as ellipsoidal bodies within greenschist-facies phyllites of the Upper Cycladic Unit. Close to their outcrops, blocks of serpentinites, metabasic rocks and metasediments were identified, implying a tectonically dismembered ophiolitic sequence in the study area. The ophicalcites comprise bre...
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Full-text available
Metamorphic rocks associated with ophiolitic rocks occur on the eroded surface of a NW–SE-trending anticline in the Allahyarlu area, NW Iran, between the Caucasus and Zagros orogenic belts. Metapelitic rocks consist mainly of quartz, muscovite chlorite, altered biotite and garnet. S 1 is the pervasive schistosity, wrapping garnet, which is folded b...
Article
This paper presents petrographic, geochemical and geochronological data for intrusions that area spatially related to gold and copper mineralization in the Poboya and Sassak areas in western Sulawesi. These data coupled with previous studies are then used to discuss the implications for the mineralization processes and magma sources. In the Poboya...
Conference Paper
Full-text available
Several active graben systems in Tibet and the Himalaya are the expression of ongoing E-W extension, but the significance and history of normal faulting in this large region are still debated (e.g. Ratschbacher et al., 2011). Here, we present geo- and thermochronological data for a granite intrusion in the footwall of an active high-angle normal fa...
Article
The Sistan Suture Zone, eastern Iran, includes blocks and lenses of eclogite-, blueschist-and/or epidote am-phibolite-facies rocks that provide an excellent opportunity to examine the exhumation history of oceanic HP/LT rocks and their retrograde derivatives. Zr-in-rutile thermometry of eclogites corroborates previous interpretations suggesting met...
Article
Small and volumetrically subordinate outcrops of alkali-rhyolitic to trachytic metavolcanic rocks are widespread in the Lahn-Dill area of the Rheinisches Schiefergebirge, Germany. These occurrences are either related to late Early Devonian or to Middle Devonian episodes of volcanic activity. An unambiguous age assignment for the time of eruption co...
Conference Paper
Full-text available
Several active graben systems in Tibet and the Himalaya are the expression of ongoing E-W extension, but the significance and history of normal faulting in this large region are still debated (e.g. Ratschbacher et al., 2011). Here, we present geo-and thermochronological data for a granite intrusion in the footwall of an active high-angle normal fau...
Article
The timeframe of eclogite- and blueschist-facies metamophism in the central Indonesian region is poorly defined. Relative to its geographic extent, the regional coverage of isotopic age data is insufficient for an unambiguous interpretation of the geologic evolution of the Central Indonesian Accretionary Collision Complex. This study reports new ge...
Article
Pre-Cenozoic blueschist- and eclogite-facies rocks occur widely scattered in the central Indonesian region, possibly representing lateral equivalents of the same subduction zone. High-pressure/low-temperature (HP/LT) metamorphism is thought to have occurred during the Early Cretaceous, which however is only constrained by K–Ar ages. This study is p...
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Full-text available
Combining high‐spatial resolution geochronology and geochemistry of zircon provides constraints on the geodynamic evolution of the Zagros orogen. This study underlines the significance of hitherto unknown magmatic/geological events in the central Urumieh–Dokhtar magmatic arc (UDMA) of Iran at ca. 35–22 and 10 Ma. Recently reported U–Pb zircon ages...
Article
This study describes the field relationships, petrography and geochemistry of various metamorphic and magmatic rocks from the Barru Block, South Sulawesi, Indonesia, and reports Rb-Sr isochron ages for clastic metasedimentary rocks. The Barru Block is composed of a tectonic stack of various lithological units, including cherts, radiolarian mudstone...
Article
Full-text available
Several active graben systems in Tibet and the Himalaya are the expression of ongoing E-W extension, but the significance and history of normal faulting in this large region are still debated. Here, we present geo- and thermochronological data for a granite intrusion in the footwall of an active high-angle normal fault at the Tangra Yumco graben to...
Article
A better understanding of the subduction zone fluid cycle and its chemical–mechanical feedback requires in-depth knowledge about how fluids flow within and out of descending slabs. Relicts of fluid-flow systems in exhumed rocks of fossil subduction zones allow for identification of the general relationships between dehydration reactions, fluid path...
Article
Abstract The Sistan Suture Zone, eastern Iran, includes blocks and lenses of eclogite-, blueschist- and/or epidote amphibolite-facies rocks that provide an excellent opportunity to examine the exhumation history of oceanic HP/LT rocks and their retrograde derivatives. Zr-in-rutile thermometry of eclogites corroborates previous interpretations sugg...
Conference Paper
Full-text available
The south Ardestan region in the Urumieh-Dokhtar arc covers an area of about 250 km2 that is characterized by plutonic rocks with a compositional spectrum ranging from gabbro, gabbro-norite, gabbroic diorite, diorite, tonalite to granodiorite. Gabbroic rocks are mainly tholeiitic in character, whereas the diorites, tonalites and granodiorites show...
Article
We describe a largely unknown listvenite deposit from Tinos, Cyclades, Greece and combine field observations with petrographic, bulk-rock geochemical, isotope (Sr, O, C), and Rb–Sr geochronological data. The volumetrically small listvenite occurrences are associated with metabasic phyllites, talc schists, meta-gabbros, ophicalcites and serpentinite...
Article
The south Ardestan plutonic rocks constitute major outcrops in the central part of Iran’s Cenozoic magmatic belt and encompass a wide compositional spectrum from gabbro to granodiorite. U–Pb laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) dating of zircon three granodiorites yielded ages of 24.6 ± 0.1, 24.6 ± 0.1, and 24.5 ±...
Article
The Esfandagheh region of the Zagros Orogenic Belt is an ideal area to address many aspects of continental convergence between Arabia and Eurasia, including incorporation of Late Neoproterozoic (Ediacaran) basement, subduction–related magmatism and the formation of HP/LT rocks. The rock units exposed here represent a presumably Jurassic magmatic ar...
Article
Full-text available
A complex high-pressure/low-temperature vein system that cross-cuts eclogitic host rocks of the Pouébo Eclogite Melange (northern New Caledonia) records the prograde blueschist-to-eclogite transition and associated formation of garnet–quartz–phengite veins. Geothermobarometry (Grt–Cpx–Ph, Zr-in-rutile) and pseudosection calculations indicate peak m...
Article
U-Pb and Rb-Sr geochronology has been used to constrain robust ages for leucosomes and high-temperature gneisses from the Anjul area in the eastern part of the Lut block. The new results do not support the previously suggested Proterozoic age for this occurrence, but instead reveal the importance of Jurassic and Cretaceous magmatic and/or metamorph...
Article
Geochemical analyses in combination with Rb–Sr (whole-rock, phengite, biotite) and U–Pb zircon ages provide important constraints on the magmatic, metamorphic and structural evolution of the Śniez2nik and Gierałtów gneisses from the Orlica–Śniez2nik complex (West Sudetes). These two gneisses have been considered to represent distinct petrogenetic u...
Article
U–Pb zircon ages of five metasedimentary rocks from the Lower Unit on Tinos Island (Cycladic blueschist belt, Greece) document supply of detritus from various Proterozoic, Paleozoic and Mesozoic source rocks as well as post-depositional metamorphic zircon formation. Essential features of the studied zircon populations are Late Cretaceous (70–80 Ma)...
Article
The Attic–Cycladic Crystalline Belt in the central Aegean region represents a major tectono-stratigraphic unit of the Hellenides. The essential geological, magmatic and tectono-metamorphic features are well documented. Unresolved questions concern the time of sediment accumulation and litho- and/or tectono-stratigraphic relationships across the stu...
Article
The focus of this study is on meta-ophiolitic rocks from Samos and the Attic–Cycladic Crystalline Belt, Greece. SHRIMP U–Pb zircon geochronology, Sr–Nd isotope and bulk-rock geochemistry have been applied to meta-gabbros that occur as blocks and lenses in blueschist-facies mélanges on Samos and Evia, and in the greenschist-facies Upper Unit on Tino...
Article
This study focuses on the status of the Makrotantalon Unit (Andros, Greece) within the framework of the Cycladic nappe stack. We document unambiguous evidence that this unit has experienced blueschist-facies metamorphism and identify previously unknown lawsonite +/- pumpellyite assemblages in glaucophane-free metasediments. The position of the pres...
Article
Barite chimneys are known to form in hydrothermal systems where barium-enriched fluids generated by leaching of the oceanic basement are discharged and react with seawater sulfate. They also form at cold seeps along continental margins, where marine (or pelagic) barite in the sediments is remobilized because of subseafloor microbial sulfate reducti...
Article
U–Pb and Rb–Sr geochronology has been used to constrain robust ages for leucosomes and high-grade gneisses from the Anjul area in the eastern part of the Lut block, Iran. The new results do not support the previously suggested Proterozoic age for this occurrence, but instead reveal the importance of Jurassic and Cretaceous magmatic and/or metamorph...
Article
Siliciclastic metasediments from the islands of Samos and Syros, Cycladic blueschist unit, Greece, were studied to determine maximum sedimentation ages. Four samples from the Ampelos unit on Samos yielded age distribution spectra that range from ~320 Ma to ~3.2 Ga with a dominance of Cambrian–Neoproterozoic zircons (500–1,100 Ma). The youngest well...
Article
Compared to the well-documented Cenozoic magmatic and metamorphic rocks of the Cyclades, Aegean Sea, Greece, the geodynamic context of older meta-igneous rocks occurring in the marble-schist sequences and melanges of the Cycladic Blueschist Unit is as yet not fully understood. Here, we report O-Hf isotopic compositions of zircons ranging in age fro...
Article
The Attic-Cycladic crystalline belt in the central Aegean region records a complex structural and metamorphic evolution that documents Cenozoic subduction zone processes and exhumation. A prerequisite to develop an improved tectono-metamorphic understanding of this area is dating of distinct P–T–D stages. To evaluate the geological significance of...
Article
The Sistan Suture Zone (SSZ) in eastern Iran extends as a N–S trending belt over more than 700 km along the border area between Iran and Afghanistan. The SSZ formed as a result of eastward-directed subduction of a Neotethyan ocean basin beneath the Afghan block and includes a tectonic mélange consisting of disrupted meta-ophiolitic rocks within a l...
Article
The Sistan Suture Zone (SSZ) in eastern Iran extends as a N-S trending belt over more than 700 km along the border area between Iran and Afghanistan. The SSZ formed as a result of eastward-directed subduction of a Neotethyan ocean basin beneath the Afghan block and includes a tectonic mélange consisting of disrupted meta-ophiolitic rocks within a l...
Article
The Sistan Suture Zone (SSZ) in eastern Iran extends as a N-S trending belt over more than 700 km along the border area between Iran and Afghanistan. The SSZ formed as a result of eastward-directed subduction of a Neotethyan ocean basin beneath the Afghan block and includes a tectonic mélange consisting of disrupted meta-ophiolitic rocks within a l...
Article
Full-text available
Most previously dated zircons in high-pressure mélange blocks and associated matrix rocks from Tinos and Syros (Cyclades), Greece, yielded ion microprobe (SHRIMP II) U-Pb ages of ca. 80 Ma. In many cases it remains unclear whether the zircons are igneous or metamorphic/hydrothermal in origin. Oxygen and hafnium isotope ratios in the dated zircons h...
Article
The Cycladic blueschist belt, Greece, is mostly submerged below sea level and regional correlations are difficult to establish. Marbles are widespread within the belt and locally used as marker horizons to subdivide monotonous schist sequences. However, owing to the lack of distinctive petrographic characteristics, the marbles have not been used fo...
Article
Full-text available
The provenance and exhumation history of paragneisses that enclose the 471-458 Ma eclogites in the Caledonian Jaeren nappe, SW Norway, were constrained by performing U-Pb analysis on detrital zircon and Rb-Sr dating of mica. Zircon grains from four samples were analysed by laser ablation inductively coupled plasma mass spectrometry, providing detri...
Article
Full-text available
Jadeitites form from hydrothermal fluids during high pressure metamorphism in subduction environments; however, the origin of zircons in jadeitite is uncertain. We report ion microprobe analyses of δ18O and Ti in zircons, and bulk δ18O data for the jadeitite whole-rock from four terranes: Osayama serpentinite mélange, Japan; Syros mélange, Greece;...
Article
Full-text available
U–Pb zircon geochronology, Sr–Nd isotope and bulk-rock geochemistry have been applied to meta-igneous and meta-sedimentary rocks from high-pressure metamorphic mélanges exposed on the Cycladic islands of Tinos, Syros and Andros. Ion microprobe (SHRIMP) U–Pb zircon dating of 7 samples representing meta-igneous blocks (Tinos), a blackwall zone (Tinos...
Article
Unieżnik complex, Bohemian Massif. Under favourable circumstances such data may help to unravel protolith ages and yet-undetermined aspects of the metamorphic evolution, for example, the time span over which eclogite-facies conditions were attained. By means of ion-probe and laser ablation techniques, a comprehensive database was compiled for sampl...
Article
Most large-scale deformational and metamorphic features in the Scandinavian Caledonides occurred during Scandian times (430-395 Ma), which involved the collision between the proto-continents Laurentia and Baltica and the deep (ca. 200 km) subduction of the Baltoscandian margin. In spite of this pervasive regional metamorphism, some crustal fragment...
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Full-text available
The Scandinavian Caledonides contain several non-cogenetic eclogite-bearing terranes that were meta-morphosed before the main orogenic stage in Scandian time (430–395 Ma). Although petrological and geochro-nological data from these terranes have provided essential information on the geodynamic history of the Caledonian orogenic cycle, the general p...
Article
The Orlica–Śnieżnik complex (OSC) is a key geological element of the eastern Variscides and mainly consists of amphibolite facies orthogneisses and metasedimentary rocks. Sporadic occurrences of eclogites and granulites record high-pressure (HP) to ultrahigh-pressure (UHP) metamorphic conditions. A multimethod geochronological approach (40Ar–39Ar,...
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Full-text available
The Scandinavian Caledonides contain several non-cogenetic eclogite-bearing terranes that were metamorphosed before the main orogenic stage in Scandian time (430–395Ma). Although petrological and geochronological data from these terranes have provided essential information on the geodynamic history of the Caledonian orogenic cycle, the general pict...
Article
Full-text available
Eclogites from the Jæren nappe in the Caledonian orogenic belt of SW Norway contain aragonite, magnesite and dolomite in quartz-rich layers. The carbonates comprise composite grains that occur interstitially between phases of the eclogite facies assemblage: garnet + omphacite + zoisite + clinozoisite + quartz + apatite + rutile ± dolomite ± kyanite...
Article
Petrological, oxygen isotope and ⁴⁰Ar/³⁹Ar studies were used to constrain the Tertiary metamorphic evolution of the lower tectonic unit of the Cyclades on Tinos. Polyphase high-pressure metamorphism reached pressures in excess of 15 kbar, based on measurements of the Si content in potassic white mica. Temperatures of 450–500° C at the thermal peak...
Article
The Cycladic blueschist unit (CBU) in the central Aegean Sea comprises a pre-Alpidic crystalline basement that is overlain by thrust sheets of a metamorphosed volcanosedimentary sequence. Melanges are widespread and enclose a wide variety of meta-igneous rock fragments in a serpentinitic and/or metasedimentary matrix. Previous geochronology has doc...