Rutile Ages Research Articles

Crustal thickening, exhumation and metamorphic cooling of Neoproterozoic eclogites in NE Brazil: Timescale for the assembly of West Gondwana

The high-pressure followed by high-temperature metamorphism related to the evolution of collisional orogens is the expected Pressure-Temperature-time (P-T-t) path for modern-style plate tectonics. However, these P-T-t paths are rarely preserved even in Phanerozoic orogens. In this matter, the Campo Grande migmatite-gneiss area presents an exhumed Archean crust with heterogeneous retrograde eclogites overprinted by amphibolite-facies in NE Brazil. Retrogressed eclogites in the area core are formed by Mn-rich garnet + clinopyroxene porphyroblasts layer with a minor amphibole + quartz + titanite assemblage, whereas the margins display dismembered lenses of Mg-rich garnet porphyroblasts with plagioclase + amphibole coronae and clinopyroxene + plagioclase + ortopyroxene sympleticte mainly within shear zones. Phase equilibria modelling reveals that these distinct retro-eclogites record similar eclogite conditions (up to 18 kbar and 660 ± 20 °C). Mn-rich eclogites display widespread magmatic zoned zircon grains from Mesoarchean to Paleoproterozoic and recrystallized metamorphic grains of 607.7 ± 5.4 Ma. Zircon from Mg-rich eclogites crystallized at 2.67 Ga and overgrowth rims formed at 2.0 Ga and 590.1 ± 1.8 Ma. REE in zircon lack Eu anomaly, displaying flat HREE patterns in 590.1 ± 1.8 Ma Neoproterozoic grains indicate recrystallization under eclogite-facies conditions. In situ U-Pb titanite dating yielded two younger age sets at 574.7 ± 0.5 and 562.8 ± 2.1 Ma. Lastly, in situ U-Pb dating of rutile inclusions in garnet cores present ages of 606.1 ± 4.0 Ma, whereas rutile included in retrograde coronae and sympleticte yielded concordant ages from 559.0 ± 2.3 to 523.2 ± 1.9 Ma. Thus, combined phase equilibria modelling and U-Pb ages reveal a progressive change in metamorphic conditions from eclogite conditions (at least 607.7 ± 5.4 to 590 ± 1.8 Ma; zircon dating and rutile ages included in eclogite garnet) to nearly isothermal decompression (574.7 ± 0.5 Ma; titanite age) of ancient Archean deep crust, which was followed by suggested final exhumation and metamorphic cooling at shallower crustal levels between 559.0 ± 2.3 and 523.2 ± 1.9 Ma (rutile age in retrogressed assemblage). Therefore, the high-pressure conditions followed by decompression and metamorphic cooling during sin- to post-collisional settings were associated with the final assembly of West Gondwana.

LA-ICP-MS U–Pb dating and trace element analyses of detrital rutile from the Elbtal Group (Saxony, Germany): provenance constraints of the Saxonian Cretaceous Basin

AbstractThe steep sandstone cliffs of the Upper Cretaceous Elbtal Group exposed in the Eastern Erzgebirge and the Zittau Sandstone Mountains are impressive remnants of the Saxo-Bohemian Cretaceous Basin. Despite the excellent exposure, little is known about the provenance. Herein, we present LA-ICP-MS U–Pb and trace element data of detrital rutile grains separated from five different formations of the Elbtal Group to characterise and differentiate potential source regions. The Cenomanian samples of the Eastern Erzgebirge (Niederschöna and Oberhäslich formations, lower Elbtal Group) yield an U–Pb rutile age cluster at 320–330 Ma. The source rock lithology is predominantly of metapelitic origin. The Zr-in-rutile temperatures indicate amphibolite- to lower granulite-facies metamorphic conditions. Thus, the Variscan basement exposed in the Erzgebirge is assumed as proto source. The Middle Turonian to Early Coniacian samples from the Zittau Sandstone Mountains (Oybin, Lückendorf and Waltersdorf formations; upper Elbtal Group) yield similar U–Pb rutile ages with a cluster at 320–330 Ma. The source rock lithology is likewise predominantly classified as metapelitic and the Zr-in-rutile temperatures cluster in upper amphibolite- to granulite-facies metamorphic conditions. Exposures with high-grade metamorphic Variscan basement are assumed as likely proto sources for these sedimentary rocks. Sedimentary structures indicate a northerly source and thus contrast with direct input from the Variscan basement located to the south and east. Thus, the most likely sedimentary model is reworking of sediments that were eroded from the Variscan basement prior to the Turonian and deposited within a basin at the northern margin of the Bohemian Massif. Graphical abstract

Tectonic and magmatic evolution of the southernmost Mariana convergent margin: Constraints from geochronology and geochemistry of the Challenger Deep sediments

The southernmost Mariana convergent margin (SMCM) is a distinct segment of the Izu-Bonin-Mariana (IBM) subduction system with unique east-west orientation, however, its nature and tectonic history remains enigmatic. Here, for the first time, we present the detailed geochemical data of detrital minerals and UPb ages of accessory minerals from two sediment samples recovered at the deepest part of Southern Marianna Trench including the Challenger Deep. Detrital magmatic zircon UPb ages can be divided into three groups. Group 1 zircons show a weighted mean age of 50.3 ± 1.2 Ma, contemporary to the published boninites from northern IBM. The εHf(t) of these zircons (11.1–16.4) are also similar to the boninites (12.6–16.8) and volcanic arc rocks (4.2–14.2), but lower than forearc basalts (17.8–22.1), suggesting that these zircons are from boninitic or arc magmatism. The apatite UPb dating obtained a similar age of 55.0 ± 5.5 Ma. Therefore, if they are all from boninites, then subduction initiation magmatism ended at SMCM was likely coeval with northern IBM. Group 2 and Group 3 zircons have εHf(t) values similar to Group 1 zircons, but recorded younger 206Pb/238U ages of 16.8 ± 1.8 Ma and 11.0 ± 0.2 Ma, respectively, which are most likely related to the arc volcanism at West Mariana Ridge (WMR). Additionally, a rutile age of 19.0 ± 0.6 Ma is identified, which is also likely related to WMR. The chemical composition and calculated P-T conditions of clinopyroxenes indicate that they are mainly from the Mariana forearc basalts and arc volcanic rocks. In situ Sr isotopic compositions of plagioclases also show strong affinity to the Mariana forearc basalts and arc volcanic rocks. Therefore, our study indicates that sediments at the deep trench can record the long-term tectonic and magmatic evolution of the convergent margin.

Lu-Hf and U-Pb dating of the Zayanderud eclogites: Implications for Jurassic subduction initiation along the Neotethys margin in Iran

The time at which the Neotethys Ocean started to subduct along the southern margin of Eurasia within Iran has been debated in recent years. This margin, referred to as the Sanandaj-Sirjan Zone (SaSZ), features a series of Jurassic calc-alkaline igneous formations which were emplaced at c. 170 Ma. However, an alternative model suggests that subduction initiation occurred during the Cretaceous period. To address this age controversy, we utilized the Lu-Hf isochron method and employed SIMS U-Pb zircon and rutile geochronology to determine the metamorphic history of the earliest known Neotethyan eclogite outcrop along the upper Zayanderud River section of the SaSZ. Two eclogites separated by ∼25 km yielded Lu-Hf garnet dates of 175.1 ± 1.0 Ma and 172.5 ± 0.6 Ma. Rare <20 μm eclogitic zircon crystals in one of the eclogites are strongly zoned and yielded U-Pb dates for which a 177 ± 10 Ma rim age was deconvolved. The relatively low Dy/Yb of these zircon rims suggests that they crystallized prior to garnet formation, or retrograde in disequilibrium with garnet. Homogeneous U-Pb rutile ages averaging 162 ± 7 Ma are only marginally younger than the Lu-Hf garnet ages, consistent with the petrographic observation that rutile is predominantly found in the matrix or within garnet rims, and open-system behavior of radiogenic Pb during cooling. The newly obtained ages are close to previously published 40Ar/39Ar phengite dates and indicate a narrow time window during the Middle Jurassic for deep burial within a subduction channel, followed by eclogitization and rapid exhumation. These new constraints on the metamorphic history support subduction initiation along the SaSZ margin in the Jurassic period.

Earth’s metamorphic secular evolution accessed by rutile

Rutile provides crucial insights into the evolution of plate tectonics and variations in tectonomagmatic modes over Earth’s history primarily because rutile predominantly tracks higher-pressure metamorphism (>1.0–1.2 GPa). Comparison of rutile age and compositional data with diverse proxies tracks the presence of low temperature/pressure (T/P) metamorphic conditions, enabling the tracing of plate tectonics onset and evolution. We present a new compilation of rutile U-Pb ages that lag zircon ages by approximately 50 Myr, potentially indicating cooling ages of metamorphic belts. The earliest rutile age peak (ca. 1.8 Ga) aligns with the oldest evidence for low T/P metamorphic conditions. This coincides with a shift in the T/P distribution of rutile whereas the T/P of Archean rutile forms a tight normal distribution. In the Paleoproterozoic, the rutile T/P distribution is skewed to lower T/P, following the broader pattern of the full metamorphic record. The degree of lower T/P skew increases through time until the lower T/P population dominates the rutile record from the Neoproterozoic to the present. These data further highlight shifts in dominant metamorphic modes that can be tied to the evolution of the tectonic system, with early Archean metamorphism being associated with plume-driven vertical tectonics or hot, shallow subduction and post-Archean metamorphism being associated with progressive less plume-driven vertical tectonics and colder, steeper subduction. Although the frequency of rutile is lower during the Mesoproterozoic, the rutile T/P during this time follows the progressive skewing pattern from the Paleoproterozoic to the present and is likely inconsistent with a phase of interrupted tectonics characterized by stagnant lid.

Two stages of gold mineralization in the Hebaoshan deposit: Evidence from the U-Pb dating and trace element geochemistry of rutile, monazite and apatite

The Hebaoshan gold deposit (41.5 t Au @ 3.5 g/t) is located in the southeastern region of the South China Block, central part of the Wuyishan metallogenic belt. The ore-hosting rocks in this area are predominantly Precambrian metasedimentary rocks and Caledonian granitic rocks. Two hydrothermal mineralization stages can be distinguished: a quartz-sericite-pyrite-native gold (stage I) and a chlorite-quartz-sericite-chalcopyrite-electrum (stage II), with hydrothermal monazite and rutile are firstly identified in separate stages. The complex geological history of the region has resulted in ongoing debates regarding the age of gold mineralization and the genesis of the major gold deposits in this area. In order to precisely constrain the mineralization age of the deposit and further establish a genetic model for the ore deposit, LA-ICP-MS U-Pb dating and trace element analysis on accessory minerals were conducted. Based on the textures mineral assemblages, and geochemical features of the accessory minerals, magmatic apatite, hydrothermal rutile, and both magmatic and hydrothermal monazite were identified. The U-Pb ages of magmatic apatite and monazite are determined to be 445.3 ± 15.80, 441.3 ± 15.10 Ma and 446.57 ± 1.03 Ma, respectively, suggesting that these ages represent the emplacement ages of the Caledonian intrusive rocks. The ages of hydrothermal monazite and hydrothermal rutile are determined to be 238.46 ± 2.01 Ma (single-mineral analysis), 238.46 ± 2.01 Ma (in-suit analysis) and 179.54 ± 7.28 Ma, respectively, suggesting that represent two mineralization events during the Late Triassic to early Jurassic in the Hebaoshan area. These data provide new constraints on the mineralization process in the Hebaoshan deposit and excludes the link between gold mineralization and the intrusion of the Caledonian granites. Regionally, It is speculated that the two mineralization events at Hebaoshan are respectively associated with intracontinental orogenic movements between the Yangtze Block and Cathaysia Block, the flat-slab subduction of the Paleo-Pacific Plate (stage I), and the subsequent extensional tectonics related to the collision between the Yangtze Block and Cathaysia Block (stage II).Our study indicates that the timing of multiple episodic mineralization can be constrained by analysis of accessory minerals, which provides a geological basis for better genetic model for the deposit and provide geological evidence for unraveling the relationships between magmatic activities and mineralization events in the region.

U-Pb geochronology of rutiles from Southern granulite Terrane, India: Implications for the cooling and exhumation of East Gondwanan terranes

The Precambrian Southern Granulite Terrane of south India figures prominently in the East African collisional orogen, linked to the assembly of the East Gondwana supercontinent along with Sri Lanka, Madagascar, Antarctica, and Africa. While the timing of this collision and associated magmatic-metamorphic processes are well constrained, the mechanisms governing the cooling and exhumation of these terranes remain uncertain. This study focuses on U-Pb rutile ages derived from granulites in the Southern Granulite Terrane and attempts to extract the cooling history of the terrane. Our new U-Pb rutile ages cluster between 422 to 458 Ma, postdating regional metamorphism and indicating an extended cooling period of ∼ 35 Ma whereas trace element signatures suggest their formation during granulite facies metamorphism with temperatures reaching up to ultrahigh-temperature conditions. Calculated cooling rates using these rutile U-Pb ages range between 2–6 °C/Ma similar to the cooling rate of ≤ 7 °C/Ma from other East Gondwanan terranes. Based on these results it is proposed that the coeval exhumation of these terranes was assisted by surface erosion after the final assembly of the East Gondwana supercontinent.

Tracking cycles of Phanerozoic opening and closing of ocean basins using detrital rutile and zircon geochronology and geochemistry

Abstract Sedimentary basins provide a deep time archive of tectonic and Earth-surface processes that can be leveraged by detrital mineral U-Pb dating and geochemistry to track paleogeography, magmatism, and crustal evolution. Zircon preserves the long-term (billions of years) record of supercontinent cycles; however, it is biased toward preserving felsic crustal records. Detrital rutile complements the detrital zircon record by providing constraints on the time and temperature of rifting and mafic magmatism, metamorphism, exhumation of the middle and lower crust, subduction, and amagmatic orogenesis. We use detrital zircon U-Pb and detrital rutile U-Pb geochronology and trace element analysis of Permian to Eocene siliciclastic rocks in the southern Pyrenees to capture supercontinent cycles of ocean basins opening and closing. Detrital rutile age spectra show peaks at ca. 100 Ma associated with rifting and hyperextension in the Pyrenean realm, 200 Ma associated with the Central Atlantic Magmatic Province, and 330 Ma, 375 Ma, and 400 Ma associated with subduction and Rheic Ocean crust formation. Zr-in-rutile thermometry and rutile Cr-Nb systematics provide further insight into metamorphic facies (peak metamorphic temperatures) and source rock lithology (mafic versus felsic affinity). Detrital zircon age spectra have peaks at ca. 300 Ma, 450 Ma, and 600 Ma associated with major orogenic events and felsic magmatism, and Th/U ratios provide information on relative zircon formation temperatures. Comparison of these independent records shows that detrital rutile reflects rifting, magma-poor orogenesis, and oceanic lithospheric processes, while detrital zircon detects continental lithospheric processes. Integrated detrital zircon and rutile data sets archive past geological events across multiple Wilson cycles.

Late Neoproterozoic tectonic evolution of the northern Tarim block: New insights from integrated detrital zircon and rutile geochronology and trace element geochemistry

In the Neoproterozoic era, the breakup of the Rodinia supercontinent had a profound impact on different aspects of Earth; yet, the precise driving mechanism behind this event has been a source of ongoing controversy. The Tarim block, as a crucial component, presents an opportunity to gain valuable insights into the breakup process through its tectonic-sedimentary evolution history and dynamic background. However, the comprehension of basin evolution is limited due to the presence of an ambiguous prototype basin during the late Neoproterozoic and its intricate interconnections with surrounding blocks. In this contribution, we integrate detailed field observations, U-Pb dating of detrital zircon and rutile, and trace element analysis of detrital rutile to elucidate the source-to-sink relationships and the tectonic setting of Ediacaran sedimentary strata in the Aksu area (northern Tarim block, China). Detrital zircon age spectra exhibit consistent distributions with ages between ∼850 and ∼600 Ma and between ∼2100 and ∼1800 Ma. Rutile age groups however exhibit an abrupt transition between the lower member of the Sugatbrak Formation and the succeeding upper member to the Qigebrak Formation in the basin, with ages between ∼1800 and ∼900 Ma and nearly identical to those between ∼2100 and ∼1800 Ma. Calculated Zr-in-rutile temperatures and Cr-Nb compositions imply that the majority of the detrital rutiles were sourced from amphibolite facies metapelites, with an abrupt transition from amphibolitic schist to amphibolite-granulite facies for the ∼1800 Ma group grains. Provenance tracing shows that the detrital sediments of the lower Sugatbrak Formation are sourced from both the Central Tianshan and the Tarim blocks, and that the overlying strata have a single source in the Tarim block. A corresponding change from syn-rift detrital facies to a shallow-marine environment in on a passive continental margin is suggested in terms of depositional setting. In light of prior published evidence from petrology, geochronology and paleomagnetism, we propose that the Neoproterozoic northern Tarim margin was affected by a protracted subduction zone retreat. Associated back-arc spreading eventually was responsible for the opening of the southern Tianshan Ocean and rifting of the Central Tianshan block from the Tarim block in the late Ediacaran. This development ultimately prevented detrital material from the Central Tianshan block from reaching the northern Tarim depocenters as the latter evolved into a passive continental margin.

Heavy mineral indicators of ridge subduction beneath the Bainaimiao arc in the southeastern Central Asian Orogenic Belt

As one of the major subduction-accretionary systems in the southeastern Central Asian Orogenic Belt, the Bainaimiao arc presents a valuable opportunity for investigating the subduction–accretion process of accretionary orogens. It is located adjacent to the northern margin of the North China Craton and developed arc-related deposits during the Silurian–Devonian period. In this paper, we employed heavy mineral geochemistry and U–Pb ages of zircon and rutile, to determine the provenance of the Silurian–Devonian deposits and reconstruct the paleogeography of the source area. The stratigraphic units involved include the Xuniwusu Formation of Early Silurian and the Xibiehe Formation of Early Devonian.Both the Xuniwusu and Xibiehe formations exhibit heavy mineral assemblages dominated by zircons and tourmalines. Nevertheless, the Xibiehe Formation contains Cr-spinels and garnets which are absent in the Xuniwusu Formation. Geochemical analyses of the detrital Cr-spinels exhibit characteristics of a supra-subduction zone ophiolite. The garnets originated from middle- to high-grade metamorphic rocks, as well as mafic and felsic rocks. The tourmalines in both formations primarily indicate a metasedimentary rock source, with a small percentage of Li-poor granitoid species in the Xuniwusu Formation. The U–Pb age spectra of both detrital zircon and rutile in the Xuniwusu Formation show multiple peaks. The age spectra consist of Precambrian ages, indicative of a recycled origin, as well as Paleozoic ages, suggesting a magmatic origin. In contrast, the U–Pb age spectra of zircon and rutile in the Xibiehe Formation display a unimodal age peak at ca. 455 and 490 Ma, respectively. These differences suggest a provenance shift from the Xuniwusu to Xibiehe formations. The Xuniwusu Formation was sourced from the Bainaimiao arc itself, whereas the Xibiehe Formation has a mixed origin of the Bainaimiao arc and Ondor Sum accretionary complex. The provenance change correlates with the unconformity between the two formations, suggesting a forearc uplift event. In combination with the previous research on the Tulinkai ophiolite, it can be inferred that the forearc uplift was triggered by ridge subduction of the Paleo-Asian Ocean plate at ca. 450–430 Ma. This research provided a new perspective on the ridge subduction of the oceanic slab in fossil orogens.

Early Jurassic initiation of the modern drainage pattern of the Dabie orogen (East China) revealed by a multi‐proxy provenance approach

AbstractThe timing of the initiation of the present‐day tectonic architecture and drainage systems in eastern China remains debated. This study presents a comprehensive provenance study of the Early Jurassic peripheral basins surrounding the Dabie orogen including framework petrography, heavy‐mineral analysis, single‐grain chronology and chemistry. Clasts of high‐grade schist, muscovite grains, rare gneissic fragments, abundant metamorphic garnet and phengite (Si &gt; 3.3 pfu), combined with a main 216–256 Ma rutile U–Pb population found in these Early Jurassic sandstones, indicate a source from the Triassic (U)HP belt in the Dabie orogen. Sedimentary lithics and ultra‐stable heavy‐mineral assemblages indicate an additional source of recycled sedimentary rocks. Combined with the continuous shift of the youngest detrital rutile age population toward younger ages toward the north that mimics the pattern of metamorphic bedrock ages in the Dabie orogen, we infer that the present surface tectonic architecture and paleodrainage patterns of the Dabie orogen were established in the Early Jurassic. Thus, the Early Jurassic exhumation of the Dabie orogen marked the development of the watershed between Northern and Southern China, namely the Huai River and several principal tributary systems of the middle‐lower Yangtze River.

In situ U-Pb dating of rutile and titanite from the Chaihulanzi lode gold deposit, northern North China Craton and its geological significance

The Chifeng-Chaoyang region, located along the northern margin of the North China Craton, is an important gold producer in China, with a proven gold reserve of about 500 tons. Most gold deposits are fault-controlled and formed in the Mesozoic, but the absolute ages of gold mineralization in this region have not been well constrained due to the lack of suitable dating minerals. This study presents in situ U-Pb ages of hydrothermal rutile and titanite for the Chaihulanzi gold deposit and obtains a distinctive age. The Chaihulanzi deposit (∼27 t Au) is located in the western portion of the Chifeng-Chaoyang region and mainly hosted in the carbonaceous mica schist of the Neoarchean-Paleoproterozoic Jianping Group along NW to NWW striking faults. It contains auriferous quartz veins and disseminated ores in hydrothermal alteration zones, with pyrite and pyrrhotite as the predominant ore minerals. Based on field and petrographic observations, four stages of mineralization process can be identified, involving stage I quartz-pyrite, stage II quartz-pyrite-pyrrhotite-chalcopyrite, stage III quartz-polymetallic sulfides, and stage IV quartz-calcite. Stage II represents the main gold stage and contains abundant hydrothermal rutile and titanite, which are intergrown with pyrite, pyrrhotite and native gold. Rutile grains have high contents of V, Nb, Fe, Cr, W and low contents of Zr and yield a Tera-Wasserburg lower intercept age of 285.4 ± 8.5 Ma (n = 37, MSWD = 3.9). Titanite grains show low Th/U and La/Yb ratios (0.03 to 0.66 and 0.26 to 3.98, respectively) and flat chondrite-normalized REE patterns (LREE/HREE = 0.88–5.72, Eu/Eu* = 0.71–1.71), with a Tera-Wasserburg lower intercept age of 282.3 ± 3.4 Ma (n = 20, MSWD = 2.1). Combined with the emplacement age of a post-ore mafic dyke (ca. 275.5 Ma), the timing of the Chaihulanzi deposit can be constrained to Early Permian, representing a new gold mineralization epoch in the Chifeng-Chaoyang region. On the basis of available geological and geochronological evidence, the Chaihulanzi deposit can be classified as an orogenic gold deposit formed during the southward subduction of the paleo-Asian Ocean. These new findings likely have important implications for future regional gold exploration.

Multistage mineralization of the Liling goldfield (NE Hunan) in the Jiangnan Orogen: Constraints from hydrothermal rutile U–Pb dating and sericite Rb–Sr dating

The Liling goldfield located in northeastern (NE) Hunan contains >200 tons of proven gold reserves. The gold mineralization age in Liling has long been controversial due to the lack of datable minerals. In this study, petrographic observations indicate that hydrothermal rutile and sericite were precipitated with auriferous pyrite/arsenopyrite in the ore veins. The electron probe microanalysis (EPMA) results show that the sericite from ores and the sericite from Neoproterozoic slate display distinct compositions (Especially Al, K, and Ti). The high W (1,081–36,456 ppm) and low Zr (21.35–288.7 ppm) contents of the rutile suggests a hydrothermal origin. We reported new laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) U-Pb ages of ore-stage hydrothermal rutile (415.2 ± 8.3 Ma) for the Tuanshanbei gold deposit, and sericite Rb-Sr ages (417.6 ± 12.9 Ma and 216.9 ± 7.8 Ma) for the Tuanshanbei and Yanlinsi gold deposits in the goldfield. The new data confirm that multistage gold mineralization has occurred in the Liling goldfield, and falls within the generally accepted timing (ca. 430–400 Ma and 250–200 Ma) of gold mineralization in the Jiangnan Orogen. Integration of geological characteristics, tectonic setting, and geochronology of the Liling goldfield suggest two Au mineralization episodes, which occurred in the Late Silurian-Early Devonian intracontinental orogeny and Triassic intracontinental orogeny, respectively.

Metamorphic Domes in Northern Tunisia: Exhuming the Roots of Nappe Belts by Widespread Post‐Subduction Delamination in the Western Mediterranean

AbstractCenozoic extension in the Western Mediterranean has been related to the dynamics of back‐arc domains. Although, in most of its orogenic belts extension propagated into the fore‐arc nappe domains. Here we revisit the structure, metamorphism and radiometric ages of the Tunisian Tell, where HP/LT rocks (350°C at 0.8 GPa), were exhumed by the sequential activity of extensional detachments after heating and decompression (410°C–440°C at 0.6–0.3 GPa) in a plate convergent setting. Normal faults thinning the Tunisian Tell detached at two different crustal levels. The shallower one cuts down into the Atlas Mesozoic sequence, involving Tellian Triassic evaporites in the hanging‐wall forming halokinetic structures in the Mejerda basin late Miocene. The deeper‐detachment bounds metamorphic domes formed by marbles and metapsammites from the Atlas domain. Illite crystallinity on Triassic rocks shows epizonal to anchizonal values, at deep and intermediate structural depths of the Tell‐Atlas nappe belt, respectively. New U‐Pb 49.78 ± 1.28 Ma rutile ages from Tellian metabasites, together with existing phlogopite 23–17 Ma K‐Ar ages in Atlas marbles from the footwall of the deepest detachment, indicate a polymetamorphic evolution. The Tell rocks underthrusted the Kabylian flysch in the early Eocene. Further, early Miocene shortening thrusted the metabasites over lower‐grade sediments, producing HP/LT metamorphism and ductile stretching at the base of the Atlas belt. The exhumation of midcrustal roots of Western Mediterranean nappe belts after tectonic shortening is a common feature related to tearing at the edges of the subduction systems and inboard delamination of their subcontinental lithospheric mantle.

Karst-bauxite formation during the Great Oxidation Event indicated by dating of authigenic rutile and its thorium content

Aluminium (Al)-rich palaeosols—i.e., palaeobauxite deposits—should have formed in karst depressions in carbonate sequences as a result of acidic solutions from oxidative weathering of sulfide minerals during the Great Oxidation Event (GOE), but no GOE-related karst-palaeobauxite deposits have so far been recorded. Here, we report results of in situ uranium–lead (U–Pb) dating of detrital zircon and spatially associated rutile from a metamorphosed Al-rich rock within a dolomite sequence in the Quadrilátero Ferrífero (QF) of Minas Gerais, Brazil, known as the Gandarela Formation. Rutile grains are highly enriched in thorium (Th = 3–46 ppm; Th/U ratio = 0.3–3.7) and yielded an isochron, lower-intercept age of ca. 2.12 Ga, which coincides with the final phase of the GOE—i.e., the Lomagundi event. The rutile age represents either authigenic growth of TiO2 enriched in Th, U and Pb during bauxite formation, or subsequent rutile crystallisation during metamorphic overprint. Both cases require an authigenic origin for the rutile. Its high Th contents can be used as a palaeoenvironmental indicator for decreased soil pH during the GOE. Our results also have implications for iron (Fe)-ore genesis in the QF. This study demonstrates that in situ U–Th–Pb-isotope analyses of rutile can place tight constraints on the age and nature of palaeosols.

Tracing the protoliths of the garnet amphibolitic and retrogressed eclogitic slices and a conceptual tectonic model for their emplacement onto the Central Menderes Massif, Turkey: New geochemical data and laser ablation-inductively coupled plasma-mass spectrometry U-Pb zircon and rutile ages

The age, emplacement, and metamorphic history of the garnet amphibolitic and retrogressed eclogitic slices in the Menderes Massif (Eastern Aegean) have been a matter of debate since the 1990’s. Late Cretaceous garnet amphibolitic and retrogressed eclogitic slices in the Bozdağ and Çine nappes show low-angle tectonic contacts with the surrounding Early Cambrian meta-siliciclastics in the Alaşehir-Yahyaalcı and late Neoproterozoic basement rocks in the Birgi and Tire-Çamlıca Klippe in the northern Menderes Massif. Lower and upper intercept ages on the discordia diagrams of the garnet amphibolitic slices are 82 ± 230 Ma and 554 ± 14 Ma, respectively, in the Yahyaalcı-Alaşehir area of the Bozdağ Nappe; and 96 ± 260 Ma and 550 ± 13 Ma, respectively, in the Camlica-Tire Klippe area of the Çine Nappe. Retrogressed eclogitic slices give dates of 81 ± 13 Ma lower intercept and 546 ± 13 Ma upper intercept discordant ages in the Yenişehir-Kiraz area of the Çine Nappe. Lower intercept age of 81 ± 13 Ma is supported by two spots dated on metamorphic zircons showing positive Eu patterns yielding 86.0 ± 1.3 Ma concordant age. Zircon U-Pb dating on the oscillatory zoning spots are dated as 537.5 ± 1.6 Ma (mean square weighted deviation [MSWD] = 1.5, n = 41) for the garnet amphibolic slices in the Yahyaalcı-Alaşehir area (Bozdağ Nappe), 539.0 ± 1.1 Ma (MSWD = 1.4, n = 56) for the garnet amphibolite slices in the Camlica-Tire Klippe area (Çine Nappe), and 536.6 ± 2.3 Ma (MSWD = 1.7, n = 32) for the retrogressed eclogitic slices (Çine Nappe). These ages combined with Eu negative anomalies on the dated spots are evaluated as representing their magmatic crystallization ages of the protoliths. Garnet isopleth intersections and pseudosections gave pressure-temperature conditions of 14 kbar and ∼680 °C for the retrogressed eclogites, whereas garnet amphibolites display disequilibrium in whole rock scale. We propose that the age of their protoliths likely correlate with the Cadomian rift-related Early Cambrian meta-mafic dykes that were subducted beneath the İzmir-Ankara-Erzincan Neotethyan lithosphere during the Late Cretaceous. The new rutile U-Pb age of 30.1 ± 2.0 Ma supports that the tectonic slices of the İzmir-Ankara oceanic lithosphere and metamorphosed Tauride-Anatolide continental margin were emplaced onto the Menderes Massif to generate the “main Menderes metamorphic terrane” during the latest Paleocene and early Eocene.

Rutile Ages and Thermometry Along a Grenville Anorthosite Pathway

AbstractThe Grenville Orogen, in North America, contains a belt of Proterozoic anorthosite massifs with an episodic emplacement history. These distinctive magmas reflect extensive fractional crystallization of plagioclase from a mafic magma and contain layers dominated by Ti‐bearing minerals including ilmenite and rutile. U‐Pb geochronology and Zr‐in‐rutile analyses from the Lac Malbaie complex in the Saint Urbain area of Quebec help to constrain the tectonothermal history of repeated anorthosite emplacement into the crust. Geologically significant dates were obtained from low‐U (&lt;2 ppm) rutile in anorthosite drill cores and a boulder. Rutile ages of c. 1158, 1069–1056, and 936–910 Ma are interpreted to reflect variable modification of cooling ages during later intrusion and fluid mobilization events. Zr‐in‐rutile temperatures track higher apparent temperatures of &gt;800°C in earlier events. Apparently younger rutile grains, and those influenced by fast pathway diffusion, record lower apparent temperatures. The Grenville Orogen comprises major trans‐lithospheric structures that facilitate the repeated bottom‐up transit of mantle‐derived magmas. At depth this led to the emplacement of anorthositic magmas whose thermal pathway is tracked by rutile passing through their Pb blocking temperature during crustal unroofing. This same broad crustal architecture, in the comparatively shallow crust, provided a favorable pathway for top‐down hydrothermal fluids to interact with younger rutile as successive anorthosites were emplaced. Rutile demonstrates that the current crustal section represents the juxtaposition of minerals preserving information from different thermal regimes, retaining vestiges of a protracted history due to incomplete re‐equilibration with subsequent chemical or thermal conditions.

A TRIASSIC OROGENIC GOLD MINERALIZATION EVENT IN THE PALEOPROTEROZOIC METAMORPHIC ROCKS: EVIDENCE FROM TWO TYPES OF RUTILE IN THE BAIYUN GOLD DEPOSIT, LIAODONG PENINSULA, NORTH CHINA CRATON

Abstract Rutile grains often occur in different types of gold deposits, and their U-Pb ages have been widely used to determine the formation time of gold mineralization. However, the origin of rutile grains in the gold deposits remains controversial. In this paper, laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) analyses of U-Pb ages and trace elements on rutile grains were applied to investigate the metamorphic and hydrothermal processes of the Baiyun gold deposit (70 t Au, avg grade: 3 g/t) in the Liaodong Peninsula in the northeastern part of the North China craton. Rutile grains in the hydrothermal altered gold schist from the Baiyun deposit yielded two group ages of 1924 ± 18 and 237.0 ± 1.8 Ma, respectively. Combined with our systematic U-Pb zircon geochronological results of the ore-hosting schists and post-ore dikes, we suggest these rutile ages record a Paleoproterozoic metamorphic event and a Triassic hydrothermal gold mineralization event, respectively. The metamorphic and hydrothermal rutile grains have no obvious textural differences, but they show distinct trace element contents of Zr, W, Nb, and Ta. Combined with previous published data, we propose that high W (&amp;gt;1,000 ppm) and low Zr (&amp;lt;200 ppm) contents in rutile can be used to distinguish hydrothermal rutile from metamorphic and magmatic rutile. The newly identified ca. 237 Ma hydrothermal event is much older than the ca. 227 to 210 Ma Triassic magmatic rocks in the region, which precludes a temporal and genetic link between the Baiyun gold mineralization and the regional Mesozoic magmatism. Rather, the ca. 237 Ma gold mineralization may be associated with the Triassic orogenic metamorphism, and Baiyun is an orogenic gold deposit. The Triassic gold deposits in the northern margin of the North China craton formed by orogenesis between the Siberian craton and the North China craton. After a hiatus, the large-scale gold deposits formed during the Early Cretaceous in the North China craton due to a westward subduction of the paleo-Pacific plate beneath the craton since the Early Jurassic. Our study highlights that rutile in gold deposits may be inherited from the host rocks and/or formed by hydrothermal fluids. Distinguishing between these two different rutile generations requires a combination of in situ age dating and trace element geochemistry in petrogenetic context.

A diachronous record of metamorphism in metapelites of the Western Gneiss Region, Norway

AbstractIn this study, data from garnet‐kyanite metapelites in ultrahigh‐pressure (UHP) domains of the Western Gneiss Region (WGR), Norway, are presented. U–Pb geochronology and trace element compositions in zircon, monazite, apatite, rutile and garnet were acquired, and pressure–temperature (P–T) conditions were calculated using mineral equilibria forward modelling and Zr‐in‐rutile thermometry. Garnet‐kyanite gneiss from Ulsteinvik record a prograde evolution passing through ~690–710°C and ~9–11 kbar. Zircon and rutile age and thermometry data indicate these prograde conditions significantly pre‐date Silurian UHP subduction in the WGR and are interpreted to record early Caledonian subduction of continental‐derived allochthons. Minimum peak conditions in the Ulsteinvik metapelite occur at ~28 kbar, constrained by an inferred garnet+kyanite+omphacite+muscovite+rutile+coesite+H2O assemblage. The retrograde evolution passed through ~740°C and ~7 kbar, first recorded by the destruction of omphacite and followed by the partial replacement of kyanite and garnet by cordierite and spinel. Garnet‐kyanite metapelite from the diamond‐bearing Fjørtoft outcrop documents a polymetamorphic history, with garnet forming during the late Mesoproterozoic and limited preservation of high‐pressure Caledonian assemblages. Similar to the Ulsteinvik metapelite, zircon and rutile age data from the Fjørtoft metapelite also record pre‐Scandian Caledonian ages. Two potential tectonic scenarios are possible: (1) The samples were exhumed at different times during pre‐Scandian subduction of the Blåhø nappe, or (2) the samples do not share a history in the same nappe complex, instead the Ulsteinvik metapelite is a constituent of the Seve‐Blåhø Nappe, whilst the Fjørtoft metapelite shares its history within a separate nappe complex.

The Age of Hubi Copper (Cobalt) Ore Mineralization in the Zhongtiao Mountain Area, Southern Margin of the Trans-North China Orogen: New Constraints from U-Pb Dating of Rutile and Monazite

The Hubi copper (cobalt) ore district, one of the largest typical examples of the sediment-hosted stratiform type in the Zhongtiao Mountain area, is located on the southern margin of the Trans-North China Orogen within the North China Craton (NCC) and has a copper reserve of 0.79 Mt. Mineralization is mainly hosted by the Zhongtiao Group, a sequence of metasedimentary rocks deposited from ~2168 Ma to ~2059 Ma. Subsequently, a collisional orogeny (Trans-North China Orogen) occurred at ~1.85 Ga. The absolute age of mineralization has not been well constrained due to the lack of suitable minerals for dating. Rutile and monazite are common accessory minerals and are intergrown with Cu mineralization in Cu-bearing veins in the Hubi-type copper (cobalt) deposits. This study presents the first new LA-ICP-MS U-Pb ages of hydrothermal rutile and monazite for the Tongmugou and Laobaotan copper (cobalt) deposits in the ore district, which yield lower intercept rutile U-Pb ages of 1815 ± 30 Ma (Mean Squared Weighted Deviation, MSWD = 5.0) and 1858 ± 27 Ma (MSWD = 5.2) for Tongmugou and 1876 ± 30 Ma (MSWD = 5.9) for Laobaotan. Monazite crystals separated from Cu-bearing carbonate veins within the orebody of Tongmugou yield a weighted mean 207Pb/206Pb age of 1856 ± 14 Ma (MSWD = 1.9), which is close to that of rutile within error. Mineralogical observations and geochemical characteristics suggest that both monazite and rutile crystallized in the hydrothermal fluid system and are closely related to Cu sulfide mineralization. Therefore, their nearly identical U-Pb isotope age of ca. 1850 Ma directly reflects the timing of metamorphic hydrothermal Cu mineralization. This age is indistinguishable from that of metamorphism during the collisional orogeny (Trans-North China Orogen) that led to the final amalgamation of the Eastern and Western Blocks. According to previous studies, the primary sedimentary mineralization of the Hubi-type copper (cobalt) deposits was synchronous with the deposition of the Zhongtiao Group. From the perspective of mineralization age, both the Congolese–Zambian Copperbelt and the Hubi copper (cobalt) ore district experienced early preorogenic sedimentary diagenetic mineralization and late metamorphic hydrothermal mineralization related to orogenesis, and the Hubi-type copper (cobalt) deposits may also be some of the oldest sediment-hosted stratiform-type deposits in the world. Moreover, this metamorphic hydrothermal Cu mineralization spread throughout the Zhongtiao Mountain area.