Diorite Xenoliths Research Articles

Mineral chemistry of gabbro- dioritic xenoliths in Monavvar volcanic rocks (Northwest of Tabriz- NW Iran)

Mineral chemistry of gabbro- dioritic xenoliths in Monavvar volcanic rocks (Northwest of Tabriz- NW Iran)

Origin and Formation Process of Gabbro and Diorite Xenoliths in the Northern Part of Uromieh-Dokhtar Magmatic Belt, NW Iran: Constraints from Mineral and Whole-Rock Chemistries

AbstractGabbro and diorite xenoliths occur within the alkaline trachyandesites in the northern part of Uromieh-Dokhtar magmatic belt (NW Iran). The host volcanic rocks are located on the upper Mioc...

島根県松江市中央部, 和久羅山デイサイト中に見出される斑れい岩-閃緑岩質捕獲岩

島根県松江市中央部, 和久羅山デイサイト中に見出される斑れい岩-閃緑岩質捕獲岩

Petrogenesis of the Wudaogou intermediate–mafic complex, NW China: zircon U–Pb dating, whole-rock and isotope geochemistry, and geological implications

The Wudaogou plutonic complex is located in the eastern Yanbian area of Jilin Province and consists of hornblende gabbros, gabbroic diorites, and quartz diorites that contain abundant dioritic microgranular xenoliths. Zircon U–Pb dating of gabbroic and quartz diorites yielded weighted mean 206Pb/238Pb ages of 263.5 ± 5.1 Ma (N = 12, mean squared weighted deviation (MSWD) = 0.78, probability = 0.66) and 262.0 ± 5.6 Ma (N = 10, MSWD = 0.50, probability = 0.87), respectively. These units are characterized by high Na2O/K2O (0.33–0.77) ratios and Al2O3 (15.05–18.91 wt%) concentrations and are large ion lithophile element (LILE) (light rare earth element (LREE), Rb, Ba, K, etc.) enriched and high field strength element (HFSE) (Nb, Ta, P, Ti) depleted. They also have initial 87Sr/86Sr values of 0.70192–0.70420 and ϵNd(t) values of +1.9 to +4.7 with two-stage model ages (TDM2) of 653–878 Ma. These characteristics indicate that these rocks formed from calc–alkaline magmas derived from partial melting of a mixture of juvenile crust formed attending the Neoproterozoic subduction of the Palaeo-Asian oceanic crust and lower crustal material. The dioritic xenoliths have whole-rock compositions that are similar to their host rocks, but with negative ϵNd(t) values (−1.6 to −4.3) and older TDM2 ages (1166–1382 Ma), further indicating that this magmatic event involved older crustal material. Combining these data with existing knowledge of the crustal evolution of this area, we conclude that this complex formed in a post-collisional extensional setting during closure of the Palaeo-Asian Ocean.

Magma mixing revealed from in situ zircon U–Pb–Hf isotope analysis of the Muhuguan granitoid pluton, eastern Qinling Orogen, China: implications for late Mesozoic tectonic evolution

In this paper, we present zircon U–Pb age and Hf isotope data to document the significance of magma mixing in the formation of Late Jurassic granitoid intrusions in the eastern Qinling Orogen, China. The Muhuguan granitoid pluton from this orogen consists of monzogranite and lesser biotite granite and granodiorite, all containing abundant hornblende-rich cumulates, dioritic xenoliths, and mafic magmatic enclaves (MMEs). The monzogranite and granodiorite are intruded by a number of lamprophyre dykes. Both a cumulate and a dioritic xenolith samples have concordant zircon U–Pb ages of ca. 161 ± 1 Ma, but possess contrasting Hf isotopic compositions. The cumulate has more radiogenic zircon Hf isotopes with negative e Hf(t) values (−7.9 to −2.5) and T DM1 ages of 0.9–1.1 Ga, indicating its derivation likely from basaltic rocks of the Neoproterozoic to early Paleozoic Kuanping Group in the area. The dioritic xenolith has much lower zircon e Hf(t) values of −19.5 to −8.8 and T DM2 ages of 2.4–1.7 Ga, consistent with a juvenile Paleoproterozoic crust source presumably represented by the metabasic rocks of the Qinling Group in the area. Individual samples of the monzogranite, MME, and a lamprophyre dyke have U–Pb ages of 150 ± 1, 152 ± 1, and 152 ± 1 Ma, respectively, demonstrating coeval mafic and felsic magmatism in the Late Jurassic. The lamprophyre dyke has homogeneous, highly negative zircon e Hf(t) values (−29.8 to −24.8) and Archean T DM2 ages (3.0–2.7 Ga), and its genesis is interpreted as partial melting of an ancient enriched subcontinental mantle source. Zircons from the fine-grained MME show a large range of e Hf(t) between −29.1 and −9.8, overlapping values of the monzogranite and lamprophyre dyke samples. Zircon U–Pb age and Hf isotopes of the MMEs are consistent with their formation by mixing of crustal- and enriched mantle-derived magmas. The main group of zircons from the monzogranite has e Hf(t) values (−17.9 to −9.3) and T DM2 ages (2.3–1.8 Ga) that are compatible with the dioritic xenoliths, indicating that the former was produced by partial melting of Paleoproterozoic crustal source with involvement of mantle-derived magmas. Mafic magmatism revealed from the Muhuguan pluton indicates that the eastern Qinling Orogen was dominated by lithospheric extension during the Late Jurassic. Compilation of existing geological and geochronological data suggests that this extensional event started in Late Jurassic (ca. 160 Ma) and persisted into the Early Cretaceous until ca. 110 Ma. The Jura-Cretaceous extension may have resulted from the late Mesozoic westward subduction of the Pacific plate beneath the East Asian continental margin.

Weathering and Degradation Assessment of Rock Properties at the West Stone Pagoda, Gameunsaji Temple Site, Korea

The West Stone Pagoda at Gameunsaji Temple Site constructed in the 7th century is mainly composed of dark grey dacitic tuff bearing small numerous dioritic xenoliths. These xenoliths resulted in small holes due to differential weathering process from the host rocks. Physical strength of the pagoda was decreased due to weathering and damage caused by petrological, biological and coastal environmental factors. The southeastern part of the pagoda was extremely deteriorated that the rock surface showed exfoliation, fracture, open cavity, granular decomposition of minerals and salt crystallization by seawater spray from the eastern coast. The stone blocks were intersected by numerous cracks and contaminated by subsequent material such as cement mortar and iron plates. Also, the pagoda was colonized by algae, fungi, lichen and bryophytes on the roof rock surface and the gaps between the blocks. As a result of ultrasonic test, the rock materials fell under Highly Weathered Grade (HW) or Completely Weathered Grade (CW). Thus, conservational intervention is essentially required to prevent further weakening of the rock materials.

Underplating and assimilation–fractional crystallization of Mesozoic intrusions in the Tongling area, Anhui Province, East China: evidence from xenoliths and host plutons

This paper presents new petrographic observations and geochemical and microprobe analyses for the Laomiaojishan, Xiaotongguanshan, and Tianebaodanshan intrusions in the Tongguanshan mineral district, East China. The plutons vary in composition from quartz monzonitic diorite to pyroxene monzonitic diorite, and contain gabbroic to dioritic xenoliths. The Xiaotongguanshan intrusion yields a SHRIMP zircon U–Pb age of 139.5±2.9 Ma, indicating Late Jurassic to Early Cretaceous magmatism in the Lower Yangtze River Valley. Relative to host rocks, the gabbro and diorite xenoliths are low in SiO2 (52.03–54.61 wt‐%), Al2O3 (12.87–14.43 wt‐%), and total alkalis (Na2O+K2O; 5.26–6.30 wt‐%), but high in MgO (5.41–11.66 wt‐%); the host rocks have high SiO2 (59.97–64.44 wt‐%), Al2O3 (16.43–17.59 wt‐%), and total alkalis (6.67–8.25 wt‐%), but are low in MgO (1.52–2.50 wt‐%). Concentrations of rare earth elements (REEs) in the xenoliths (165.70–190.40 ppm) are similar to those in the host rocks (166.12–185.95 ppm), although the ratio of light REEs to heavy REEs in the xenoliths (3.39–4.27) is lower than that in the host plutons (4.86–5.94). All of the analysed rocks show similar REE patterns, although the xenoliths display marked positive Eu anomalies and the host rocks show slightly negative Eu anomalies. Values of epsilon Nd (t) ranges from −4.9 to −9.9 in the gabbro xenoliths and from −11.4 to −11.9 in the host intrusives. Initial 87Sr/86Sr ratios are 0.7064–0.7073 in the xenoliths and 0.7072–0.7084 in the quartz monzonitic diorite host rocks. Crystallization temperatures of hornblende and plagioclase in the gabbro xenoliths, diorite xenoliths, and host rocks are 816, 773–790, and 664–725°C, respectively, based on an amphibole–plagioclase geothermometer. The pressures recorded by these phases indicate that they formed at depths of 26, 12–15, and 3–4 km, respectively, based on an aluminum‐in‐hornblende geobarometer. The petrological and geochemical features of the analysed intrusions and xenoliths are consistent with their derivation from basic to intermediate‐acidic magmas that possibly formed via a series of complex interactions between underplated, mantle‐derived basaltic magma and varying amounts of middle‐ to lower‐crustal material, followed by assimilation–fractional crystallization.

Midcrustal emplacement of the Sausfjellet pluton, central Norway: Ductile flow, stoping, and in situ assimilation

Midcrustal (25–30 km) emplacement of the dioritic Sausfjellet pluton into rocks of the Helgeland Nappe Complex, central Norway, occurred in two stages. Stage 1 consists of two-pyroxene hornblende gabbro and diorite. Stage 2 is asymmetrically zoned, with a modally layered central zone of diorite and anorthosite and a western/annular zone of quartz-bearing monzodioritic rocks. Igneous layering was locally attenuated, folded, and boudinaged in the hyper-solidus state. The magmatic foliation trajectory pattern in the pluton defi nes a shallowly southwest-plunging synform that crosscuts compositional zones. Mineral lineations plunge shallowly to moderately to the southwest. The pluton intruded a major lithologic boundary within the nappe; migmatitic pelitic gneisses are the main host rocks to the western part of the pluton, whereas the eastern and central parts are hosted predominantly by metacarbonate rocks. Calc-silicate, marble, quartzo-feldspathic, and dioritic xenoliths (up to 200 m in length) are present throughout the pluton; they are most common in Stage 1 and the central zone of Stage 2. Metapelitic xenoliths are conspicuously absent. Ductile fl ow during emplacement produced an ~1-kmwide structural aureole in which host-rock structures were defl ected into subparallelism with the steeply inward-dipping margin of the pluton. Tight antiforms developed along the northeastern, southeastern, and southwestern margins. Amphibolite-grade shear zones in the host rocks preserve plutonside-up kinematic indicators. In addition to the abundance of dioritic, calc-silicate, and quartzo-feldspathic gneiss xenoliths and geochemical evidence for assimilation in the western/annular zone, regional discordance of the pluton–host-rock contacts indicates that stoping was also an important emplacement process at midcrustal depths. Following magma emplacement, foundering of the central portion of the chamber combined with possible ca. 445 Ma regional contraction produced the map-scale synform defi ned by magmatic foliations and igneous layers. This study demonstrates that stoping and assimilation may occur simultaneously with host-rock ductile fl ow during magma chamber evolution at midcrustal levels and offers an explanation of why xenolith preservation may be compositionally dependent.

The Role of Tonalite and Diorite in Mauna Kea Volcano, Hawaii, Magmatism: Petrology of Summit-Region Leucocratic Xenoliths

A tonalite (∼66 wt % SiO2; 2·4 wt % K2O) xenolith from the Mauna Kea summit region provides information on the origin of silicic liquids in mafic magma systems. This leucocratic rock has ∼40 vol. % quartz interstitial to and enclosing Ca-andesine, plus phlogopite (∼11 vol. %), clinopyroxene (mg-number ∼74), orthopyroxene, and Fe–Ti oxides. Also, it contains lithic fragments (≤5 cm) of gabbro (MgO 7·2 wt %; An60–50; clinopyroxene mg-number ∼78–75; phlogopite). The tonalite has Sr–Nd–Pb isotopic ratios of 87Sr/86Sr 0·703610, 144Nd/143Nd 0·512976, 206Pb/204Pb 18·58, 207Pb/204Pb 15·49, and 208Pb/204Pb 38·15, which agree with the isotopic composition of Mauna Kea post-shield Hamakua Volcanics (tholeiitic and alkalic basalts). A positive Eu anomaly and poikilitic texture indicate a cumulate origin. Leucocratic diorite (∼50–53 wt % SiO2; 1–2·4 wt % K2O) xenoliths coexist with the tonalite. These have intergranular andesine–oligoclase (∼68–85 vol. % of An50–15), evolved clinopyroxene (mg-number 76–69), and biotite (± orthopyroxene, zircon). The tonalite represents SiO2-rich liquids that accumulated, perhaps in a small reservoir, after segregation from a hydrous basalt-magma solidification front; gabbro inclusions within the tonalite are probably remnants of that source. Hydrous conditions (implied by abundant phlogopite) were necessary for this silicic-liquid segregation; namely, relatively high H2O facilitated crystallization of SiO2-deficient phases (oxide; phlogopite) to leave SiO2-enriched residual liquids, and H2O vapor pressure helped segregate silicic liquids by gas-pressured filter pressing. The diorites are coarse-grained equivalents of hawaiite and mugearite produced by clinopyroxene-dominant crystallization of Hamakua alkalic basalt. On the basis of normative Ol–Di–Ne, diorite xenoliths originated under intermediate and high pressures, apparently reflecting the transition from low- to high-P crystallization regimes that are identified for Mauna Kea post-shield magmas (where the high-P regime is approximately at the crust–mantle boundary). Leucocratic xenoliths, particularly tonalite, provide additional insights into Hamakua post-shield magma evolution by manifesting differentiation that is more extensive and complex, approaching granitic compositions, than that represented by Hamakua lavas, and by showing that quartz can crystallize appreciably during Hawaiian magmatism. Quartz-bearing rock on Hawaii has global relevance in terms of providing better understanding of the circumstances for oceanic basalt–rhyolite magmatism.

Origin of high-silica liquids at Stromboli volcano (Aeolian Islands, Italy) inferred from crustal xenoliths

High-silica igneous xenoliths (granophyre and obsidian fragments with SiO2 ca. 75 wt.%) and high-silica glass (SiO2 between ca. 64 and 75 wt.%) within glass-bearing tonalitic and dioritic xenoliths have been discovered at Stromboli. They are well beyond the silica range of the volcanic rocks erupted during the subaerial activity of the volcano. The granophyre and the obsidian fragments occur within the Petrazza pyroclastics (high-K andesite pumiceous scoriae) of the Paleostromboli I period ( 61 ka), whereas the glass-bearing tonalites and diorites are hosted in the Omo basaltic-andesite lava flows of the Paleostromboli II period (64–55 ka). The obsidian represents an extremely evolved liquid derived from low-pressure fractional crystallization of high-K calc-alkaline magmas of Stromboli, coupled with minor assimilation of upper crust or terrigenous sediments. The other studied high-silica products have an anatectic origin. The granophyre composition is compatible with a genesis by low-degree melting of leucotonalites similar to some Calabrian Arc lithotypes. Partial melting of crustal rocks from the Stromboli basement is also demonstrated by interstitial glass in the tonalite and diorite xenoliths. Textural evidence and the presence of variable glass compositions suggest that in these plutonic xenoliths the melt chemistry was controlled by dehydration melting of biotite and non-modal melting of local mineralogy. High-degree undercooling of granophyre melt and of the partially melted xenoliths is consistent with rapid rise of the host magmas leading to eruption. Whether partial melting was initiated during stoping and transport of xenoliths within the rising magma or in situ during magma storage within the crust has not been unequivocally established.

Interpretation of field relationships of Diorites and associated rocks with particular reference to northwest Guernsey, Channel Islands

AbstractIn northwest Guernsey, excellently exposed sections of coast reveal a wide variety of diorites and associated rocks which are particulariy instructive in understanding field relationships in diorite complexes generally. In this area, three groups of rocks may be distinguished. A Diorite Group consists of even grained diorite, acicular diorite and appinite, believed to be related to each other by fractionation. This group was intruded by a Granodiorite Group which contains diorite xenoliths. In turn, both of these were intruded by an Inhomogeneous Suite of rocks varying from meladiorite through to tonalite. Field evidence and geochemistry show that this last, highly variable suite of rocks was formed by the unusual process of fractional crystallization coupled with disruption and partial redigestion of early solid fractionates by derivative liquids, leading to the marked inhomogeneity. Such a mechanism may be more generally applicable but clear evidence for it seems to be restricted to rocks of dioritic composition. The margins of the Inhomogeneous Suite usually consist of tonalite which has piped into the surrounding diorites of the Diorite Group, and the two rock groups are thought to have been at least partially liquid at the same time. The exact shape of pipes may prove to be a useful indicator of physicai conditions at the time of magma emplacement in this and other intimate associations of magmas of contrasted composition. Although the Diorite Group was emplaced first, dark (apparently chilled) margins sometimes occur in diorites of this Group where they are in contact with the later Inhomogeneous Suite. In such intimate associations as this, dark margins must be interpreted with extreme caution.

The origin of the diorites and associated rocks of Chouet, north-western Guernsey, Channel Islands

The origin of the diorites and associated rocks of Chouet, north-western Guernsey, Channel Islands

Glass-bearing gabbro inclusions in hyaloclastites from Tindfjallajökull, Iceland

Gabbro inclusions from Tindfjallajökull are divided into two types: I. Panidiomorphic gabbros of non-cumulative origin composed of plagioclase + olivine ± clinopyroxene and interstitil vesicular glass. They have formed in equilibrium with the host magma and may either represent a marginal facies or a highly solidified magma body. In the latter case the host magma or part of it could be mobilized interstitial liquid. II. Allotriomorphic-hypidiomorphic tholeiitic olivine gabbro and diorite xenoliths with scarce Ti-pargasite which have undergone less than 10% partial melting in the host magma forming melts of alkali basaltic or Hekla andesite-like compositions dependent on the original mineral assemblage. Such liquids, enriched in K 2O and possibly other incompatible elements, may contaminate basaltic magmas rising slowly through a gabbroic lower crust. Large scale production of andesites by partial melting of such rocks is not possible but would need more hydrous or differentiated source rocks.

Generation of Icelandic rhyolites by melting of plagiogranites in the oceanic layer

Trondhjemite and quartz diorite xenoliths ejected in recent Icelandic eruptions are believed to be derived from plagiogranites within layer 3, formed by fractional crystallisation of basaltic magmas in the lower crust. Evidence indicates that rift jumping to older crust can lead to partial melting of plagiogranites at depth and their eruption as rhyolitic magmas.

Emplacement of an epizonal granodiorite pluton λ by vertical block elevation

SummaryThe Carrai Granodiorite is an intrusive magmatic pluton with steeply dipping margins surrounded by a well-developed contact metamorphic aureole. Emplacement of the body was accompanied by little distortion of neighbouring rocks and involved vertical displacement of pre-existing material. Scarcity of country rock blocks, and the presence of numerous dioritic xenoliths indicate that stoping was unimportant, and the pluton was accommodated in the upper crust by vertical uplift of earlier rocks (‘block elevation’). A close relationship existed between faulting and granodiorite emplacement. Deep shears possibly account for the generation of the linear zone of plutons in which the Granodiorite is located.

The origin of the Kennethmont granite-diorite series, Insch, Aberdeenshire

SummaryThe Insch granite-diorite complex of Aberdeenshire consists of acid and intermediate igneous rocks that are quite distinct from, and younger than, the differentiates of the Insch basic mass.The main components of the complex include two types of uniform granite (one pink, one grey), and a variety of inhomogeneous dioritic rocks (diorite xenoliths in grey granite matrix, granodiorite with residual mafic inclusions, and more uniform diorite). Full chemical analyses for major and trace elements are presented for sixteen rocks representative of all types, together with initial 87Sr/86Sr ratios and rare-earth-element distribution patterns for a selection of samples. The pink granite is not chemically related to the remaining members of the complex. Comparison with chemical data for a range of basic igneous rocks of the Insch and Boganclogh basic masses discredits the hypothesis that the diorite rocks were produced by assimilation of any of these in the grey granite magma. A primary diorite magma is recognized as essential to the petrogenesis of the complex.

Disposition des enclaves du granite et granitisation [with discussion

Abstract The orientation of diorite xenoliths in granite of the Saint-Jean-du- Doigt region, Finistere, France, indicates that they are in place and represent the relics of diorite which was granitized by recrystallization in the solid state.