scholarly journals The Upper Cretaceous intrusive rocks with extensive crustal contribution in Hacımahmutuşağı Area (Aksaray/Turkey)

2019 ◽  
Vol 70 (3) ◽  
pp. 261-276
Author(s):  
Serhat Köksal
Keyword(s):  
Mafic Magma ◽  
The Other ◽  
Granitic Rocks ◽  
Geochemical Data ◽  
Magma Source ◽  
Accessory Zircon ◽  
Fine Grained ◽  
Intrusive Rocks ◽  
Crustal Contribution ◽  
Opaque Minerals

Abstract The Hacımahmutuşağı area (Aksaray/Turkey) is located in the western part of the Central Anatolian Crystalline Complex (CACC). Gneiss and marble compose the basement units, while intrusive rocks are gabbros and granitoids. The pegmatitic hornblende gabbros contain pegmatitic to fine-grained hornblendes, plagioclase, clinopyroxene, and accessory opaque minerals. The fine-grained gabbros, on the other hand, are composed of plagioclase, hornblende, and biotite as major components whereas the apatite and opaque minerals are present in accessory content. Granitic– granodioritic rocks are the common intrusive rock types in the area, and constitute quartz, orthoclase, plagioclase and biotite, and accessory zircon and opaque minerals. Leucogranites, comprising quartz, orthoclase, plagioclase with minor biotite, hornblende, and with accessory apatite and opaque minerals, are found as dykes intruding the marble and the granitic–granodioritic rocks. Strontium–neodymium isotope data of gabbros and granitoids have high 87Sr/86Sr(i) ratios (0.7076 to 0.7117) and low ɛNd(i) values (−5.0 to −9.8) point out enriched source and pronounced crustal contribution in their genesis. In the Hacımahmutuşağı area, it is plausible that the heat increase caused by the hot zone, which was generated by underplating mafic magma along with the hydrous mafic sills in the lower crust, might have resulted in partial melts from crystallized mafic sills and older crustal rocks. It can be suggested that these hybrid melts adiabatically rose to the shallow crust, ponded and crystallized there and formed the magma source of the intrusive rocks within the Hacımahmutuşağı area and the other hybrid granitic rocks with crustal signatures in the CACC. Geochemical data indicate that granitoids and gabbros are collision to post-collision related sub-alkaline rocks derived from an enriched source with extensive crustal inputs.

scholarly journals Petrogenesis and Tectonic Setting of Early Cretaceous Intrusive Rocks in the Northern Ulanhot Area, Central and Southern Great Xing’an Range, NE China

Minerals ◽  
2021 ◽  
Vol 11 (12) ◽  
pp. 1414
Author(s):  
Baoqiang Tai ◽  
Wentian Mi ◽  
Genhou Wang ◽  
Yingjie Li ◽  
Xu Kong
Keyword(s):  
Early Cretaceous ◽  
Tectonic Setting ◽  
Granite Porphyry ◽  
Granitic Rocks ◽  
Magma Source ◽  
Isotopic Data ◽  
Quartz Porphyry ◽  
Intrusive Rocks ◽  
Quartz Monzonite ◽  
Great Xing’An Range

Abundant Early Cretaceous magmatism is conserved in the central and southern Great Xing’an Range (GXR) and has significant geodynamic implications for the study of the Late Mesozoic tectonic framework of northeast China. In this study, we provide new high-precision U–Pb zircon geochronology, whole-rock geochemistry, and zircon Hf isotopic data for representative intrusive rocks from the northern part of the Ulanhot area to illustrate the petrogenesis types and magma source of these rocks and evaluate the tectonic setting of the central-southern GXR. Laser ablation inductively coupled plasma–mass spectrometry (LA-ICP-MS) zircon U–Pb dating showed that magmatism in the Ulanhot area (monzonite porphyry: 128.07 ± 0.62 Ma, quartz monzonite porphyry: 127.47 ± 0.36, quartz porphyry: 124.85 ± 0.34, and granite porphyry: 124.15 ± 0.31 Ma) occurred during the Early Cretaceous. Geochemically, monzonite porphyry belongs to the metaluminous and alkaline series rocks and is characterized by high Al2O3 (average 17.74 wt.%) and TiO2 (average 0.88 wt.%) and low Ni (average 4.63 ppm), Cr (average 6.69 ppm), Mg# (average 31.11), Y (average 15.16 ppm), and Yb (average 1.62 ppm) content with enrichment in Ba, K, Pb, Sr, Zr, and Hf and depletion in Ti, Nb, and Ta. The granitic rocks (e.g., quartz monzonite porphyry, quartz porphyry, and granite porphyry) pertain to the category of high-K calc-alkaline rocks and are characterized by high SiO2 content (>66 wt.%) and low MgO (average 0.69 wt.%), Mg# (average 31.49 ppm), Ni (average 2.78 ppm), and Cr (average 8.10 ppm) content, showing an affinity to I-type granite accompanied by Nb, Ta, P, and Ti depletion and negative Eu anomalies (δEu = 0.57–0.96; average 0.82). The Hf isotopic data suggest that these rocks were the product of the partial melting of juvenile crustal rocks. Notably, fractionation crystallization plays a crucial role in the process of magma emplacement. Combining our study with published ones, we proposed that the Early Cretaceous intrusive rocks in the Ulanhot area were formed in an extensional tectonic background and compactly related to the subduction of the Paleo-Pacific Ocean plate.

scholarly journals Mineralized biosignatures in ALH-77005 Shergottite - Clues to Martian Life?

2019 ◽  
Vol 28 (1) ◽  
pp. 32-39
Author(s):  
Ildikó Gyollai ◽  
Márta Polgári ◽  
Szaniszló Bérczi ◽  
Arnold Gucsik ◽  
Elemér Pál-Molnár
Keyword(s):  
The Other ◽  
Coarse Grained ◽  
Geochemical Data ◽  
Biogenic Elements ◽  
Geological Samples ◽  
Iron Oxidizing Bacteria ◽  
Opaque Minerals ◽  
Microbial Mediation ◽  
Forms Of Iron ◽  
Section Sample

Abstract The ALH-77005 Martian meteorite was found in Allan Hills on Antarctica during the Japanese National Institute of Polar Research (1977-1978) mission. One thin section sample was studied by optical microscopy for microtexture and by FTIR-ATR microscopy for interpretation of biogenic minerals and embedded organic materials. The geochemical data (biogenic elements, δ13C) of ALH-77005 meteorite from literature implementing recent results were compared to terrestrial geological samples. The ALH-77005 has poikilitic textures with coarse pyroxenes and brown olivines, and with recrystallized melt pocket. The coarse-grained minerals do not contain any alteration along the grain boundaries. Melt pocket and vicinity of opaque minerals contain biogenic signatures as filamentous, coccoidal forms of iron-oxidizing bacteria. The biosignatures were determined by 1) coccoidal, filamentous forms, 2) presence of embedded organic material, 3) presence of biogenic minerals, like ferrihydrite, goethite, and hematite. The other signatures for biogenicity of this meteorite are strong negative δ13C, enrichment of Fe, Mn, P, Zn in shock melt support scenario. This study proposes presence of microbial mediation on Mars.

Carbonate enrichment at the margins of a basic dyke, Ardnamurcha

1974 ◽  
Vol 39 (305) ◽  
pp. 514-524 ◽  
Author(s):  
M. K. Wells ◽  
A. C. S. Smith ◽  
J. F. W. Bowles
Keyword(s):  
Mineral Content ◽  
Microprobe Analysis ◽  
The Other ◽  
Transient Effects ◽  
Basic Dyke ◽  
X Ray ◽  
Fine Grained ◽  
Titaniferous Magnetite ◽  
Oxide Phases ◽  
Opaque Minerals

SummaryA gradational increase in concentration of CO2 towards the margins of a very fine-grained basalt dyke has led to the development of a pale marginal facies, enriched in carbonates, particularly siderite. Increases in CO2 from about 3 % in the interior of the dyke to 8 % at the margins are accompanied by decreases in SiO2 and Fe2O3, increases in Al2O3, and less significant changes in the other major components. Cu, Co, and Zn change only slightly, and Cr, Ni, and Li remain constant. Petrographic variation is considerable, even in the superficially homogeneous interior of the dyke, in which it ranges from a type containing a titanaugite (analysed) to one devoid of pyroxene, but containing conspicuous opaque minerals. Microprobe analysis for Fe and Ti shows that these comprise: cotahedral titaniferous magnetite; rodlets, less than 1 µm thick, of rutile partly altered to, or overgrown by, ilmenite; and sub-opaque patches with a very low Ti/Fe ratio. Plagioclase, An55, is the most abundant and constant crystalline phase in the interior of the dyke, but changes to An20 in the marginal facies. Mineral-content of the latter, deduced from optical, chemical, and X-ray data, also includes siderite, serpentine and clay minerals, leucoxene, and apatite. There is no evidence of quartz, sericite, or calcite.Petrographic evidence shows that variations in concentrations of CO2 and H2O affected phase equilibria from the start of magmatic crystallization. Data on the fO2 required for TiO2 and Fe-oxide phases to co-exist at magmatic temperatures indicate that, initially, the concentrations of CO2 and H2O in the interior of the dyke were higher than the values recorded in analyses of the rocks. From this evidence and the field relationships, it is concluded that the intruding magma was rich in volatiles, which diffused towards the dyke margins and, in part, became trapped as the magma congealed, producing a changed marginal assemblage of minerals. The dyke provides a unique glimpse of influences on a basic magma exerted by what S. J. Shand has aptly termed the ‘fugitive constituents’, the transient effects of which are rarely preserved in the rocks.

scholarly journals Epizonal I- and A-type granites and associated ash-flow tuffs, Fogo Island, northeast Newfoundland

1995 ◽  
Vol 32 (11) ◽  
pp. 1835-1844 ◽  
Author(s):  
Hamish A. Sandeman ◽  
John Malpas
Keyword(s):  
Alkali Feldspar ◽  
Granitic Rocks ◽  
Calc Alkaline ◽  
Fine Grained ◽  
Sedimentary Sequences ◽  
Intrusive Rocks ◽  
High Silica ◽  
Composite Nature ◽  
End Members ◽  
Devonian Age

Magmatic activity of Silurian–Devonian age is widespread in the Appalachian–Caledonian Orogen. A marked characteristic of this magmatism is the composite nature of the igneous suites, which range from peridotite to granodiorite in single plutonic bodies. The origin of these suites is still enigmatic, and the assumption that all are the same not proven. Such a suite of intrusive rocks, ranging in composition from minor peridotite to granodiorite, intrudes an openly folded sequence of Silurian volcanogenic sandstones and ash-flow tuffs on Fogo Island, northeast Newfoundland. Two units, the Rogers Cove and Hare Bay microgranites, consist of fine-grained hastingsite granites with spherulitic and flow-banded textures, and exhibit drusy cavities and microfractures that contain the mineral assemblage hastingsitic hornblende + plagioclase + magnetite + zircon. These rocks are characterized by elevated high field strength element contents (e.g., Zr = 74–672 and Y = 21–103 ppm), very high FeO*/MgO ratios (FeO*/MgO = 2.4–93.5), and 10 000 Ga/Al ratios of 1.67–10.52, indicating an A-type granitoid affinity. A third and the most voluminous granitic unit, the Shoal Bay granite, is an alkali-feldspar-phyric, medium-grained, equigranular biotite–hastingsite granite with hastingsite and annitic biotite interstitial to euhedral plagioclase, anhedral quartz, and perthite crystals. The Shoal Bay granite exhibits mineral parageneses similar to the microgranites, but chemical characteristics more typical of calc-alkaline, I-type granitoids. Volcanic–sedimentary sequences spatially associated with the granitic rocks include dense, welded, high-silica, hastingsite-bearing ash-flow tuffs with compositions that suggest they represent erupted equivalents of fractionated end members of the Shoal Bay granite. The rocks making up the Fogo Island batholith have been directly equated with the bimodal, calc-alkaline Mount Peyton batholith of northeast Newfoundland, but the specialized A-type nature of the Fogo granites suggests differing source conditions for the two suites.

scholarly journals Petrology of plagiogranite from Sjenica, Dinaridic Ophiolite Belt (southwestern Serbia)

2012 ◽  
Vol 63 (2) ◽  
pp. 97-106 ◽  
Author(s):  
Dragan Milovanović ◽  
Danica Srećković-Batoćanin ◽  
Marija Savić ◽  
Dana Popovic
Keyword(s):  
Hydrothermal Alteration ◽  
Sea Water ◽  
Mafic Magma ◽  
Granitic Rocks ◽  
Field Observations ◽  
Secondary Minerals ◽  
Sea Floor ◽  
Fine Grained ◽  
Mantle Origin ◽  
Ophiolite Belt

Petrology of plagiogranite from Sjenica, Dinaridic Ophiolite Belt (southwestern Serbia)The Sjenica plagiogranite occurs in the southern part of the Dinaridic Ophiolite Belt, 5 km northwest of Sjenica. The main minerals are albite with strongly altered biotite (replaced with chlorite), with occasional amphibole (magnesio hornblende to tschermakite) and quartz. An enclave of fine-grained granitic rocks with garnet grains was noted too. Secondary minerals are calcite and chlorite (daphnite). Major, trace and REE geochemistry coupled with field observations support a model by which the Sjenica plagiogranite could be formed by fractional crystallization of mantle origin mafic magma in a supra-subduction zone setting. Occurrences of calcite and chlorite nests in the Sjenica plagiogranites revealed that these rocks underwent hydrothermal alteration due to intensive sea water circulation in a sub-sea-floor environment.

Magma source and evolution of Late Neoproterozoic granitoids in the Gabal El-Urf area, Eastern Desert, Egypt: geochemical and Sr–Nd isotopic constraints

1999 ◽  
Vol 136 (3) ◽  
pp. 285-300 ◽  
Author(s):  
ABDEL-KADER M. MOGHAZI
Keyword(s):  
Mafic Magma ◽  
Eastern Desert ◽  
Crustal Thickening ◽  
Geochemical Data ◽  
Magma Source ◽  
Crustal Thinning ◽  
North Eastern ◽  
Nubian Shield ◽  
Late Neoproterozoic ◽  
Arabian Nubian Shield

Granitoids in the Gabal El-Urf area in Eastern Egypt consist of a monzogranite pluton, belonging to the Younger Granite province, emplaced in granodioritic rocks. Whole rock Rb–Sr dating indicate ages of 650±95 Ma and 600±11 Ma for the granodiorites and monzogranites, respectively. The granodiorites (65–70% SiO2) are calc-alkaline and metaluminous with low Rb/Sr, Th and Nb contents, moderate enrichment in the LILE (K2O, Rb, and Ba) and display most of the chemical and field characteristics of syn-to late-tectonic I-type granitoids described elsewhere in the Arabian–Nubian Shield. The monzogranites (72–77% SiO2) are metaluminous to mildly peraluminous, highly fractionated and depleted in Al2O3, MgO, CaO, TiO2, Sr and Ba with corresponding enrichment in Rb, Nb, Zr, and Y. They can be correlated with the undeformed post-orogenic granites in the Arabian–Nubian Shield that chemically resemble A-type granites emplaced in extensional settings. The mineralogical and chemical variations within the granodiorites and monzogranites are consistent with their evolution by fractional crystallization. The granodiorites have a low initial 87Sr/86Sr ratio (0.7024) and high ∈Nd values (+6.9–+7.3) and are significantly different from those (initial 87Sr/86Sr ratio=0.7029, ∈Nd values=+5.2–+5.8) of the monzogranites. These data suggest a predominant mantle derivation for both granite types and demonstrate that they originated from different source materials.The granodiorite melt was most probably generated through vapour-saturated partial melting of an early Neoproterozoic depleted mafic lower-crust reservoir due to crustal thickening associated with orogenic compression and/or arc magma underplating. The mineralogical and geochemical data of the A-type monzogranites are consistent with their derivation as a residual granitic liquid from a LILE-enriched mafic magma through crystal-liquid fractionation of plagioclase, amphibole, Fe–Ti oxides and apatite. The parental mafic magma was originated in the upper mantle due to crustal thinning associated with extension in the late stage of the Neoproterozoic crustal evolution of north-eastern Egypt.

Petrogenesis and tectonic implications of Late Jurassic – Early Cretaceous granitic magmatism in the Xing’an Block, Northeast China: geochronological, geochemical, and Hf isotopic evidence

2018 ◽  
Vol 55 (6) ◽  
pp. 571-588 ◽  
Author(s):  
Yue He ◽  
Zhong-Hua He ◽  
Wen-Chun Ge ◽  
Hao Yang ◽  
Zhi-Hui Wang ◽  
...  
Keyword(s):  
Partial Melting ◽  
Early Cretaceous ◽  
Northeast China ◽  
Late Jurassic ◽  
Granitic Rocks ◽  
Geochemical Data ◽  
Magma Source ◽  
Isotopic Evidence ◽  
Depleted Mantle ◽  
Microgranular Enclaves

This study presents new geochronological, whole-rock geochemical, and zircon Hf isotopic evidence for the age, petrogenesis, and source of Mesozoic granitic rocks of the Xing’an Block, Northeast China. This evidence reveals the Late Mesozoic tectonic evolution of the eastern section of the Central Asian Orogenic Belt. Laser-ablation inductively coupled plasma – mass spectrometryzircon U–Pb age data indicate that the syenogranite, monzogranite, and alkali feldspar granite units, as well as their associated diorite microgranular enclaves, were emplaced between 150–142 Ma, providing evidence of Late Jurassic to Early Cretaceous magmatic events within the Xing’an Block. The granites contain high concentrations of SiO2 (65.24%–75.73 wt.%) and K2O (3.94%–5.30 wt.%), low concentrations of MgO (0.10%–1.30 wt.%), and A/CNK values of 0.92–1.06. In addition, Hf isotopic analysis of zircons from the 150–142 Ma granites yields εHf(t) values of +4.54 to +12.16 and two-stage Hf model aged from 906 to 423 Ma, indicating that they formed from magmas generated by partial melting of a juvenile Neoproterozoic–Phanerozoic accreted crustal source. The basic magma source for the diorite microgranular enclaves most likely formed from partial melting of a depleted mantle that had been metasomatized by subduction-related fluids. Combining these new geochemical data with the geology of this region, Late Jurassic to Early Cretaceous magmatism in the Xing’an Block most likely occurred in an extensional environment associated with closure of the Mongol–Okhotsk Ocean.

scholarly journals Geochemistry and petrogenesis of post-collisional ultrapotassic syenites and granites from southernmost Brazil: the Piquiri Syenite Massif

2008 ◽  
Vol 80 (2) ◽  
pp. 353-371 ◽  
Author(s):  
Lauro V.S. Nardi ◽  
Jorge Plá-Cid ◽  
Maria de Fátima Bitencourt ◽  
Larissa Z. Stabel
Keyword(s):  
Granitic Rocks ◽  
Geochemical Data ◽  
Fine Grained ◽  
Enriched Mantle ◽  
Calcic Amphibole ◽  
Pan African ◽  
High K ◽  
Mantle Sources ◽  
Orogenic Cycle ◽  
Tholeiitic Magmatism

The Piquiri Syenite Massif, southernmost Brazil, is part of the post-collisional magmatism related to the Neoproterozoic Brasiliano-Pan-African Orogenic Cycle. The massif is about 12 km in diameter and is composed of syenites, granites, monzonitic rocks and lamprophyres. Diopside-phlogopite, diopside-biotite-augite-calcic-amphibole, are the main ferro-magnesian paragenesis in the syenitic rocks. Syenitic and granitic rocks are co-magmatic and related to an ultrapotassic, silica-saturated magmatism. Their trace element patterns indicate a probable mantle source modified by previous, subduction-related metasomatism. The ultrapotassic granites of this massif were produced by fractional crystallization of syenitic magmas, and may be considered as a particular group of hypersolvus and subsolvus A-type granites. Based upon textural, structural and geochemical data most of the syenitic rocks, particularly the fine-grained types, are considered as crystallized liquids, in spite of the abundance of cumulatic layers, schlieren, and compositional banding. Most of the studied samples are metaluminous, with K2O/Na2O ratios higher than 2. The ultrapotassic syenitic and lamprophyric rocks in the Piquiri massif are interpreted to have been produced from enriched mantle sources, OIB-type, like most of the post-collisional shoshonitic, sodic alkaline and high-K tholeiitic magmatism in southernmost Brazil. The source of the ultrapotassic and lamprophyric magmas is probably the same veined mantle, with abundant phlogopite + apatite + amphibole that reflects a previous subduction-related metasomatism.

scholarly journals Crystallization and Segregation of Syenite in Shallow Mafic Sills: Insights from the San Rafael Subvolcanic Field, Utah

2020 ◽  
Author(s):  
Aurelie Germa ◽  
Danielle Koebli ◽  
Paul Wetmore ◽  
Zachary Atlas ◽  
Austin Arias ◽  
...  
Keyword(s):  
Volcanic Rocks ◽  
Mafic Magma ◽  
Coarse Grained ◽  
Geochemical Data ◽  
Fine Grained ◽  
Mantle Sources ◽  
Plumbing Systems ◽  
Order Of Magnitude ◽  
Magma Compositions ◽  
San Rafael

Abstract Exposed plumbing systems provide important insight into crystallization and differentiation in shallow sills beneath volcanic fields. We use whole rock major element, trace element and radiogenic isotopic compositions, along with mineral geochemical data on 125 samples to examine the conditions of melt differentiation in shallow sills from the exposed 4-Ma-old San Rafael subvolcanic field (SRVF), Utah. The field consists of ∼2000 dikes, 12 sills and 63 well preserved volcanic conduits. Intrusive rocks consist of mainly fine-grained trachybasalts and coarse-grained syenites, which are alkaline, comagmatic and enriched in Ba, Sr and LREE. Within sills, syenite is found as veins, lenses, and sheets totally enveloped by the basalt. The SRVF intrusions have geochemical signatures of both enriched sub-continental lithospheric and asthenospheric mantle sources. We estimate partial melting occurred between 1·2 and 1·9 GPa (50–70 km), with mantle potential temperatures in the range 1260–1326 ± 25°C, consistent with those estimated for volcanic rocks erupted on the Colorado Plateau. Geobarometry results based on clinopyroxene chemistry indicate that (1) basalt crystallized during ascent from at least 40 km deep with limited lithospheric storage, and (2) syenites crystallized only in the sills, ∼1 km below the surface. San Rafael mafic magma was emplaced in sills and started to crystallize inward from the sill margins. Densities of basalt and syenite at solidus temperatures are 2·6 and 2·4 g/cc, respectively, with similar viscosities of ∼150 Pa s. Petrographic observations and physical properties suggest that syenite can be physically separated from basalt by crystal compaction and segregation of the tephrophonolitic residual liquid out of the basaltic crystal mush after reaching 30–45% of crystallization. Each individual sill is 10–50 m thick and would have solidified fairly rapidly (1–30 years), the same order of magnitude as the duration of common monogenetic eruptions. Our estimates imply that differentiation in individual shallow sills may occur during the course of an eruption whose style may vary from effusive to explosive by tapping different magma compositions. Our study shows that basaltic magmas have the potential to differentiate to volatile-rich magma in shallow intrusive systems, which may increase explosivity.

Mineral chemistry, petrogenesis, and tectonic setting of the Wateranga layered intrusion, southeast Queensland, Australia

2005 ◽  
Vol 42 (11) ◽  
pp. 1967-1985 ◽  
Author(s):  
Reddy VR Talusani ◽  
Warwick J Sivell ◽  
Paul M Ashley
Keyword(s):  
Tectonic Setting ◽  
Parental Magma ◽  
Layered Intrusion ◽  
Mafic Magma ◽  
Mineral Chemistry ◽  
Geochemical Data ◽  
Magma Source ◽  
Olivine Gabbro ◽  
Layered Mafic Intrusion ◽  
Southeast Queensland

The Wateranga layered mafic intrusion (28 km2 in area, > 500 m thick) is a tholeiitic, undeformed, unmetamorphosed, Permo-Triassic layered gabbroic pluton intruded into the late Carboniferous Goodnight beds of the Goodnight Block in southeast Queensland. The intrusion mainly consists of gabbro and norite, associated with subordinate amounts of troctolite, anorthosite, and orthopyroxenite, and rare picrite. Olivine gabbro is the dominant rock type of the intrusion. Fractionation followed a tholeiitic trend with iron enrichment in the liquid. Petrographic, mineral chemical, and whole-rock geochemical data have been used to divide the intrusion into Lower, Middle, and Upper zones, which are interpreted as reflecting magma chamber replenishment. The observed changes in the crystallization order between the zones reveal that a single parental magma is inadequate to explain the data. The common differentiation indices, such as An content of plagioclase, Mg#s of olivine, clinopyroxene, orthopyroxene and whole-rocks, and the whole-rock concentrations of various incompatible trace elements (Zr, Y, Nb, La Ba, Rb, Sr, and Nd), all vary widely with stratigraphic depth and display abrupt shifts at the zone boundaries, indicating open system addition of new mafic magma. Temperatures estimated from two-pyroxene geothermometer vary from 1057 to 927 °C. During the course of crystallization, pressure probably was > 2 and < 4 kbar (1 kbar = 100 MPa). The variation trend of anorthite content of plagioclase versus the forsterite content of olivine precludes an arc-related magma source. The composition and geological setting of the intrusion are consistent with emplacement in a post-subduction extensional tectonic environment.

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