Pyroxene Diorite Research Articles

Early Silurian adakitic high‐Mg diorite from the Longshan area: Implication for melting of mantle lithosphere in the south‐eastern Qilian Orogenic Belt

The Longshan area is located in the junction zone between the Qinling and eastern Qilian orogenic belts. Early Palaeozoic igneous rocks in this area can provide important insights into the evolution of Shangdan Ocean. This paper reports new petrology, chronology, major and trace element geochemistry, Sr–Nd isotope, and zircon Lu–Hf isotopic compositions for the Early Silurian pyroxene diorite in the Longshan area. The pyroxene diorite has a zircon U–Pb age of 432 ± 1 Ma (MSWD = 0.25, n = 27). The pyroxene diorite intrusion displays low SiO2 (53.34 to 56.32 wt.%), high Na2O (3.11% to 3.79 wt.%) and Sr (1112 to 1234 ppm) contents, and moderate Mg# (52.70 to 55.00) values, high Sr/Y (67 to 84) ratios, depleted in Y and HREE; these features are identical with the low‐Si adakite or sanukitoids that derived from melting of metasomatized mantle wedge. The pyroxene diorite intrusion has evolved Sr–Nd isotopic compositions, (87Sr/86Sr) i = 0.705286 to 0.705310, εNd(t) = −3.4 to −3.9. Zircons from the pyroxene diorite display variable εHf(t) values of −3.6 to +0.1. These features suggest that the pyroxene diorite intrusion was derived from a hydrous melting metasomatized mantle wedge which has been modified by slab melts. The occurrence of pyroxene diorite indicates an Early Silurian active continental margin setting in the south‐eastern Qilian Orogenic Belt.

The characteristics, origin, and significance of mafic microgranular enclaves in the granitoids from the Bailingshan complex, Eastern Tianshan, NW China

The Bailingshan complex is located to the south of the Jueluotage tectonic belt of Eastern Tianshan, consisting of quartz monzodiorite, granodiorite, monzogranite, and granite. Mafic microgranular enclaves (MME) are commonly found in granodiorites and monzogranites and have sharp contacts with the host rocks. Sometimes, the fine veins of the host rocks cut through the enclaves. The MMEs are mainly fine‐grained dioritic rocks, including diorite and pyroxene diorite with igneous textures, and having condensing edges with rich fine dark minerals. Among the enclaves, the orthoclase xenocryst with hornblende aggregation rim at its edge, acicular apatites in plagioclase, sometimes late‐crystallized biotites between the oscillatory zonings of plagioclase, and hornblende metasomatic rims occur around the pyroxene phenocrysts can be observed. Both the host rocks and the enclaves are metaluminous and calc‐alkaline to high‐K calc‐alkaline rocks. The enclaves have lower SiO2 and higher Al2O3, FeOT, MgO, CaO, and TiO2 concentrations, as well as higher amounts of the trace elements Cr, Sc, and Th than the host rocks. The host rocks and the enclaves exhibit similar rare earth elements patterns and linear relation of oxides. The sulphur isotopes (δ34S(V‐CDT) = −1.7‰ to +0.7‰) from the iron ores in the Bailingshan area indicate that the mineralization materials originated from the upper mantle. All of these lithology and geochemistry characteristics demonstrate that the enclaves were formed by the mixture of mantle‐derived mafic magma and crust‐derived felsic magma. The iron ore mineralization in the Bailingshan area may be associated with the magma mixing.

The magma evolution sequence and geodynamic setting in the Qibaoshan ore area, Wulian County, Shandong Province, China

The Qibaoshan ore area is located in Wulian town, Shandong Province, which is an important polymetallic metallogenic zone containing gold, copper, lead, and zinc. The polymetallic mineralization is mostly related to the Qibaoshan complex. The Qibaoshan complex is composed mainly of pyroxene diorite, andesitic porphyrite, pyroxene andesite porphyrite, amphibole andesite porphyrite, diorite porphyrite, and granodiorite porphyry, among which granodiorite–porphyry is the main wall rock of gold and copper ore body, whereas lead and zinc mineralization is closely related to diorite porphyrite. A combined study of laser ablation–inductively coupled plasma–mass spectrometry zircon U–Pb dating and geochemical analyses (major and trace elements) for 5 Mesozoic plutons from the Qibaoshan complex was carried out to determine their ages, petrogenesis, and tectonic setting. The U–Pb zircon ages measured by laser ablation–inductively coupled plasma–mass spectrometry indicate that the Qibaoshan complex was emplaced in 3 stages, represented by the ~175 Ma pyroxene diorite, ~129 Ma andesitic porphyrite/ porphyrite, ~125 Ma granodiorite‐porphyry, and ~112 Ma diorite porphyrite. Systematic diagenetic chronology and rock geochemistry show that formation of ~175 Ma pyroxene diorite in Qibaoshan ore‐concentrated area is possibly related to the transformation environment from compression to extension of the Sulu orogenic belt and/or of the subduction of the Pacific Plate, whereas the formation of the Early Cretaceous subvolcanic rock has a volcanic arc affinity related to subduction of the Pacific Plate. Based on the previous studies, this paper argues that the metallogenic age of Qibaoshan polymetallic ore‐concentrated area is 125–105 Ma, which is formed in the volcanic arc dynamics environment of the Pacific Plate subduction in the Late Yanshanian. In addition, a small amount of 610–799 Ma and 1.8 Ga was developed in the samples of the pyroxene diorite and andesitic porphyrite, suggesting their source may have great affinities with South China.

Zircon U-Pb geochronology, Hf isotopes and geochemistry of intrusive rocks in the Simorgh prospecting area, Lut Block, eastern Iran: petrogenesis and geological implications

The Simorgh prospecting area is located in the central part of the Lut Block in eastern Iran. The Lut Block, the eastern part of the Central Iranian Microcontinent (CIM), has a complex tectonic evolution and is characterized by extensive magmatic activities with a range of geochemical signatures. The Simorgh intrusions have features typical of calc-alkaline to high-K calc-alkaline rocks, metaluminous to slightly peraluminous and formed in a volcanic arc setting. Mineralization in the area is believed to be related to these intrusions. To better understand the petrogenesis of these intrusions, we report zircon U-Pb dating and Hf isotopes and whole rock geochemistry of two granites and one diorite. Age dating using Zircon U-Pb method on pyroxene diorite porphyry stock and two granite porphyry dikes revealed 24.85 ± 0.51 Ma, 25.37 ± 0.56 Ma and 25.94 ± 0.76 Ma ages respectively (late Oligocene, Chattian). Field observations and U-Pb dating indicate that there are at least two stages of emplacement: pre-mineralization intrusions (diorite porphyry) and syn-mineralization intrusions (granite porphyry, granodiorite porphyry and pyroxene diorite porphyry). Mantle-normalized, trace-element spider diagrams display enrichment in large ion lithophile elements (LILE) and light rare earth elements ((La/Yb)N = 9.26–14.48), and depletion in high field strength elements (HFSE) and heavy rare earth elements, as well as negative Eu anomalies (Eu/Eu* = 0.49–0.91). Zircon Hf isotope data from the Simorgh intrusive rocks show largely positive eHf(t) (average = 3.6 ± 2.0). Hf model ages are ranging from 720 to 1320 Ma, indicating its derivation from a relatively juvenile source. The presence of zircon xenocrysts may prove its contamination by older continental crust (Siderian).

Geochemical contrasts between Late Triassic ore-bearing and barren intrusions in the Weibao Cu\u2013Pb\u2013Zn deposit, East Kunlun Mountains, NW China: constraints from accessory minerals (zircon and apatite)

The Weibao copper–lead–zinc skarn deposit is located in the northern East Kunlun terrane, NW China. Igneous intrusions in this deposit consist of barren diorite porphyry (U–Pb zircon age of 232.0 ± 2.0 Ma) and ore-bearing quartz diorite and pyroxene diorite (U–Pb zircon ages of 223.3 ± 1.5 and 224.6 ± 2.9 Ma, respectively). Whole-rock major and trace element and accessory mineral (zircon and apatite) composition from these intrusions are studied to examine the different geochemical characteristics of ore-bearing and barren intrusions. Compared to the barren diorite porphyry, the ore-bearing intrusions have higher Ce4+/Ce3+ ratios of zircon and lower Mn contents of apatite, indicating higher oxidation state. Besides, apatite from the ore-bearing intrusions shows higher Cl contents and lower F/Cl ratios. These characteristics collectively suggest the higher productivity of ore-bearing quartz diorite and pyroxene diorite. When compared with ore-bearing intrusions from global porphyry Cu deposits, those from Cu–Pb–Zn skarn deposits display lower Ce4+/Ce3+ and EuN/EuN* ratios of zircon and lower Cl and higher F/Cl ratios of apatite. We conclude that these differences reflect a general geochemical feature, and that zircon and apatite composition is a sensitive tool to infer economic potential of magmas and the resulting mineralization types in intrusion-related exploration targets.

Geochronology and geochemistry of early Paleozoic intrusive rocks from the Khanka Massif in the Russian Far East: Petrogenesis and tectonic implications

This paper presents new geochronological and geochemical data for early Paleozoic intrusive rocks from the Khanka Massif in the Russian Far East, with the aim of elucidating the Paleozoic evolution and tectonic attributes of the Khanka Massif. New U–Pb zircon data indicate that early Paleozoic magmatism within the Khanka Massif can be subdivided into at least four stages: ~502, ~492, 462–445, and ~430Ma. The ~502Ma pyroxene diorites contain 58.28–59.64wt% SiO2, 2.84–3.69wt% MgO, and relatively high Cr and Ni contents. Negative εHf(t) values (−1.8 to −0.4), along with other geochemical data, indicate that the primary magma was derived from partial melting of mafic lower crust with the addition of mantle material. The ~492Ma syenogranites have high SiO2 and K2O contents, and show positive Eu anomalies, indicating the primary magma was generated by partial melting of lower crust at relatively low pressure. The ~445Ma Na-rich trondhjemites display high Sr/Y ratios and positive εHf(t) values (+1.8 to +3.9), indicating the primary magma was generated by partial melting of thickened hydrous mafic crust. The ~430Ma granitoids have high SiO2 and K2O contents, zircon εHf(t) values of −5.4 to +5.8, and two-stage model ages of 1757–1045Ma, suggesting the primary magma was produced by partial melting of heterogeneous Proterozoic lower crustal material. The geochemistry of these early Paleozoic intrusive assemblages indicates their formation in an active continental margin setting associated with the subduction of a paleo-oceanic plate beneath the Khanka Massif. The εHf(t) values show an increasingly negative trend with increasing latitude, revealing a lateral heterogeneity of the lower crust beneath the Khanka Massif. Regional comparisons of the magmatic events indicate that the Khanka Massif in the Russian Far East has a tectonic affinity to the Songnen–Zhangguangcai Range Massif rather than the adjacent Jiamusi Massif.

Paleozoic tectonic evolution of the Dananhu-Tousuquan island arc belt, Eastern Tianshan: Constraints from the magmatism of the Yuhai porphyry Cu deposit, Xinjiang, NW China

The Yuhai intrusions (quartz diorite, granite and pyroxene diorite) are located in the eastern part of the Dananhu-Tousuquan island arc belt of the Eastern Tianshan, and associated with the early Paleozoic porphyry Cu mineralization. LA-ICP-MS zircon U-Pb dating yielded emplacement ages of 443.5±4.1Ma for the quartz diorite, 325.4±2.5Ma for the granite, and 291±3.0Ma for the pyroxene diorite. These rocks are tholeiitic to calc-alkaline and metaluminous, with A/CNK values ranging from 0.66 to 1.10. The Silurian ore-bearing Yuhai quartz diorite is rich in LREEs and LILEs (e.g., K, Ba, Pb and Sr), and depleted in HREEs and HFSEs (e.g., Nb, Ta and Ti). These rocks are MgO-rich (1.90–3.80wt.%; Mg#=37–72), with high Sr/Y, La/Yb and Ba/Th ratios, positive εNd(t) (6.31–6.84) and εHf(t) (13.26–16.40), low (87Sr/86Sr)i (0.7037–0.7039), and low Nb/U and Ta/U ratios. The data suggest that the quartz diorite was generated by the partial melting of subducted juvenile oceanic slab. The oxygen fugacity (ƒO2) of the quartz diorite, calculated by zircon Ce4+/Ce3+ ratios, is higher than that of the granite and pyroxene diorite, implying that the quartz diorite was more favorable to porphyry Cu mineralization. The Carboniferous Yuhai granite reveals similar geochemical features with the quartz diorite, except for the lower Mg# (27–33), and the more elevated Th/U and Th/La ratios. Furthermore, these rocks also show high εNd(t) (5.2–5.8) and εHf(t) (11.03–14.85) values, and low (87Sr/86Sr)i (0.7036–0.7037). These features indicate that the parental magma of the granite was probably derived from a juvenile lower crust with no significant mantle component involvement. Different from the Yuhai quartz diorite and granite, the early Permian Yuhai pyroxene diorite contains low SiO2 (50.76–55.74 wt.%) and high MgO (3.96–4.33 wt.%; Mg#=40–44). The εNd(t), εHf(t) and (87Sr/86Sr)i values of the pyroxene diorite are 5.77–6.42, 7.99–12.10 and 0.7035–0.7040, respectively. The pyroxene diorite shows slight enrichments in LREEs ((La/Yb)N=2.04–2.55), Ba, U, K and Pb, weak depletions in Nb, Ta and Ti, elevated Th/U ratios, and low Ni contents and Ce/Pb ratios. Integrating with the regional tectonic evolution, we suggest that the pyroxene diorite was likely originated from the partial melting of depleted mantle metasomatized by subducted slab-derived fluids. In addition, crustal contamination likely occurred when the pyroxene diorite magma traversed the continental crust.Integrating our new results with published works on the early Paleozoic Dananhu-Tousuquan and Bogeda-Haerlike island arc belts, we propose that the Yuhai quartz diorite may have formed in a subduction setting related to the N-dipping subduction of the North Tianshan oceanic plate. The younger Yuhai granite was likely generated by the bipolar subduction of the North Tianshan oceanic plate, which formed both of the Dananhu-Tousuquan belt to the north and the Aqishan-Yamansu belt to the south. The youngest Yuhai pyroxene diorite was likely formed under a post-collisional extension setting after the Dananhu-Tousuquan and Aqishan-Yamansu belts had collided.

Ages, geochemistry and tectonic implications of the Cambrian igneous rocks in the northern Great Xing’an Range, NE China

The Xinlin–Xiguitu suture zone, located in the Great Xing’an Range, NE China, in the eastern segment of the Central Asian Orogenic Belt (CAOB), represents the boundary between the Erguna and Xing’an micro-continental blocks. The exact location of the Xinlin-Xiguitu suture zone has been debated, especially, the location of the northern extension of the suture zone. In this study, based on a detailed field, geochemical, geochronological and Sr–Nd–Hf isotope study, we focus our work on the Cambrian igneous rocks in the Erguna-Xing’an block. The Xinglong granitoids, mainly include ∼520Ma diorite, ∼470Ma monzogranite and ∼480Ma pyroxene diorite. The granitoids show medium to high-K calc-alkaline series characteristics with post-collision granite affinity. The circa 500Ma granitoids have low εHf (t) values (−16.6 to +2.2) and ancient two-stage model (TDM2) ages between 1317Ma and 2528Ma. These results indicate the primary magmas of the Xinglong granitoids were probably derived from the partial melting of a dominantly Paleo-Mesoproterozoic “old” crustal source with possible different degrees of addition of juvenile materials, and formed in a post-collision tectonic setting after the amalgamation of the Erguna and Xing’an blocks. Compared with the Xinglong granitoids, the Duobaoshan igneous rocks are consisted of the approximately coeval rhyolitic tuffs (491±5Ma) and ultramafic intrusions (497±5Ma) within the Duobaoshan Formation. They are generally enriched in large ion lithophile elements (LILEs) and depleted in high field strength elements (HFSEs; e.g., Nb, Ta, and Ti), consistent with the geochemistry of igneous rocks from island arcs or active continental margins. The ultramafic rocks have high positive εHf (t) values (+1.3 to +15) and εNd (t) (+1.86 to +2.28), and relatively young two-stage model (TDM2) ages and low initial 87Sr/86Sr ratios (0.70628–0.70853), indicating the partial melting of a depleted mantle source from a subducted slab in the ocean basin between the Erguna-Xing’an and Songliao blocks. The rhyolitic tuffs contain a group of Phanerozoic zircons with εHf (t) values (−4.6 to +15.0), suggesting that the rhyolitic tuffs were derived from juvenile lower crustal material with some ancient crustal material.Coupled with our previous geochemical and isotopic studies on Early Paleozoic igneous rocks, we proposed that the collision of the Erguna and Xing’an blocks at least took place ca. 500Ma ago, and that there exist in a westward subduction of an oceanic plate between the Eruguna-Xing’an and Songliao blocks, took place during the Early Ordovician. Up to now, there are more evidences and constraints that the northern extension location of the Xinlin-Xiguitu suture zone is located in the Jifeng–Xinglong areas.

Petrology and geochemistry of the Juzzak Sill, western Chagai arc (Pakistan): implications for petrogenesis and emplacement

The Juzzak Sill occurs in the western part of the east-west trending, subduction-related magmatic belt known as the Chagai arc. The sill is concordantly emplaced in the Paleocene Juzzak Formation and locally cross-cuts the Early to Middle Eocene Robat Limestone and Eocene Saindak Formation. The sill is a porphyritic pyroxene diorite that grades into a porphyritic andesite (60.12–61.57 wt% SiO2) along the chilled margins. It comprises phenocrysts of hypersthene and plagioclase (An32–45) in a medium- to fine-grained groundmass of these minerals, opaque oxide, and apatite. The rocks are high-K (2.37–2.86 wt% K2O) calc-alkaline with low Mg# (42–55), Cr (51–80 ppm), and Ni (22–30 ppm) contents. Mantle-normalized trace element patterns, exhibited by marked negative Nb anomalies and positive spikes for Sr, Rb, and Zr and are akin to island arc signatures. The relatively higher ratios of Zr/Y (3.57–6.58), Ti/V (46.05–54.36), Ta/Yb (0.14–0.15), and Th/Yb (2.56–2.65) and high 87Sr/86Sr ratio (0.70524) suggest the role of continental crust materials, thus implying continental margin-type arc affinity. The source diagnostic ratios including K/Ba, P/Zr, and La/Ce of Juzzak Sill andesite and Eocene andesite from the Chagai arc are more or less similar, but the former has a much higher K/Y and Ba/Y ratios, which suggests assimilations of the host sediments during intrusion.

Geochemical characteristics of the Shujiadian Cu deposit related intrusion in Tongling: Petrogenesis and implications for the formation of porphyry Cu systems in the Middle–Lower Yangtze River Valley metallogenic belt, eastern China

Porphyry Cu deposits can form in intracontinental or post-collision settings; however, both the genesis of fertile magmas and the mechanism of metal enrichment remain controversial. The Shujiadian porphyry Cu deposit is located in the Tongling area of the Middle–Lower Yangtze River Valley metallogenic belt. It is hosted by the Shujiadian complex, which mainly consists of quartz diorite porphyry (143.7±1.7Ma) and pyroxene diorite (139.8±1.6Ma). They both belong to the calc-alkaline series, with enrichment in large-ion lithophile elements (LILE) and light rare earth elements (LREE), depletion in high field-strength elements (HFSE) and heavy rare earth elements (HREE), and slightly negative Eu anomalies. Both quartz diorite porphyry and pyroxene diorite have geochemical affinities with adakite, and their low MgO (1.5–3.7wt%), and Ni (3.7–6.9ppm), Cr (2.0–44ppm), and Th/Ce contents (0.06–0.11) indicate that the intrusive rocks have some characteristics of adakite-like rocks derived from thickened lower crust and melts from metabasaltic rocks and eclogites. Plagioclases from the quartz diorite porphyry are andesine (An value=31.8–40.5) and from the pyroxene diorite are felsic albite and oligoclase with large-scale zones and variable An value (An value=8.9–18.3), Fe and Sr contents, which indicate that mixing of mafic and felsic magma may have occurred in the shallow magma chamber. Compared to the barren quartz diorite porphyry, relatively lower SiO2 contents (49.5–55.2wt.%), higher εNd(t) values (−7.4 to −6.9), εHf(t) values (−11.0 to −9.1) compositions, Ti-in-zircon temperatures (714–785°C), and variations of HREE contents of the mineralization-related pyroxene diorite suggest mixing with high-temperature mafic magma. Calculated Ce4+/Ce3+ values of pyroxene diorite plot between the Ni–NiO buffer (NNO) and magnetite–hematite buffer (MH), and barren quartz diorite porphyry samples plot below the Ni–NiO buffer (NNO). Geochemical features of relatively enriched LILEs, depleted HFSEs, and markedly negative Nb–Ta anomalies, imply that the mafic magma was generated by partial melting of enriched lithospheric mantle, which had been metasomatized by slab-derived fluids from Neoproterozoic-subducted oceanic lithosphere; as a result, the parental magma was rich in H2O, S, and metals (e.g. Cu), with high fO2.

Geochronology and Geochemistry of Mafic Rocks in the Xuhe, Shaanxi, China: Implications for Petrogenesis and Mantle Dynamics

AbstractThe Xuhe mafic rocks, located in Ziyang county of Shaanxi Province, are dominated by diabase‐porphyrite, gabbro–diabase, diabase, and pyroxene diorite. Primitive mantle‐normalized multi‐element patterns show that, the Xuhe mafic rocks are enriched in large ion lithophile elements (LITE), such as Ba and Pb, depleted in K and Sr for basic rocks, and are depleted in Sr, P and Ti for pyroxene diorite. Chondrite‐normalized REE patterns display LREE enrichment (LaN/YbN = 9.34–13.99) and have normalized patterns for trace element and REE similar to that of typical OIB. Detailed SEMS zircon U–Pb dating yields emplacement ages of 438.4 ± 3.1 Ma for Xuhe mafic rocks. The relatively low MgO (basic rock: 3.11–7.21 wt%; pyroxene diorite: 0.89–1.21 wt%) and Mg# (0.20–0.49) for Xuhe mafic rocks suggest that they were possibly originated from an extremely evolved magma. The rising parental mafic magmas underwent pyroxene and plagioclase fractionation. Crustal contamination of pyroxene diorite before emplacement occurred at a higher crustal level compared to other lithology in Xuhe mafic rocks. The degree of partial melt was low (5%‐10%) and in garnet‐spinel transition facies. Sr‐Nd isotope of pyroxene diorite and enrichment mantle characteristics for Xuhe mafic rocks suggest that mafic rocks in the North Daba Mountains were derived from a mixture of HIMU, EMU and small amount of EMI components. Furthermore, this study discusses mantle geodynamic significance of Xuhe mafic rocks in the Silurian, which indicates subduction and uplift of magma caused back‐arc extension.

Cretaceous Cu–Au, pyrite, and Fe-oxide–apatite deposits in the Ningwu basin, Lower Yangtze Area, Eastern China

The Cretaceous Ningwu volcanic basin of the Middle and Lower Yangtze River Valley metallogenic belt of eastern China hosts numerous Fe-oxide–apatite, Cu–Au, and pyrite deposits. The mineralization in the Ningwu basin is associated with subvolcanic rocks, consisting of gabbro–diorite porphyry and/or pyroxene diorite. However, the mineralization is associated with subvolcanic and volcanic rock suite belonging to the Niangniangshan Formation in the Tongjing Cu–Au deposit, including nosean-bearing aegirine–augite syenites, quartz syenites, and quartz monzonites. The zoning displayed by the alteration and mineralization comprises: (1) an upper light-colored zone of argillic, carbonate, and pyrite alteration and silicification that is locally associated with pyrite and gold mineralization, (2) a central dark-colored zone of diopside, fluorapatite–magnetite, phlogopite, and garnet alteration associated with fluorapatite–magnetite mineralization, and (3) a lowermost light-colored zone of extensive albite alteration. The Cu–Au and pyrite orebodies are peripheral to the Fe-oxide–apatite deposits in this area and overlie the iron orebodies, including the Meishan Cu–Au deposit in the northern Ningwu basin and the pyrite deposits in the central Ningwu basin. The δ34S values of sulfides from the Fe-oxide–apatite, Cu–Au, and pyrite deposits in the Ningwu basin show large variation, with a mixed sulfur source, including magmatic sulfur and/or a mixture of sulfur derived from a magmatic component, country rock, and thermochemical reduction of sulfate at 200–300°C. The ore-forming fluids associated with iron mineralization were derived mainly from magmatic fluids, and the late-stage ore-forming fluids related to Cu–Au and pyrite mineralization may have formed by the introduction of cooler meteoric water to the system. The Fe-oxide–apatite, Cu–Au, and pyrite deposits of the Ningwu basin formed in an extensional environment and are associated with a large-scale magmatic–hydrothermal system.

Petrogenesis and zircon U-Pb dating of skarnified pyroxene-bearing dioritic rocks in Bisheh area, south of Birjand, eastern Iran

در منطقه بیشه واقع در شرق بلوک لوت، هورنبلند دیوریت های پورفیری در سنگهای رسوبی و آذرین (توف‌ها و سنگهای دیوریتی پیروکسن‌دار) نفوذ کرده و به‌ترتیب تشکیل اگزواسکارن و اندواسکارن داده است. بخشهای تغییر نیافته سنگهای دیوریتی پیروکسن‌دار، دارای ماهیت کالک آلکالن پتاسیم بالا و متاآلومین (78/1 A/NK≥ و 95/0(A/CNK≤ هستند. نمودار چند عنصری به‌هنجار شده با گوشته اولیه نشان دهنده غنی شدگی از عناصر LIL مانند Rb، Ba، Cs و تهی شدگی از عناصر HFS نظیر Nb، P، Ti، Y و Yb است. نمودار عناصر نادر خاکی بیانگر مقادیر (La/Yb)N از 75/7 تا 63/8 و بی هنجاری منفی ضعیف Eu می باشد. این خصوصیات به همراه مقادیر بالای Th/Yb و Ta/Yb نشان‌دهنده ماگماتیسم وابسته به مناطق فرورانش حاشیه قاره هاست. تهی‌شدگی مشخص Nb و Ti ، میزان نسبتا بالای Mg#، نسبتهای اولیه 87Sr/86Sr ( 70606/0)، 143Nd/144Nd ( 512424/0) و Nd e (05/3-) نشان می دهد که ماگمای سازنده سنگهای مورد مطالعه از گوشته غنی شده منشأ گرفته و دچار آغشتگی پوسته ای شده است. مقادیر بالای Rb، Th، K و مقدار پایین P و Ti در سنگهای مورد بررسی مؤید آلودگی ماگما در پوسته فوقانی طی تکامل ماگما است. میزان Ba/Rb پایین (4/7-6/4) و Rb/Sr بالا (22/0-17/0)، نشاندهنده حضور فلوگوپیت در گوشته منشأ است. با توجه به میزان بالای CaO+ Al2O3 نمونه های مورد مطالعه (متوسط 3/22 درصد)، میتوان گارنت پیروکسنیت فلوگوپیتدار را به‌عنوان منشأ ماگما در نظر گرفت. سن‌سنجی به روش زیرکن-اورانیم-سرب بر روی پیروکسن دیوریت پورفیری نشان می‌دهد که این ماگماتیسم در 07/44 میلیون سال پیش یعنی در ائوسن میانی(Lutetian) رخ داده است.

Petrology, geochemistry and geochronology of the magmatic suite from the Jianzha Complex, central China: Petrogenesis and geodynamic implications

The intermediate–mafic–ultramafic rocks in the Jianzha Complex (JZC) at the northern margin of the West Qinling Orogenic Belt have been interpreted to be a part of an ophiolite suite. In this study, we present new geochronological, petrological, geochemical and Sr–Nd–Hf isotopic data and provide a different interpretation. The JZC is composed of dunite, wehrlite, olivine clinopyroxenite, olivine gabbro, gabbro, and pyroxene diorite. The suite shows characteristics of Alaskan-type complexes, including (1) the low CaO concentrations in olivine; (2) evidence of crystal accumulation; (3) high calcic composition of clinopyroxene; and (4) negative correlation between FeOtot and Cr2O3 of spinels. Hornblende and phlogopite are ubiquitous in the wehrlites, but minor orthopyroxene is also present. Hornblende and biotite are abundant late crystallized phases in the gabbros and diorites. The two pyroxene-bearing diorite samples from JZC yield zircon U–Pb ages of 245.7±1.3Ma and 241.8±1.3Ma. The mafic and ultramafic rocks display slightly enriched LREE patterns. The wehrlites display moderate to weak negative Eu anomalies (0.74–0.94), whereas the olivine gabbros and gabbros have pronounced positive Eu anomalies. Diorites show slight LREE enrichment, with (La/Yb)N ratios ranging from 4.42 to 7.79, and moderate to weak negative Eu anomalies (Eu/Eu∗=0.64–0.86). The mafic and ultramafic rocks from this suite are characterized by negative Nb–Ta–Zr anomalies as well as positive Pb anomalies. Diorites show pronounced negative Ba, Nb–Ta and Ti spikes, and typical Th–U, K and Pb peaks. Combined with petrographic observations and chemical variations, we suggest that the magmatism was dominantly controlled by fractional crystallization and crystal accumulation, with limited crustal contamination. The arc-affinity signature and weekly negative to moderately positive εNd(t) values (−2.3 to 1.2) suggest that these rocks may have been generated by partial melting of the juvenile sub-continental lithospheric mantle that was metasomatized previously by slab-derived fluids. The lithologies in the JZC are related in space and time and originated from a common parental magma. Geochemical modeling suggests that their primitive parental magma had a basaltic composition. The ultramafic rocks were generated through olivine accumulation, and variable degrees of fractional crystallization with minor crustal contamination produced the diorites. The data presented here suggest that the subduction in West Qinling did not cease before the early stage of the Middle Triassic (∼242Ma), a back-arc developed in the northern part of West Qinling during this period, and the JZC formed within the incipient back-arc.

Source characteristics and tectonic setting of the Early and Middle Devonian volcanic rocks in the North Junggar, Northwest China: Insights from Nd–Sr isotopes and geochemistry

Andesite and pyroxene diorite porphyry in the North Junggar, NW China yield zircon U–Pb age of 412.9±1.7Ma and 380.7±3.8Ma, suggesting that they were formed in the Early and Middle Devonian. The Early Devonian lavas consist of basalt, basaltic andesite and andesite, dacitic porphyry and rhyolite. The enrichment of LILE and LREE, remarkably negative Nb, Ta and Ti anomalies, and low (87Sr/86Sr)i ratios and high εNd(t) values in these volcanic rocks, indicate that the Early and Middle Devonian igneous rocks were formed in an intra-oceanic arc, and no continental crust was involved.The wide range of lava types, abundant phenocrysts and overall chemical and isotopic coherence of the Early Devonian lavas clearly suggest that fractional crystallization was the dominant process controlling the evolution of Early Devonian lavas, and is accompanied by the reinjection of parental melt into the magma chamber which can be clearly verified by reverse zoning of plagioclase phenocrysts and their abrupt increase of An content from sieved-textured core to rim. Andesite and basaltic andesite displaying adakitic characteristics have negligible relation to melting of subducted basaltic crust; instead, they are products of basaltic replenishment and fractional crystallization of plagioclase+clinopyroxene+hornblende from mafic magmas. The mantle source of Early Devonian lavas was enriched by much more slab-derived component than that of pyroxene diorite porphyry. With the evolvement of an island arc, involvement of slab-derived components in arc magmatism could decrease; moreover, the high-level crustal contamination may be a more important mechanism than source enrichment.

Incremental growth and origin of the Cretaceous Renjiayingzi pluton, southern Inner Mongolia, China: Evidence from structure, geochemistry and geochronology

The Renjiayingzi intermediate-acid pluton is located along a pre-existing ENE–WSW-trending dextral shear zone that forms part of the Xar Moron suture zone that marks the final closure of the Paleo-Asian Ocean. The pluton is composed of three small intrusions, which from northwest to southeast, are named the Shuangjianshan (SI), the Qianweiliansu (QI) and the Xingshuwabeishan (XI) intrusions. LA-ICPMS zircon U–Pb dating of a pyroxene diorite from the SI yields an age of 138±1Ma; the SHRIMP zircon U–Pb age of a tonalite from the QI records an age of 134±2Ma, whereas LA-ICPMS zircon U–Pb dating of a monzogranite from the XI has an age of 126±1Ma, suggesting the entire pluton was built up by three separate emplacement events that young to the ESE: this is further supported by the contact relations. Incremental growth of plutons by amalgamation of repeated small magma pulses is the most viable emplacement model. The pluton was probably emplaced by updoming of the roof along previous tensile fractures and by upward stacking of the three intrusions. The SI and QI have similar U–Pb ages and geochemical characteristics, and most likely had the same magma source and underwent similar petrogenetic processes. They have high MgO concentrations at low silica contents, are enriched in large ion lithophile elements, depleted in high field strength elements, have negative εNd(t) values of −1.8 to −3.7, with Nd model ages of 1.07–1.19Ga. Pyroxene diorites of the SI also have variable zircon εHf(t) values (from −0.8 to +6.1), indicating that they were mainly derived from juvenile crust with minor crustal contamination and clinopyroxene-dominated fractional crystallization. The late monzogranites from the XI show weak negative εNd(t) values of −2.3 to −2.5, young Nd model ages of 0.99–1.00Ga, positive zircon εHf(t) values (+1.3 to +4.6) and higher SiO2 and K2O contents, with strong depletion in Eu, P and Ti, indicating derivation from a distinct petrogenetic process from the two earlier intrusions. The monzogranites were the result of partial melting of juvenile crust in response to mantle-derived magma underplating, together with plagioclase-dominated fractional crystallization.

Chronology, Hf isotopes, geochemistry, and petrogenesis of the magmatic rocks in the Shizishan ore field of Tongling, Anhui Province

LA-ICPMS zircon U-Pb dating of intrusive rocks from the Shizishan ore field, Tongling, Anhui Province shows that the crystallization ages of Baimangshan pyroxene diorite, Shizishan and Dongguashan quartz diorite are 139±1.9, 138.0±1.7, and 138.4±1.7 Ma, respectively. These three intrusions are high-potassium, alkali-rich, meta-aluminous, and are characterized by enrichment of light rare earth elements and large-ion lithophile elements, depletion of heavy rare-earth elements (HREE) and high field strength elements, and slightly negative Eu anomalies. In-situ Hf analysis of zircon for these three intrusions shows large ranges of Hf isotope compositions: the ɛ Hf(t) values are ɛ Hf(t)= ∼3.3 to ∼14.4 for Baimangshan, ∼14.1 to ∼23.9 Dongguashan, and ∼14.7 to ∼26.9 for Shizishan. The ɛ Hf(t) values of both the Dongguashan and Shizishan quartz diorites are significantly lower than those of Baimangshan pyroxene diorite. Elemental geochemistry and in-situ zircon Hf isotope analyses indicate that the three intrusions were formed through mixing of granitic magma formed by partial melting of the lower crust and water-rich basic magma derived from the enriched lithospheric mantle. The Dongguashan and Shizishan quartz diorites involved greater crustal components than Baimangshan pyroxene diorite. The Dongguashan and Shizishan quartz diorites have geochemical features similar to the adakite, such as high Sr, low Y, and high Sr/Y ratios. Such geochemical features can be attributed to some fractional crystallization of apatite and sphene, and insignificant plagioclase fractional crystallization after magma mixing. These three intrusions are the products of complex crust-mantle interaction during the regional tectonic regime transition from compression to extension.

Petrogenesis of Late Triassic intrusive rocks in the northern Liaodong Peninsula related to decratonization of the North China Craton: Zircon U–Pb age and Hf–O isotope evidence

Major and trace element, whole rock Sr‐, Nd‐and Hf‐isotopes and zircon U–Pb age and Hf–O isotope data have been determined for mafic to felsic intrusive rocks from the Late Triassic Mayihe (MYH), Longtou–Chaxinzi–Xiaoweishahe (LCX) and Nankouqian–Xidadingzi (NX) intrusions in the northern Liaodong Peninsula, NE China, in order to investigate their sources and petrogenesis related to decrationization of the North China Craton. The rocks include clinopyroxene diorite, monzodiorite, quartz diorite, granodiorite, monzogranite and mafic microgranular enclaves. Laser ablation inductively coupled plasma mass spectrometry (LA–ICPMS) and secondary ion mass spectrometer (SIMS) U–Pb analyses of zircon from MYH, LXC to NX intrusions yield Late Triassic ages of 224–218Ma, establishing that the mafic and felsic magmas were coeval. The clinopyroxene diorites from the MYH pluton have high MgO concentrations at low silica contents, with positive whole rock εNd(t) (up to +3.8) and εHf(t) (up to +6.2) and zircon εHf(t) values and some mantle-like δ18O values. They are enriched in large ion lithophile (LILEs) and light rare earth elements (LREEs) and depleted in high field strength elements (HFSEs), which can be explained as melts derived from a depleted mantle, with some subsequent crustal contamination. However, the diorites from the LXC and NX intrusions are high‐K rocks and have high MgO concentrations and mantle-like δ18O values, but with negative whole rock εNd(t) (−12.9 to −7.6) and εHf(t) (−14.0 to −5.6) and zircon εHf(t) values, distinct from those of MYH pyroxene diorites, indicating that their parental magmas were derived from partial melting of an ancient lithospheric mantle. The granitoids from three plutons have high SiO2 contents and low MgO concentrations, suggesting they were mainly derived from crustal sources. However, the MYH monzogranite and granodiorite have positive whole rock εNd(t) and εHf(t) (up to +3.0) and zircon εHf(t) values, indicating a juvenile crustal source, whereas, the LXC and NX granitoids have strong negative and variable whole rock εNd(t) and εHf(t) and zircon εHf(t) values, indicating that they were derived from partial melting of ancient lower crustal materials with involvement of mantle components. Field observations, geochronology, geochemistry, Sr–Nd–Hf isotopic and zircon Hf–O isotopic compositions point to a complex petrogenesis, where mantle- and crust-derived magma mixing was coupled with crystal fractionation, thus explaining the genetic link between mafic and felsic rocks. Identification of four components, i.e., depleted and enriched mantle and juvenile and ancient crust in the Late Triassic magmatism in the northern Liaodong Peninsula suggests a strong mantle–crust interaction process related to decratonization of the North China Craton.

Early Cretaceous dioritic rocks in the Tongling region, eastern China: Implications for the tectonic settings

The Tongling district in the Lower Yangtze River belt is one of the most important Cu-polymetal producers in China. Copper–Au deposits in the region are closely related to Early Cretaceous dioritic intrusions, which can be classified into three rock associations: pyroxene diorite–pyroxene monzodiorite, quartz diorite–quartz monzodiorite and granodiorite. The dioritic rock series (SiO2=54.6–64.5wt.%) are calc-alkaline, with high Al2O3 (>15.4wt.%), Ba (Ba>700ppm) and Sr concentrations (~920ppm in average), and low Y and Yb concentrations, all of which are typical for adakite. Geochemical characteristics suggest that the Tongling adakitic rocks are genetically related to slab melting and subsequent interaction with the mantle, likely during a ridge subduction along the Lower Yangtze River Belt in the Early Cretaceous. Geothermometers show high formation temperatures of 800–900°C, which is consistent with interaction with the asthenosphere mantle as indicated. The relatively low εNd(t) values (−11.2 to −16.7) and high (87Sr/86Sr)i ratios (0.7067 to 0.7095) may be plausibly interpreted by contamination of enriched mantle materials and/or continental crust. The Tongling dioritic rocks are characterized by high radiogenic Pb isotopes with (206Pb/204Pb)i=17.80–18.56, (207Pb/204Pb)i=15.46–15.60, and (208Pb/204Pb)i=37.92–38.48, which mostly plot in the field of MORB, near the intersection of EM-1 and EM-2, and are clearly different from those of the upper and lower continental crust and Dabie adakites. These exclude major contamination from the continental crust. Given that eastern China has both EM-1 and EM-2 types of enriched mantle, whereas the Tongling region is located near the transition from EM-1 to EM-2, the enriched Sr–Nd isotopic characteristics of Tongling adakites are best explained by slab melts with assimilation of enriched mantle components.

Mass balance of major elements in relation to weathering in soils developed on igneous rocks in a semiarid region, northwestern Iran

This study was conducted to evaluate the weathering intensity of the major soils developed on igneous rocks in semiarid region of northwestern Iran. Eight parent materials were selected including monzodiorite , alkali granite , granodiorite, syenite , pyroxene diorite , hornblend e andesite , pyroxene andesite , and dacite . Representative soil profiles were described and soil samples were collected and analyzed for selected chemical and physical properties and total concentrations of major elements and Zr, V, Ti and Y. Bulk densities as well as Ti, Zr and V concentrations were used to estimate the strain factors and mass balance equations were used to quantify the net result of pedogenic weathering, i.e. elemental loss and gain. The results of clay content and pedogenic iron variability as well as index of compositional variability (ICV), chemical index of alteration (CIA) and, A-CN-K and MFW ternary plots showed that the soils developed on volcanic rocks (hornblende andesite> pyroxene andesite> dacite) were more weathered than those on the plutonic parent rocks (alkali granite, granodiorite, monzodiorite, syenite, pyroxene diorite) . The results of mass balance calculations based on the strain factors revealed that the Ca and Na depleted during weathering progress mostly from plagioclase grains. In the semiarid regions Ca is precipitated as pedogenic calcite in the soil horizons. K and Mg depletion is less than Ca and Na especially in the profiles on the hornblende andesite with the highest clay and LOI content. The results of this study clearly suggest that the behavior of K and Mg during the weathering can not only be explained by the disintegration of the primary minerals, since they are fixed on the secondary clay minerals. Iron did not change in the soils compared to the parent material and was precipitated as the pedogenic iron and conserved in the soil horizons. Overall, the results on the weathering indicators and major elements mass balance enrichment/depletion in the study area confirmed that the soil profiles developed on volcanic rocks are more weathered than those on the plutonic igneous rocks.