Diorite Suite Research Articles

Early Paleozoic tectonic affinity of the Lesser Xing'an–Zhangguangcai Range, NE China: A continental arc along the western margin of the Jiamusi Block

The Lesser Xing'an–Zhangguangcai Range (LXZGCR) in NE China was traditionally interpreted to be the eastern part of the Songliao–Xilinhot Accretionary Terrane, separated from the Jiamusi–Khanka Block to the east by the Heilongjiang Complex. However, recent studies have shown that the Heilongjiang Complex formed in the late Paleozoic–early Mesozoic. Therefore, the tectonic affinity of the LXZGCR during the early Paleozoic remains unclear. To constrain this key issue, we present new zircon UPb ages, Hf isotopic compositions, and whole-rock geochemical data for early Paleozoic igneous rocks in the LXZGCR. The new ages, along with previously published data, suggest that the early Paleozoic magmatism in the LXZGCR can be divided into four stages: Middle–Late Cambrian (523–486 Ma), Early Ordovician (485–469 Ma), Late Ordovician (464–443 Ma), and Late Silurian (433–423 Ma). Middle–Late Cambrian igneous rocks are dominated by calc-alkaline I-type granitoids and high-Mg andesite–dacite–rhyolite association. Early Ordovician igneous rocks consist of a suite of calc-alkaline diorites, granodiorites, monzogranites, alkali-feldspar granites, and rhyolites, with I-type affinities. Late Ordovician igneous rocks consist mainly of I-type granitoids with minor A-type granitoids and rhyolites. Late Silurian igneous rocks are composed of calc-alkaline I-type granitoids with minor dacites. The early Paleozoic granitoids and felsic volcanic rocks originated from partial melting of dominantly Paleoproterozoic–Mesoproterozoic lower crust, whereas the Late Cambrian high-Mg andesite–dacite–rhyolite association was probably derived from partial melting of a depleted mantle wedge metasomatized by subduction-related fluids. The rock associations and geochemical characteristics suggest that these early Paleozoic igneous rocks formed in active continental margin and back-arc extension settings. Comparing the early Paleozoic magmatism, zircon Hf isotopic compositions, Nd model ages, and Precambrian basement features of the LXZGCR and the Jiamusi Block suggest that the LXZGCR was part of the same tectonic unit as the Jiamusi Block during the early Paleozoic. We argue that the formation of the early Paleozoic igneous rocks in the LXZGCR was related to the eastward subduction of a branch ocean of the Paleo-Asian Ocean beneath the Jiamusi–Khanka Block.

Petrogenesis of the Carboniferous Intrusive Rock in the Xiaobaishitou District of East Tianshan, Northwest China: Magma Evolution and Tectonic Significance

AbstractThe Xiaobaishitou gabbro‐diorite pluton comprises a medium‐grained gabbro‐diorite suite and a fine‐grained diorite suite, which intrude the Kawabulag Group in the East Tianshan Orogen of the Central Asian Orogenic Belt (CAOB). A combination of mineral chemistry, zircon U‐Pb age, whole‐rock geochemistry, Sr‐Nd isotopes, and in situ zircon Hf isotopes for newly found gabbro‐diorite from the Xiaobaishitou district in the Central Tianshan Terrane (CTT) is presented to investigate the petrogenesis and tectonic or even crustal evolution of the East Tianshan Orogen. Laser ablation inductively coupled plasma mass spectrometry (LA‐ICP‐MS) zircon U‐Pb analyses indicate that the gabbro‐diorite was formed at 324.7 ± 2.4 Ma. The isolated clinopyroxene formed under higher P‐T‐ƒO2 melt conditions (10.7–14.6 kbar; 1199–1269°C; high ƒO2) than those for the hornblende, plagioclase, and zircon (557–687°C; moderate ƒO2) in the gabbro‐diorite, which reveals a multilevel, magmatic storage system. The gabbro‐diorite is characterized by fractioned REE patterns, enriched LILEs (e.g., Ba and Pb), negative anomalies of HFSEs (e.g., Nb and Ta), and low La/Yb and Sr/Y ratios, which are typically indicative of crustal contamination and accounted for by subduction‐related fluids. The rock also characterized by typical features of high compatible elements (MgO = 3.14–11.65 wt%, Cr = 1–157 ppm, Ni = 6–830 ppm), high Mg# (47 –74), positive ɛHf(t) values (+5.1 to +10.3) and ɛNd(t) values (+2.3 to +4.4). These features suggest that the Xiaobaishitou gabbro‐diorite was most likely derived from metasomatic mantle and contaminated minor crustal components. Taking into account the spatial and temporal distribution of the Carboniferous magmatic rocks in the CTT, we suggest the formation of the Xiaobaishitou gabbro‐diorite was attributed to southward subduction of the Kangguer Ocean.

Geochemistry and zircon U[sbnd]Pb geochronology of Late Mesozoic igneous rocks from SW Vietnam – SE Cambodia: Implications for episodic magmatism in the context of the Paleo-Pacific subduction

Late Mesozoic igneous rocks in Vietnam are predominantly found in the Dalat zone (southern Vietnam), but smaller volumes also occur within southernmost Indochina (SW Vietnam-SE Cambodia). Within the latter area, six different rock suites can be distinguished based on field relations, geochemical characteristics, and zircon UPb geochronology: (1) Bay Nui-Ba Den diorite suite; (2) Bay Nui-Phnom Den granitoid suite, (3) Pha Aok granite suite, (4) Nui Sam-Angkor Borei suite, (5) Bach Ho granitoid suite, and (6) Con Dao gabbro/granite suite. These igneous rock suites indicate several pulses of magmatism during the late stages of a long-lived convergent margin. The Bay Nui-Ba Den diorite suite (ca. 107–96 Ma) is composed of monzogabbro, monzodiorite, diorite, and syenite, characterized by a metaluminous (I-type) nature, and shows several characteristics of alkali-rich primitive arc melts. The Bach Ho granitoid suite (ca. 110 Ma) consists of granodiorite and granite and displays a calc-alkaline (moderate in potassium) signature. The Bay Nui-Phnom Den granitoid suite (ca. 94–91 Ma) is the most widespread igneous group, consists mainly of granodiorite and granite of I-type affinity. These three rock suites show typical characteristics of arc-related magmatism similar to the I-type granitoids previously described in the Dalat area. The younger magmatic suites (<90 Ma) include the fined-grained granites of the Con Dao suite (ca. 83 Ma), coarse-grained two-mica granites of the Pha Aok suite (ca. 78 Ma), and fine-grained fluorite-bearing biotite granites of the Nui Sam-Angkor Borei granitoid suite (ca. 75 Ma). They display characteristics of A-type affinity with strongly negative Eu, Sr, Ba, Ti, and P anomalies. Geochemical signatures of these young igneous rocks indicate an extensional tectonic setting, possibly related to basaltic injection/asthenospheric upwelling. This additional heat input is required for partial melting of a dry residual crustal source. Geochemical and geochronological results demonstrate that the Late Mesozoic magmatism in southern Indochina can be related to two significant tectonic stages in Indochina and adjacent areas: (1) the Paleo-Pacific subduction (110–90 Ma) and (2) a transitional phase leading to the opening of the South China Sea (83–75 Ma).

The formation of TTGs by hydrous partial melting and anatexis from a gabbroic mantle source in Viti Levu, Fiji Islands

Tonalite, trondhjemite, granodiorite (TTG) rocks in Viti Levu, Fiji Islands formed through hydrous partial melting of gabbroic oceanic crust at low-pressure amphibolite-facies conditions caused by flat subduction of an oceanic plateau from Yavuna creek during late-Eocene time. This was followed by the formation of a quartz diorite unit by anatexis of the gabbro in the mid-Miocene. The TTGs occur as migmatitic discordant stocks and dykes within the older gabbroic unit of the Yavuna Pluton. Zircon ages show the parental gabbro to be ∼ 47.5 Ma in age, whereas the TTGs, consisting of a tonalite and a quartz diorite suite, are ∼ 37.1 Ma and ∼ 16.5 Ma old, respectively. The average δ18O value of 4.8‰ in zircons from the gabbro and the tonalite suggest a homogenous mantle source. However, about 50% of the analyzed zircons from the gabbroic and tonalitic rock samples show lower δ18O values than this average, and are interpreted as reflecting interaction of hydrothermally altered seafloor with the deep mantle source. The zircon εHf of 13 in the analyzed TTGs is interpreted as reflecting typical juvenile continental crust. PerpleX whole-rock calculations supports that the tonalite formed by hydrous partial melting of the gabbro through decompression under water-saturated amphibolite-facies conditions at a temperature of ∼ 770 °C at ∼ 3.8 kbar, whereas the quartz diorite formed by anatexis under granulite-facies conditions at ∼ 800 °C at ∼ 1.7 kbar at very shallow depth. Our investigation provides new evidence that the tonalite formed by hydrous partial melting and the quartz diorite by metasomatism and anatexis of an extant gabbroic rock/crust at < 0.1 Ga in the South Pacific region.

Petrogenesis of the early Carboniferous Xilinhot gabbro–diorite pluton in central Inner Mongolia: Magma evolution and tectonic significance

The Xilinhot gabbro–diorite pluton in central Inner Mongolia comprises a microgabbro–hornblende gabbro–quartz diorite suite and diorite–microdiorite–quartz microdiorite suite, which intrude the Erdaojing complex in the northern orogenic belt of the southeastern Central Asian Orogenic Belt (CAOB). Zircons separated from hornblende gabbro and quartz diorite yielded sensitive high-resolution ion microprobe U–Pb ages of 326.8 ± 3.4 and 324.0 ± 1.9 Ma, respectively. There are two types of hornblende in the hornblende gabbro: isolated hornblende and hornblende clusters surrounding orthopyroxene. Only hornblende clusters occur in the quartz diorite. The amphibole is edenite in the diorite, whereas the microdiorite and quartz microdiorite contain hornblende. The isolated hornblende formed at higher P–T–H2Omelt conditions (3.3–5.0 kbar; 749–814 °C; 7.4–8.3 wt% H2O) than the hornblende clusters in the hornblende gabbro (0.9–2.2 kbar; 670–731 °C; 3.8–5.5 wt% H2O). Edenite in the diorite crystallized at higher P–T and lower H2Omelt conditions (1.8–4.8 kbar; 777–979 °C; 3.2–5.2 wt% H2O) than hornblende in the microdiorite (1.3–1.5 kbar; 697–711 °C; 5.0–5.6 wt% H2O). These thermodynamic parameters reveal a multi-level magmatic storage system. Hornblende gabbro, quartz diorite, diorite, microdiorite, and quartz microdiorite are generally characterized by flat middle to heavy rare earth element patterns and no Eu anomalies. Geochemical modeling of heavy rare earth element concentrations in hornblende gabbro suggest that the magma was generated by >17.5% partial melting of spinel lherzolite. Slab-derived fluid input can account for the enrichments in Sr, Th, and light rare earth elements, and depletions in Nb and Ta. The multi-level magmatic storage system and slab-derived fluid input suggest that the early Carboniferous magmatism was generated in an arc-related tectonic setting. The northern orogenic and Hegenshan ophiolite belts constitute an early Carboniferous fore-arc basin–arc–back-arc basin system.

Late Cryogenian magmatic activity in the North Lhasa terrane, Tibet: Implication of slab break-off process

The North Lhasa terrane in Tibet is generally interpreted to be paleotectonically unrelated to the East African Orogen (EAO) and is instead thought to have derived from northeastern India or northwestern Australia. In this study, we present petrogenetic and geochronological results pertaining to the analysis of gabbros (ca. 652 Ma), diorites (ca. 658 and 646 Ma), and tonalites (ca. 652 Ma) from the North Lhasa terrane. The gabbros are calc-alkaline and exhibit arc-like geochemical features. Low positive zircon εHf(t) values (+1.0 to +3.8), high zircon δ18O (6.25‰ to 7.94‰), and low negative whole-rock εNd(t) values (−3.5 to −1.4) indicate that the gabbros were derived from the lithospheric mantle, with geochemical modification by a subduction component. The diorite suite is characterized by a wide range of whole-rock chemistries (e.g., SiO2 = 51.33–61.98 wt%) and Hf–O–Sr isotopic compositions (εHf(t) = −10.8 to −0.1; δ18O = 5.17‰ to 7.11‰; ISr = 0.706 to 0.710), and negative whole-rock εNd(t) values (−7.0 to −4.7). These diorites are geochemically similar to OIB and are interpreted to be products of the partial melting of a relatively deep mantle source (>85 km) prior to extensive modification by continental crustal material. The tonalites are adakitic and have moderate Mg# values (47–54), low compatible element abundances, positive zircon εHf(t) values (+3.4 to +6.2), high ISr values (0.714 to 0.715), and small negative whole-rock εNd(t) values (−1.6 to −0.4). These tonalites most likely formed by the melting of thickened Mesoproterozoic continental crust. The generation of these ca. 650 Ma magmatic rocks was related to slab break-off in a collision zone. By integrating the findings of previous studies with the data of the present study, we suggest that the North Lhasa terrane was most likely located in the northern segment of the EAO in paleotectonic reconstructions of the Gondwana supercontinent.

The petrogenesis of the Neoarchean Kukuluma Intrusive Complex, NW Tanzania

The Kukuluma Intrusive Complex (KIC) is a late Archean igneous complex, dominated by monzonite and diorite with subordinated granodiorite. The monzonite and the diorite suites have low silica content (SiO2 ≤ 62 wt%), moderate Mg# (Mg#average = 49), high Sr/Y (Sr/Yaverage = 79) and high La/Yb (La/Ybaverage = 56) ratios, and strongly fractionated (Lan/Ybn = 9–69) REE patterns. Their moderate Ni (Niaverage = 50 ppm), Cr (Craverage = 85 ppm), variable Cr/Ni ratio (0.65–3.56) and low TiO2 (TiO2average = 0.5 wt%) indicate little to no interaction with the peridotitic mantle. For most major elements (Al2O3, FeOt, Na2O, TiO2 and P2O5) the monzonite and the diorite suites display subparallel trends for the same SiO2 content indicating they represent distinct melts. Intrusions belonging to the diorite suite have high Na2O (Na2Oaverage = 4.2 wt%), Dy/Ybn (Dy/Ybn-average = 1.6), a positive Sr anomaly and uncorrelated Nb/La and Zr/Sm ratios suggesting derivation from partial melting of garnet-bearing amphibolite. Intrusions belonging to the monzonite suite have higher Na2O (Na2Oaverage = 5.61 wt%), Dy/Ybn (Dy/Ybn-average = 2.21), a negative Sr anomaly and correlated Nb/La and Zr/Sm ratios consistent with derivation from partial melting of eclogite with residual rutile. Small variations in the Th/U ratio and near chondritic/MORB average values (Th/Umonzonite = 3.65; Th/Udiorite = 2.92) are inconsistent with a subducting slab signature, and it is proposed that the monzonite and the diorite suites of the KIC formed by partial melting of garnet-bearing, lower mafic crust of an oceanic plateau. The granodiorite suite has lower Mg# (Mg#average = 41), moderately fractionated REE, low Sr/Y (Sr/Yaverage = 20), La/Yb (La/Ybaverage = 15), Dy/Ybn (DyYbn-average = 1.24) and small negative Eu anomalies suggesting derivation from partial melting of amphibolite and plagioclase fractionation. Near-MORB Th/U (Th/Uaverage = 2.92) and Zr/Sm (Zr/Smaverage = 30.21) ratios are consistent with intracrustal melting of amphibolite.Archean rocks with an “adakitic” geochemical signature have been used to argue in favour of a plate tectonics regime in the Archean. The results presented here suggest that tectonic models for the Tanzania Craton, which invoke a subduction-related setting for all greenstone belts may need revision.

Multiple magmatism in an evolving suprasubduction zone mantle wedge: The case of the composite mafic–ultramafic complex of Gaositai, North China Craton

The suprasubduction zone mantle wedge of active convergent margins is impregnated by melts and fluids leading to the formation of a variety of magmatic and metasomatic rock suites. Here we investigate a composite mafic–ultramafic intrusion at Gaositai, in the northern margin of the North China Craton (NCC). The hornblende gabbro–serpentinite–dunite–pyroxenite–gabbro–diorite suite surrounded by hornblendites of this complex has long been considered to represent an “Alaskan-type” zoned pluton. We present petrologic, mineral chemical, geochemical and zircon U–Pb and Lu–Hf data from the various rock types from Gaositai including hornblende gabbro, serpentinite, dunite, pyroxenite, diorite and the basement hornblendite which reveal the case of multiple melt generation and melt–peridotite interaction. Our new mineral chemical data from the mafic–ultramafic suite exclude an “Alaskan-type” affinity, and the bulk geochemical features are consistent with subduction-related magmatism with enrichment of LILE (K, Rb, and Ba) and LREE (La and Ce), and depletion of HFSE (Nb, Ta, Zr, and Hf) and HREE. Zircon U–Pb geochronology reveals that the hornblendites surrounding the Gaositai complex are nearly 2billionyears older than the intrusive complex and yield early Paleoproterozoic emplacement ages (2433–2460Ma), followed by late Paleoproterozoic metamorphism (1897Ma). The serpentinites trace the history of a long-lived and replenished ancient sub-continental lithospheric mantle with the oldest zircon population dated as 2479Ma and 1896Ma, closely corresponding with the ages obtained from the basement rock, followed by Neoproterozoic and Phanerozoic zircon growth. The oldest member in the Gaositai composite intrusion is the dunite that yields emplacement age of 755Ma, followed by pyroxenite formed through the interaction of slab melt and wedge mantle peridotite at 401Ma. All the rock suites also carry multiple population of younger zircons ranging in age from Paleozoic to Mesozoic, suggesting continuous mantle metasomatism through melts and fluids associated with prolonged subduction, which is also substantiated by the pervasive hydration of all the ultramafic units. Zircon Lu–Hf isotopic data from the basement rock (hornblendite) on concordant grains yield εHf(t) values in the range of −23.8 to −5.2 with TDM of 1979–2424Ma and TDMC between 2754 and 2899Ma, suggesting Mesoarchean to Neoarchean reworked and juvenile sources. Concordant grains in the serpentinite also display a large range of εHf(t) values (−5.0 to 5.8) suggesting multiple sources, whereas the concordant magmatic zircon grains in the dunite have a tight range of εHf(t) values between −2.3 and 0.1 indicating primitive source. Those from the pyroxenite are characterized by highly negative εHf(t) values of −21.5 to −18.6 suggesting reworked ancient components. The diverse ages, lack of typical geochemical imprints, and magmas derived from multiple sources including Mesoarchean to Neoarchean reworked and primitive components within the same mafic–ultramafic complex exclude an “Alaskan-type” affinity and suggest multiple magmatism in an evolving and metasomatized suprasubduction zone mantle wedge. We correlate the tectonics with the prolonged subduction regime of the Paleo-Asian Ocean with melt–peridotite interaction and geologic history spanning through compression to extension.

Tectonic significance and geodynamic processes of large‐scale Early Cretaceous granitoid magmatic events in the southern Great Xing'an Range, North China

AbstractThe origin and geodynamic evolution of peak Early Cretaceous magmatism in the southern Great Xing'an Range, North China, have long been controversial. Here we report new U‐Pb zircon ages (141–129 Ma) of a suite of dioritic‐granitic rocks from central Inner Mongolia, far from the sutures or plate boundaries of the Paleo‐Pacific and Mongol‐Okhotsk oceans, thus delineating an Early Cretaceous intracontinental magmatic province, which had a peak activity at 130–120 Ma. Dioritic suite including diorite, tonalite, and granodiorite shows variable zircon εHf(t) of +1.4 to + 11.8 and δ18O values of +5.7 to +6.9‰, while granitic suite consisting of monzogranite, syenogranite, and granite porphyry also records variable zircon εHf(t) of −0.9 to +15.0 and δ18O values of +6.3 to +8.1‰, suggesting crustal melting by preexisting crustal source with important recycled supracrustal components including fluids. Furthermore, these rocks show variable whole‐rock δ7Li values (−0.6 to +12.1‰), indicating fluids played an important role in magma source. We propose a deep‐sourced water‐fluxed melting scenario by ancient hydrous slabs inherited from the Paleo‐Asian Ocean that were trapped in the deep interior, thus releasing aqueous fluids to melt the lithospheric mantle and produce water‐rich mafic magmas. These mafic magmas were underplated into crust where they promoted water‐fluxed partial melting to generate the large‐scale Early Cretaceous magmatism in the southern Great Xing'an Range. Such melting due to fluxing of aqueous fluids was probably operating as a widespread process responsible for the Early Cretaceous dramatically tectonomagmatic events and evolution of continental crust in NE Asia.

Neoproterozoic post-collisional extension of the central Jiangnan Orogen: Geochemical, geochronological, and Lu-Hf isotopic constraints from the ca. 820–800 Ma magmatic rocks

Neoproterozoic magmatic rocks in South China contain important information on evaluating crustal reworking during the Yangtze-Cathaysia collision and post-collisional extension. We present here geochemical, geochronological, and Lu-Hf isotopic data of a suite of granitoids and diorites from the Jiuling and Meixian plutons of the central Jiangnan Orogen. The granitoids display intermediate geochemical features between S-type and I-type granites. They exhibit arc-like patterns of REE and trace element partition, reflecting inheritance of juvenile arc-derived crust. Igneous zircons from the Jiuling and Meixian granitoids yield U-Pb ages of 822–819Ma and 816–815Ma, respectively. Inherited zircons from the granitoids commonly yield a major age population of 980–860Ma, consistent with the time of the Shuangxiwu volcanic arc. The igneous and inherited zircons have highly variable εHf(t) values ranging from −9 to +12.2. We interpret the granitoids to have been generated by remelting and binary mixing of (1) juvenile arc-derived crustal material and (2) supracrustal material of the Shuangqiaoshan meta-sedimentary rocks. The previous crustal thickening achieved by the Yangtze-Cathaysia collision is a prerequisite for their generation. The two granitoids, together with regional 825–815Ma S-type granites, indicate incipient post-collisional collapse of thickened crust, heralding tectonic switch from compression to extension. The Meixian diorites display arc-like geochemical characteristics, and yield zircon U-Pb ages of 805–804Ma and neutral to positive zircon εHf(t) values (−0.1–+7.5). The diorites were generated by decompression melting of arc-derived lower crust, associated with asthenospheric mantle upwelling during continental rifting. Such rifting may be part of global Neoproterozoic rifting events that finally led to breakup of the Rodinia supercontinent.

Mid-Ordovician and Late Devonian magmatism in the Togtokhinshil Complex: new insight into the formation and accretionary evolution of the Lake Zone (western Mongolia)

New field, petrographic, geochemical and geochronological data from the Togtokhinshil Complex (western margin of the Lake Zone, Central Asian Orogenic Belt) reveal the presence of two separate Early Palaeozoic magmatic pulses: Mid-Ordovician and Late Devonian. The Mid-Ordovician (c. 460 Ma) magmatism produced various types of mafic plutonic rocks (gabbro–diorite suite) emplaced into the volcanosedimentary sequence of the Baatar Fm. Gabbros to gabbrodiorites have metaluminous and mostly low to normal-K calc-alkaline or possibly tholeiitic character. The majorand trace-element as well as Nd isotopic signatures suggest its magmatic-arc geotectonic setting and imply the derivation either exclusively from the mantle or in part from the juvenile mafic crust. The Late Devonian (c. 376 Ma) granite suite intruded the rocks of both the gabbro–diorite suite and the Baatar Fm. Granites are subaluminous and have a high-K calc-alkaline to shoshonitic character. Their magmatic arc-like geochemical signature is interpreted as inherited from the recycled arc-related crustal source. The granite suite seems a product of extensive mantle heat-induced crustal anatexis. The Depleted Mantle Nd model ages (c. 0.75 Ga) indicate derivation of the magmatic rocks of the both suites from relatively juvenile, and geochemically immature, sources. These results provide a clear evidence of the Mid-Ordovician arc-related magmatism in the western part of the Lake Zone. They thus prolong the assumed period of magmatic-arc activity and constrain onset of accretionary processes in this part of the Central Asian Orogenic Belt. The gabbro–diorite suite represents either part of a long-lived magmatic-arc or, more likely, a member of multiple island-arc system along the western margin of the Lake Zone. Newly described Late Devonian magmatism in the Togtokhinshil Complex provides further evidence of tectono-thermal event that was widespread in the Central Asian Orogenic Belt. The geodynamic cause for this event remains uncertain, but effects of lithospheric thinning and/or asthenospheric mantle upwelling are considered the most likely.

Exploration of gold occurrences in alteration zones at Dungash district, Southeastern Desert of Egypt using ASTER data and geochemical analyses

The present study aims at exploration of new gold occurrences in the alteration zones at Dungash district. Processed ASTER images band ratios 7/6 × 4/6 and (7 + 9/8), field geology and mineralogical and geochemical data help characterize three types of alterations in three areas 1 to 3 that may be targeted for Au exploration. Area1 confined to the metavolcanics located in the SE of Dungash gold mine and revealed silicified and sericitized type alterations, composed of quartz, epidote, chlorite, biotite and opaque minerals mainly pyrite and chalcopyrite. Area2 occurs in the gabbro-diorite rocks at Abu Meraiwa area NE of Dungash gold mine, which are rich in kaolinite, illite, sericite, pyrite, arsenopyrite and chalcopyrite that record kaolinitized alteration. Area3 is hosted in carbonaceous listwaenized serpentinite thus indicating the role of listwaenitization type alteration in ore genesis. It is composed of calcite, chromite, pyrite, arsenopyrite, chalcopyrite and Ni-bearing sulphides.Au contents in area 1 range between 0.12 and 14.91 ppm, and between 6.1 and 16.3 ppm in area 2, while gold values in area 3 vary from <0.01 to 0.03 ppm.Dungash district is comprised of Pan-African assemblages of ophiolitic ultramafics thrusted over the island arc metavolcanics of dacitic- andesite composition. Gabbro-diorite rocks are intruded in the ultramafics and the acidic metavolcanics as well as diorite-quartz diorite suite intruded in the intermediate metavolcanics. Several acidic dykes, granitic dykes and quartz veins cut through the different rocks types.

Paleoproterozoic crustal growth in the North China Craton: Evidence from the Lüliang Complex

The building of continental blocks and their assembly into supercontinents are linked to episodic crustal growth through Earth history, where both vertical and horizontal accretions in convergent plate margins play a significant role. Here we investigate the Paleoproterozoic crustal growth in the North China Craton (NCC) from a traverse covering continent-trench-ocean section in the Lüliang Complex within the western margin of the Trans-North China Orogen, a major accretionary belt that sutures the Eastern and Western Blocks in the NCC. We present petrological, geochemical and zircon U–Pb and Lu–Hf data from a suite of samples including meta granitoids and gabbroic diorite that built the continental arc, and metabasalts, felsic tuff, mafic and pelitic schists, and garnet amphibolites that form part of an imbricated package of oceanic and continental material that was accreted onto the eastern margin of the Western Block in the NCC. The salient geochemical features of the magmatic suite such as high Th/Ta and La/Nb ratios, negative Nb–Ta anomalies, and high concentration of LILE as compared to HFSE suggest magma derivation from sub-continental mantle source which has undergone different degree of enrichment with crustal components or material derived from subduction-related older components. In tectonic discrimination diagrams, the granitoids show VAG affinity and all the rocks straddle the field between IAB and MORB reflecting subduction-related arc signature. The majority of zircon grains in all the rock types from the Lüliang Complex show typical magmatic crystallization textures and high Th/U values. Zircons from the meta-granitoids and diorite enclave yield upper intercept or 207Pb/206Pb mean ages in the range of 2250±20 to 2084±69Ma. Those in the mafic schist show a mean age of 2234±9Ma. In the felsic schist group, the mean ages are in the range of 2298±15 to 1933±11Ma. A minor older population of zircons with ages of 2992±28Ma and 2610±80Ma also occurs in these rocks. In the metabasalt, zircon 207Pb/206Pb mean ages are between 2391±40 and 2022±39Ma with rare magmatic xenocrysts showing Mesoarchean age of 3294±21Ma. Zircons in the felsic tuff show mean ages of 2155±25 to 1897±24Ma, with xenocryst populations yielding mean ages of 2528±31Ma and 2710±20Ma. The youngest zircons with 207Pb/206Pb mean age of ca. 1.9Ga from the felsic schist (metasediment) and felsic tuff (volcanic suite) suggest deposition within the trench of an active convergent margin at this time. In the garnet-bearing amphibolite, the zircons yield a limited age range of 1996±17Ma to 1984±12Ma. The Lu–Hf data on zircons from all samples show dominantly positive ɛHf(t) values. In the granitoid–diorite suite, the ɛHf(t) values range up to 7.6 with crustal residence ages (TDMC) of 2371–2729Ma. Zircons in the mafic and felsic schists also possess positive ɛHf(t) values (up to 9.6) with TDMC in the range of 2366–2798Ma. In the metabasalt, both positive and negative ɛHf(t) values are displayed (3.8 to −3.2) with TDMC in the range of 2495–2830Ma. Zircons in the felsic tuff also show prominent positive ɛHf(t) value (up to 7.4) and crustal residence ages range from 2274 to 2607Ma. In the garnet-bearing amphibolite, the ɛHf(t) values lie between 3.3 and 4.8 and TDMC are in the range of 2321–2413Ma. The majority of ɛHf(t) values from all the rock types in the present study are compatible with juvenile magma sources, with limited input from crustal components. Their TDMC values indicate that both Neoarchean and Paleoproterozoic components were involved in the source, attesting to a continental arc setting. The Hf data also suggest the possible presence of Mesoarchean vestiges among the dominantly Neoarchean–Paleoproterozoic basement. Our data demonstrate active plate tectonics and major crustal growth during the Paleoproterozoic history of the NCC, broadly coeval with the making of the global supercontinent Columbia, and provide insights into continent building through subduction–accretion–collision tectonics analogous to those in Phanerozoic orogenic belts.

Early Mesozoic southward subduction history of the Mongol–Okhotsk oceanic plate: Evidence from geochronology and geochemistry of Early Mesozoic intrusive rocks in the Erguna Massif, NE China

In this paper we present new zircon U–Pb ages, Hf isotope data, and whole-rock major and trace element data for Early Mesozoic intrusive rocks in the Erguna Massif of NE China, and we use these data to constrain the history of southward subduction of the Mongol–Okhotsk oceanic plate, and its influence on NE China as a whole. The zircon U–Pb dating indicates that Early Mesozoic magmatic activity in the Erguna Massif can be subdivided into four stages at ~246Ma, ~225Ma, ~205Ma, and ~185Ma. The ~246Ma intrusive rocks comprise a suite of high-K calc-alkaline diorites, quartz diorites, granodiorites, monzogranites, and syenogranites, with I-type affinities. The ~225Ma intrusive rocks consist of gabbro–diorites and granitoids, and they constitute a bimodal igneous association. The ~205Ma intrusive rocks are dominated by calc-alkaline I-type granitoids that are accompanied by subordinate intermediate–mafic rocks. The ~185Ma intrusive rocks are dominated by I-type granitoids, accompanied by minor amounts of A-types. These Early Mesozoic granitoids mainly originated by partial melting of a depleted and heterogeneous lower crust, whereas the coeval mafic rocks were probably derived from partial melting of a depleted mantle modified by subduction-related fluids. The rock associations and their geochemical features indicate that the ~246Ma, ~205Ma, and ~185Ma intrusive rocks formed in an active continental margin setting related to the southward subduction of the Mongol–Okhotsk oceanic plate. The ~225Ma bimodal igneous rock association formed within an extensional environment in a pause during the subduction process of the Mongol–Okhotsk oceanic plate. Every magmatic stage has its own corresponding set of porphyry deposits in the southeast of the Mongol–Okhotsk suture belt. Taking all this into account, we conclude the following: (1) during the Early Mesozoic, the Mongol–Okhotsk oceanic plate was subducted towards the south beneath the Erguna Massif, but with a pause in subduction at ~225Ma; and (2) the southward subduction of the Mongol–Okhotsk oceanic plate not only caused the intense magmatic activity, but was also favorable to the formation of porphyry deposits.

AMPHIBOLITES OF THE CENTRAL ZONE: NEW SHRIMP U-PB AGES AND IMPLICATIONS FOR THE EVOLUTION OF THE DAMARA OROGEN, NAMIBIA

Research Article| June 01, 2014 AMPHIBOLITES OF THE CENTRAL ZONE: NEW SHRIMP U-PB AGES AND IMPLICATIONS FOR THE EVOLUTION OF THE DAMARA OROGEN, NAMIBIA L. LONGRIDGE; L. LONGRIDGE School of Geosciences, University of the Witwatersrand, PVT Bag 3, Wits, 2050, South Africa VM Investment Company, 24 Fricker Rd, Illovo, Johannesburg, South Africa, e-mail: lukelongridge@gmail.com Search for other works by this author on: GSW Google Scholar J.A. KINNAIRD; J.A. KINNAIRD School of Geosciences, University of the Witwatersrand, PVT Bag 3, Wits, 2050, South Africa, e-mail: judith.kinnaird@wits.ac.za; roger.gibson@wits.ac.za Search for other works by this author on: GSW Google Scholar R.L. GIBSON; R.L. GIBSON School of Geosciences, University of the Witwatersrand, PVT Bag 3, Wits, 2050, South Africa, e-mail: judith.kinnaird@wits.ac.za; roger.gibson@wits.ac.za Search for other works by this author on: GSW Google Scholar R.A. ARMSTRONG R.A. ARMSTRONG PRISE, Australian National University, Research School of Earth Sciences, Building 61, Mills Road, Acton, 0200, Australia, e-mail: richard.armstrong@anu.edu.au Search for other works by this author on: GSW Google Scholar Author and Article Information L. LONGRIDGE School of Geosciences, University of the Witwatersrand, PVT Bag 3, Wits, 2050, South Africa VM Investment Company, 24 Fricker Rd, Illovo, Johannesburg, South Africa, e-mail: lukelongridge@gmail.com J.A. KINNAIRD School of Geosciences, University of the Witwatersrand, PVT Bag 3, Wits, 2050, South Africa, e-mail: judith.kinnaird@wits.ac.za; roger.gibson@wits.ac.za R.L. GIBSON School of Geosciences, University of the Witwatersrand, PVT Bag 3, Wits, 2050, South Africa, e-mail: judith.kinnaird@wits.ac.za; roger.gibson@wits.ac.za R.A. ARMSTRONG PRISE, Australian National University, Research School of Earth Sciences, Building 61, Mills Road, Acton, 0200, Australia, e-mail: richard.armstrong@anu.edu.au Publisher: Geological Society of South Africa First Online: 09 Mar 2017 Online ISSN: 1996-8590 Print ISSN: 1012-0750 © 2014 Geological Society of South Africa South African Journal of Geology (2014) 117 (1): 67–86. https://doi.org/10.2113/gssajg.117.1.67 Article history First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation L. LONGRIDGE, J.A. KINNAIRD, R.L. GIBSON, R.A. ARMSTRONG; AMPHIBOLITES OF THE CENTRAL ZONE: NEW SHRIMP U-PB AGES AND IMPLICATIONS FOR THE EVOLUTION OF THE DAMARA OROGEN, NAMIBIA. South African Journal of Geology 2014;; 117 (1): 67–86. doi: https://doi.org/10.2113/gssajg.117.1.67 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietySouth African Journal of Geology Search Advanced Search Abstract New SHRIMP U-Pb zircon and titanite data are presented for two amphibolites from the Central Zone of the Damara Orogen, Namibia. These data (the first ages for amphibolites in the Central Zone) show that amphibolites are derived from both Palaeoproterozoic (2026.9 ± 2.3 Ma – sample ACAM-1) and Pan-African (557.2 ± 7.4 Ma – sample LKR021) precursors emplaced into the Palaeoproterozoic Abbabis Complex basement in the Central Zone. The younger amphibolites are interpreted as part of a mafic to dioritic phase of magmatism in the Central Zone (the Goas Suite), and major- and trace-element geochemistry from a suite of amphibolites from the southwestern Central Zone confirms this relationship. This phase of mafic to dioritic magmatism is contemporaneous with the onset of collision between the Congo and Kalahari Cratons. It is suggested that delamination of dense mafic lower crust and underplating of mantle-derived magmas following crustal thickening may have led to partial melting of pre-Pan-African mafic lower crust, generating this mafic to dioritic suite of rocks. Metamorphic zircon overgrowths in sample LKR021 give an age of 520 ± 6.9 Ma, consistent with recent estimates for the age of peak metamorphism in the southwestern Central Zone. Titanites from LKR021 give an age of 493.4 ± 6.4 Ma, and this is interpreted as a cooling age for the Central Zone. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Late Palaeoproterozoic post-collisional magmatism in the North China Craton: geochemistry, zircon U–Pb geochronology, and Hf isotope of the pyroxenite–gabbro–diorite suite from Xinghe, Inner Mongolia

The North China Craton (NCC) witnessed a prolonged subduction–accretion history from the early to late Palaeoproterozoic, culminating with final collision at ca. 1.85 Ga and assembling the continental blocks into the cratonic framework. Subsequently, widespread post-collisional magmatism occurred, particularly along the Trans-North China Orogen (TNCO) that sutures the Eastern and Western blocks of the NCC. Here we present petrological, geochemical, and zircon U–Pb geochronological and Lu–Hf data from a pyroxenite (websterite)–gabbro–diorite suite at Xinghe in Inner Mongolia along the northern segment of the TNCO. The internal structures and high Th/U values of the zircons from the gabbro–diorite suite suggest magmatic crystallization. LA-ICP-MS U–Pb age data on three gabbros and one diorite from the suite yield emplacement ages of 1786.1 ± 4.8, 1783 ± 15 ,1754 ± 16 and 1767 ± 13 Ma, respectively. The εHf(t) shows mostly positive values (up to 5.8), with the lowest value at –4.2, suggesting that the magma was derived from dominantly juvenile sources. The generally low SiO2 and high MgO values, and other trace element features of the Xinghe suite are consistent with fractionation from a mantle-derived magma with a broadly E-MORB affinity, with no significant crustal contamination. Recent studies clearly establish that the major magmatic pulse associated with rifting of the NCC within the Columbia supercontinent occurred in the late Mesoproterozoic at ca. 1.3–1.2 Ga associated with mantle plume activity. This, together with the lack of robust geochemical imprints of rift-related magmatism in the Xinghe suite, prompts us to suggest a tectonic model that envisages magma genesis associated with post-collisional extension during slab break-off, following the westward subduction of the Eastern Block and its collision with the Western Block. The resulting asthenospheric upwelling and heat input might have triggered the magma generation from a heterogeneous, subduction-modified sub-lithospheric mantle source for the Xinghe rocks, as well as for similar late Palaeoproterozoic suites in the TNCO.

Geochronology and geochemistry of Early–Middle Triassic magmatism in the Erguna Massif, NE China: Constraints on the tectonic evolution of the Mongol–Okhotsk Ocean

In this paper, we present new zircon U–Pb dating, Hf isotope, major and trace elements, and Sr–Nd isotope data for Early–Middle Triassic intrusive rocks in the Erguna Massif of NE China, in the eastern segment of the Central Asian Orogenic Belt (CAOB). Our aim is to elucidate the tectonic evolution of the Mongol–Okhotsk Ocean and its influence on NE China. Zircons from five representative intrusions in the Erguna Massif are euhedral–subhedral in shape, display oscillatory growth zoning in CL images, and have Th/U ratios of 0.17–1.54, and in combination these features indicate that the zircons are of igneous origin. Zircon U–Pb dating results demonstrate that the Early–Middle Triassic magmatism in the Erguna Massif took place between 241 and 247Ma. The Early–Middle Triassic rocks are composed mainly of a suite of diorites, quartz–diorites, granodiorites, monzogranites, and syenogranites. They have SiO2=57.71–72.86wt.%, Mg#=19–52, Al2O3=14.27–17.23wt.%, and Na2O/K2O=0.67–1.59. Chemically, they are metaluminous to peraluminous and belong to the high-K calc-alkaline series. Moreover, they are enriched in light rare earth elements and large ion lithophile elements, and depleted in heavy rare earth elements and high field strength elements (e.g., Nb, Ta, and Ti). The whole-rock εNd(t) and zircon εHf(t) values of these samples range from −4.68 to −3.42, and from −2.0 to +6.6, respectively, indicative of formation from primary magmas generated by partial melting of juvenile crustal material with a contribution from mantle-derived mafic magmas. These magmas subsequently underwent fractional crystallization, contamination, and magma mixing. Geochemically, these Early–Middle Triassic intrusive rocks have affinities with intrusive rocks from active continental margin settings. We conclude, therefore, that the Early–Middle Triassic magmatism in the Erguna Massif was generated within an active continental margin setting related to the southwards subduction of the Mongol–Okhotsk oceanic plate beneath the Erguna Massif. This conclusion is supported by the occurrence of Early Mesozoic porphyry and skarn deposits along the southeastern side of the Mongol–Okhotsk suture belt.

Zetland Diorite, Karamea Batholith, west Nelson: field relationships, geochemistry and geochronology demonstrate links to the Carboniferous Tobin Suite

Field observations, petrography, geochemistry and U–Pb geochronology of the I-type Zetland Diorite from New Zealand's Western Province reveal a Carboniferous age of emplacement and chemical affinity with the Tobin dioritic suite. New U–Pb zircon dating by isotope-dilution thermal-ionisation mass spectrometry (ID-TIMS) provides a robust age of 347.19±0.24 Ma for a sample of Zetland Diorite. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U–Pb zircon dating of a Zetland quartz leucodiorite sample is complicated by significant inheritance from Karamea and Paringa granitoid suites but yields an estimated crystallisation age of 350.6±8.7 Ma, consistent with the field evidence for emplacement coeval with the dated mafic dioritic phase. Our results show that Zetland Diorite is at least c. 10 Ma younger and geochemically distinct from the 369–360 Ma I-type dioritic intrusives of the Paringa Suite, including the Riwaka Complex, as well as from the 370–368 Ma Karamea Suite S-type granites with which the Zetland Diorite had previously been deemed coeval. It therefore cannot serve as a mafic end-member source component of the Karamea Suite and its emplacement does not constrain the minimum age of amalgamation of the Buller and Takaka terranes.

Magma mixing in the genesis of the Kalatongke dioritic intrusion: Implications for the tectonic switch from subduction to post-collision, Chinese Altay, NW China

The Kalatongke complex, located in south Chinese Altay of the Central Asian Orogenic Belt (CAOB), consists of the ~308Ma dioritic suite intruded by the 287Ma noritic suite. The noritic suite is composed of olivine norite and hornblende norite and hosts sulfide mineralization. The dioritic suite is composed of ferrodiorite, diorite and quartz diorite.Ferrodiorites have 43.6 to 51.8wt.% SiO2, 8.2 to 12.1wt.% Fe2O3T, 2.87 to 4.86wt.% MgO, with Mg# ranging from 42 to 53. They have highly variable Al2O3 (17.4–20.7wt.%), Na2O (2.78–4.50%), K2O (0.58–3.70%), Sr (280–1300ppm) and Ba (219–3100ppm). Diorites and quartz diorites have 15.2–19.6wt.% Al2O3, 239–890ppm Sr and170–1100ppm Ba, 11.2–25.5ppm Y and1.2–2.2ppm Yb. All rocks have LREE enriched REE patterns and do not display Eu anomalies. They have primitive mantle-normalized trace element patterns enriched in large ion lithosphile elements (LILE) (e.g. Ba and Sr) and depleted in Ti, Nb and Ta.Both ferrodiorites and diorites have relatively constant initial 87Sr/86Sr ratios of 0.7037 to 0.7040 but highly variable εNd(t) values of +4.5 to +11.6, whereas quartz diorites have higher initial 87Sr/86Sr ratios (0.7056) and lower εNd(t) values (+0.5). Plagioclase from ferrodiorites, diorites and quartz diorites has similar initial 87Sr/86Sr ratios of 0.7015 to 0.7055.The dioritic suite formed from a mixed magma of an evolved mantle-derived basaltic magma by partial melting of subduction-modified mantle source in response to slab breakoff and a crustal-derived granitic magma at ~308Ma. Before mixing with granitic magmas, basaltic magmas underwent fractional crystallization of olivine to form ferrodiorite. The mixed magma also formed diorite and quartz diorite combining fractionation clinopyroxene, amphibole and plagioclase. The noritic suite formed from a mantle-derived high-Mg magma in a post-collisional environment. Both the dioritic and noritic suites in Kalatongke suggest the switch from subduction to extension and the final collision between the Junggar Block and Chinese Altay at ~308Ma.

Geochemistry of Tertiary Igneous Rocks of Northern Luzon, Philippines: Evidence for a Back-Arc Setting for Alkalic Porphyry Copper-Gold Deposits and a Case for Slab Roll-Back?

Oligocene to early Miocene volcanic rocks are preserved in the Central Cordillera range and Cagayan Valley of northern Luzon, Philippines. Basaltic and andesitic rocks of the Pugo Formation in the Baguio district of the Central Cordillera were intruded by the ~27 to 20 Ma calc-alkaline Central Cordillera Diorite Complex. In the southern Cagayan Valley the subalkaline to alkaline late Oligocene Mamparang Formation overlies the Cretaceous Caraballo Formation and has been intruded by the Didipio Igneous Complex, the Cordon Syenite Complex, and the Palali batholith. The Didipio complex comprises an early suite of diorites, which were intruded by the strongly mineralized stocks of the Dinkidi Cu-Au porphyry deposit. Whole-rock geochemical data for intrusive and extrusive rocks of the Baguio district range from low K calc-alkaline to shoshonitic basalts to dacites with rare earth element (REE) and high field strength element (HFSE) characteristics of suprasubduction zone magmas and are all interpreted to have been sourced from the same parent melt. Samples from Didipio display higher alkali contents but similar trace element characteristics. New age dates for the Didipio area range from 25.7 to 24.8 Ma. The potassic magmas of the Cagayan Valley are interpreted to have formed in a back-arc coeval to the mainarc sequence that is preserved in the Baguio Miocene rocks. This contradicts earlier models, which invoke an early Miocene arc reversal in the northern Luzon archipelago with the switch from early westward subduction to later eastward subduction attributed to a variety of causes. The lack of a single compelling trigger for arc reversal combined with the coeval emplacement of arc magmas in the west and back-arc magmas in the east in northern Luzon is best interpreted as the result of eastward subduction since the late Oligocene. The presence of ~20 Ma adakitic magmas in the Baguio district may indicate that flattening of the downgoing slab resulted in a hiatus in magmatism and termination of back-arc rifting.