Zircon Trace Element Geochemistry Research Articles

Geochronology and petrogenesis of multiple magmatic events in the Tianbaoshan orefield, NE China: Implications for tectonic evolution

Recent studies have shown that multistage magmatic and metallogenic events in NE China were dominated by the Paleo-Asian Ocean tectonic regime and the Paleo-Pacific Ocean tectonic regime. However, outstanding questions remain on the petrogenesis and fertility of ore-causative magma in each metallogenic event. In this study, we report new geochronologic and geochemical data on ore-causative intrusions from the Tianbaoshan orefield in the east Jilin-Heilongjiang belt (EJHB), aiming to identify their petrogenesis, magma fertility, and their implications for the geodynamic evolution of the EJHB. Middle Permian Lishan ore-causative quartz monzodiorites with abundant mafic microgranular enclaves (MMEs) were emplaced at ca. 264.9 ± 2.6 Ma. Petrographic and geochemical characteristics (87Sr/86Sr(i) = 0.7049–0.7053, εNd(t) = 2.9–3.7, and εHf(t) = 4.7–11.7) indicate a juvenile crust source injected by a slab-metasomatized mantle component. The Early Jurassic Beishan monzogranites (ca. 192.5 ± 1.8 Ma) were generated by the partial melting of the juvenile underplating basaltic lower crust with subsequent fractional crystallization in response to their highly evolved geochemical features, combined with their depleted Sr-Nd-Hf isotopic signature (ISr = 0.7032–0.7037, εNd(t) = 2.8–3.3, and εHf(t) = 7.2–12.2). Based on the zircon trace element geochemistry, we infer that the Middle Permian quartz monzodiorites had a high oxygen fugacity (Ce4+/Ce3+ = 40–216), potentially generating the Pb-Zn-Cu mineralization. Early Jurassic Beishan monzogranites had a lower magmatic oxygen fugacity (Ce4+/Ce3+ = 14–106), which may account for the Mo-dominated mineralization. A combination of this study and previous results corroborates that the Tianbaoshan orefield records the superposition of different tectonic regimes during metallogenesis.

The northbrae rhyolite of Berkeley (California, USA) constrains motion of the proto-Hayward Fault

ABSTRACT Right-lateral transform motion associated with the Pacific-North American plate boundary in the modern-day San Francisco Bay Area occurs across a series of sub-parallel fault zones. Much of this motion is accommodated east of the San Andreas Fault by the faults of the East Bay fault system. A major tool for reconstructing the spatial and temporal history of fault motion is the correlation of offset Neogene volcanic rocks. These Neogene volcanics within the California Coast Ranges formed in association with the slab gap that grew as the Mendocino Triple Junction migrated northward. Some of the volcanic centres have been variably offset by subsequent strike-slip faulting. A felsic volcanic unit exposed in Berkeley, CA, known as the Northbrae rhyolite has variably been interpreted to be one of these Neogene volcanic units or to be a Mesozoic volcanic unit associated with the Coast Range ophiolite. A new U-Pb zircon date of 11.10 ± 0.09 Ma confirms the Neogene volcanic interpretation. This date is indistinguishable from previously published Ar/Ar dates from the Burdell Mountain volcanics of the North Bay region as well as a new U-Pb zircon date of 11.07 ± 0.10 Ma. In addition to the indistinguishable ages, similarities in bulk lithology, zircon crystallization/dissolution textures, and zircon trace element geochemistry are consistent with these rhyolites being associated with the same volcanic centre. This correlation implies that 40 ± 5 km of right-lateral offset occurred to the west of the modern-day position of the Hayward-Rodgers Creek fault zone. This offset represents ∼ 20% of the total offset along the East Bay fault system. A proto-Hayward Fault with a different geometry than that of the present-day played a significant role in the evolution of the fault system. This result highlights the dynamic spatiotemporal variability of strike-slip faults along transform margins.

Contrasting magma chemistry in the Candelaria IOCG district caused by changing tectonic regimes

Iron oxide-copper-gold (IOCG) deposits are a vital source of copper and critical elements for emerging clean technologies. Andean-type IOCG deposits form in continental arcs undergoing extension, and they have a temporal relationship with magmatism although they do not exhibit a close spatial relation with the causative intrusions. The processes required to form IOCG deposits and their potential connections to iron oxide–apatite (IOA)-type mineralization remain poorly constrained, as well as the characteristics of magmatism linked to both deposit types. Here we combine zircon U–Pb geochronology with zircon trace element geochemistry of intrusive rocks associated with the Candelaria deposit, one of the world’s largest IOCG deposits, to unravel distinctive signatures diagnostic of magmatic fertility. Our results reveal a marked transition in the geochemistry of intrusions in the Candelaria district, characterized by changes in the redox state, water content and temperature of magmas over time. The oldest magmatic stage (~ 128–125 Ma), prior to the formation of the Candelaria deposit, was characterized by zircon Eu/Eu* ratios of 0.20–0.42, and redox conditions of ΔFMQ − 0.4 to + 1.0. The earliest magmatic stage related to the formation of Fe-rich mineralization at Candelaria (118–115 Ma) exhibits low zircon Eu/Eu* ratios (0.09–0.18), low oxygen fugacity values (ΔFMQ ~− 1.8 to + 0.2) and relatively high crystallization temperatures. In contrast, the youngest stage at ~ 111–108 Ma shows higher zircon Eu/Eu* (~ 0.37–0.69), higher oxygen fugacity values (ΔFMQ ~ + 0.4 to + 1.3) and a decrease in crystallization temperatures, conditions that are favorable for the transport and precipitation of sulfur and chalcophile elements. We conclude that Candelaria was formed through two distinct ore-forming stages: the first associated with a reduced, high temperature, water-poor magma developed under a low tectonic stress, followed by a more oxidized, water-rich, and low temperature magmatic event related to a compressional regime. The first event led to Fe-rich and S-poor IOA-type mineralization, while the second event with geochemical signatures similar to those of porphyry copper systems, generated the Cu- and S-rich mineralization. This late stage overprinted preexisting IOA mineralization resulting in the formation of the giant Candelaria IOCG deposit.

Trace elements in zircon record changing magmatic processes and the multi-stage build-up of Archean proto-continental crust

Zircon trace element geochemistry has become an increasingly popular tool to track crustal evolution through time. This has been especially important in early-Earth settings where most of the crust has been lost, but in some fortuitous instances detrital zircons derived from that lost crust have been preserved in younger sediments. To study the formation and geochemical evolution of continental crust from the Hadean to the Paleoarchean, the 3.6 to 3.2 Ga Barberton Greenstone Belt in southern Africa is an excellent target due to its outstanding preservation and presence of detrital zircons that span almost a billion years. Here, we use trace elements, in combination with hafnium and oxygen isotopes, of 3.65 to 3.22 Ga detrital and tuffaceous zircons of the Moodies and Fig Tree groups and compare their geochemistry to previously studied 4.2 to 3.3 Ga detrital zircons from the Green Sandstone Bed of the Onverwacht Group. The major detrital zircon age clusters in the former at 3.55 Ga, 3.46 Ga, and 3.26–3.23 Ga overlap with episodes of TTG emplacement and felsic volcanism in the Barberton area, suggesting a local provenance. In contrast, age clusters at 3.65 Ga and 3.29 Ga of the Moodies and Fig Tree groups as well as 4.2 to 3.3 Ga detrital zircons from the Green Sandstone Bed do not have known intrusive sources and were likely derived from outside the present-day Barberton belt. This indicates that more than half of the felsic igneous events in the detrital zircon record do not have a whole-rock representation that can be directly studied. The similar compositions and inferred crustal evolution histories recorded in zircons from the Fig Tree and Moodies groups, as well as from the Green Sandstone Bed, suggest that they were derived from connected terranes experiencing similar crustal processes diachronously. Together, they show three phases of felsic continent formation, reflecting different crustal processes: (1) long-lived protocrust formed in the Hadean from undepleted mantle sources. These zircons are vastly different from younger zircons and, hence, Barberton TTGs are not good analogues of Hadean crust formation. (2) At 3.8 Ga, onset of significant crustal growth though cyclic juvenile additions and hydrous melting, possibly within a volcanic plateau setting but an arc-like setting cannot be excluded based on this data. (3) Between 3.4 and 3.3 Ga, felsic crust is generated through a previously unrecognized episode of crustal growth by shallow melting of mafic, mantle-derived sources. This is immediately followed by the onset of crustal thickening through the transport of surface-altered, hydrated materials to deep crustal levels. Since there is geological evidence for extension and shortening at that time this may reflect the onset of horizontal movement. Whether this last geodynamic setting reflects modern-style plate tectonics or not, continent formation and the onset of plate tectonics in the Barberton area occurred through complex multi-stage processes spanning almost a billion years, most of which is only accessible through the detrital zircon record.

Geochronology and Geochemistry of the Xianghualing Granitic Rocks: Insights into Multi-Stage Sn-Polymetallic Mineralization in South China

Multi-stage magmatic events associated with large tungsten-tin polymetallic deposits in the Nanling Range have been the subject of extensive research spanning many years. In this paper we report the results of a systematic study of the petrology, whole-rock geochemistry, zircon U-Pb chronology, and trace element geochemistry of granite bodies exposed in the Xianghualing ore field. They show that the granites in the study area are characterized by high SiO2 (63.83%–75.29%), Al2O3 (13.12%–18.87%), Rb (565–3260 ppm), Nd (67.3–113.5 ppm) and Ta (23.2–129.0 ppm) and by low MgO (0.02%–0.22%), TiO2 (0%–0.02%), Sr (5.3–80.5 ppm) and Ba (7.9–66.4 ppm). The rocks are highly differentiated A-type peraluminous granite, which originated in an extensional within-plate tectonic setting. Based on U-Pb dating and trace element analysis, the following multi-stage magma-hydrothermal events were identified: (1) Paleozoic (~347 Ma) and Triassic (~206 Ma) magmatic stages (initial enrichment epochs of ore-forming elements), (2) Jurassic (~161 Ma) magmatic-hydrothermal stage (mineralization epoch), and (3) Cretaceous hydrothermal overprinting stage (with peaks in the Early Cretaceous ~120 Ma and Late Cretaceous ~80 Ma). From an economic point of view, the Late Cretaceous appears to have great potential for tungsten-tin mineralization. Zircon trace element geochemistry indicates that the ore-forming fluids related to tin mineralization in the Cretaceous originated from the crust and underwent highly differentiated evolutionary processes under relatively reducing conditions. This paper emphasizes the Cretaceous tungsten-tin metallogenic events in the Nanling Range and provides an essential basis and new ideas for further tin-tungsten exploration.

Generation and redox state of two episodes of Early Cretaceous granitoid in the Xiaoqinling area, North China Craton: Implications for lithosphere thinning and metallogenic potential

The late Mesozoic granitoids in the Xiaoqinling area are of great significance for their associated gold deposits and for understanding the geodynamics of craton destruction. The Niangniangshan pluton in the Xiaoqinling area records three phases of magmatic activity, with biotite monzogranites formed in Phases1 and Phases2 and monzogranites in Phase3. Field investigations and LA–ICP–MS zircon UPb dating indicate that the Niangniangshan pluton was formed during two episodes of magmatism at ~134 Ma (Phase1 and Phases2) and ~ 123 Ma (Phase3). The ~134 Ma granitoids exhibit higher Sr/Y ratios (57–164) and higher contents of Sr (563–1114 ppm) and Ba (1455–1958) than the ~123 Ma granitoids (Sr = 88–124 ppm, Ba = 60–117 ppm, Sr/Y = 16–52). In addition, the ~134 Ma granitoids do not display significant Eu anomalies (0.75–1.06), while the ~123 Ma granitoids show negative Eu anomalies (0.73–0.84). However, all of the granitoids have low contents of MgO, Cr, Co and Ni, relatively high initial 87Sr/86Sr ratios (0.7072 to 0.7108), and low values of εNd(t) (−16.97 to −14.49) and εHf(t) (−29.62 to −14.41). These geochemical characteristics indicate that the ~134 Ma granitoids were generated by partial melting of the ancient metamorphic basement at high pressures, whereas the ~123 Ma granitoids were formed by partial melting of the ancient metamorphic basement at relatively low pressures. The differences in the formation of the two episodes of granitoid provide further evidence that there was a transformation from lithospheric thickening of the North China Craton in the Xiaoqinling area to a stage of lithospheric thinning, this probably taking place between ~134 and ~ 123 Ma. Zircon trace-element geochemistry indicates that the ~123 Ma granitoids had higher oxygen fugacities and zircon crystallisation temperatures than the ~134 Ma granitoids. We also found that ΔFMQ values show a positive correlation with temperature for the ~134 Ma granitoids, but a negative correlation for the ~123 Ma granitoids. This indicates that the ~134 Ma magma became more reduced with evolution whereas the ~123 Ma magma became more oxidised. These features, combined with the redox state of typical magmatic hydrothermal gold deposits globally, suggest that the ~123 Ma granitoids had a greater potential to form magmatic hydrothermal gold deposits than the ~134 Ma granitoids.

Metamorphic PT path, U-Pb zircon dating and tectonic implications of High-pressure Pelitic Granulites from the Kharta region, Southern Tibet, China

HP pelitic granulites associated with eclogites from the Kharta Gneiss are found in the Thongmön area, central Himalaya, which provides significant constraints for the tectonic evolution of the Himalayan orogeny. Three generations of garnets are identified in pelitic granulites (DR15P15). The first generation of garnet is core sections of euhedral to subhedral porphyroblasts (Grt-I core) followed by growth of Grt-I mantle during the heating stage. The third generation of garnet is represented by thin rims of Grt-I and small grains (Grt-II) in the matrix, which likely nucleated and grew in response to peritectic reaction during exhumation. Petrographic evidence and P–T pseudosection calculation reveal a four-stages metamorphic evolution: 1) a prograde metamorphic stage (M1) represented by Grt-I core and its mineral inclusions rutile, ilmenite and quartz with metamorphic conditions of 740–760 °C and 13–16 kbar; 2) a near isobaric heating stage with slightly decompression to HP granulite-facies (M2, 820–840 °C, 13–14 kbar) indicated by the composition of Grt-I mantle and the increase of Zr concentrations of rutile in it; 3) a heating decompression stage (M3) supported by a decrease in grossular content in the Grt-I rim and higher XAn in plagioclase, yielding T > 860 °C and P = 10–11 kbar in the sillimanite stability field; 4) a final decompression stage followed by cooling (M4, T ~ 800 °C and P = 6–8 kbar) indicated by biotite replacing sillimanite and lower Ti content in biotite in the matrix. Based on the zircon trace element geochemistry, zircon inclusions, and the REE partitioning between garnet and zircon, the metamorphic zircon rims with middle Miocene age (16–13 Ma) probably grew during Grt-I rim/Grt-II formation at granulite facies stage (M3). The P–T history of the pelitic granulites of the Kharta Gneiss indicates that they were subducted beneath the Asian plate and exhumed to middle-lower crustal depths prior to 14–13 Ma due to the activity of STDS.

The detrital zircon U-Pb-Hf isotopes of the Triassic sediments in northern Pakistan: Implications for crustal evolution of the NW Indian continent

Detrital zircon analysis of the Triassic Kashala Formation of the Alpurai Group in Swat, Pakistan, west of Indus syntaxis, record Archean to Paleozoic ages. The U-Pb age spectra show distinctive age clusters at 3510–3100 Ma, 2700–2400 Ma, 1750–1500 Ma, 1350–750 Ma, 700–600 Ma and 580–470 Ma, with one youngest age of 229 Ma, suggesting secular and episodic continental growth. The prominent negative εHf(t) values indicate dominantly crustal reworking together with a minor contribution from a juvenile crust. The age pattern is similar to the detrital zircon from Tethyan Himalaya and South India, showing two major peaks at 926 Ma and 532 Ma, and corresponding to Greenville and Pan-African orogenies, respectively. The U-Pb age peaks between ca. 1750–1600 Ma and 900–750 Ma are correlated well with the peaks of detrital zircon from Precambrian and Ordovician rocks in the Hazara region. Detrital zircon analysis suggests proximal source areas. Based on combined U-Pb and Hf isotope analysis and grain morphology, Paleoproterozoic detrital zircon grains were derived from basement rocks of the Besham Complex, which is presently exposed in the Indus syntaxis. The zircon trace element geochemistry reveals mainly felsic and mafic igneous rocks of the continental crust, suggesting that proximal Proterozoic-Paleozoic intrusions in the Swat and Hazara regions as a possible source.

Zircon Trace Element Geochemistry and Ti-in-Zircon Thermometry of the Ngazi-Tina Pan-African Post-Collisional Granitoids, Adamawa Cameroon

In Cameroon, the Ngazi-Tina region belongs to the Adamawa-Yade domain of the Pan-African Central African Fold Belt (CAFB). It is composed of two petrographic types: quartz-monzonites (majority) and nepheline syenites. Two morphological types, prismatic and pyramidal, were recognized in the zircon grains samples. These zircon types display internal structures typical of magmatic zircons. Zircons separated from the Ngazi-Tina samples contain higher abundances of Hf (close to 8000 ppm) and moderate trace elements (Y, Th, U, Nb, Ta) and REE contents, suggesting a variable degree of magmatic evolution. The chondrite-normalized REE patterns of zircons are characterized by LREE depletion relative to HREE with positive Ce and negative Eu anomalies, typical of magmatic zircons. The high Hf content together with high Ce/Ce*, Th/U, Zr/Hf ratios suggest magma crystallization under variable oxidation and oxygen fugacity. The application of Ti-in-zircon thermometer reveals crystallization temperatures ranging from 678°C to 811°C and 658°C to 768°C for quartz monzonites and nepheline syenites respectively. These features indicate probably a partial melting of continental crust as the source of these zircons grains and emplacement in the magmatic-arc setting.

Geochronology, petrogenesis and oxidation state of the Wenyu igneous suite in the Xiaoqinling district, North China Craton: Implications for lithospheric thinning and magma fertility

Recent studies have shown that the Mesozoic metallogenic event in the southern margin of the North China Craton (NCC) is related to the coeval magma activities generated by the lithospheric thinning and asthenosphere upwelling. However, the reason why some Mesozoic magmatic systems in this area are barren is not clear. In this study, we report new geochronological and geochemical data for a Mesozoic igneous suite of Wenyu monzogranites from the Xiaoqinling area in the southern margin of the NCC, focusing on the petrogenesis and oxidation state with their implications on lithospheric thinning and magma fertility. The Wenyu monzogranites have zircon UPb ages between 141.4 and 122.2 Ma. Whole-rock major and trace element, SrNd and zircon Hf isotope geochemistry suggest that the Wenyu monzogranites were dominantly derived from partial melting of the metamorphic and volcanic rocks from the Neoarchean to Paleoproterozoic, with potential replenishments of mantle-derived magmas triggered by the lithospheric thinning and hot asthenosphere upwelling. Zircon trace element geochemistry suggests a low oxidation state for the Wenyu magmatic system, which probably resulted in early sulfide saturation. Most of the ore-forming chalcophile elements (Au and Cu) were locked in a sulfide phase that was retained in cumulate rocks at depth due to the early sulfide saturation, so that when the magma became fluid saturated at the later stage of magmatic evolution, it did not have access to the Au and Cu. As a consequence, our study suggests that the Wenyu pluton was not prospective for magmatic-hydrothermal Au ± Cu deposits.

Metallogenic controls on the granite-related W–Sn deposits in the Hunan–Jiangxi region, China: evidence from zircon trace element geochemistry

The Nanling Range in South China is well known for its rich granite-related W–Sn deposits. To elucidate the controls of different granite-related W–Sn metallogenesis in the region, we chose five representative ore-related granites (Yanbei, Mikengshan, Tieshanlong, Qianlishan, and Yaogangxian intrusions) in the Hunan–Jiangxi region, and studied their magmatic zircon ages and trace element geochemistry. Our new zircon data showed the differences in ages, temperatures and oxygen fugacity of the ore-forming magmas. Zircon U–Pb ages of the Yanbei and Mikengshan intrusions are characterized by 142.4 ± 2.4 and 143.0 ± 2.3 Ma, respectively, whereas the Tieshanlong and Qianlishan intrusions are 159.5 ± 2.3 and 153.2 ± 3.3 Ma, respectively. The Sn-related intrusions were younger than the W-related intrusions. The Ti-in-zircon thermometry showed that there was no systematic difference between the Sn-related Yanbei (680–744 °C) and Mikengshan (697–763 °C) intrusions and the W-related Tieshanlong (730–800 °C), Qianlishan (690–755 °C) and Yaogangxian (686–751 °C) intrusions. However, the zircon Ce4+/Ce3+ ratios of the Yanbei (averaged at 18.3) and Mikengshan (averaged at 18.8) intrusions are lower than those of the Tieshanlong (averaged at 36.9), Qianlishan (averaged at 38.4) and Yaogangxian (averaged at 37) intrusions, indicating that the Sn-related granitic magmas might have lower oxygen fugacities than those of the W-related. This can be explained by that, in more reduced magmas, Sn is more soluble than W and thus is more enriched in the residual melt to form Sn mineralization. The difference in source materials between the Sn-related and the W-related granites seems to have contributed to the different redox conditions of the melts.

Maturation and rejuvenation of a silicic magma reservoir: High-resolution chronology of the Kneeling Nun Tuff

Knowledge of the conditions of magma storage prior to volcanic eruptions is key to their forecasting, yet little is known about how melt compositions, crystallinity and intensive parameters within individual magma reservoirs evolve over time. To address this, we studied the Kneeling Nun Tuff, a voluminous (>900 km3) deposit of an Eocene caldera-forming eruption from the Mogollon–Datil volcanic field in New Mexico, USA. Whole-rock, feldspar and amphibole compositions were combined with zircon trace-element geochemistry and precise isotope dilution-thermal ionisation mass spectrometry (ID-TIMS) U–Pb zircon crystallisation ages to arrive at a detailed, time-resolved record of chemical and physical changes within the voluminous, upper-crustal (∼2.2 kbar) magma reservoir. Chemical compositions and zircon ages from the Kneeling Nun Tuff and from co-magmatic clasts hosted within it reveal prolonged (>1.5 million years) growth and maturation of the magma reservoir that was heterogeneous in terms of temperature, melt composition and crystallinity. This protracted storage at a dominant crystallinity in excess of 50% culminated in a period of ca. 50 ky of increase in recharge heat supply and related homogenisation, decrease in crystallinity to 40–50%, and potential increase in average melt temperature, leading up to eruption at 35.299 ± 0.039 Ma. Sampling of co-magmatic lithic clasts derived from early-cooled domains of the reservoir shows that the long, million year-scale maturation time is shared across all erupted domains of the magmatic system, irrespective of their final cooling history. This study provides key observations from a natural system against which thermal and mechanical models of upper-crustal magma reservoir construction can be validated.

Marine Volcaniclastic Record of Early Arc Evolution in the Eastern Ritter Range Pendant, Central Sierra Nevada, California

AbstractMarine volcaniclastic rocks in the Sierra Nevada preserve a critical record of silicic magmatism in the early Sierra Nevada volcanic arc, and this magmatic record provides precise minimum age constraints on subduction inception and tectonic evolution of the early Mesozoic Cordilleran convergent margin at this latitude. New zircon Pb/U ages from the Ritter Range pendant and regional correlations indicate arc inception no later than mid‐Triassic time between 37°N and 38°N. The regional first‐order felsic magma eruption rate as recorded by marine volcanic arc rocks was episodic, with distinct pulses of ignimbrite emplacement at ca. 221–216 and 174–167 Ma. Ignimbrites range from dacite to rhyolite in bulk composition, and are petrographically similar to modern arc‐type, monotonous intermediate dacite or phenocryst‐poor, low‐silica rhyolite. Zircon trace element geochemistry indicates that Jurassic silicic melts were consistently Ti‐enriched and light rare earth‐enriched and U‐depleted in comparison to Triassic melts of the juvenile arc, suggesting Jurassic silicic melts were hotter, drier, and derived from distinct lithospheric sources not tapped in the juvenile stage of arc construction. Pulses of ignimbrite deposition were coeval with granodioritic to granitic components of the underlying early Mesozoic Sierra Nevada batholith, suggesting explosive silicic volcanism and batholith construction were closely coupled at 1–2 million‐year time scales.

Geochemistry and tectonic implications of Early Permian granitic rocks in the Xingxingxia area of Chinese Central Tianshan Arc Terrane

The Chinese Central Tianshan Arc Terrane (CTA) in the southern Central Asian Orogenic Belt is characterized by voluminous Palaeozoic to Mesozoic (500–240 Ma) granites, with a magmatic “flare‐up” at Early Permian time (ca. 280 Ma). However, the tectonic setting of the Early Permian granites in the CTA is highly debated. In this study, Early Permian (ca. 280 Ma) granitic intrusions, including quartz diorite and dioritic enclave, amphibole granite, biotite granite, dioritic porphyry dyke, and a weakly mylonitic granitic dyke, were revealed from the Xingxingxia area of the CTA by LA‐ICP‐MS zircon UPb dating. These granitic rocks show magnesian and calc‐alkaline affinities and are characterized by Nb, Ta, P, Ti, and MREE depletion [(Dy/Yb)N = 1.02–1.51] with no significant Eu anomalies, suggesting geochemical characteristics of typical active continental margin magmatic rocks. Zircon trace element geochemistry of these Early Permian granitic rocks also indicates a continental arc setting with high U/Yb and Gd/Yb ratios. Among these granitic intrusions, the dioritic porphyry dyke has negative zircon εHf(t) values (−8.0 to −5.7), suggesting that the magma was produced by partial melting of the ancient crustal basements of the CTA. The rest intrusions show positive but largely varied zircon εHf(t) values of +4.1 to +10.9 (5 samples), suggesting that the magmas were probably derived from the mantle wedge with variable contributions from ancient crustal component during the magma evolution. These granitic intrusions were coeval with high‐temperature metamorphic rocks, mafic‐ultramafic rocks, and Cu‐Ni sulphide deposits in the CTA. Therefore, we propose a geodynamic model of oceanic ridge subduction of the South Tianshan Ocean during Early Permian involving upwelling of asthenospheric mantle through slab window and partial melting of the mantle wedge. The multiple‐derived magmas, including those from mantle wedge and/or ancient crustal basement, and their blendings formed the studied Early Permian granitic associations in the CTA.

Trace Element and U–Pb Core Age for Zircons from Western Meiganga Gold Placer, Cameroon: Their Genesis and Archean-Proterozoic Sources

Trace element concentrations and U–Pb ages were obtained using Laser Ablation Split Stream Method from the core of 115 zircon grains from the western Meiganga gold placer deposit. The data was used to characterize zircon, to understand the history of crystallization and to locate source rocks within the local and regional geological settings. Zircon trace element geochemistry was used to distinguish between magmatic and metamorphic affinity. The magmatic zircons have characteristics compatible with their probable origin from granitoid, syenite, tonalite, charnockite and mafic to ultramafic rocks. The metamorphic zircons composition is compatible with growth from anatectic melts and by sub-solidus crystallization in equilibrium with garnet. The zircon ages reveal Archean, Paleoproterozoic, Mesoproterozic, and Neoproterozoic events with the principal source could mainly belong to Paleoproterozoic magmatic lineage. Some of the Paleoproterozoic magmatic zircons were probably sourced from two mica granite found within the local geology, whereas the remaining zircons have features indicating source rocks within the Congo Craton. We suggest that the geologic history of these zircons is related to crustal-scale magmatic and/or tectono-metamorphic events, possibly linked to Eburnean and Pan-African orogeny.

Physicochemical Control of the Early Permian Xiangshan Fe-Ti Oxide Deposit in Eastern Tianshan (Xinjiang), NW China

The Xiangshan mafic-ultramafic complex is one of the major Early Permian mafic-ultramafic intrusions in eastern Tianshan (Xinjiang, NW China), and consists of two major intrusive phases. The first intrusive phase is mainly gabbroic rocks hosting ilmenite mineralization, while the second intrusive phase is mainly lherzoilite associated with Ni-Cu sulfide mineralization. The Xiangshan ilmenite orebodies hosted in the Fe-Ti oxide-bearing gabbro occur along the contact between hornblende gabbros and leucogabbros. The hornblende gabbros and Fe-Ti oxide rich gabbros at Xiangshan are newly dated to be Early Permian (280.1 and 279.2 Ma, respectively). Major and trace element compositions of zircons and whole rocks from Xiangshan hornblende gabbro and Fe-Ti oxide gabbro have been measured by in situ excimer laser ablation ICP-MS. Zircon Ce4+/Ce3+ ratios based on lattice-strain model and Ti-in-zircon temperatures of hornblende gabbro and Fe-Ti oxide gabbro of the Xiangshan complex are calculated to evaluate the physicochemical variations during the ilmenite mineralization. Whole-rock geochemistry and zircon trace element geochemistry suggest that Fe-Ti oxide gabbros were formed from a basaltic parent magma which had undergone a transfromation from being H2O-rich to H2O-poor. During the magmatic evolution, primitive, H2O-poor basaltic melts may have been replenished into the system, increasing its solidus temperature and decreasing its oxygen fugacity and H2O contents. This may have supperessed the Ti-rich poikilitic hornblende fractionation and promoted the plagioclase fractionation, which consequently concentrated the ore-forming components in the residual melts and generated the ilmenite mineralization.

Long‐Term Geochemical and Geodynamic Segmentation of the Paleo‐Pacific Margin of Gondwana: Insight From the Antarctic and Adjacent Sectors

AbstractCombined zircon geochemistry and geochronology of Mesozoic volcaniclastic sediments of the central Transantarctic Mountains, Antarctica, yield a comprehensive record of both the timing and geochemical evolution of the magmatic arc along the Antarctic sector of the paleo‐Pacific margin of Gondwana. Zircon age populations at 266–183 Ma, 367–328 Ma, and 550–490 Ma correspond to episodic arc activity from the Ediacaran to the Jurassic. Zircon trace element geochemistry indicates a temporal shift from granitoid‐dominated source(s) during Ediacaran to Early Ordovician times to mafic sources in the Devonian through Early Jurassic. Zircon initial εHf shifts to more radiogenic Hf isotope compositions following the Ross Orogeny and is inferred to reflect juvenile crustal growth within an extensional arc system during progressive slab rollback. These new ages and Hf isotopic record are similar to those from the Australian sector, indicating that these regions constituted an ~3,000 km laterally continuous extensional arc from at least the Carboniferous to the Permian. Conversely, the South American sector records enriched zircon Hf isotopic compositions and compressional/advancing arc tectonics during the same time period. Our new data constrain the location of this profound along‐arc geochemical and geodynamic “switch” to the vicinity of the Thurston Island block of West Antarctica.

Insights into the emplacement of upper-crustal plutons and their relationship to large silicic calderas, from field relationships, geochronology, and zircon trace element geochemistry in the Stillwater – Clan Alpine caldera complex, western Nevada, USA

Geologic mapping, new U-Pb zircon ages, and new and published 40Ar/39Ar sanidine ages document the timing and extent of Oligocene magmatism in the southern Stillwater Range and Clan Alpine Mountains of western Nevada, where Miocene extension has exposed at least six nested silicic calderas and underlying granitic plutons to crustal depths locally ≥9km. Both caldera-forming rhyolitic tuffs and underlying plutons were emplaced in two episodes, one from about 30.4–28.2Ma that included the Deep Canyon, Job Canyon, and Campbell Creek calderas and underlying plutons, and one from about 25.3–24.8Ma that included the Louderback Mountains, Poco Canyon, and Elevenmile Canyon calderas and underlying plutons. In these two 1–2m.y. periods, almost the entire Mesozoic upper crust was replaced by Oligocene intrusive and extrusive rocks to depths ≥9km over an estimated total area of ~1500km2 (pre-extension). Zircon trace element geochemistry indicates that some plutonic rock can be solidified residual magma from the tuff eruptions. Most plutons are not solidified residual magma, although they directly underlie calderas and were emplaced along the same structures shortly after to as much as one million years after caldera formation. Magma chambers and plutons grew by floor subsidence accommodated by downward transfer of country rocks. If other Great Basin calderas are similar, the dense concentration of shallowly exposed calderas in central Nevada is underlain by a complexly zoned mid-Cenozoic batholith assembled in discrete pulses that coincided with formation of large silicic calderas up to 2500–5000km3.

Oxygen isotope and trace element geochemistry of zircons from porphyry copper system: Implications for Late Triassic metallogenesis within the Yidun Terrane, southeastern Tibetan Plateau

It is intriguing to investigate the generation of the magmatic system and the geochemical signatures that distinguish the ore-bearing ones from barren ones, especially by examining the oxygen isotopic and trace element compositions of zircon. The oxygen isotopic composition and trace element abundances of zircons from the mineralized Pulang porphyries and the coeval Disuga and Lannitang andesites of the Yidun Terrane, eastern Tibetan Plateau, have been determined by secondary ion mass spectrometry (SIMS) and laser ablation–inductively coupled plasma–mass spectrometry (LA–ICP–MS) in this study, respectively. Analyzed zircons have relatively high but invariant δ18O values (~5.8‰–6.9‰) that are indicative of derivation from homogeneous mantle or mantle-derived magmas together with contribution of mature crustal materials. We propose a model for the Late Triassic magmatism in the Yidun Terrane involving magmas derived from partial melting of subduction-metasomatized mantle peridotites that subsequently experienced melting–assimilation–storage–homogenization (MASH) processes. The low calculated Ti-in-zircon temperatures (644°C–863°C, generally between 640°C and 690°C) for these zircons may be caused by the lower solidus temperature for zircon in hydrous magmas, and partly controlled by the crystallization of amphibole. Zircon grains from porphyry copper system display small negative europium anomalies (mostly Eu/Eu*>0.5), contrasting with pronounced negative Eu anomalies in zircons (mostly Eu/Eu*<0.5) associated with magmato-hydrothermal quartz-vein Cu-Mo-W/Mo-W deposits. Calculated REE compositions of the melt that was in equilibrium with zircons from porphyry copper system display depletion in the middle rare earth elements (MREE) without negative Eu anomaly, while that of zircons from magmato-hydrothermal quartz-vein Cu-Mo-W/Mo-W system show depletion in the MREE with negative Eu anomaly. It is speculated that the parental melts of zircon have decreasing magmatic oxidation state in the following sequence: porphyry copper system>magmato-hydrothermal quartz-vein Cu-Mo-W deposit>magmato-hydrothermal quartz-vein Mo-W deposit. This study suggests that zircon trace element geochemistry probably bears significant implications for elucidating the origin of the arc magmatism and guiding exploration strategies for porphyry copper deposits.

Zircon Trace Element Geochemistry of the Granodiorite Porphyry from the Baoshan Deposit, South China and Their Geological Implications

Acta Geologica Sinica - English EditionVolume 88, Issue s2 p. 582-583 Meeting Abstracts Zircon Trace Element Geochemistry of the Granodiorite Porphyry from the Baoshan Deposit, South China and Their Geological Implications Jiaru MI, Corresponding Author Jiaru MI School of Earth Sciences and Mineral Resources, China University of Geosciences, Beijing 100083 ChinaCorresponding author. E-mail: mjr345874153@163.comSearch for more papers by this authorShunda YUAN, Shunda YUAN MLR Key Laboratory of Metallogeny and Mineral Assessment, Institute of Mineral Resources, CAGS, Beijing 100037 ChinaSearch for more papers by this authorYabin YUAN, Yabin YUAN School of Earth Sciences and Mineral Resources, China University of Geosciences, Beijing 100083 ChinaSearch for more papers by this author Jiaru MI, Corresponding Author Jiaru MI School of Earth Sciences and Mineral Resources, China University of Geosciences, Beijing 100083 ChinaCorresponding author. E-mail: mjr345874153@163.comSearch for more papers by this authorShunda YUAN, Shunda YUAN MLR Key Laboratory of Metallogeny and Mineral Assessment, Institute of Mineral Resources, CAGS, Beijing 100037 ChinaSearch for more papers by this authorYabin YUAN, Yabin YUAN School of Earth Sciences and Mineral Resources, China University of Geosciences, Beijing 100083 ChinaSearch for more papers by this author First published: 29 December 2014 https://doi.org/10.1111/1755-6724.12374_40Citations: 1Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article.Citing Literature Volume88, Issues2Special Issue: Meeting Abstracts: The 14th Quadrennial International Association on the Genesis of Ore Deposits Symposium. August 19–22, 2014, Kunming, ChinaDecember 2014Pages 582-583 RelatedInformation