Melting Of Lithospheric Mantle Research Articles

Petrogenesis of Early Permian within-plate-type gabbros in the Western Qiangtang Terrane, Tibet: partial melting of lithospheric mantle metasomatized by subducted oceanic sediments on the northern margin of the Gondwana

ABSTRACT The extensively distributed Early Permian mafic rocks in the Qiangtang Terrane of the central Tibetan Plateau are the magmatic records of separation of this terrane from the Gondwana. Nevertheless, the origins and mantle source characteristics of these rocks continue to be subjects of debate. This study reports zircon U-Pb and Lu-Hf isotopic and whole-rock geochemical and Sr-Nd-Hf isotopic data on gabbros exposed in the Zougou Region, western Qiangtang Terrane. Our zircon U-Pb isotope age suggests that the Zougou gabbros (ZGs) were formed at ca. 290 Ma, representing newly discovered Early Permian mafic rocks within the Qiangtang Terrane. The ZGs display geochemical affinities with within-plate-basalts given that they are tholeiitic and have high Zr/Y and Ti/V ratios. Compared to previously examined Early Permian mafic rocks in the western Qiangtang Terrane, the ZGs are characterized by their distinct, nonradiogenic Nd (εNd(t) = -0.54 to −2.18) isotopic signatures, which cannot be attributed to crustal contamination or assimilation. This assertion is supported by their uniform whole-rock εNd(t), εHf(t), and zircon εHf(t) values, as well as by magma mixing modelling. In conjunction with regional geology, we propose that the ZGs were derived from an isotopically enriched lithospheric mantle metasomatized by previous subduction events. Furthermore, the positive decoupling of Hf-Nd isotopes (ΔεHf(t) = +2.21 to + 2.72), negative Nb-Ta anomalies, and variable Ba/Th ratios within the ZGs indicate that the metasomatic agents were fluids released from oceanic sediments. Our study provides insights into the compositions of the lithospheric mantle beneath the Qiangtang Terrane during the Permian, which is pivotal to discriminating the role of asthenospheric and lithospheric components in the formation of the contemporaneous mafic rocks in response to Gondwana break-up.

Late Triassic extension of thickened lithosphere of the East Kunlun orogenic Belt, northern Tibetan Plateau: Evidence from the geochemistry and geochronology of mafic magmatism

The East Kunlun Orogenic Belt (E-KOB) evolved into an extensional tectonic setting with plenty of mafic magmatism after the closure of the Paleo-Tethys Ocean. However, the deep tectonic system and geodynamic processes in this context still need further clarification. The detailed field geological, petrological, geochronological and geochemical works carried out on the Yeniugou gabbros in this study could provide key evidence for clarifying this issue. The gabbros are predominantly composed of clinopyroxene, orthopyroxene, plagioclase, olivine and ilmenite. Zircon U–Pb dating results suggest that their formation at ca. 209–207 Ma. Characterized by a relatively low SiO2 content and a moderate total alkaline content, these rocks are classified as alkalic to subalkaline series. High values of Mg# (42.2–59.4) and high concentrations of compatible elements (V, Cr, Co, Ni) suggest that their parent magma was generated through high partial melting of a lithospheric mantle source. The left-leaning rare earth element distribution patterns, combined with the characteristic spikes of Nb-Ta, indicate that they were originated from the lithospheric mantle metasomatized by subducting components. The positive zircon εHf(t) values (0.1–5.7), along with elevated Nb/La ratios (0.45–0.67), further confirm a small amount of asthenosphere mantle contribution. Elevated Zr/Y ratios, plus a slightly positive correlation between Alz and TiO2 in clinopyroxene, imply that they formed within an extensional setting, where the upwelling of the asthenospheric mantle provided heat for partial melting of the metasomatic lithospheric mantle. Combined with previous data, we suggest that E-KOB underwent delamination of thickened lithosphere in the late Triassic, following the closure of the Paleo-Tethys Ocean.

Geochronology and Geochemistry of Granodiorite Porphyry in the Baoshan Cu-Pb-Zn Deposit, South China: Insights into Petrogenesis and Metallogeny

The Baoshan Cu-Pb-Zn deposit is situated at the intersection of the Qin-Hang Cu polymetallic and Nanling W-Sn polymetallic metallogenic belts. The age, lithology, petrogenesis, and tectonic setting of granodiorite porphyry within the deposit remain subjects of debate. Additionally, there is a lack of comparative studies with the W-Sn-related granites in the region. This study conducted whole-rock major and trace element analysis, Sr-Nd isotope analysis, and zircon U-Pb dating on the Baoshan granodiorite porphyry. The zircon U-Pb age of the granodiorite porphyry is 162 ± 1 Ma. The whole-rock SiO2 and K2O contents range from 65.87 to 68.21 wt.% and 3.42 to 5.62 wt.%, respectively, indicating that the granodiorite porphyry belongs to high-potassium calc-alkaline I-type granite. The granodiorite porphyry is characterized by enrichment in LREE and depletion in HREE (LREE/HREE ratio = 6.2–21.2). The samples of granodiorite porphyry generally exhibit weak negative Eu anomalies or no Eu anomalies (δEu = 0.62–1.04, mean = 0.82). The (87Sr/86Sr)i and εNd(t) values are 0.707717–0.709506 and −7.54 to −4.87, respectively. The whole-rock geochemical composition and Sr-Nd isotopic values indicate that the magma originated from the partial melting of the Mesoproterozoic ancient crust and Neoproterozoic mafic juvenile lower crust, with the addition of high oxygen fugacity and water-rich lithospheric mantle melts. The source of the granodiorite porphyry in the Baoshan deposit is significantly different from the crust-derived metapelite source of the W-Sn-related granite in the area, indicating that different magma sources might be the main reason for the co-spatial and nearly contemporaneous development of Cu-Pb-Zn and W-Sn mineralization in the southern Hunan region.

Upper Triassic igneous rocks of the southern Kenai Peninsula, Alaska—prelude to Early Jurassic subduction along the Western Wrangellia composite terrane margin

New U–Pb zircon geochronology identifies a latest Triassic (ca 214–201 Ma) igneous suite of tuff, hypabyssal dikes, and a pluton on the southern Kenai Peninsula, Alaska. The igneous suite was emplaced within Upper Triassic sedimentary rocks along the southern margin of Western Wrangellia, the western-most fragment of the Wrangellia composite terrane. The igneous rocks range from mafic (50.6% SiO2) to felsic (78.3% SiO2), characteristically have less than 1.55% K2O, and generally have low trace element abundances. The tonalitic and trondhjemitic magmas were largely sourced in mafic-rich lower crust and incompletely assimilated quartz and other mineral xenocrysts are common. Fractionation involving plagioclase and amphibole is indicated for some magmas and composite intrusions and igneous xenoliths indicate magma mixing was possible. Paleozoic and Precambrian inherited zircons and initial 87Sr/86Sr (0.704103–0.705609) and 143Nd/144Nd (0.512396–0.512777) ratios indicate that the Western Wrangellia crustal sources are heterogeneous and contain sialic components. The latest Triassic magmatism reflects processes that preceded Early Jurassic subduction along the Wrangellia composite terrane and Pacific Ocean plate boundary. These processes involved heating and melting of mantle lithosphere and lower crust as mantle instabilities accompanied the breaking of the plate boundary linkages. The Late Triassic transition to subduction along the Wrangellia composite terrane margin coincided with the transition to subduction cessation in the Late Triassic arcs of the western Intermontane terranes of Canada. The shift to subduction along the outboard Wrangellia composite terrane margin marks the beginning of the Pacific Ocean–Cordillera plate interactions that came to dominate the tectonic evolution of the northern Cordillera from the Early Jurassic to today.

Delamination Magmatism in Eastern Anatolia: A Geochemical Perspective

AbstractThe Sr‐Nd‐Hf‐Pb isotope geochemistry of the Late Miocene Tunceli Volcanics suggests that they are the products of mixed asthenospheric and lithospheric mantle melts. The combined elemental and mineral chemistry data additionally indicate that a pyroxenite component of lithospheric origin is involved in their genesis. Calculations favor melting depths of ∼2 GPa for the Tunceli lavas, that is, deeper than the current lithosphere‐asthenosphere boundary beneath Eastern Anatolia. Geochemical data suggest that during regional Neo‐Tethyan subduction, dense (i.e., pyroxenite‐bearing) domains formed by progressive melt intrusion into the lower lithosphere resulted in gravitational instabilities. This unstable density configuration eventually led to the foundering of the eastern Anatolian lithosphere in the Late Miocene, resulting in progressive melting of fusible pyroxenite‐bearing domains at asthenospheric depths. We demonstrate that these pyroxenitic melts mixed with ambient asthenospheric melts and generated the Tunceli lavas.

Whole-Rock and Apatite Geochemistry of Late Triassic Plutonic Rocks in the Eastern Songpan-Ganzi Orogenic Belt: Petrogenesis and Implications for Tectonic Evolution

Abstract To constrain the late Triassic tectonic evolution of the Songpan-Ganzi orogenic belt, we present new whole-rock and in situ apatite geochemistry for plutonic rocks in its eastern margin. The Taiyanghe pluton can be classified into two rock types: dioritic and granitic rocks. The former exhibits low SiO2 and MgO contents but high Al2O3, Th, LREE contents, and Th/Yb and Th/Nb ratios, as well as low Ba/La and Ba/Th ratios and enriched Sr-Nd isotopic compositions, which, together with apatite geochemistry and Nd isotopes, indicate that they were derived from low degrees of partial melting of lithospheric mantle metasomatized by sediment-derived melts. The latter is characterized by high Sr and low Y and Yb, with elevated Sr/Y and (La/Yb)N ratios, implying an adakitic affinity. Notably, their similar Sr-Nd isotopic compositions indicate an origin from partial melts of a newly underplated lower crust. The Maoergai granitic rocks, characterized by high Sr and low Y and Yb contents with high Sr/Y and (La/Yb)N ratios, are indicative of adakitic rocks. In combination with the enriched whole-rock Sr-Nd isotopes and the apatite Nd isotopic data, we suggest that they were generated by the partial melting of the ancient thickened mafic lower crust. The Markam and Yanggonghai felsic granitoid rocks are peraluminous and similar to typical S-type granitoids, indicating an origin from remelting of the Triassic metasedimentary rocks. Based on the temporal-spatial relationship of the late Triassic plutonic rocks in the orogenic belt, we suggest that these rocks were formed in association with the roll-back and subsequent break-off of a subducted slab of the Paleo-Tethys Ocean. During the subduction, the formation of the Maoergai adakitic rocks was triggered by slab roll-back, whereas the magmatic “flare up” (ca. 216–200 Ma) was likely caused by slab break-off. This indicates that the final closure of the Paleo-Tethys Ocean happened in the end of the Triassic or Early Jurassic.

Neoproterozoic slab window in the western Yangtze Block, South China: Evidence from adakitic granodiorites, gabbro-diorites and high-K granites in the Panxi arc belt

Neoproterozoic igneous rocks are widespread along the margins of the Yangtze Block and record key information on the tectonic evolution of the South China Craton. In this paper, we present a comprehensive study of zircon U-Pb ages, whole-rock geochemistry and Sr-Nd-Hf isotopes on the Neoproterozoic granodiorites, gabbro-diorites, and high-K granites in the western Yangtze Block. The granodiorites, gabbro-diorites and high-K granites were dated at 848 ± 5.3 Ma, 824 ± 5.1 Ma and 819 ± 1.5 Ma, respectively. The granodiorites have high Sr (567 ∼ 607 ppm) contents and Sr/Y (84.4 ∼ 88.0) ratios and low alkalis (Na2O + K2O = 4.3 ∼ 4.9 wt%) and Y (6.6 ∼ 7.1 ppm) and Yb (0.7 ∼ 0.9 ppm) contents, similar to typical adakitic rocks. They show low MgO (0.9 ∼ 1.3 wt%), Cr (15.2 ∼ 26.7 ppm) and Ni (3.6 ∼ 4.4 ppm) contents and positive εNd(t) (+1.7 to + 4.2) and εHf(t) (+3.0 to + 8.2) values. The parental magmas for granodiorites were generated by partial melting of thickened juvenile mafic lower crust. The gabbro-diorites are characterized by the enrichment in LREEs, significantly negative Nb, Ta and Ti anomalies, and positive εNd(t) (+2.2 to + 4.2) and εHf(t) (+5.8 to + 10.4) values. They are inferred to be derived from partial melting of lithospheric mantle modified by subduction-related fluids. The high-K granites display high Zr + Nb + Ce + Y (208 ∼ 366 ppm) and alkali (Na2O + K2O = 7.6 ∼ 8.4 wt%) contents, high 10000*Ga/Al (2.31 ∼ 2.64) ratios and zircon saturation temperatures, similar to A-type granites. We suggest that these granites were formed by the partial melting of felsic crustal materials under low pressure and high temperature conditions. The association of granodiorites, gabbro-diorites and high-K granites indicates Neoproterozoic oceanic slab subduction in the western Yangtze Block. We suggest that a subducting oceanic slab window can account for Neoproterozoic magmatism in the western Yangtze Block.

Tithonian mafic intrusions in north-central Newfoundland: link to Atlantic rifting?

The small volume, Mesozoic alkali gabbro intrusions of the Budgell Harbour and Dildo Pond stocks and associated alkaline lamprophyre dykes in Notre Dame Bay in Newfoundland are an example of onshore magmatism that may be associated with North Atlantic Ocean opening. Chemical abrasion isotope dilution thermal ionization mass spectrometry U–Pb dating of zircon from Budgell Harbour Stock drill core samples yielded a weighted average 206Pb/238U age of 147.9 ± 0.5 Ma (95% confidence interval, mean square weighted deviation = 0.10). Five 40Ar/39Ar laser step-heating, single phlogopite grain analyses from the Budgell Harbour and Dildo Pond stocks, plus a lamprophyre dyke, yielded ages ranging from 146.3 ± 0.2 to 149.5 ± 0.5 Ma. The data demonstrate a ca. 148 Ma (Jurassic and Tithonian) alkaline magmatic event in Newfoundland, contemporaneous with rifting and offshore basin formation. These new age data and published determinations from magmatic rocks on conjugate margins and adjacent regions reveal long-lived episodic magmatism in the embryonic North Atlantic rift environment. We propose a new model whereby magmatism occurred in Notre Dame Bay at the convergence of older crustal-scale faults and localized Moho depth variations that may have triggered lithospheric mantle melting through isothermal, distal, and edge-driven upwelling related to regional extension.

Miocene Volcanism of the Baikal Rift Across the Boundary of the Siberian Craton: Evidence for Lithospheric Mantle Melting

Abstract Continental rifting is usually viewed in terms of two contrasting models of active and passive extension. The origin of the Baikal Rift, adjacent to the southern part of the Siberian Craton, has been described by both models in the past. It is expected that basaltic magmatism in an active model scenario should be primarily sourced from a mantle plume or plume-fed asthenosphere, whereas melting of the lithospheric mantle is expected to be a predominant source for magmatism in the passive model. In this paper, we focus on the Miocene volcanic rocks sampled along two 60-km-long profiles that cross the boundary between the Neoproterozoic Tuva-Mongolian massif and the Archean-Paleoproterozoic Siberian Craton. Most of the samples studied are trachybasalts. In terms of trace element concentrations normalised to primitive mantle, the lavas mimic oceanic island basalt-like patterns with troughs at Rb, Th–U, Pb, and Y, and peaks at Ba, Nb, Ta, K, and Sr. Moreover, similar trace element patterns to the studied samples are also observed for Miocene and Quaternary lavas located in the southwestern of the Baikal Rift, and adjacent regions of non-rifted Mongolia. According to the ratio of CaO to MgO, and TiO2/Al2O3 to SiO2, the compositions of the studied lavas coincide with experimental melts derived from mafic lithologies. Trace element data of samples suggest that garnet was a residual phase during partial melting. The Sr-Nd isotopic characteristics of the studied lavas are 87Sr/86Sr 0.70427–0.70469 and 143Nd/144Nd 0.51267–0.51284. They are identical to the coeval Miocene lavas of neighbouring volcanic fields, but they differ from the Quaternary lavas that extend to lower 87Sr/86Sr (0.7038–0.7044) with near identical 143Nd/144Nd. Isotopes of Hf for studied samples show values εHf = 6.0–7.7, except for the two samples taken within the boundary between two lithospheric blocks with εHf 4.6 and 4.8. The δ18O of olivine from lava samples is everywhere higher than that of the asthenospheric mantle and ranges from 5.5 to 6.4‰. Variations of δ18O versus Mg#, 87Sr/86Sr and εHf in the studied samples do not correlate, but do unequivocally rule out crustal assimilation. The isotopic variations are consistent with recycling of mafic crustal lithologies at mantle depths. Lavas from the Tuva-Mongolian massif and the Siberian Craton differ in lead isotopes by lower values of 206Pb/204Pb (< 17.785) and higher values of Δ8/4Pb (61–75) for on-cratonic samples and the reverse relationship for off-cratonic lava (> 17.785 and 55–61), respectively. The equation for Δ8/4Pb = [208Pb/204Pb-(1.209*(206Pb/204Pb) +15.627)] *100 is from Hart (Nature, 309, 753–757, 1984). The correlation of lead isotopes with the mafic recycled component, the sharp change of lead isotopic values at the cratonic boundary and decoupling of lead isotope ratios from other isotopic ratios lead us to suggest that the values of 206Pb/204Pb and Δ8/4Pb are associated with an ancient accessory mineral phase such as sulphide confined within the lithospheric mantle. The predominant role of the lithospheric sources in the formation of the Miocene volcanic rocks indicate that the volcanism of the Baikal Rift was caused by a passive tectonic process, rather than active rifting.

Insights into the petrogenetic evolution of the Khallari layered intrusion and coeval granites of the Paleoproterozoic Dongargarh Supergroup, Bastar Craton, India

Several layered igneous complexes around the globe host ultramafic-mafic lithologies at the base to more evolved lithologies at the roof sections. In this study, we report U-Pb zircon ages and geochemistry of Paleoproterozoic granites and Khallari layered intrusion from the Dongargarh Supergroup of Bastar craton, central India. The Khallari layered intrusion hosts pyroxenites at the base to more evolved lithologies including gabbro, layered gabbro and anorthositic gabbros towards the roof section of the magma chamber. The estimated weighted mean U-Pb zircon ages of granites (2443 ± 13 Ma) and layered intrusion (2494 ± 19 Ma and 2469.2 ± 5.2 Ma) are in conjunction with the major Siderian crust building peak identified at the craton. The granitic plutons of the Dongargarh Supergroup are chemically similar to post-collisional/anorogenic granitic rocks, in which the rapakivi granites exhibit a fractional crystallization relation with the Khallari layered intrusion. The Dongargarh granites and enclaves were derived by a combination of fractional crystallization and mixing of partial melts from the pre-existing crust of the Bastar craton. Petrogenetic modeling indicates Khallari layered intrusion is formed by the fractional crystallization of lithospheric mantle melt followed by crystal accumulation. The parental melt also experienced localized crustal contamination (up to 10%) during its evolution. The layered intrusion and the granites formed in a post-collisional rift setting where magmatism postdates the proposed subduction and collisional orogenesis at 2.5 Ga involves cratonic domains of Eastern and Western Bastar cratons.

The Formation of the Jiaodong Gold Province

AbstractGold deposits in Jiaodong, termed Jiaodong‐type, are tectonically located in the southeastern margin of the North China Craton. Their major features are reviewed in this paper to highlight the differences between Jiaodong deposits and other genetic types of gold deposits. The mineralization was synchronized with asthenosphere upwelling indicated by syn‐ore OIB‐like mafic dike and large‐scale crustal thinning suggested by decrease of Sr/Y from pre‐ore to syn‐ore granites. Asthenosphere upwelling induced by the roll‐back of Paleo‐Pacific Plate drove partial melting of lithospheric mantle and devolatilization, which induced the release of the ore‐forming fluids. In concomitant with magmatic records, mineralization migrated from the western Jiaobei terrane (133–127 Ma) to the eastern Sulu orogenic belt (114–108 Ma), corresponding to the eastward roll‐back of Paleo‐Pacific Plate. Gold mineralization in Jiaodong formed in the transitions of ductile to brittle deformation, rapid to slow crustal uplift, and regional compression to extension. In the regional‐scale, the gold deposits in the Jiaobei terrane are mostly situated at intersections between NE‐trending faults and EW‐trending basement faults, and gold orebodies dominantly controlled by the lithologic contacts between Precambrian metamorphic rocks and Mesozoic granites. The mineralization was dominated by the disseminated‐veinlet ores related to quartz–sericite alteration in strong cataclasite‐breccia zone, with subsidiary thick quartz‐sulfide veins developed in secondary fault zones. The ore‐forming fluids belong to a H2O–CO2–NaCl±CH4system and show minor variations in salinity among different types of ore. Structure‐fluid feedback involving fluid‐rock reaction and hydrofracturing triggered the fluid phase separation and resultant gold deposition. The Jiaodong gold deposits are distinct from orogenic and intrusion‐related gold deposits in terms of tectonic setting, origin of ore‐forming fluids, and mechanism of gold deposition.

Petrogenesis and tectonic implications of the Late Triassic intrusions in the North China Craton: Case study on the Huata complex in the western Yanshan

This paper presents geochemical and age data for Late Triassic lamprophyre, syenite, and granite in the Huata area of the western Yanshan belt of the North China Craton, to provide constraints on the origin and tectonic settings of these Late Triassic igneous rocks. The zircons from the Huata lamprophyres and syenites yielded a mean U Pb age of 203 and 206 Ma, respectively. The lamprophyres are enriched in incompatible elements, with (La/Yb) N = 30.57–33.89, (Gd/Yb) N = 3.54–3.64, and Sr-Nd-Hf isotopic signatures ( 87 Sr/ 86 Sr (initial) = 0.7053–0.7061, εNd(t) = −11.11 to −10.50, εHf(t) = −9.33 to −7.70), consistent with them originating from the low-degree melting of previously metasomatized lithospheric mantle in the garnet-stable area. The syenites display similar incompatible elements to the lamprophyres, but have relatively low (La/Yb) N = 14.26–17.23 and (Gd/Yb) N = 1.81–2.15 ratios. Their Sr-Nd-Hf isotopic compositions ( 87 Sr/ 86 Sr (initial) = 0.7045–0.7050, εNd(t) = −12.10 to −11.35 and εHf(t) = −8.64 to −6.81) were also similar to the lamprophyres, and they are considered to have been generated from the low-degree melting of lithospheric mantle in the garnet-spinel transition zone. The granites have major and trace element patterns and Sr Nd isotopes quite different from the syenites, but are similar to the crust-derived felsic rocks, being enriched in large ion lithosphere elements and depleted in high field strength elements. They are enriched in Nd isotope (εNd(t) = −16.63 to −15.18), and are inferred to have been generated by lower crust anataxis. The presence of igneous rocks in the Huata district indicates that the northern margin of the NCC had already entered a non-orogenic regime by the late Late-Triassic. • Lamprophyres and syenites derive from a metasomatized mantle. • Granites originate from the modified lower continental crust. • The tectonic regime transformed from post-collisional to intraplate at 206 Ma.

Late Jurassic syn-rift deposition in the Flemish Pass basin, offshore Newfoundland: Evidence for Tithonian magmatism and Appalachian-Variscan sediment sources from quantitative mineral and detrital zircon U–Pb-Hf isotope studies of Mizzen discovery strata

Quantitative mineral and detrital zircon U–Pb-Hf isotope studies of syn-rift sandstone units in the Mizzen F-09 delineation well, northern Flemish Pass basin, were conducted to test competing models for Grand Banks paleogeography and Late Jurassic development of the Newfoundland-Iberia magma-poor rift system. Bodhrán formation (informal nomenclature) strata yield ca. 145–155 Ma detrital zircon grain populations that indicate a late Tithonian (146 ± 1 Ma) maximum depositional age for syn-rift fluvial to tide-modulated fluvial strata in Mizzen F-09 and evidence for Grand Banks rift magmatism to have occurred throughout the Late Jurassic. Late Tithonian tectonic subsidence and magmatism in the northern Flemish Pass basin region were coincident with the onset of necking processes and extreme crustal thinning within the Newfoundland-Iberia rift system. The chondritic to superchondritic Hf isotope compositions of Late Jurassic detrital zircon grains indicate repeated partial melting of lithospheric mantle during rift development, perhaps along master detachment faults or transfer zone systems. Bodhrán formation strata have chemically unstable minerals (plagioclase, potassium feldspar, garnet, muscovite, rutile, staurolite) and late Paleozoic to Paleoarchean detrital zircon age populations that together show provenance from Appalachian-Variscan basement and cover assemblages. A positive correlation between the abundance of metamorphic minerals and unique-aged, mid-Permian (ca. 271–280 Ma) detrital zircon grains from post-Variscan igneous rocks indicate Iberian provenance contributions to Bodhrán formation strata. The new results from Mizzen F-09 are consistent with models for WNW-directed fluvial discharge into the northern Flemish Pass basin and sediment derivation from upper Paleozoic foreland basin or cover assemblages located west of Variscan front, some which may have been stripped off Beothuk Knoll, Flemish Cap, or adjacent highlands.

Two-stage Cu[sbnd]Pb[sbnd]Zn mineralization of the Baoshan deposit in southern Hunan, South China: Constraints from zircon and pyrite geochronology and geochemistry

The Baoshan CuPbZn deposit is one of the representative polymetallic deposits in the middle of the Nanling Range, the western part of the Qin–Hang ore belt. In order to better understand the magmatic activity (granodiorite porphyry and porphyritic granodiorite) and mineralization in the Baoshan deposit, in situ UPb and LuHf isotope studies of zircons and trace element compositions of two generations of pyrite (ore stage: Py I and post-ore stage: Py II) have been carried out. This constrains the geochronology, magma source, fluid composition, and the origin of the ore-forming materials. The zircon UPb dating results from two types of intrusions show two geochronological populations: (i) ~180 Ma for the Cu (PbZn) mineralization that is related to the porphyritic granodiorite, and (ii) ~160 Ma for the CuPbZn mineralization which is associated with the granodiorite porphyry. The similar REE patterns, Hf/U, Nb/Ta, and Y/Ho ratios along with Hf isotopic characteristics of both granite types indicate that these rocks were sourced from the partial melting of lithospheric mantle and lower crust. Zircons from the granodiorite porphyry have higher Nb, Ta, Lu, and Hf contents, but lower Ti contents and Th/U ratios than those from the porphyritic granodiorite, suggesting that the magma-forming granodiorite porphyry had lower temperature, higher oxygen fugacity, and probably experienced strong crystal fractionation. Py I and Py II are associated with the porphyritic granodiorite and are related to the mineralization that occurred at ~180 Ma. The composition of pyrite in the two stages indicates the contribution of granite and limestone to mineralization. The higher contents of metals (Cu, Pb, Zn, Bi, Ag, except Co and Ni) in Py I than in Py II indicate the cooling and mixing process of ore-forming fluid with meteoric water. The geochemical characteristics of the pyrite generations and UPb dating of zircons suggest that the small-scale mineralization occurred at ~180 Ma under a relatively high-temperature and lower oxidized magmatic environment, whereas the major metallogenic event occurred at ~160 Ma under a low-temperature, medium oxidized, and strongly fractionated magmatic environment. This study reveals that the multi-stage magmatic and mineralization processes mainly occurred during the Early to Late Jurassic in South China.

Crust–mantle interaction recorded by Early Cretaceous volcanic rocks within the southern margin of the North China Craton

This study presents new geochronological and geochemical data for Early Cretaceous volcanic rocks in the southern margin of the North China Craton (NCC), to discuss the crust–mantle interaction. The studied rocks include pyroxene andesites from Daying Formation, hornblende andesites and andesites from Jiudian Formation, and rhyolites from a hitherto unnamed Formation. These rocks formed in Early Cretaceous (138–120 Ma), with enrichment in light rare earth elements (REE), depletion in heavy REE and arc-like trace elements characteristics. Pyroxene andesites show low SiO2 contents and enriched Sr–Nd–Pb–Hf isotopic compositions, with orthopyroxene phenocryst and Paleoproterozoic (2320–1829 Ma) inherited zircons, suggesting that they originated from lithospheric mantle after metasomatism with NCC lower crustal materials. Hornblende andesites have low SiO2 contents and high Mg# (Mg# = 100 Mg/(Mg + Fe2+)) values, indicating a lithospheric-mantle origin. Considering the distinct whole-rock Sr isotopic compositions we divide them into two groups. Among them, the low (87Sr/86Sr)i andesites possess amount inherited Neoarchean to Neoproterozoic (2548–845 Ma) zircons, indicating the origin of lithospheric mantle with addition of Yangtze Craton (YC) and NCC materials. In comparison, the high (87Sr/86Sr)i andesites, with abundant Neoarchean–Paleozoic inherited zircons (3499–261 Ma), are formed by partial melting of lithospheric mantle with incorporation of NCC supracrustal rocks and YC materials. Rhyolites have extremely high SiO2 (77.63–82.52 wt.%) and low total Fe2O3, Cr, Ni contents and Mg# values, combined with ancient inherited zircon ages (2316 and 2251 Ma), suggesting an origin of NCC lower continental crust. Considering the presence of resorption texture of quartz phenocryst, we propose a petrogenetic model of ‘crystal mushes’ for rhyolites prior to their eruption. These constraints record the intense crust–mantle interaction in the southern margin of the NCC. Given the regional data and spatial distribution of Early Cretaceous rocks within NCC, we believe that the formation of these rocks is related to the contemporaneous far-field effect of the Paleo-Pacific Plate.

Partial Melting of Lithospheric Mantle and Formation of the Early Cretaceous Alkaline Rocks in the Guandimiao REE Deposit, Luxi Terrane, Eastern China

The Luxi Terrane (eastern China) exposes widespread Early Cretaceous alkaline rocks, whereas their petrogenesis remains controversial, including fractional crystallization, partial melting and crustal contamination regime. Here, we present petrology, geochemistry, sphene U-Pb geochronology and trace element data from the syenogranite, quartz syenite and quartz monzonite of the Guandimiao alkaline complex rocks to investigate their petrogenesis. Geochemical data suggest that these alkaline rocks show alkalic and peralkaline characters, and high Ga/Al ratios, SiO2, light rare-earth element (LREE), Zr and Nb, and low MgO, CaO, Eu contents, corresponding to A-type granites. Sphene trace elements in syenogranite and quartz monzonite show obvious fractionation between LREE and heavy rare-earth element (HREE) and high Th/U ratios, indicating a magmatic origin. They yield U-Pb lower intercept ages of 128 ± 2.3 Ma and 127 ± 1.3 Ma, representing the crystallization ages of these alkaline rocks. The negative correlations between CaO, Fe2O3 (Total), MgO, P2O5, TiO2, MnO and the pronounced depletion in Nb, Ta and Ti suggest that the alkaline rocks were formed by fractional crystallization. Additionally, the positive correlation between La/Hf and La, Th and Th/V, Ce/Yb and K2O, and Tb/Yb and Yb suggest that the alkaline melts are generated by partial melting. Such high Rb/Nb, (Th/Nb)N and Nb/Th ratios indicate crustal contamination during the magma emplacement. We, therefore, propose the magma source of the alkaline rocks in the Guandimiao complex originated by partial melting of lithospheric mantle, which experienced fractional crystallization and crustal contamination processes during its emplacement. Such complex alkaline rocks were probably formed in an extensional back-arc setting induced by the retreat of the subducting Izanagi plate.

Petrogenesis of the quartz diorite from the Lietinggang-Leqingla Pb-Zn-Fe-Cu-(Mo) deposit in southern Tibet: Implications for the genesis of a skarn-type polymetallic deposit in the Tibetan-Himalayan collisional orogen

The Lietinggang-Leqingla deposit is a representative skarn-type polymetallic deposit in the eastern of the central Lhasa subterrane. It comprises Pb-Zn and Fe-Cu-(Mo) mineralization that are part of the same metallogenic system. Garnet-skarn hosting Fe-Cu-(Mo) mineralization distributed in the contact zone between the Jubuzhari complex intrusions and carbonate strata of the Mengla Formation. The Pb-Zn mineralization is hosted in distal garnet-pyroxene and pyroxene-actinolite skarns, which formed in the strata of Mengla Formation. Here, we investigate quartz diorites (61.06 ± 0.93 Ma) that are related to Fe-Cu mineralization in the northern part of the mining area. The quartz diorites are characterized by low SiO2 (61.57–65.88 wt%), low K2O (2.53–3.07 wt%), and high total alkali (Na2O + K2O) contents (5.69–6.35 wt%). They are enriched in large-ion lithophile elements and light rare earth elements, but depleted in high field strength elements and heavy rare earth elements. The quartz diorites yield variably low (La/Yb)N ratios (4.29–7.07, the average value is 6.36) with moderately negative Eu anomalies (Eu/Eu* = 0.49–0.72). Furthermore, they exhibit a narrow range in (87Sr/86Sr)i ratios (0.706355–0.706807) and weakly negative εNd (t) (−2.08 to −1.57), and positive εHf (t) (+0.14 to +3.46) values. Based on the geochemical characteristics presented in this study and previously published data, we propose that the ore-forming rocks related to Fe-Cu and Pb-Zn mineralization were formed at the same time. The intermediate intrusions associated with Fe-Cu mineralization were derived from partial melting of lithospheric mantle mixed with the rejuvenated lower crustal melts, after which the mixed magma underwent minor fractional crystallization during upwelling. The felsic intrusions associated with Pb-Zn mineralization were formed by melting of mantle-derived basaltic magmas with old lower crust component contributions and which underwent extensive fractional crystallization.

Origin and Age of Magmatism in the Northern Philippine Sea Basins

AbstractA Robust tectonic reconstruction of the Philippine Sea Plate around ∼52 Ma is a prerequisite in understanding the process of subduction initiation and establishment of the Izu‐Bonin‐Mariana arc. This study investigates origins and timing of basin formation in the still poorly understood oldest part of the northern Philippine Sea plate. We have established that andesitic magmatism in the form of the Northern Philippine Sea volcanics is widely distributed across this area. It is founded on both a Mesozoic arc terrane (Daito Ridge Group) and an intervening basin (Kita‐Daito Basin). Their narrow Eocene age range (45‐41 Ma) and lack of systematic spatial variation in geochemistry implies that this magmatism was not associated with on‐going subduction, but related to the rifting/spreading event forming the Kita‐Daito Basin. The arc‐like geochemistry of the volcanics seems to indicate melting of lithospheric mantle which had been previously metasomatized by Mesozoic subduction of a plate with Pacific‐MORB isotopic characteristics. Late Eocene basaltic magmatism also found in the Kita‐Daito Basin does not have arc‐like characteristics, and could have formed from low‐degree melts of asthenospheric mantle associated with the final stage of Kita‐Daito Basin spreading. As onset of activity of the Northern Philippine Sea volcanics is essentially synchronous with the magmatism associated with the Oki‐Daito mantle plume, it is possible that both magmatism and rifting of the Kita‐Daito Basin were triggered by the arrival of the Oki‐Daito mantle plume in this region. These results demonstrate that the Kita‐Daito Basin postdates subduction initiation of the Pacific Plate along the Izu‐Bonin‐Mariana arc.

Whole-Rock Geochemistry, Zircon U-Pb geochronology and Lu-Hf isotopic constraints on metasedimentary rocks (Paragneisses) in Stornes Peninsula, Larsemann Hills，East Antarctica

ABSTRACT Understanding the geological history of the Larsemann Hills and other exposures along the southeastern coast of Prydz Bay is essential for reconstructing the formation and evolution of the East Gondwana continent. This research involves analyses of the major elements, trace elements, REE, U-Pb and Lu-Hf isotopes of zircons from the metasedimentary rocks found in the Larsemann Hills. The results suggest that the provenance of the metasedimentary rocks within the Larsemann Hills is mainly Mesoproterozoic to early Neoproterozoic magmatic rocks. The age of the protolith of the metasedimentary rocks is between ~1019 and ~970 Ma. Our data show that at least two tectono-metamorphic events at ~913 Ma and ~552–555 Ma affected the metasedimentary rocks. Furthermore, Prydz Bay has been an integral whole since before the Palaeozoic era and was subsequently reactivated by Pan-African tectonic events. The thickened crust stretched and thinned, accompanied by partial melting of lithospheric mantle into the lower crust. The real Prydz Bay Pan-African collision orogenic belt should be located under the ice sheet east of the Grove Mountains and strikes close to north-northeast.

Petrogenesis of the Early Silurian Renda appinite suite in the southeastern Qilian Orogen, NW China: Implications for the evolution of a Proto-Tethys magmatic arc

ABSTRACT Early Paleozoic subduction beneath peri-Gondwana microcontinents formed a major Proto-Tethys magmatic arc system. Appinite suite rocks constitute important components within that magmatic arc. Herein, we report hornblende 40Ar/39Ar and zircon U–Pb geochronology data, zircon Hf isotope, mineral chemistry, whole-rock geochemistry, and Sr–Nd–Pb isotope data for the rocks of hornblende gabbro-diorite-quartz diorite-quartz monzodiorite from the Renda appinite suite and adjacent granite porphyry in the southeastern Qilian Orogen. Hornblende 40Ar/39Ar and zircon U–Pb isotopic data constrain ages of the intrusions of the Renda appinite suite to 439–435 Ma. Rocks in this suite represent the calc-alkalic to alkali-calcic series, and they are enriched in large-ion lithophile elements and depleted in high-field-strength elements. The hornblende gabbros exhibit moderate initial 87Sr/86Sr ratios (0.7046–0.7055) and higher whole-rock εNd(t) (–1.3 to +1.7) and zircon εHf(t) (+7.2 to +11.2) values relative to the other rocks of the suite (0.7047–0.7064, – 7.7 to – 1.1, and – 6.6 to +6.8, respectively) as well as Pb isotopic features similar to EM2 lithospheric mantle. These geochemical characteristics suggest that the Renda appinite suite originates from partial melting of an enriched lithospheric mantle, with subsequent fractional crystallization and hybridization with crustal components. The granite porphyry formed by partial melting of the crust coeval with the emplacement of juvenile magma. This study suggests emplacement occurred during a short-lived collision with slab failure (breakoff) after latest stage (cessation) of Proto-Tethys oceanic subduction along the northern side of the southeastern Qilian Orogen. The heat supplied by the asthenospheric upwelling through a gap in the subducted slab induced melting in lithospheric mantle and deep crust producing Renda appinite suite rocks and granite porphyry.