Negative Zircon eHf Research Articles

Early Cretaceous granitoids and gabbro in the Liaodong Peninsula: implications for delamination of the North China Craton and Paleo-Pacific Plate subduction

New petrological, whole-rock geochemical, zircon U–Pb geochronological, and zircon Lu–Hf isotopic data have been reported for Early Cretaceous intrusive rocks in the Wulong region of the Liaodong Peninsula on the North China Craton. The zircon U-Pb chronology shows that the crystallization age of six groups of intrusive rocks from this region is 129–123 Myr ago. These intrusive rocks can be categorized into A-type granite (granodiorite), K-rich adakite (porphyritic-like monzogranite), highly fractionated I-type granites (porphyritic-like biotite monzogranite, porphyritic-like syenogranite, and syenogranite), and gabbro. These granitoids are shown to have negative zircon eHf(t) values(-21.0 to -11.1) with old two-stage Hf model ages (TDM2(Hf)) (1.88–2.50 Ga), while gabbro has higher zircon eHf(t) values(-14.3 to -9.4) with younger TDM2(Hf) (1.77–2.08 Ga) model ages. According to our results, we believe that the porphyritic-like monzogranite was produced through partial melting of the thickened eclogitic lower crust, the gabbro was generated by partial melting of a source formed by the mixing of enriched lithospheric mantle and delaminated eclogitic lower crust, the granodiorite was formed by mixing crust materials and mafic melts, the porphyritic-like biotite monzogranite, porphyritic-like syenogranite, and syenogranite originated from the medium- to high-K basaltic lower crust. The bimodal intrusive rocks (gabbro, porphyritic-like monzogranite, and porphyritic-like biotite monzogranite) and A-type granites (granodiorite) were emplaced in an extensional setting associated with Paleo-Pacific Plate subduction. We also determined that the tectonic setting changed from extension to transpression during 125–120 Myr ago (porphyritic-like syenogranite and syenogranite). Moreover, we confirmed the hypothesis that the Early Cretaceous delamination is the result of Paleo-Pacific Plate subduction.

Petrogenesis of Jurassic Granitoids on Liaodong Peninsula, Northeast China: Constraints on the Evolution of the Mongol-Okhotsk and Pacific Tectonic Regimes

The tectonic setting of Jurassic magmatism in the Northeast China (NE China) is unclear. Here, we present new petrological, whole-rock geochemical, zircon U-Pb geochronological, and zircon Lu-Hf isotope data for Jurassic granitoids of the Wulong region, Liaodong Peninsula, NE China. Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) zircon U-Pb data indicate that these granitoids were emplaced at 165–156 Ma. The biotite monzogranite, two-mica monzogranite, monzogranite, granodiorite, biotite granodiorite, and syenogranite are strongly peraluminous (A/CNK=1.09–1.29), contain peraluminous minerals such as muscovite, have high normative corundum abundances (1.26 wt.%–3.28 wt.%), and have high K2O/Na2O ratios (0.76–1.48), all of which indicate an S-type granite affinity. However, the biotite granodiorite and syenogranite have high Sr (391 ppm–570 ppm) and low Y (3.06 ppm–5.94 ppm) contents, with high Sr/Y (65.8–185.9) ratios, and the two-mica monzogranite, monzogranite, and granodiorite have relatively high Sr (138 ppm–379 ppm) and low Y (3.38 ppm–8.71 ppm) contents, with high Sr/Y ratios (19.1–77.9). All of the analyzed samples have negative zircon eHf(t) values (−41.4 to −20.6) with old two-stage Hf model ages (TDM2(Hf)=2.50–3.76 Ga). Therefore, we infer that the biotite monzogranite is the typical feature of S-type granite that was derived by partial melting of metagraywacke. The monzogranite, two-mica monzogranite, granodiorite, biotite granodiorite, and syenogranite exhibit geochemical characteristics of S-type granite with K-rich adakitic features, and were possibly derived by mixing of melts from clastic crustal materials and adakitic magmas. There are voluminous Jurassic igneous rocks in the NE China. By combining our study with the previous researches, this paper infers that the Jurassic magmatism within the Erguna-Xing’an Massif was related to the southward subduction and closure of the Mongol-Okhotsk Ocean; the Early Jurassic magmatism to the east of the Songliao Basin and in the northern North China Craton (NCC) was related to the subduction of the Pacific Plate; however, the Middle-Late Jurassic igneous rocks to the west of the Songliao Basin were related to the closure of the Mongol-Okhotsk Ocean and, in the northern NCC, were related to closure of the Mongol-Okhotsk Ocean with an influence from flat-slab subduction of the Pacific Plate.

Post-collisional ca. 800 Ma A-type felsic volcanic rocks in the eastern Jiangnan orogen, South China

Abstract Neoproterozoic igneous rocks in the Jiangnan orogen can provide important information to unravel the tectonic evolution of the South China Block and are thus important for the reconstruction of Rodinia. Dacites and rhyolites in the Shangshu region, the eastern Jiangnan orogen, contain zircon grains with U-Pb ages of ca. 800 Ma. These felsic rocks have high Ga/Al ratios (2.3–3.7) and HFSE and HREE contents relative to the primitive mantle, thus resembling A-type granitoids. Dacites have negative zircon eHf(t) values (–2.8 to –18.7), indicative of derivation from primary magmas generated by partial melting of ancient continental crust. In contrast, rhyolites show positive eHf(t) values (+1.9 to +8.8) and are explained as derived from partial melting of juvenile lower mafic crust. Felsic volcanic rocks in Shangshu were formed in a post-orogenic extension setting shortly after the final amalgamation of the Yangtze and Cathaysia blocks at around 830 Ma. Combining our results with the previously published ones, we demonstrate that the 800 Ma extension-related magmatic activity was likely the earliest phase of the Neoproterozoic rifting in the South China Block. The tectonic transition from continental collision to a post-orogenic setting should have occurred after ca. 800 Ma.

Origin of Early Creceouscalc-alkaline granite, Taxkorgan: Implications for evolution of Tethys evolution in central Pamir

The Pamir plateau may have been a westward continuation of Tibet plateau. Meanwhile, the Rushan-Pshart suture is correlative to the Bangong-Nujiang suture of Tibet, and the Central Pamir is the lateral equivalent of the Qiangtang Block. We present the first detailed LA-ICPMS zircon U-Pb chronology, major and trace element, and Lu-Hf isotope geochemistry of Taxkorgan two-mica monzogranite to illuminate the Tethys evolution in central Pamir. LA-ICPMS zircon U-Pb dating shows that two-mica monzogranite is emplaced in the Cretaceous (118 Ma). Its geochemical features are similar to S-type granite, with enrichment in LREEs and negative Ba, Sr, Zr and Ti anomalies. All the samples show negative zircon eHf(t) values ranging from −17.0 to −12.5 (mean −14.5), corresponding to crustal Hf model (TDM2) ages of 1906 to 2169 Ma. It is inferred that these granitoids are derived from partial melting of peliticmetasedimentary rocks analogous to the Paleoproterozoic Bulunkuole Group, predominantly with muscovite schists component. Based on the petrological and geochemical data presented above, together with the regional geology, this work provides new insights that Bangong-Nujiang Ocean closed in Early Cretaceous(120–114 Ma).

The Middle–Late Silurian granitoids in the Eastern Kunlun Orogenic Belt, NW China: petrogenesis and implications for tectonic evolution

The Eastern Kunlun Orogenic Belt lay on a significant tectonic boundary between Gondwana and Eurasia, produced widespread granitoids, and recorded at least two orogenic episodes since the Phanerozoic eon. In this paper, we provided new petrography, geochemistry, zircon U–Pb dating, and Lu–Hf isotopic research on the Middle–Late Silurian granitoids from the eastern segment of The Eastern Kunlun Orogenic Belt. These granitoids comprised of Zhongzhigou granodiorites and Xintuo alkali-feldspar granites, formed in the Middle–Late Silurian (420–425 Ma). Geochemically, the granodiorites exhibit high Sr/Y (31.2–35.2) as adakitic affinities, and alkali-feldspar granites belong to highly fractionated I-type granites. Additionally, granodiorites have zircon eHf(t) values show limited positive variations from − 0.5 to + 3.2, with two-stage Hf model ages (TDM2) of 1105–1306 Ma, while alkali-feldspar granites show negative zircon eHf(t) values ranged from − 4.6 to − 0.1 with two-stage Hf model ages (TDM2) of 1289–1541 Ma, implying that their primary magma originated from different sources. Taken together, we conclude that granodiorites had been derived from partial melting of the juvenile newly underplated mafic lower crust, while alkali-feldspar granites were derived from partial melting of the shallower ancient crustal source. Combined with temporal and spatial distribution of magmatic activities, sedimentation, and metamorphism, it can be concluded that the whole EKOB underwent a transition from syn-collision compression to post-collision extension and extensive crustal reworking occurred during the Middle–Late Silurian.

Early-Middle Triassic Intrusions in Western Inner Mongolia, China: Implications for the Final Orogenic Evolution in Southwestern Xing-Meng Orogenic Belt

The end-Permian to Early-Middle Triassic magmatic rocks in Inner Mongolia can provide valuable insights into the relationships between the collisional processes and the magmatic responses during the final orogenic evolution of Xing-Meng orogenic belt (XMOB). This paper presents zircon U-Pb ages and Hf isotopes, whole rock geochemical and Sr-Nd-Pb isotopic data for the Early-Middle Triassic diabases and monzogranites from the Langshan area, southwestern XMOB. Our results suggest that the studied diabases and monzogranites were respectively formed during Early Triassic and Middle Triassic. The Early Triassic diabases are characterized by “arc-like” geochemical signatures, including enrichment in Rb, U and K, and depletion in Nb, Ta, P and Ti. They have negative to weak positive eNd (t) values (−3.1 to +1.5) and relatively high initial ratios of 208Pb/204Pb (35.968–37.346), 207Pb/204Pb (15.448–15.508) and 206Pb/204Pb (16.280–17.492), indicating a subduction-metasomatized enriched lithospheric mantle source. Their low Ba/Rb (2.72–6.56), Ce/Y (0.97–1.39) and (Tb/Yb)N ratios (1.31–1.45) suggest that the parental magma was likely originated from low degree partial melting of the phlogopite-bearing lherzolite in a spinel-stability field. The Middle Triassic monzogranites show high Sr/Y ratios, low MgO, Cr and Ni contents, high Zr/Sm ratios (40–64), negative zircon eHf(t) values (−25.8 to −8.8), as well as relatively flat heavy rare earth element patterns. They were likely derived from low degree partial melting of a moderately thickened ancient lower crust. The diabases and the slightly postdated high Sr/Y granites in this study represent the magmatic responses to the final orogenic evolution in the southwestern XMOB. Together with regional works, we propose that the slab break-off of the Paleo-Asian oceanic lithosphere following the terminal collision between the North China Craton and the South Mongolia terranes triggered asthenospheric upwelling, and the ongoing convergence further initiated moderately crustal thickening and uplift in the XMOB.

Geochemistry, Zircon U-Pb Age and Hf Isotope of the Huilanshan Granitoids in the North Dabie Terrane: Implications for Syn-Collapse Magmatism of Orogen

Syn-collapse magmatism is a critical issue for evolution of the continental orogen. The Dabie Orogen is a typical orogen which was suffered from a complete collapse. Two kinds of granitoids, namely, the coarse-grained diorite and the fine-grained granite, are recognized at the center of the Luotian extensional dome, providing an opportunity to decipher the syn-collapse magmatism in the Dabie Orogen. The diorites (125±3 Ma) are high K calc-alkaline rocks, with low SiO2 (51.9 wt.%–56.6 wt.%) and high MgO (3.5 wt.%–4.0 wt.%) contents. They are enriched in LREE and LILEs (e.g., Ba, K, Rb) and depleted in HFSEs (e.g., Ta, Nb, and Hf) with low ratio of Sr/Y (30.82–46.89). The granites (118±2 Ma) are shoshonite series rocks, with relatively high SiO2 (68.9 wt.%–72.6 wt.%) and low MgO (0.32 wt.%–0.66 wt.%) contents. They are also enriched in LREE and LILEs with weakly negative Eu anomalies (δEu=0.81–0.85), and are depleted in HFSEs with low Sr contents (338 ppm–477 ppm) and Sr/Y ratios (23.80–33.13). Therefore, the two kinds of granitoids have no geochemical characteristics of adakitic rocks, suggesting that they were generated from a normal or thinned crust level. The diorites have quite negative zircon eHf(t) values (-18.4 to -21.1), suggesting they were from partial melting of the mafic lower continental crust. The granites have relatively higher zircon eHf(t) values (-14.4 to -18.1). The granites also contains a series of old inherited zircon cores, such as two upper intercept ages of 2 628±41 and 1 840±37 Ma, and a concordant age of 807±9 Ma. All these features suggest that the granites were generated from partial melting of the felsic middle-lower continental crust. Thus, the Huilanshan Early Cretaceous granitoids coupled with the Luotian extensional dome revealed the collapsed process of the Dabie Orogen.

Early Mesozoic magmatism and tectonic evolution of east-central Tibet

The Early Mesozoic granitoids in the east-central Tibet are the key to understand the tectonic evolution of the Tibetan Plateau. In this study, three stages of Early Mesozoic granitic magmatism were indicated by LA-ICP-MS zircon U–Pb dating on 14 samples. The Early Triassic (248–243 Ma) and the Late Triassic (213–208 Ma) were distributed in the North Qiangtang terrane, and the Early Jurassic (ca. 187 Ma) occurred in the Tongka and Jiayuqiao blocks. The Late Triassic and Early Jurassic granitoids show similar negative zircon eHf(t) values (− 5.5 to − 16.6) with TDM2 model ages of 1.60–2.28 Ga, suggesting a Paleoproterozoic crustal source, whereas the Early Triassic granitoids have zircon eHf(t) values from − 3.4 to + 5.3 with TDM2 model ages of 0.94–1.50 Ga, indicating a Mesoproterozoic crustal source. Based on the whole-rock geochemical data, we suggest that the Early Triassic rocks from the North Qiangtang terrane include I- and S-type granites and the Late Triassic rocks are S-type granites, which were related to the northward subduction of the Longmu Tso–Shuanghu–Dingqing Paleo-Tethys Ocean and subsequent collision between the North Qiangtang terrane and Tongka block, respectively. The Early Jurassic granitoids from the Tongka and Jiayuqiao blocks also included both I- and S-type granites and were probably generated in an arc-related setting during the northward subduction of the Bangong–Nujiang Tethys Ocean. Therefore, we suggest a collision–accretion model that attributes the Early Mesozoic tectonic-magmatic event to the sequential multistage subduction and collision in the east of central Tibet.

Petrogenesis and Geotectonic Significance of Early-Neoproterzoic Olivine-Gabbro within the Yangtze Craton: Constrains from the Mineral Composition, U-Pb Age and Hf Isotopes of Zircons

The olivine-gabbroic rocks located at the Huangling anticline within the Yangtze Craton are dated at circa 857–854 Ma by LA-ICP-MS method. The rocks belong to the sub-alkaline series and consist of pyroxene (35%–40%), plagioclase (40%–45%), olivine (8%–10%) and spinel (3%–5%). Olivine has Fo values of 73–83 that is classified as chrysolite. Pyroxene has relative low contents of FeO (6.60 wt.%–8.23 wt.%) but high CaO (20.23 wt.%–21.25 wt.%) contents, however, plagioclase has high Al2O3 (31.78 wt.%–32.37 wt.%), CaO (16.08 wt.%–16.25 wt.%) and An (79–80) values, but low Na2O contents (1.95 wt.%–2.11 wt.%). Spinel are magnesioferrite with characteristics of high contents of MgO (13.65 wt.%–13.68 wt.%), FeO (23.27 wt.%–23.40 wt.%) and Al2O3 (62.43 wt.%–62.74 wt.%). Chemical compositions of these minerals are similar to those of gabbro rocks that were formed in the post-orogeny environment. The olivine-gabbro samples have negative zircon eHf values (-16.57±0.47) that resemble the mafic rocks in the same region, indicating that they are derived from the extremely enriched mantle source. On the compilation of documented Neoproterozoic mafic rocks in the Yangtze Craton, it is proposed that the mantle in the northern Yangtze Craton has experienced different degrees enrichment during the Neoproterozoic.

Zircon Hf-O isotope evidence for recycled oceanic and continental crust in the sources of alkaline rocks

Post-orogenic and intraplate extensional alkaline rocks are believed to have formed by partial melting of metasomatized ultramafic rocks in the subcontinental lithospheric mantle. Their variable incompatible element abundances and radiogenic isotopic ratios reflect recycling of subducted oceanic or continental crustal material into their source reservoirs. However, whole-rock geochemical and Sr-Nd isotopic data do not well constrain the nature of this recycled crustal material because of complex petrogenetic processes, i.e., crustal assimilation, fractional crystallization, magma mixing, and post-magmatic alteration. Here we present an integrated study of in situ Hf-O isotopes in zircons from two Triassic alkaline complexes in the northeastern Sino-Korean craton, i.e., the Hekanzi and Saima alkaline complexes. The Hekanzi alkaline rocks have zircon eHf(t) values of —2.5 to +0.6 and sub-normal mantle δ18O (+3.8‰ to +5.4‰), indicating a component of high-temperature altered oceanic crust involved in their mantle source prior to magma generation. In contrast, the Saima alkaline rocks have extremely negative zircon eHf(t) (—11 to —14) and elevated δ18O (+7.1‰ to +8.4‰) values, suggesting continental crust recycled into their mantle source prior to magma generation. Our results show that the combined zircon Hf and O isotopes are powerful tracers to distinguish recycled continental crust from recycled oceanic crust and, importantly, provide compelling evidence for recycled continental crust in the sources of alkaline rocks.

Record of Permian–Early Triassic continental arc magmatism in the western margin of the Jiamusi Block, NE China: petrogenesis and implications for Paleo-Pacific subduction

In this paper, we report zircon U–Pb ages, Hf isotopes and whole-rock geochemical data for the Permian to Early Triassic granitoids from the western margin of the Jiamusi Block (WJB), NE China. The intermediate to felsic (SiO2 = 59.67–74.04 wt%) granitoids belong to calc-alkaline series and are characterized by enrichments in light rare earth elements and large ion lithophile elements with pronounced negative Nb, Ta and Ti anomalies, revealing typical continental magmatic arc geochemical signatures. The zircon U–Pb determinations on the granodiorite, monzogranite, syenogranite and quartz diorite samples yielded ages between ca. 275–245 Ma, which, together with the published coeval intrusive rocks, indicates that Permian to Early Triassic continental arc magmatism occurred extensively in the WJB. The low and mainly negative zircon e Hf(t) values between −7.6 and +1.6 and the zircon Hf model ages of 1.2–1.8 Ga, which are significantly older than their crystallization ages, suggest that they were mainly derived from reworking of ancient crustal materials with a limited input of juvenile components. The geochemical systematics and petrogenetic considerations indicate that the studied granitoids were generated from a zone of melting, assimilation, storage, and homogenization, i.e., a MASHed zone at the base of Paleo- to Mesoproterozoic continental crust, where large portions of igneous rocks and minor clay-poor sediments involved in the source region. In combination with regional geological data, we argue that the Jiamusi Block was unlikely the rifted segment of the Songliao Block and two possible geodynamical models were proposed to interpret the formation of the ca. 275–245 Ma granitoids in the WJB. In the context of Permian global plate reconstruction, we suggest that Paleo-Pacific plate subduction was initiated in the Permian to Early Triassic beneath the Jiamusi Block, and even whole eastern NE China.

Magma mixing revealed from in situ zircon U–Pb–Hf isotope analysis of the Muhuguan granitoid pluton, eastern Qinling Orogen, China: implications for late Mesozoic tectonic evolution

In this paper, we present zircon U–Pb age and Hf isotope data to document the significance of magma mixing in the formation of Late Jurassic granitoid intrusions in the eastern Qinling Orogen, China. The Muhuguan granitoid pluton from this orogen consists of monzogranite and lesser biotite granite and granodiorite, all containing abundant hornblende-rich cumulates, dioritic xenoliths, and mafic magmatic enclaves (MMEs). The monzogranite and granodiorite are intruded by a number of lamprophyre dykes. Both a cumulate and a dioritic xenolith samples have concordant zircon U–Pb ages of ca. 161 ± 1 Ma, but possess contrasting Hf isotopic compositions. The cumulate has more radiogenic zircon Hf isotopes with negative e Hf(t) values (−7.9 to −2.5) and T DM1 ages of 0.9–1.1 Ga, indicating its derivation likely from basaltic rocks of the Neoproterozoic to early Paleozoic Kuanping Group in the area. The dioritic xenolith has much lower zircon e Hf(t) values of −19.5 to −8.8 and T DM2 ages of 2.4–1.7 Ga, consistent with a juvenile Paleoproterozoic crust source presumably represented by the metabasic rocks of the Qinling Group in the area. Individual samples of the monzogranite, MME, and a lamprophyre dyke have U–Pb ages of 150 ± 1, 152 ± 1, and 152 ± 1 Ma, respectively, demonstrating coeval mafic and felsic magmatism in the Late Jurassic. The lamprophyre dyke has homogeneous, highly negative zircon e Hf(t) values (−29.8 to −24.8) and Archean T DM2 ages (3.0–2.7 Ga), and its genesis is interpreted as partial melting of an ancient enriched subcontinental mantle source. Zircons from the fine-grained MME show a large range of e Hf(t) between −29.1 and −9.8, overlapping values of the monzogranite and lamprophyre dyke samples. Zircon U–Pb age and Hf isotopes of the MMEs are consistent with their formation by mixing of crustal- and enriched mantle-derived magmas. The main group of zircons from the monzogranite has e Hf(t) values (−17.9 to −9.3) and T DM2 ages (2.3–1.8 Ga) that are compatible with the dioritic xenoliths, indicating that the former was produced by partial melting of Paleoproterozoic crustal source with involvement of mantle-derived magmas. Mafic magmatism revealed from the Muhuguan pluton indicates that the eastern Qinling Orogen was dominated by lithospheric extension during the Late Jurassic. Compilation of existing geological and geochronological data suggests that this extensional event started in Late Jurassic (ca. 160 Ma) and persisted into the Early Cretaceous until ca. 110 Ma. The Jura-Cretaceous extension may have resulted from the late Mesozoic westward subduction of the Pacific plate beneath the East Asian continental margin.

Formation of high 18O fayalite-bearing A-type granite by high-temperature melting of granulitic metasedimentary rocks, southern China

The genesis of A-type granites has been controversial. Fayalite granite is a member of the most reduced A-type granites, commonly thought to have been primarily sourced from tholeiitic rocks. In this paper we report petrography, whole-rock geochemistry, Sr-Nd isotope, and in situ zircon Hf-O isotope results for a fayalite-bearing A-type granite suite at Jiuyishan in southern China. High zircon δ 18 O (8.0‰–9.8‰), negative zircon eHf(t) (–6.2 to –2.3), and evolved whole-rock Sr-Nd isotopes ( I Sr = 0.7151–0.7181; eNd(t) = –7.4 to –6.6) indicate the reworking of old supracrustal rocks. Isotopic and geochemical results, particularly downward inflections of Zr and Ba at ∼70 wt% SiO 2 , point to fractional crystallization rather than magma mixing as the controlling process for the evolution of the igneous suite. Integrated petrological, geochemical, and isotopic studies present the first convincing case that reduced A-type granites can also be generated by high-temperature (>960 °C) melting of granulitic metasedimentary rocks, likely related to the upwelling of the asthenosphere and/or underplating and intrusion of basaltic melts. We emphasize that key factors for the genesis of this unique rock type are low oxygen fugacity ( f O 2 ), low f H 2 O , and high temperature.