Eastern China continental lithosphere thinning is a consequence of paleo-Pacific subduction: A review and new perspectives

Understanding the processes that lead to the lithosphere thinning is a key aspect of continental geology research. In this paper, we present essential observations and summarize our understandings on the lithosphere thinning and accompanying magmatism in eastern continental China since the Mesozoic as a straightforward consequence of plate tectonics. We show that the lithosphere thinning in the Mesozoic resulted from basal hydration weakening with the water coming from dehydration of the paleo-Pacific plate in the mantle transition zone. The weakening effect is to convert the basal lithosphere into asthenosphere by reducing its viscosity, having thus thinned the lithosphere while triggering mantle melting and crustal magmatism marked by the widespread Mesozoic basalts and granitoids in space and time. These observations and logical reasoning require the existence and effect of subducted paleo-Pacific plate in the mantle transition zone, whose active subduction ended at ~ 90 Ma with the suture located off the continental China marked by the arc-shaped southeast coastline. As a result, the thinned lithosphere began a 40-Myr period (i.e., ~ 90 to ~ 50 Ma) of basal accretion manifested by compositional systematics of basalts erupted in this period. The initiation of the present-day western Pacific subduction at ~ 50 Ma and its eastward retreat caused eastward drift of continental China, leaving the older portions of the present-day Pacific slab stagnant in the mantle transition zone with resumed water supply in the form of hydrous melt to maintain the thinned lithosphere, which is the same as creating and maintaining the oceanic-type seismic low velocity zone (LVZ) beneath eastern China, responsible for the Cenozoic alkali basalt volcanism in the region. That is, the present-day lithosphere-asthenosphere boundary (LAB) beneath eastern China is a petrological boundary, either as an amphibole dehydration solidus or water-saturated solidus. As predicted, the Cenozoic alkali basalts in eastern China demonstrate that lithosphere thickness (i.e., the LAB depth) controls the compositions of mantle melts, i.e., the lid effect. The latter further confirms the LAB beneath eastern China as a solidus, below which decompression melting happens, and above which melt solidifies or ascends rapidly to the surface. Our studies thus lead us to the unavoidable conclusion that the lithosphere thinning in the Mesozoic, the present-day LAB, the seismic LVZ and the widespread Mesozoic-Cenozoic magmatism in eastern China are all consequences of plate tectonics in response to paleo-Pacific plate subduction, which is of global significance for understanding intra-continental magmatism at present and in Earth’s histories

Sublithosphere mantle crystallization and immiscible sulphide melt segregation in continental basal magmatism: evidence from clinopyroxene megacrysts in the Cenozoic basalts of eastern China

This study explores the effects of high-pressure crystallization and immiscible sulphide melt segregation under mantle conditions on the compositional variation of basaltic magmas, using clinopyroxene megacrysts in the Cenozoic basalts of eastern China. These clinopyroxene megacrysts are large (up to > 10 cm in size) and homogeneous at the grain scale. They were crystallized from variably evolved parental magmas and then captured by their host basalts. The large and systematic variations of [Sm/Yb]N, Lu/Hf, Fe/Mn, Sc/La, Ni and Cu with Mg# in the clinopyroxene megacrysts suggest their co-precipitation with garnet and with immiscibility between sulphide and silicate melts. This is consistent with the appearance of garnet megacrysts in the host basalts and abundant sulphide globules in the clinopyroxene megacrysts. The covariation between Ni contents of sulphide globules and Mg# of the clinopyroxene megacrysts suggests a genetic relationship between sulphide globules and clinopyroxene megacrysts. High-pressure crystallization of clinopyroxene and garnet results in decrease of Mg# and concentrations of CaO, MnO and heavy rare earth elements (e.g., Yb) and increase of Fe/Mn and [Sm/Yb]N in the residual melts. Therefore, geochemical characteristics of low Mg#, low CaO and MnO contents and high Fe/Mn and [Sm/Yb]N in basalts do not necessarily indicate a pyroxenite mantle source. In addition, caution is needed when applying the olivine addition method to infer the primary compositions of alkali basalts without considering the effects of highpressure crystallization of clinopyroxene and garnet. The calculated P-T conditions of the clinopyroxene megacrysts are close to those of the lithosphere-asthenosphere boundary (LAB) beneath eastern China, and the low primitive [Sm/Yb]N (~ 4.0) of melts parental to the clinopyroxene megacrysts suggests final equilibration at relatively low pressures most likely beneath the LAB. Hence, a melt-rich layer is expected close beneath the LAB. Melt pools in this melt-rich layer provide a stable and closed environment for the growth of compositionally homogeneous clinopyroxene megacrysts. As a result, melts in these melt pools are compositionally evolved with low and variable Mg#. Subsequent pulses of melt aggregation/supply from depths with primitive compositions and high Mg# will disturb these melt pools, cause magma mixing and trigger the eruption of magmas carrying clinopyroxene and garnet megacrysts

A Co-axial Multi-tube Heat Exchanger Applicable for a Geothermal ORC Power Plant

AbstractThe study proposes a Co-axial multi-tube heat exchanger (CMTHE) applicable to geothermal heat extraction. The heat exchanger is integrated with a 50kW geothermal ORC power plant having a working fluid of R-245fa. Two field tests were performed to examine the system response of the ORC system subject to change of CMTHE. In case 1 where the flow rate in the shell-side of CMTHE is maintained, the pressure variation in the shell-side of CMTHE casts minor variations on heat extraction, ORC power generation, and ORC efficiency during the transient. Moreover, the effect of pressure has barely any influence of the final states of heat extraction, ORC power generation, and ORC efficiency. In case 2 where the pressure is preserved in the CMTHE, it is found that a decrease of flow rate in the CMTHE results in degradation of heat extraction, ORC power generation and ORC system efficiency. On the contrary, increasing the flow rate in the CMTHE leads to a rise of heat extraction, ORC power generation and ORC system efficiency. Unlike that in case 1, the effect of flow rate has a detectable effect on the final states of heat extraction, ORC power generation, and ORC efficiency

Petrogenesis of the early Cretaceous intra-plate basalts from the western North China Craton: Implications for the origin of the metasomatized cratonic lithospheric mantle

We present new bulk-rock 40Ar/39Ar age, major and trace elements and Sr-Nd-Hf isotopic data on the early Cretaceous intra-plate alkali basalts from the Western North China Craton (WNCC) to study the origin of the metasomatized cratonic lithosphere mantle. The age of these basalts is ~116 Ma. These basalts have elevated incompatible element abundance with high [La/Sm]N (2.80–4.56) and enriched Sr-Nd-Hf isotopic compositions (87Sr/86Sri = 0.7062–0.7075, εNd(t) = −6.0 to −13.0 and εHf(t) = −8.3 to −17.4), being similar to the contemporary analogues from the Western North China Craton and Paleozoic kimberlites and mantle xenoliths. The WNCC basalts also show good correlations between ɛNd(t) and ɛHf(t), and high [La/Sm]N. All these geochemical observations are consistent with the interpretation that these basalts originated from partial melting of the lithospheric mantle that experienced melt metasomatism. Two types metasomatism melts are required to explain the geochemical characteristics of these rocks. The obvious negative Nbsingle bondTa (compared with K)-Ti and positive Basingle bondPb anomalies observed in these basalts further constrain that one of the metasomatic melts was derived from the subducted terrigenous sediment. Furthermore, the overall higher P/Nd, Nb/La and Nb/Th and lower Lu/Hf of basalts in the WNCC suggest that there is also contribution of low-F melts from asthenosphere mantle. Collectively, we suggest that the formation of the metasomatized lithosphere mantle beneath the WNCC is the process of metasomatic reaction between mantle peridotite and the melts of different origin to generate metasomatic veins containing amphibole/phlogopite. Partial melting of the metasomatic lithospheric mantle at 106–120 Ma in the WNCC was considered to be induced by thermal perturbation that was ultimately related to the breakoff of the subducted oceanic slab following the closure of the Mongolia-Okhotsk ocean

Growth factor in f(T) gravity

We derive the evolution equation of growth factor for the matter over-dense perturbation in $f(T)$ gravity. For instance, we investigate its behavior in power law model at small redshift and compare it to the prediction of $\Lambda$CDM and dark energy with the same equation of state in the framework of Einstein general relativity. We find that the perturbation in $f(T)$ gravity grows slower than that in Einstein general relativity if \p f/\p T>0 due to the effectively weakened gravity.Comment: 15 pages,1 figure; v2,typos corrected; v3, discussions added, accepted by JCA

Iron isotope compositions of coexisting sulfide and silicate minerals in Sudbury-type ores from the Jinchuan Ni-Cu- sulfide deposit: A perspective on possible core-mantle iron isotope fractionation

Many studies have shown that the average iron (Fe) isotope compositions of mantle-derived rocks, mantle peridotite and model mantle are close to those of chondrites. Therefore, it is considered that chondrite values represent the bulk Earth Fe isotope composition. However, this is a brave assumption because nearly 90% Fe of the earth is in the core, whose Fe isotope composition is unknown, but is required to construct bulk earth Fe isotope composition. We approach the problem by assuming that the earth’s core separation can be approximated in terms of the Sudbury-type Ni-Cu sulfide mineralization, where sulfide-saturated mafic magmas segregate into immiscible sulfide liquid and silicate liquid. Their density/buoyancy controlled stratification and solidification produced net-textured ores above massive ores and below disseminated ores. The coexisting sulfide minerals (pyrrhotite (Po) > pentlandite (Pn) > chalcopyrite (Cp)) and silicate minerals (olivine (Ol) > orthopyroxene (Opx) > clinopyroxene (Cpx)) are expected to hold messages on Fe isotope fractionation between the two liquids before their solidification. We studied the net-textured ores of the Sudbury-type Jinchuan Ni-Cu sulfide deposit. The sulfide minerals show varying δ56Fe values (-1.37 ~ -0.74‰ (Po) < 0.09 ~ 0.56‰ (Cp) < 0.53 ~ 1.05‰ (Pn), but silicate minerals (Ol, Opx, Cpx) have δ56Fe values close to chondrites (δ56Fe = -0.01±0.01‰). The heavy δ56Fe value (0.52 ~ 0.60‰) of serpentines may reflect Fe isotopes exchange with the coexisting pyrrhotite with light δ56Fe. We ob- tained an equilibrium fractionation factor of Δ56Fesilicate-sulfide = ~ 0.51‰ between reconstructed silicate liquid (δ56Fe = ~ 0.21‰) and sulfide liquid (δ56Fe = ~ -0.30‰), or Δ56Fesilicate-sulfide = ~ 0.36‰ between the weighted mean bulk-silicate minerals (δ56Fe[0.70ol,0.25opx,0.05cpx] = 0.06‰) with weighted mean bulk- sulfide minerals (δ56Fe = ~ -0.30‰). Our study indicates that significant Fe isotope fractionation does take place between silicate and sulfide liquids during the Sudbury-type sulfide mineralization. We hypothesize that significant iron isotope fractionation must have taken place during core-mantle segregation, and the bulk earth may have lighter Fe isotope composition than chondrites although Fe isotope analysis on experimental sulfide-silicate liquids produced under the varying mantle depth conditions is needed to test our results. We advocate the importance of further research on the subject. Given the close Fe-Ni association in the magmatic mineralization and the majority of Earth’s Ni is also in the core, we infer that Ni isotope fractionation must also have taken place during the core separation that needs attention

The lithospheric thickness control on the compositional variation of continental intraplate basalts: A demonstration using the Cenozoic basalts and clinopyroxene megacrysts from eastern China

Studies on intra‐plate ocean island basalts have demonstrated the control of lithosphere thickness on the extent of melting and pressure of melt extraction (i.e., the lid‐effect). However, whether lithosphere thickness also controls the composition of within‐continent basalts remains unclear. Here we test this hypothesis by studying the Cenozoic basalts containing clinopyroxene megacrysts from 10 localities throughout eastern continental China with a north‐south spatial coverage in excess of 2500 km. Indeed, the geochemical parameters (e.g., abundances and ratios of major and trace elements) correlate well with the depth of the lithosphere‐asthenosphere boundary (LAB) calculated using the clinopyroxene barometry, showing significant lithospheric thickness control on basalt compositions. These observations offer further evidence for melt pooling (a melt rich layer) close beneath the LAB as a “stable magma reservoir” for crystallizing compositionally uniform clinopyroxene megacrysts to be carried by subsequent pulses of melt transport and eruption

HIV-1 Infection Induces Interleukin-1β Production via TLR8 Protein-dependent and NLRP3 Inflammasome Mechanisms in Human Monocytes

The induction of inflammatory cytokines such as IL-1β is associated with the progression of human immunodeficiency virus, type 1 (HIV-1) disease or AIDS. Unlike most inflammatory cytokines that are regulated by NF-κB at the transcriptional level, production of mature IL-1β also depends on inflammasome activation. The mechanism by which HIV-1 induces pro-IL-1β expression and activates inflammasomes to cleave pro-IL-1β into its bioactive form is not clearly defined. We report here that HIV-1 infection in human monocytes efficiently induced IL-1β expression and inflammasome activation. Toll-like receptor 8 (TLR8) was required for inducing pro-IL-1β expression, whereas the NLRP3 inflammasome was required for IL-1β maturation and release. Furthermore, the lysosomal protease cathepsin B and HIV-1 induced production of reactive oxygen species were critical for HIV-induced inflammasome activation and IL-1β production. HIV-1 entry, reverse transcription, and integration were all required for both pro-IL-1β expression and inflammasome activation. Finally, we show that HIV-1-derived RNA was sufficient to induce both pro-IL-1β expression and inflammasome activation. We conclude that HIV-1 infection induced the expression of pro-IL-1β via TLR8-mediated mechanisms and activated caspase-1 through the NLRP3 inflammasome to cleave pro-IL-1β into bioactive IL-1β. These findings help to elucidate mechanisms of HIV-1 disease progression and identify novel targets for treating HIV-1 induced inflammation and immune activation