The mafic enclaves from Paleoproterozoic domain are considered to be the results of large-scale crust-mantle interaction and magma mixing. In this paper, petrography, mineralogy and geochemistry were jointly used to d...The mafic enclaves from Paleoproterozoic domain are considered to be the results of large-scale crust-mantle interaction and magma mixing. In this paper, petrography, mineralogy and geochemistry were jointly used to determine the origin of the mafic enclaves and their relationship with the host granitoids of the Kan granite-gneiss complex. This study also provides new information on crust-mantle interactions. The mafic enclaves of the Kan vary in shape and size and have intermediate chemical compositions. The diagrams used show a number of similarities in the major elements (and often in the trace elements) between the mafic enclaves and the host granitoids. Geochemical show that the Kan rock are metaluminous, enriched in silica, medium to high-K calc-alkaline I-type granite. The similarities reflect a mixing of basic and acid magma. Mafic enclaves have a typical magmatic structure, which is characterized by magma mixing. The genesis of these rocks is associated with the context of subduction. They result from the mixing of a mafic magma originating from the mantle and linked to subduction, and a granitic magma (type I granite) that arises from the partial melting of the crust.展开更多
Abstract: Enclaves in intermediate-acid plutons from Tongling can be divided into three types: xenoliths, relics and magmatogenic enclaves. The magmatogenic enclaves consist of cumulates, micrograined dioritite mixtit...Abstract: Enclaves in intermediate-acid plutons from Tongling can be divided into three types: xenoliths, relics and magmatogenic enclaves. The magmatogenic enclaves consist of cumulates, micrograined dioritite mixtite and dioritic chilled border enclaves. Petrologically, relics with eyed and meta-poikilitic texture are characterized by high content of biotite (>80%) and low content of cordierite and grossular. The cumulates with accumulate texture consist of a great amount of pyroxene, hornblende and minor spinel and phlogopite. The micrograined dioritic mixtite is composed of more hornblendes and feldspar and less needle apatites and an ellipsoid basic core included in plagioclase. The chilled border enclaves have the same mineral association, but more dark minerals than the host rocks consisting of plagioclase, quartz, alkaline feldspar, hornblende and biotite. Geochemically, the relics exhibit high REE content (455.8×10?6) and high ratio of LREE/HREE, more obvious Eu negative anomaly and are rich in Cr and Ni, poor in Ba, Nb and Sr. All kinds of magmatogenic enclaves have the same REE pattern without Eu anomaly, and the total REE is 74.9×10?6 for spinel pyroxene cumulate, 179.7×10?6 for hornblende cumulate, 226.9 × 10?6 for hornblende cumulate crystal, 289.9×10?6 for micrograined dioritic mixtite and 131.2×10?6 for chilled border enclaves. Calculation with the thermometer and barometer for minerals shows that the temperature and pressure of formation are 1126 °C and 8.44 kbar (7.15–9.04 kbar) for the spinel pyroxene cumulate, 1065 °C-1029 °C and 8.23 kbar (7.13–9.50 kbar) for the hornblende pyroxene cumulate, 959 °C and 3.40 kbar (2.86–4.09 kbar) for the micrograined dioritic mixtite enclaves, and 951 °C and 0.59 kbar for the dioritic chilled border enclaves, respectively. Thus, the following conclusions can be drawn. Relic enclaves were derived from the crustal partial melting and all cumulate enclaves originated from deep magma chambers near the Moho in the lower crust, which are cumulate fragments formed by fractional crystallization of basic magma; mixtite came from shallow magma chambers in the middle-upper crust, formed by the mixture of mantle-derived magma and acid magma derived from the crustal partial melting; and the chilled border enclaves came from the border fragments of early intrusive bodies.展开更多
The field and microstructural features coupled with mineral chemical data from microgranular enclave(ME)and host Mesoproterozoic Kanigiri granite(KG)pluton of Nellore Schist Belt(NSB),Southeastern India,have been docu...The field and microstructural features coupled with mineral chemical data from microgranular enclave(ME)and host Mesoproterozoic Kanigiri granite(KG)pluton of Nellore Schist Belt(NSB),Southeastern India,have been documented in order to infer the likely processes responsible for the origin and evolution of ME and host KG magma.The ME and host KG bear the same mineral assemblages barring the KG which does not contain amphibole;however,they are modally disequilibrated.The ME in KG is originated due to multiple intrusions of ME magmas into the crystallizing host KG magma chamber.Field and textural features indicate the dynamic magma flow,mingling,and undercooling of the ME against a relatively cooler surface of host KG magma.The presence of NSB country rock xenoliths and its diffuse boundaries suggest the intrusive relation and marginal assimilation by the intruding KG magma.The occasional cumulate texture in the ME appears to have formed by the accumulation of early-formed minerals that crystallized rapidly in the ME magma globules.The ME shows the magmatically deform features developed due to the flowage and erosion by the subsequent intrusions of ME magma pulses into the crystallizing host KG magma chamber.The ME amphiboles show unusual composition as ferro-edenitic hornblende to potassian-hastingsitic hornblende,that crystallized in the subalkaline-alkaline transition,low fO_(2)(reducing to mildly oxidizing)magma.The unusual extremely low Mg/Mg+Fe^(t)=0.015(avg.)of ME amphiboles may be related to the changing physico-chemical(P,T,fO_(2),and H_(2)O)condition of the ME magma or they might have crystallized in equilibrium with more evolved KG magma.The KG(FeOt/MgO=37.04,avg.)and ME(FeO~t/MgO=77.72,avg.)biotites are siderophyllite,and buffered between QFM and NNO syn-crystallizing in the water undersaturated(H_(2O)≈3.58 wt.%in KG;≈3.53wt.%in ME),alkaline anorogenic(A-type)host magmas that were emplaced at mid-crustal(4–5 kbar;17 km)depth.Field,microtextural and mineral chemical evidences suggest that the alkaline KG magma originated from crustal source and evolved through synchronous fractionation,mixing,and mingling with coeval ME magmas in the KG magma chamber.展开更多
Many igneous rocks distribute in Gejiu tin polymetallic ore-field at Yunnan province, rocks including basalt, gabbro, mafic microgranular enclaves, granites (porphyritic granite and equigranular granite) and akaline...Many igneous rocks distribute in Gejiu tin polymetallic ore-field at Yunnan province, rocks including basalt, gabbro, mafic microgranular enclaves, granites (porphyritic granite and equigranular granite) and akaline rocks. The ages of the granites and akaline rocks which are considered to have genetic connecting with the mineralization have been comfirmed, but the gabbro- mafic microgranular enclaves-granite assemblage's ages are still unknown. By means of LA-ICP-MS zircon U-Pb dating, the data of Shenxianshui equigranular granite, the mafic microgranular enclave in Jiasha area, the host rock of the mafic microgranular enclaves and the Jiasha gabbro are around ~80 Ma. Besides the above mentioned data, a group of new ages at ~30 Ma were discovered in this study, which is from gabbro and mafic microgranular enclaves. Based on the previous data and the new data gained this time, we suggest the major geochronology framework of the magmatism and mineralization events in Gejiu area is ~80 Ma, which is consistent with the Late Cretaceous magmatism and mineralization events in the whole southeast Yunnan and west Guangxi area and they were suggested to belong to the same geotectonic setting in late Yenshannian. And the new ages of the ~30 Ma obtained in this study is considered to represent a responding to the complicate tectonic evolution history of the Tibetan orogenic events in Cenozoic.展开更多
LA-ICP-MS zircon U-Pb dating has revealed that the Huangyangshan pluton in Eastern Junggar was formed at 311±12 Ma,and that microgranular enclaves were formed at 300±6 Ma;both ages are very consistent within...LA-ICP-MS zircon U-Pb dating has revealed that the Huangyangshan pluton in Eastern Junggar was formed at 311±12 Ma,and that microgranular enclaves were formed at 300±6 Ma;both ages are very consistent within errors.It is the first time that the microgranular enclaves age in Kalamaili area was determined.Petrochemistry and geochemistry research shows the characteristics of host rock as follows:展开更多
In this contribution,detailed field descriptions together with petrographic and bulk-rock major,trace and rare earth elements(REE)data are used to constrain the origin and geodynamic setting of the mafic magmatic encl...In this contribution,detailed field descriptions together with petrographic and bulk-rock major,trace and rare earth elements(REE)data are used to constrain the origin and geodynamic setting of the mafic magmatic enclaves(MMEs)recently discovered within the Pan-African Ngaoundal pluton,Adamawa area,central Cameroon.The investigated MMEs are dark-colored with chilled margins,and display medium to coarse-grain igneous textures.The mineral assemblage is either dominated by K-feldspar and carbonate(group Ⅰ),or by amphibole and plagioclase(group Ⅱ),though the overall mineral phases made of amphibole,plagioclase,K-feldspar,and biotite are similar to that of their host syenite but in different proportions.The MMEs in Ngaoundal area are foid-gabbro in composition with SiO_(2) contents ranging between 41.52% and 43.74% and are contiguous with their host granitoids of intermediate composition(SiO_(2)=57.52% to 58.98%).The host granitoid rocks are metaluminous,and belong to the shoshonitic series.Petrographic and geochemical data have revealed that the Ngaoundal MMEs derived from rapid cooling of hot injected lithospheric mantle-derived magma within cooler host granitoids magma and were emplaced in the intraplate geodynamic setting.展开更多
Recent eruption of Unzen Volcano in 1991-1995 caught attention of scientists all over the world because of disastrous character of previous one in 1792. Intrusion of andesitic magma to the chamber with rhyolitic magma...Recent eruption of Unzen Volcano in 1991-1995 caught attention of scientists all over the world because of disastrous character of previous one in 1792. Intrusion of andesitic magma to the chamber with rhyolitic magma is proposed to be a trigger for these eruptions. T-P-X parameters of two end-member magmas have been estimated several times, but usually estimations are based on phenocrysts assemblages. New results of this research are based on mafic enclaves and groundmass. These results are significant for magma mixing and mingling theory.展开更多
The petrology, geochronology and geochemistry of the mafic enclaves in the Mid-Late Triassic Jiefangyingzi pluton from Chifeng area, southern Inner Mongolia, in China are studied to reveal their petrogenetic relations...The petrology, geochronology and geochemistry of the mafic enclaves in the Mid-Late Triassic Jiefangyingzi pluton from Chifeng area, southern Inner Mongolia, in China are studied to reveal their petrogenetic relationship with the host pluton. Furthermore, the coeval magmatic assemblage and its petrogenesis on the northern margin of the North China craton(NCC) are studied synthetically to elucidate their tectonic setting and the implications for the destruction of the NCC. Zircon U-Pb dating reveals that the mafic enclaves formed at 230.4 ± 2.2 Ma, which is similar to the age of the host pluton. The most basic mafic enclaves belong to weak alkaline rocks, and they display rare earth element(REE) and trace element normalized patterns and trace element compositions similar to those of ocean island basalt(OIB). In addition, they have positive εNd(t) values(+3.84 to +4.94) similar to those of the Cenozoic basalts on the northern margin of the NCC. All of these geochemical characteristics suggest that the basic mafic rocks originated from the asthenosphere. Petrological and geochemical studies suggest that the Jiefangyingzi pluton and the intermediate mafic enclaves were formed by the mixing of the asthenosphere-derived and crust-derived magmas in different degrees. The Mid-Late Triassic magmatic rocks on the northern margin of the NCC could be classified into three assemblages according to their geochemical compositions: alkaline series, weak alkaline–sub-alkaline series and sub-alkaline series rocks. Petrogenetic analyses suggest that the upwelling of the asthenosphere played an important role in the formation of these Mid-Late Triassic magmatic rocks. Basing on an analysis of regional geological data, we suggest that the northern margin of the NCC underwent destruction due to the upwelling of the asthenosphere during the Mid-Late Triassic, which was induced by the delamination of the root of the collisional orogeny between Sino-Korean and Siberian paleoplates in Late Permian.展开更多
In this paper, we present the occurrence and mineral components of the enclaves firstly discovered in the Cenozoic Pulu volcanic rocks in west Kunlun Mountains, and propose that the enclave is accumulated by fractiona...In this paper, we present the occurrence and mineral components of the enclaves firstly discovered in the Cenozoic Pulu volcanic rocks in west Kunlun Mountains, and propose that the enclave is accumulated by fractional crystallization within high-level magma chamber. In addition, the chemical compositions of its primary magma are calculated. The calculated compositions are similar to those of the Kangxiwa volcanic rocks that belong to the same volcanic belt in the Pulu volcanic region, suggesting their origin from the same source region. However, the temperatures and oxygen fugacity of magmas at high-level magma chamber decreased along with fractional crystallization.展开更多
The Late Cretaceous Uckapth Granitoid including mafic microgranular enclaves intruded into metapelitic and metabasic rocks, and overlain unconformably by Neogene ignimbrites in the Ni^de area of Turkey. It is mostly g...The Late Cretaceous Uckapth Granitoid including mafic microgranular enclaves intruded into metapelitic and metabasic rocks, and overlain unconformably by Neogene ignimbrites in the Ni^de area of Turkey. It is mostly granite and minor granodiorite in composition, whereas its enclaves are dominantly gabbro with a few diorites in composition. The Uckapdl Granitoid is composed mainly of quartz, K-feldspar, plagioclase, biotite, muscovite and minor amphibole while its enclaves contain mostly plagioclase, amphibole, minor pyroxene and biotite. The Uckapth Granitoid has calcalkaline and peraluminous (AJCNK= 1.0-1.3) geochemical characteristics. It is characterized by high LILE/HFSE and LREE/HREE ratios ((La/Lu)N 3-33), and has negative Ba, Ta, Nb and Eu anomalies, resembling those of comsion granitoids. The {)fkaplh Granitoid has relatively high STSr/S6Sr0) ratios (0.711189--0.716061) and low eNd(t) values (-5.13 to -7.13), confirming crustal melting. In contrast, the enclaves are tholeiitic and metaluminous, and slightly enriched in LILEs (K, Rb) and Th, and have negative Ta, Nb and Ti anomalies; propose that they were derived from a subduction-modified mantle source. Based on mineral and whole rock chemistry data, the Uckapth granitoid is H-(hybrid) type, post-collision granitoid developed by mixing/mingllng processes between crustal melts and mantle-derived mafic magmas.展开更多
This work focused on the prediction modeling of Cerrado occurrences in the Atlantic Rainforest predominance in the São Paulo Metropolitan Region (SPMR), the fourth largest urban area, in the city of Guarulhos...This work focused on the prediction modeling of Cerrado occurrences in the Atlantic Rainforest predominance in the São Paulo Metropolitan Region (SPMR), the fourth largest urban area, in the city of Guarulhos, southeastern Brazil. The methodology was based on the selection of records of occurrence of Cerrado in georeferenced databases, thematic maps of geoenvironmental layers, and modeling of the distribution of species through the MaxEnt tool. Besides that, field research confirmed the presence or not of the species in the areas with a high probability of occurrence of Cerrado (≥0.7). As a result, the model observed a great capacity for the prediction of the occurrence of Cerrado in Ecotonal and anthropic regions (AUC = 0.82), revealing important hotspots such as relics from the past or Cerrado enclaves of high biodiversity. The work also points priority areas for the conservation and preservation of this increasingly endangered biome.展开更多
The Mako area, located in eastern Sénégal</span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verda...The Mako area, located in eastern Sénégal</span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">,</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"> constitute</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">s</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"> a segment of Paleoproterozoic (Birimian) formations of the Kédougou-Kéniéba Inliers (KKI) in the western part of the West African craton.</span></span></span><span><span><span style="font-family:""> </span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">The basic volcanism of the Birimian formations of the KKI has long been considered to be related to a single magmatic event associated with a Mid Oceanic Ridge Basalts (MORB) setting.</span></span></span><span><span><span style="font-family:""> </span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">The aim of this paper is to demonstrate on the basis of the architectural characteristics of the granitoids dark enclaves, the occurrence of at least two distinct phases of basic Magamtism in the Birimian of the KKI.</span></span></span><span><span><span style="font-family:""> </span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">The methodology consists of a cartography, a petrographic and architectural characterization of the dark enclaves within the Mako granitoids, in order to constrain their spatial and temporal relationships with the granitic magma. The results obtained are compared with those of the bibliography. We have pinpointed two types of enclaves depending on their shapes and the characteristics of their edge with the enclosing rocks: angular enclaves with straight edges (ante-granitoids) and the soft enclaves with uneven edges (syn-granitoids).</span></span></span><span><span><span style="font-family:""> </span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">The enclaves with straight and well-defined rectilinear edges (ante-granitoids) would be linked to a basic magma which is already consolidated before being fragmented, torn and carried away as enclaves in the granitoids. These enclaves would come from enclosing outcrops of metabasalts and metagabbros which are locally cross-cut</span></span></span><span><span><span style="font-family:""> </span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">by the granitoids.</span></span></span><span><span><span style="font-family:""> </span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">The soft enclaves with uneven edges (syn-granitoids) were co-magmatic and not solid during their incorporation into the granitoids. They come from a basic magma which is contemporaneous to the granitic one.</span></span></span><span><span><span style="font-family:""> </span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">Thus, the occurrence of two generations of dark enclaves </span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">is</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"> related to</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">,</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"> at last, two different phases of basic magmatism in the Birimian formations of the KKI.展开更多
We report the zircon Hf-O isotopic data for mafic enclaves from the Taihang Yanshanian intermediate to felsic plutons, and use them, along with the petrological, whole-rock chemical and Nd-Sr isotopic data, to reveal ...We report the zircon Hf-O isotopic data for mafic enclaves from the Taihang Yanshanian intermediate to felsic plutons, and use them, along with the petrological, whole-rock chemical and Nd-Sr isotopic data, to reveal the petrogenesis of mafic enclaves. Mafic enclaves show magmatic textures and are finer-grained than host rocks. In places they are highly elongated due to stretching within the partially crystallized, convective felsic magma, but show no solid-state deformation. These data suggest that mafic enclaves and host rocks were co-existing, but compositionally distinct magmas. The mafic enclaves contain abundant hydrous minerals such as hornblende and biotite, with pyroxene relict being surrounded by hornblende reaction rim. Plagioclase xenocrysts from mafic enclaves show a complicated compositional and textural disequilibrium. Comparison between mafic enclaves and the immediate host rocks suggests that the two rock units are compositionally correlated. The εNd values of mafic enclaves are generally higher than the host rocks, though the Sr isotopic ratios of the two rock units are indistinguishable. Zircons from a single enclave sample show a significant variation in Hf isotopic compositions, with εHf = -10―-22, suggesting an origin through magma mixing between mafic and felsic magmas. This is supported by the relatively large variation of zircon O isotopic ratios (δ 18O = 5.5‰- 7.8‰) of the mafic enclaves. The petrogenesis of mafic enclaves could be described as below. Evolved basaltic magma (via fractionation of olivine and pyroxene) first mixed with crustally derived granitic melts in depths, forming a hybrid magma; then the hybrid magma broke up into discrete lumps upon entering the above felsic magma. Subsequently, the enclave-forming magma experienced a double mechanical transfer of plagioclase, and inward chemical transfer of fluid and Na, P, Y, Nb and Pb at the contacts with host felsic magmas.展开更多
There are three types of zircon (i.e. Zircon A, Zircon B and Zircon C) in the microgranitoid enclaves from the Qingtian granite. Zircon A is of the smallest Ipr, Ipy and Iel values with the largest range of variations...There are three types of zircon (i.e. Zircon A, Zircon B and Zircon C) in the microgranitoid enclaves from the Qingtian granite. Zircon A is of the smallest Ipr, Ipy and Iel values with the largest range of variations; Zircon C is of the largest Ipr, Ipy and Iel values with the smallest range of variations; and Zircon B is intermediate among the three types. The microprobe analysis of zircon demonstrates that the contents of trace elements (Hf, U, Y, Th) increase progressively with larger and larger variation from Zircon A through Zircon B to Zircon C. These characters snggest that the three types of zircon in the enclaves may have formed successively during the cooling mess of enclave magma, corresponding to different sites along with the intrusion of enclave magma. Because of positive correlations of the UO2/HfO2ratio with Ipr, the Th02/Y203 ratio with Ipy, and the UO2/(ThO2+Y203) ratio with Iel, it is suggested that the variation in zircon typology is caused by selective substitution of trace elements on different surfaces of zircon. On the basis of enclave petrology and zircon typomorphism, it is believed that the enclave magma may be generated from partial melting of residual materials in deep regions where the granitic magma has been extracted.展开更多
The Hesar pluton in the northern Urumieh-Dokhtar magmatic arc hosts numerous mafic-microgranular enclaves(MMEs).Whole rock geochemistry,mineral chemistry,zircon U-Pb and Sr-Nd isotopes were measured.It is suggested th...The Hesar pluton in the northern Urumieh-Dokhtar magmatic arc hosts numerous mafic-microgranular enclaves(MMEs).Whole rock geochemistry,mineral chemistry,zircon U-Pb and Sr-Nd isotopes were measured.It is suggested that the rocks are metaluminous(A/CNK=1.32-1.45),subduction-related I-type calc-alkaline gabbro to diorite with similar mineral assemblages and geochemical signatures.The host rocks yielded an U-Pb crystallization age of 37.3±0.4 Ma for gabbro-diorite.MMEs have relatively low SiO_(2) contents(52.9-56.6 wt%)and high Mg^(#)(49.8-58.7),probably reflecting a mantle-derived origin.Chondrite-and mantle-normalized trace element patterns are characterized by LREE and LILE enrichment,HREE and HFSE depletion with slight negative Eu anomalies(Eu/Eu^(*)=0.86-1.03).The host rocks yield(^(87)Sr/^(86)Sr)_(i) ratios of 0.70492-0.70510,positive ε_(Nd)(t)values of+1.55-+2.06 and T_(DM2)of 707-736 Ma,which is consistent with the associated mafic microgranular enclaves((^(87)Sr/^(86)Sr)_(i)=0.705014,ε_(Nd)(t)=+1.75,T_(DM2)=729 Ma).All data suggest magma-mixing for enclave and host rock formation,showing a complete equilibration between mixed-mafic and felsic magmas,followed by rapid diffusion.The T_(DM1)(Nd)and T_(DM2)(Nd)model ages and U-Pb dating indicate that the host pluton was produced by partial melting of the lower continental crust and subsequent mixing with injected lithospheric mantlederived magmas in a pre-collisional setting of Arabian-Eurasian plates.Clinopyroxene composition indicates a crystallization temperature of~1000℃ and a depth of~9 km.展开更多
Paired assistance is an important means for developed regions to help lessdeveloped regions achieve common prosperity.Despite its advantages,governmentmandated paired assistance tends to be less effective due to the l...Paired assistance is an important means for developed regions to help lessdeveloped regions achieve common prosperity.Despite its advantages,governmentmandated paired assistance tends to be less effective due to the lack of economic incentives for assisting localities.Therefore,local governments in China have explored an incentivecompatible paired assistance model.Based on the paired assistance between cities in the Pearl River Delta(PRD)region and the eastern,western and northern parts of Guangdong Province,this study designed a natural experiment for the network relationship of paired assistance.Empirical results based on industrial and commercial registration data and land transfer data indicate that paired assistance has enhanced bilateral investment linkages,and that the inter-regional benefit sharing mechanism has incentivized assisting localities to provide paired assistance.Our heterogeneity analysis reveals that a shorter distance between assisting and beneficiary localities may lead to better results of paired assistance.This study contributes to the understanding of incentive mechanisms for local government cooperation and offers insights for balancing regional development and achieving common prosperity.展开更多
The data of REE for the dioritic enclaves of the second intrusive bodies and for apatite,sphene,magnetite,zircon amphibole,biotite,plagioclase,and K-feldspar of the host rock are systematically reported andthe feature...The data of REE for the dioritic enclaves of the second intrusive bodies and for apatite,sphene,magnetite,zircon amphibole,biotite,plagioclase,and K-feldspar of the host rock are systematically reported andthe features of their compositions,overall characteristics and changing regularities,and their petrogenetic signifi-cance are discussed.The characteristics of the compositiom of the mineral rare-earth elements and their changingregularities for the Fangshan Rock Body show that there is a cognate evolution relation between the enclavesand the rock body.It is oonsidered that the dioritic enclaves might be the product derived from the earlycrystallization of homogeneous magma.展开更多
The major and trace elements and Sr-Nd-Pb isotopes of Miocene host granitoid rocks and their mafic microgranular enclaves(MMEs) were studied to understand the petrogenesis of MMEs in the Kashan complex, which is par...The major and trace elements and Sr-Nd-Pb isotopes of Miocene host granitoid rocks and their mafic microgranular enclaves(MMEs) were studied to understand the petrogenesis of MMEs in the Kashan complex, which is part of the Urumieh-Dokhtar magmatic belt(Iran). The host rocks consist of quartz-diorite and tonalite associated with a dioritic intrusion. The enclaves show microgranular texture and the same mineralogy as their respective host with plagioclase, quartz and biotite. MMEs have a diorite to quartz-diorite composition and show geochemical characteristics mostly between their granitoid host and the diorite intrusion. Chondrite-normalized REE patterns of all samples are moderately fractionated [(La/Yb)N=2.1 to 12.9]. The MMEs display in part small negative Eu anomalies(Eu/Eu*=0.54 to 0.99), with enrichment of LILE and depletion of HFSE. The enclaves show emplacement depth of -4 to 6 km which is comparable with the host rocks. Moreover, the Hornblende-plagioclase equilibrium temprature of MMEs yields average temperatures of 795℃ which is slightly higher than the host ones. Identical mineral compositions and Nd-Sr-Pb isotopic features of MME-host granitoid pairs indicate interactions and parallel evolution of MME and enclosing granitoid in the Kashan plutons. Additionally, the geochemical and isotopic investigations of host and dioritic intrusions suggest a common source for their genesis. A thermal anomaly induced by underplated basic magma into a hot crust would have caused partial melting in the lower crust to generate Kashan granitoid rocks.展开更多
Abundant mafic microgranular enclaves (MMEs) extensively distribute in granitoids in the Gangdise giant magmatic belt, within which the Qüxü batholith is the most typical MME-bearing pluton. Systematic sampl...Abundant mafic microgranular enclaves (MMEs) extensively distribute in granitoids in the Gangdise giant magmatic belt, within which the Qüxü batholith is the most typical MME-bearing pluton. Systematic sampling for granodioritic host rock, mafic microgranular enclaves and gabbro nearby at two locations in the Qüxü batholith, and subsequent zircon SHRIMP II U-Pb dating have been conducted. Two sets of isotopic ages for granodioritic host rock, mafic microgranular enclaves and gabbro are 50.4±1.3 Ma, 51.2±1.1 Ma, 47.0±l Ma and 49.3±1.7 Ma, 48.9±1.1 Ma, 49.9±1.7 Ma, respectively. It thus rules out the possibilities of mafic microgranular enclaves being refractory residues after partial melting of magma source region, or being xenoliths of country rocks or later intrusions.Therefore, it is believed that the three types of rocks mentioned above likely formed in the same magmatic event, i.e., they formed by magma mixing in the Eocene (c. 50 Ma). Compositionally, granitoid host rocks incline towards acidic end member involved in magma mixing, gabbros are akin to basic end member and mafic microgranular enclaves are the incompletely mixed basic magma clots trapped in acidic magma. The isotopic dating also suggested that huge-scale magma mixing in the Gangdise belt took place 15-20 million years after the initiation of the India-Asia continental collision, genetically related to the underplating of subduction-collision-induced basic magma at the base of the continental crust. Underplating and magma mixing were likely the main process of mass-energy exchange between the mantle and the crust during the continental collision, and greatly contributed to the accretion of the continental crust, the evolution of the lithosphere and related mineralization beneath the portion of the Tibetan Plateau to the north of the collision zone.展开更多
文摘The mafic enclaves from Paleoproterozoic domain are considered to be the results of large-scale crust-mantle interaction and magma mixing. In this paper, petrography, mineralogy and geochemistry were jointly used to determine the origin of the mafic enclaves and their relationship with the host granitoids of the Kan granite-gneiss complex. This study also provides new information on crust-mantle interactions. The mafic enclaves of the Kan vary in shape and size and have intermediate chemical compositions. The diagrams used show a number of similarities in the major elements (and often in the trace elements) between the mafic enclaves and the host granitoids. Geochemical show that the Kan rock are metaluminous, enriched in silica, medium to high-K calc-alkaline I-type granite. The similarities reflect a mixing of basic and acid magma. Mafic enclaves have a typical magmatic structure, which is characterized by magma mixing. The genesis of these rocks is associated with the context of subduction. They result from the mixing of a mafic magma originating from the mantle and linked to subduction, and a granitic magma (type I granite) that arises from the partial melting of the crust.
文摘Abstract: Enclaves in intermediate-acid plutons from Tongling can be divided into three types: xenoliths, relics and magmatogenic enclaves. The magmatogenic enclaves consist of cumulates, micrograined dioritite mixtite and dioritic chilled border enclaves. Petrologically, relics with eyed and meta-poikilitic texture are characterized by high content of biotite (>80%) and low content of cordierite and grossular. The cumulates with accumulate texture consist of a great amount of pyroxene, hornblende and minor spinel and phlogopite. The micrograined dioritic mixtite is composed of more hornblendes and feldspar and less needle apatites and an ellipsoid basic core included in plagioclase. The chilled border enclaves have the same mineral association, but more dark minerals than the host rocks consisting of plagioclase, quartz, alkaline feldspar, hornblende and biotite. Geochemically, the relics exhibit high REE content (455.8×10?6) and high ratio of LREE/HREE, more obvious Eu negative anomaly and are rich in Cr and Ni, poor in Ba, Nb and Sr. All kinds of magmatogenic enclaves have the same REE pattern without Eu anomaly, and the total REE is 74.9×10?6 for spinel pyroxene cumulate, 179.7×10?6 for hornblende cumulate, 226.9 × 10?6 for hornblende cumulate crystal, 289.9×10?6 for micrograined dioritic mixtite and 131.2×10?6 for chilled border enclaves. Calculation with the thermometer and barometer for minerals shows that the temperature and pressure of formation are 1126 °C and 8.44 kbar (7.15–9.04 kbar) for the spinel pyroxene cumulate, 1065 °C-1029 °C and 8.23 kbar (7.13–9.50 kbar) for the hornblende pyroxene cumulate, 959 °C and 3.40 kbar (2.86–4.09 kbar) for the micrograined dioritic mixtite enclaves, and 951 °C and 0.59 kbar for the dioritic chilled border enclaves, respectively. Thus, the following conclusions can be drawn. Relic enclaves were derived from the crustal partial melting and all cumulate enclaves originated from deep magma chambers near the Moho in the lower crust, which are cumulate fragments formed by fractional crystallization of basic magma; mixtite came from shallow magma chambers in the middle-upper crust, formed by the mixture of mantle-derived magma and acid magma derived from the crustal partial melting; and the chilled border enclaves came from the border fragments of early intrusive bodies.
基金UGC-Dr.D.S.Kothari Postdoctoral FellowshipNo.F.4-2/2006(BSR)/ES/20-21/0005supported under a research grant[Mo ES/P.O.(Geo)/101(v)/2017]to SK。
文摘The field and microstructural features coupled with mineral chemical data from microgranular enclave(ME)and host Mesoproterozoic Kanigiri granite(KG)pluton of Nellore Schist Belt(NSB),Southeastern India,have been documented in order to infer the likely processes responsible for the origin and evolution of ME and host KG magma.The ME and host KG bear the same mineral assemblages barring the KG which does not contain amphibole;however,they are modally disequilibrated.The ME in KG is originated due to multiple intrusions of ME magmas into the crystallizing host KG magma chamber.Field and textural features indicate the dynamic magma flow,mingling,and undercooling of the ME against a relatively cooler surface of host KG magma.The presence of NSB country rock xenoliths and its diffuse boundaries suggest the intrusive relation and marginal assimilation by the intruding KG magma.The occasional cumulate texture in the ME appears to have formed by the accumulation of early-formed minerals that crystallized rapidly in the ME magma globules.The ME shows the magmatically deform features developed due to the flowage and erosion by the subsequent intrusions of ME magma pulses into the crystallizing host KG magma chamber.The ME amphiboles show unusual composition as ferro-edenitic hornblende to potassian-hastingsitic hornblende,that crystallized in the subalkaline-alkaline transition,low fO_(2)(reducing to mildly oxidizing)magma.The unusual extremely low Mg/Mg+Fe^(t)=0.015(avg.)of ME amphiboles may be related to the changing physico-chemical(P,T,fO_(2),and H_(2)O)condition of the ME magma or they might have crystallized in equilibrium with more evolved KG magma.The KG(FeOt/MgO=37.04,avg.)and ME(FeO~t/MgO=77.72,avg.)biotites are siderophyllite,and buffered between QFM and NNO syn-crystallizing in the water undersaturated(H_(2O)≈3.58 wt.%in KG;≈3.53wt.%in ME),alkaline anorogenic(A-type)host magmas that were emplaced at mid-crustal(4–5 kbar;17 km)depth.Field,microtextural and mineral chemical evidences suggest that the alkaline KG magma originated from crustal source and evolved through synchronous fractionation,mixing,and mingling with coeval ME magmas in the KG magma chamber.
基金supported by the National Science Foundation of China(40930419)Special Research Funding for the Public Benefits Sponsored by MLR (200911007–12)+2 种基金Research Program of Yunnan Tin Group (2010–04A)Geological Investigation Program by CGS (1212011120994)the Fundamental Research Funds for the Central Universities(2–9–2010–21)
文摘Many igneous rocks distribute in Gejiu tin polymetallic ore-field at Yunnan province, rocks including basalt, gabbro, mafic microgranular enclaves, granites (porphyritic granite and equigranular granite) and akaline rocks. The ages of the granites and akaline rocks which are considered to have genetic connecting with the mineralization have been comfirmed, but the gabbro- mafic microgranular enclaves-granite assemblage's ages are still unknown. By means of LA-ICP-MS zircon U-Pb dating, the data of Shenxianshui equigranular granite, the mafic microgranular enclave in Jiasha area, the host rock of the mafic microgranular enclaves and the Jiasha gabbro are around ~80 Ma. Besides the above mentioned data, a group of new ages at ~30 Ma were discovered in this study, which is from gabbro and mafic microgranular enclaves. Based on the previous data and the new data gained this time, we suggest the major geochronology framework of the magmatism and mineralization events in Gejiu area is ~80 Ma, which is consistent with the Late Cretaceous magmatism and mineralization events in the whole southeast Yunnan and west Guangxi area and they were suggested to belong to the same geotectonic setting in late Yenshannian. And the new ages of the ~30 Ma obtained in this study is considered to represent a responding to the complicate tectonic evolution history of the Tibetan orogenic events in Cenozoic.
文摘LA-ICP-MS zircon U-Pb dating has revealed that the Huangyangshan pluton in Eastern Junggar was formed at 311±12 Ma,and that microgranular enclaves were formed at 300±6 Ma;both ages are very consistent within errors.It is the first time that the microgranular enclaves age in Kalamaili area was determined.Petrochemistry and geochemistry research shows the characteristics of host rock as follows:
文摘In this contribution,detailed field descriptions together with petrographic and bulk-rock major,trace and rare earth elements(REE)data are used to constrain the origin and geodynamic setting of the mafic magmatic enclaves(MMEs)recently discovered within the Pan-African Ngaoundal pluton,Adamawa area,central Cameroon.The investigated MMEs are dark-colored with chilled margins,and display medium to coarse-grain igneous textures.The mineral assemblage is either dominated by K-feldspar and carbonate(group Ⅰ),or by amphibole and plagioclase(group Ⅱ),though the overall mineral phases made of amphibole,plagioclase,K-feldspar,and biotite are similar to that of their host syenite but in different proportions.The MMEs in Ngaoundal area are foid-gabbro in composition with SiO_(2) contents ranging between 41.52% and 43.74% and are contiguous with their host granitoids of intermediate composition(SiO_(2)=57.52% to 58.98%).The host granitoid rocks are metaluminous,and belong to the shoshonitic series.Petrographic and geochemical data have revealed that the Ngaoundal MMEs derived from rapid cooling of hot injected lithospheric mantle-derived magma within cooler host granitoids magma and were emplaced in the intraplate geodynamic setting.
文摘Recent eruption of Unzen Volcano in 1991-1995 caught attention of scientists all over the world because of disastrous character of previous one in 1792. Intrusion of andesitic magma to the chamber with rhyolitic magma is proposed to be a trigger for these eruptions. T-P-X parameters of two end-member magmas have been estimated several times, but usually estimations are based on phenocrysts assemblages. New results of this research are based on mafic enclaves and groundmass. These results are significant for magma mixing and mingling theory.
基金funded by the National Key Research and Development Program of China from the Ministry of Science and Technology of China(Grant No.2017YFC0601301)National Natural Science Foundation of China(Grant No.41472055)the China Geological Survey(Grant No.DD20160201-01)。
文摘The petrology, geochronology and geochemistry of the mafic enclaves in the Mid-Late Triassic Jiefangyingzi pluton from Chifeng area, southern Inner Mongolia, in China are studied to reveal their petrogenetic relationship with the host pluton. Furthermore, the coeval magmatic assemblage and its petrogenesis on the northern margin of the North China craton(NCC) are studied synthetically to elucidate their tectonic setting and the implications for the destruction of the NCC. Zircon U-Pb dating reveals that the mafic enclaves formed at 230.4 ± 2.2 Ma, which is similar to the age of the host pluton. The most basic mafic enclaves belong to weak alkaline rocks, and they display rare earth element(REE) and trace element normalized patterns and trace element compositions similar to those of ocean island basalt(OIB). In addition, they have positive εNd(t) values(+3.84 to +4.94) similar to those of the Cenozoic basalts on the northern margin of the NCC. All of these geochemical characteristics suggest that the basic mafic rocks originated from the asthenosphere. Petrological and geochemical studies suggest that the Jiefangyingzi pluton and the intermediate mafic enclaves were formed by the mixing of the asthenosphere-derived and crust-derived magmas in different degrees. The Mid-Late Triassic magmatic rocks on the northern margin of the NCC could be classified into three assemblages according to their geochemical compositions: alkaline series, weak alkaline–sub-alkaline series and sub-alkaline series rocks. Petrogenetic analyses suggest that the upwelling of the asthenosphere played an important role in the formation of these Mid-Late Triassic magmatic rocks. Basing on an analysis of regional geological data, we suggest that the northern margin of the NCC underwent destruction due to the upwelling of the asthenosphere during the Mid-Late Triassic, which was induced by the delamination of the root of the collisional orogeny between Sino-Korean and Siberian paleoplates in Late Permian.
基金This paper is funded by Ministry of Land and Mineral Resources (Nos. DKD2001001, 2001010204 and 20001010201).
文摘In this paper, we present the occurrence and mineral components of the enclaves firstly discovered in the Cenozoic Pulu volcanic rocks in west Kunlun Mountains, and propose that the enclave is accumulated by fractional crystallization within high-level magma chamber. In addition, the chemical compositions of its primary magma are calculated. The calculated compositions are similar to those of the Kangxiwa volcanic rocks that belong to the same volcanic belt in the Pulu volcanic region, suggesting their origin from the same source region. However, the temperatures and oxygen fugacity of magmas at high-level magma chamber decreased along with fractional crystallization.
基金financially supported by the Seluk University Scientific Research Projects Coordination (Project No: 2004/37)
文摘The Late Cretaceous Uckapth Granitoid including mafic microgranular enclaves intruded into metapelitic and metabasic rocks, and overlain unconformably by Neogene ignimbrites in the Ni^de area of Turkey. It is mostly granite and minor granodiorite in composition, whereas its enclaves are dominantly gabbro with a few diorites in composition. The Uckapdl Granitoid is composed mainly of quartz, K-feldspar, plagioclase, biotite, muscovite and minor amphibole while its enclaves contain mostly plagioclase, amphibole, minor pyroxene and biotite. The Uckapth Granitoid has calcalkaline and peraluminous (AJCNK= 1.0-1.3) geochemical characteristics. It is characterized by high LILE/HFSE and LREE/HREE ratios ((La/Lu)N 3-33), and has negative Ba, Ta, Nb and Eu anomalies, resembling those of comsion granitoids. The {)fkaplh Granitoid has relatively high STSr/S6Sr0) ratios (0.711189--0.716061) and low eNd(t) values (-5.13 to -7.13), confirming crustal melting. In contrast, the enclaves are tholeiitic and metaluminous, and slightly enriched in LILEs (K, Rb) and Th, and have negative Ta, Nb and Ti anomalies; propose that they were derived from a subduction-modified mantle source. Based on mineral and whole rock chemistry data, the Uckapth granitoid is H-(hybrid) type, post-collision granitoid developed by mixing/mingllng processes between crustal melts and mantle-derived mafic magmas.
文摘This work focused on the prediction modeling of Cerrado occurrences in the Atlantic Rainforest predominance in the São Paulo Metropolitan Region (SPMR), the fourth largest urban area, in the city of Guarulhos, southeastern Brazil. The methodology was based on the selection of records of occurrence of Cerrado in georeferenced databases, thematic maps of geoenvironmental layers, and modeling of the distribution of species through the MaxEnt tool. Besides that, field research confirmed the presence or not of the species in the areas with a high probability of occurrence of Cerrado (≥0.7). As a result, the model observed a great capacity for the prediction of the occurrence of Cerrado in Ecotonal and anthropic regions (AUC = 0.82), revealing important hotspots such as relics from the past or Cerrado enclaves of high biodiversity. The work also points priority areas for the conservation and preservation of this increasingly endangered biome.
文摘The Mako area, located in eastern Sénégal</span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">,</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"> constitute</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">s</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"> a segment of Paleoproterozoic (Birimian) formations of the Kédougou-Kéniéba Inliers (KKI) in the western part of the West African craton.</span></span></span><span><span><span style="font-family:""> </span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">The basic volcanism of the Birimian formations of the KKI has long been considered to be related to a single magmatic event associated with a Mid Oceanic Ridge Basalts (MORB) setting.</span></span></span><span><span><span style="font-family:""> </span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">The aim of this paper is to demonstrate on the basis of the architectural characteristics of the granitoids dark enclaves, the occurrence of at least two distinct phases of basic Magamtism in the Birimian of the KKI.</span></span></span><span><span><span style="font-family:""> </span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">The methodology consists of a cartography, a petrographic and architectural characterization of the dark enclaves within the Mako granitoids, in order to constrain their spatial and temporal relationships with the granitic magma. The results obtained are compared with those of the bibliography. We have pinpointed two types of enclaves depending on their shapes and the characteristics of their edge with the enclosing rocks: angular enclaves with straight edges (ante-granitoids) and the soft enclaves with uneven edges (syn-granitoids).</span></span></span><span><span><span style="font-family:""> </span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">The enclaves with straight and well-defined rectilinear edges (ante-granitoids) would be linked to a basic magma which is already consolidated before being fragmented, torn and carried away as enclaves in the granitoids. These enclaves would come from enclosing outcrops of metabasalts and metagabbros which are locally cross-cut</span></span></span><span><span><span style="font-family:""> </span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">by the granitoids.</span></span></span><span><span><span style="font-family:""> </span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">The soft enclaves with uneven edges (syn-granitoids) were co-magmatic and not solid during their incorporation into the granitoids. They come from a basic magma which is contemporaneous to the granitic one.</span></span></span><span><span><span style="font-family:""> </span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">Thus, the occurrence of two generations of dark enclaves </span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">is</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"> related to</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">,</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"> at last, two different phases of basic magmatism in the Birimian formations of the KKI.
基金Supported by National Natural Science Foundation of China (Grant Nos. 40625005 and 40821002)National Basic Research Program of China (Grant No. 2006CB403501)
文摘We report the zircon Hf-O isotopic data for mafic enclaves from the Taihang Yanshanian intermediate to felsic plutons, and use them, along with the petrological, whole-rock chemical and Nd-Sr isotopic data, to reveal the petrogenesis of mafic enclaves. Mafic enclaves show magmatic textures and are finer-grained than host rocks. In places they are highly elongated due to stretching within the partially crystallized, convective felsic magma, but show no solid-state deformation. These data suggest that mafic enclaves and host rocks were co-existing, but compositionally distinct magmas. The mafic enclaves contain abundant hydrous minerals such as hornblende and biotite, with pyroxene relict being surrounded by hornblende reaction rim. Plagioclase xenocrysts from mafic enclaves show a complicated compositional and textural disequilibrium. Comparison between mafic enclaves and the immediate host rocks suggests that the two rock units are compositionally correlated. The εNd values of mafic enclaves are generally higher than the host rocks, though the Sr isotopic ratios of the two rock units are indistinguishable. Zircons from a single enclave sample show a significant variation in Hf isotopic compositions, with εHf = -10―-22, suggesting an origin through magma mixing between mafic and felsic magmas. This is supported by the relatively large variation of zircon O isotopic ratios (δ 18O = 5.5‰- 7.8‰) of the mafic enclaves. The petrogenesis of mafic enclaves could be described as below. Evolved basaltic magma (via fractionation of olivine and pyroxene) first mixed with crustally derived granitic melts in depths, forming a hybrid magma; then the hybrid magma broke up into discrete lumps upon entering the above felsic magma. Subsequently, the enclave-forming magma experienced a double mechanical transfer of plagioclase, and inward chemical transfer of fluid and Na, P, Y, Nb and Pb at the contacts with host felsic magmas.
基金Project supported by the National Natural Science Foundation of China (Grant No. 49632080).
文摘There are three types of zircon (i.e. Zircon A, Zircon B and Zircon C) in the microgranitoid enclaves from the Qingtian granite. Zircon A is of the smallest Ipr, Ipy and Iel values with the largest range of variations; Zircon C is of the largest Ipr, Ipy and Iel values with the smallest range of variations; and Zircon B is intermediate among the three types. The microprobe analysis of zircon demonstrates that the contents of trace elements (Hf, U, Y, Th) increase progressively with larger and larger variation from Zircon A through Zircon B to Zircon C. These characters snggest that the three types of zircon in the enclaves may have formed successively during the cooling mess of enclave magma, corresponding to different sites along with the intrusion of enclave magma. Because of positive correlations of the UO2/HfO2ratio with Ipr, the Th02/Y203 ratio with Ipy, and the UO2/(ThO2+Y203) ratio with Iel, it is suggested that the variation in zircon typology is caused by selective substitution of trace elements on different surfaces of zircon. On the basis of enclave petrology and zircon typomorphism, it is believed that the enclave magma may be generated from partial melting of residual materials in deep regions where the granitic magma has been extracted.
基金supported by the Iran National Science Foundation(INSF)(Grant No.98012578)projects from the National Natural Science Foundation of China(Grant Nos.41473033,41673031)。
文摘The Hesar pluton in the northern Urumieh-Dokhtar magmatic arc hosts numerous mafic-microgranular enclaves(MMEs).Whole rock geochemistry,mineral chemistry,zircon U-Pb and Sr-Nd isotopes were measured.It is suggested that the rocks are metaluminous(A/CNK=1.32-1.45),subduction-related I-type calc-alkaline gabbro to diorite with similar mineral assemblages and geochemical signatures.The host rocks yielded an U-Pb crystallization age of 37.3±0.4 Ma for gabbro-diorite.MMEs have relatively low SiO_(2) contents(52.9-56.6 wt%)and high Mg^(#)(49.8-58.7),probably reflecting a mantle-derived origin.Chondrite-and mantle-normalized trace element patterns are characterized by LREE and LILE enrichment,HREE and HFSE depletion with slight negative Eu anomalies(Eu/Eu^(*)=0.86-1.03).The host rocks yield(^(87)Sr/^(86)Sr)_(i) ratios of 0.70492-0.70510,positive ε_(Nd)(t)values of+1.55-+2.06 and T_(DM2)of 707-736 Ma,which is consistent with the associated mafic microgranular enclaves((^(87)Sr/^(86)Sr)_(i)=0.705014,ε_(Nd)(t)=+1.75,T_(DM2)=729 Ma).All data suggest magma-mixing for enclave and host rock formation,showing a complete equilibration between mixed-mafic and felsic magmas,followed by rapid diffusion.The T_(DM1)(Nd)and T_(DM2)(Nd)model ages and U-Pb dating indicate that the host pluton was produced by partial melting of the lower continental crust and subsequent mixing with injected lithospheric mantlederived magmas in a pre-collisional setting of Arabian-Eurasian plates.Clinopyroxene composition indicates a crystallization temperature of~1000℃ and a depth of~9 km.
基金supported by the National Natural Science Fund of China(NSFC)under the project“Civil Rights,Collective Welfare and Local Finance:A Natural Experiment of the Real Estate Market”(Grant No.71973080).
文摘Paired assistance is an important means for developed regions to help lessdeveloped regions achieve common prosperity.Despite its advantages,governmentmandated paired assistance tends to be less effective due to the lack of economic incentives for assisting localities.Therefore,local governments in China have explored an incentivecompatible paired assistance model.Based on the paired assistance between cities in the Pearl River Delta(PRD)region and the eastern,western and northern parts of Guangdong Province,this study designed a natural experiment for the network relationship of paired assistance.Empirical results based on industrial and commercial registration data and land transfer data indicate that paired assistance has enhanced bilateral investment linkages,and that the inter-regional benefit sharing mechanism has incentivized assisting localities to provide paired assistance.Our heterogeneity analysis reveals that a shorter distance between assisting and beneficiary localities may lead to better results of paired assistance.This study contributes to the understanding of incentive mechanisms for local government cooperation and offers insights for balancing regional development and achieving common prosperity.
基金the Scientific Development Fund of Peking UniversityZhongguancun Testing Fund Beijing,Chjna
文摘The data of REE for the dioritic enclaves of the second intrusive bodies and for apatite,sphene,magnetite,zircon amphibole,biotite,plagioclase,and K-feldspar of the host rock are systematically reported andthe features of their compositions,overall characteristics and changing regularities,and their petrogenetic signifi-cance are discussed.The characteristics of the compositiom of the mineral rare-earth elements and their changingregularities for the Fangshan Rock Body show that there is a cognate evolution relation between the enclavesand the rock body.It is oonsidered that the dioritic enclaves might be the product derived from the earlycrystallization of homogeneous magma.
文摘The major and trace elements and Sr-Nd-Pb isotopes of Miocene host granitoid rocks and their mafic microgranular enclaves(MMEs) were studied to understand the petrogenesis of MMEs in the Kashan complex, which is part of the Urumieh-Dokhtar magmatic belt(Iran). The host rocks consist of quartz-diorite and tonalite associated with a dioritic intrusion. The enclaves show microgranular texture and the same mineralogy as their respective host with plagioclase, quartz and biotite. MMEs have a diorite to quartz-diorite composition and show geochemical characteristics mostly between their granitoid host and the diorite intrusion. Chondrite-normalized REE patterns of all samples are moderately fractionated [(La/Yb)N=2.1 to 12.9]. The MMEs display in part small negative Eu anomalies(Eu/Eu*=0.54 to 0.99), with enrichment of LILE and depletion of HFSE. The enclaves show emplacement depth of -4 to 6 km which is comparable with the host rocks. Moreover, the Hornblende-plagioclase equilibrium temprature of MMEs yields average temperatures of 795℃ which is slightly higher than the host ones. Identical mineral compositions and Nd-Sr-Pb isotopic features of MME-host granitoid pairs indicate interactions and parallel evolution of MME and enclosing granitoid in the Kashan plutons. Additionally, the geochemical and isotopic investigations of host and dioritic intrusions suggest a common source for their genesis. A thermal anomaly induced by underplated basic magma into a hot crust would have caused partial melting in the lower crust to generate Kashan granitoid rocks.
基金the grants of the National Key Project for Basic Research of China(No.2002CB412600)the National Natural Science Foundation of China(Nos.40172025,40103003,49802005,49772107,40473020)the key project on the Tibetan Plateau of the Ministryof Land and Resources of China(No.20010102401).
文摘Abundant mafic microgranular enclaves (MMEs) extensively distribute in granitoids in the Gangdise giant magmatic belt, within which the Qüxü batholith is the most typical MME-bearing pluton. Systematic sampling for granodioritic host rock, mafic microgranular enclaves and gabbro nearby at two locations in the Qüxü batholith, and subsequent zircon SHRIMP II U-Pb dating have been conducted. Two sets of isotopic ages for granodioritic host rock, mafic microgranular enclaves and gabbro are 50.4±1.3 Ma, 51.2±1.1 Ma, 47.0±l Ma and 49.3±1.7 Ma, 48.9±1.1 Ma, 49.9±1.7 Ma, respectively. It thus rules out the possibilities of mafic microgranular enclaves being refractory residues after partial melting of magma source region, or being xenoliths of country rocks or later intrusions.Therefore, it is believed that the three types of rocks mentioned above likely formed in the same magmatic event, i.e., they formed by magma mixing in the Eocene (c. 50 Ma). Compositionally, granitoid host rocks incline towards acidic end member involved in magma mixing, gabbros are akin to basic end member and mafic microgranular enclaves are the incompletely mixed basic magma clots trapped in acidic magma. The isotopic dating also suggested that huge-scale magma mixing in the Gangdise belt took place 15-20 million years after the initiation of the India-Asia continental collision, genetically related to the underplating of subduction-collision-induced basic magma at the base of the continental crust. Underplating and magma mixing were likely the main process of mass-energy exchange between the mantle and the crust during the continental collision, and greatly contributed to the accretion of the continental crust, the evolution of the lithosphere and related mineralization beneath the portion of the Tibetan Plateau to the north of the collision zone.