Island-arc geochemical signatures of Cenozoic alkali-rich intrusive rocks from western Yunnan and their implication

Alkali-rich intrusive rocks in western Yunnan were derived from an enriched lithospheric mantle (EMⅡ) source. The data available indicated they are alkali-rich (K-2ONa-2O>8wt%) and shoshonitic. Although formed in a within-plate environment they exhibit signatures of arc magmatic rocks, such as high amounts of LILE and LREE relative to the HFSE and HREE, and thus high Ba/Nb, Ba/Zr, Sr/Y, La/Yb ratios as well as mimic chondrite-normalized REE and primitive mantle-normalized trace element patterns of subducted sediments, and they fall in the collision- or arc-related tectonic setting field on all discrimination diagrams. This might suggest the enrichment be related to the substantial extent of sediment contamination by the Mesozoic Tethyan subduction processes.

Alkali-rich intrusive rocks in the Qinghai-Xizang Plateau and its vicinities as exemplified by Kuganzi and Taihe plutons

The alkali-rich intrusive rocks in the Qinghai-Xizang Plateau can be divided into two series in terms of dark-colored rock-forming minerals, petrochemical composition and trace elements: i ) sodic alkaline series rocks consisting of alkaline rocks and alkali granite which contain dark-colored minerals, such as aegirine augite, aegirine and riebeckite, and being petrochemically enriched in alkali and sodium but low in Ca, Sr and Ba; ii ) potassic alkaline series rocks consisting of alkaline rocks and alkali granite which contain non-alkaline dark-colored minerals (diopside, edenite), and being petrochemically enriched in alkali, K and Ca with high abundances of Sr and Ba.

Spatial Distribution and Ages of Alkaline Intrusive Rocks in China and Related Tectonics

: On the basis of the geological data from 220 intrusions and isotope ages of 115 rock bodies, the paper discusses the distribution of 18 alkaline intrusive rock belts along deep faults and their relations to the plate tectonic activity. In view of the presence of a large amount of Variscan alkaline rocks of deep-source character, it is inferred that mantle diapirism was very strong in China during the Variscan. Besides anorogenic and postorogenic alkaline granites, there also occur alkaline granites formed in the terminal orogenic stage when the regional tectonic activity was of compressional nature. Finally, the paper discusses the tectonic environment of the Maoniuping nordmarkite in Mianning county, Sichuan province, and the authors consider it to be a compressional environment originating after rift closing.

Petrogenesis of Adakitic Intrusive Rocksin Xu-Huai Area, Eastern China

The research of the petrology and the geochemistry of the Mosozoic intrusive rocks in Xu-Huai area indicated that they are mainly composition of dioritic porphyry and monzodioritic porphyry, and the features of the petrology and geochemistry of the Mosozoic intrusive rocks are extremely similar to those with the typical adakites. Combined with the petrography and the testimated results of the deep-seated xenoliths in the intrusive rocks, it indicates that the petrogenesis of the Mosozoic intrusive rocks could be resulted from the partial melting of amphibole-bearing garnet pyroxenite and garnet amphibolite in lower continental crust in this area.

Distributive characteristics of reservoirs and exploration potential associated with intrusive rocks of Yingcheng Formation in Yingtai rift depression, NE China

Petroleum geologists have paid great attentions to the volcanic reservoirs of Songliao Basin in NE Chi- na. There are plenty of subvolcanic rocks in the Songliao Basin accompanying the Early Cretaceous Yingeheng Formation. The logging data show the good reservoir potential of these intrusive rocks but the distribution char- acteristics and formation mechanisms of these reservoirs are not clearly understood. Based on the previous stud- ies by using coring, cuts and logging data of Yingtai rift depression, the reservoirs＇ characteristics of intrusive rocks are presented. There are two types of intrusive rocks namely the syenodiorite-porphyrite and diabase which occur as laccolith and/or sill, both having the characteristics of low gamma and high density with little primary porosity and permeability. The prevalent reservoir porosity is the secondary porosity, such as spongy/cavernous pore, tectonic fracture. The laboratory data of porosity of diabase can reach 6.7%, but the permeability is less than 0.6 x 10-3μm2, median pressure is high, indicating that the pore throat of this kind reservoir is small. The maximum logging porosity is about 12%. The change of porosity does not correlate to the buried depth. It is the major significant differences in the distributive characteristics compared to the normal sedimentary rock reservoirs. Most of intrusive rocks underwent alteration diagenesis whilst some were subjected to precipitation diagenesis. The spongy and cavernous pore can be formed during the alteration processes of plagioclase to illite and pyroxene to chlorite. The secondary porosity is greatly correlated with the alteration intensity of matrix, pla- gioclase and pyroxene. There are pyroxenes and more plagioclases in diabase, which cause the higher alteration intensity than the syenodiorite-porphyrites in the same acid fluid. So the porosity of diabase is higher than that of syenodiorite-porphyrites. The top or/and bottom part of intrusive rocks develop the higher porosity. Because those parts are easy to contact formation fluid, and the shrink fractures give the more surface for reaction be- tween fluid and rock. The porosity of intrusive rocks is same to the volcanic rocks in Yingtai rift depression and Xujiaweizi rift depression which bear the prolific gas. It suggests good reservoir potential. Intrusive rocks are hosted by the dark mudstone which indicates semi-deep and deep lake facies belt.

Geochronology and geochemistry of early Paleozoic intrusive rocks from the Khanka Massif of the Russian Far East

The Russian Far East and Northeast（NE）China are located in the eastern part of the Central Asian Orogenic Belt（CAOB）,which consists of a series of micro-continental massifs including the Erguna,Xing’an,Songnen–Zhangguangcai Range,Bureya,Jiamusi,and Khanka massifs.The Khanka Massif is located in the easternmost part of the CAOB,mainly cropping out in the territory of Russia,with a small segment in NE China.To the north and west of the Khanka Massif are the Jiamusi and Songnen–Zhangguangcai Range massifs,respectively.The boundary between these massifs is marked by the Dunhua–Mishan Fault.To the south lies the North China Craton,and to the east is the Sikhote–Alin Orogenic Belt separated by the Arsenyev Fault.However,the early Paleozoic evolution and tectonic attributes of the Khanka Massif are debated.These conflicting ideas result from the lack of systematic research on early Paleozoic igneous rocks from the Russian part of the Khanka Massif.It is generally accepted that the CAOB represents the largest known Phanerozoic accretionary orogenic belt.However,questions remain concerning the nature of the deep crust beneath the Khanka Massif,and whether Precambrian crust exists within the massif itself. In this paper,we report new zircon U–Pb ages,Hf isotopic data,and major-and trace-element compositions of the early Paleozoic intrusive rocks from the Khanka Massif of the Russian Far East,with the aim of elucidating the early Paleozoic evolution and the tectonic attributes of the Khanka Massif,as well as the nature of the underlying deep crust. New U–Pb zircon data indicate that early Paleozoic magmatism within the Khanka Massif can be subdivided into at least four stages:;02 Ma,;92 Ma,462–445 Ma,and;30 Ma. The;02 Ma pyroxene diorites show negative Eu anomalies,and the;92 Ma syenogranites,intruding the;02 Ma diorites,show positive Eu anomalies.These observations indicate that the primary parental magmas of these rocks were derived from different origins. The 462–445 Ma magmatism is made up of syenogranites and tonalites.The;45 Ma Na-rich tonalites contain low REE concentrations,and are enriched in Eu and Sr.These observations,together with the positiveεHf（t）values,indicate that they were derived from magmas generated by partial melting of cumulate gabbros. The;30 Ma I-type granodiorites and monzogranites from the northern Khanka Massif,and the A-type monzogranites from the central Khanka Massif display zirconεHf（t）values ranging from–5.4 to+5.8.This suggests that they formed from magmas generated by partial melting of heterogeneous lower crustal material. Zircon Hf isotopic data reveal the existence of Precambrian crustal material within the Khanka Massif.The geochemistry of the Middle Cambrian intrusive rocks is indicative of formation in an extensional setting,while Late Cambrian–middle Silurian magmatism was generated in an active continental margin setting associated with the subduction of a paleo-oceanic plate beneath the Khanka Massif.Regional comparisons of the magmatic events indicate that the Khanka Massif has a tectonic affinity to the Songnen–Zhangguangcai Range Massif rather than the Jiamusi Massif.

Discussion on the interrelationship among Cu-Ni sulfide deposits,mafic volcanic rocks and intrusive rocks in the Sipu region,northern Guangxi,China

The Sipu region of North Guangxi is located in the southwest of the "Jiangnan Ancient Land",where there are developed the oldest stratum in southern China,the Proterozoic Sipu Group,and there are also largely ex-posed mafic intrusive rocks,mafic volcanic rocks and copper-nickel sulfide deposits.Both mafic intrusive rocks and volcanic rocks are rich in MgO(6.52%-26.39%),but poor in K2O(0.05%-1.00%) and TiO2(0.33%-0.89%).They are also rich in trace elements such as Rb and Ba while poor in Ta,Nb and the like.Both of them have medium con-tents of rare-earth elements,30.26×10-6-126.71×10-6,in which LREEs are slightly rich with ΣLREE/ΣHREE of 1.35-2.46,δEu 0.79-1.33,displaying weak or no δEu anomaly,with the same geochemical features.The right-inclined distribution patterns and the features show that magma would be formed at the comagmatic un-diagenetic stage.All studies show that mafic intrusive rocks and volcanic rocks are the products of the same source region evolving in different stages and times.The copper-nickel sulfide deposits are characterized by liquation,crys-tallization and fractionation of mafic rocks,and have some interrelations with mafic intrusive rocks and volcanic rocks with respect to magmatic genesis.

Geology and Geochemistry of Reworking Gold Deposits in Intrusive Rocks of China-I.Features of the Intrusive Rocks

Most gold deposits in intrusive rocks were formed as a result of reworking processes.The intrusive rocks containing gold deposits and consisting of ultramafic-mafic, intermediate-acid and alkaline rocks of the Archean, Proterozoic, Caledonian, Hercynian and Yenshanian periods occur in cratons, activated zones of cratons and fold belts. Among them, ultramafic-mafic rocks, diorite, alkaline rocks, and anorthosite are products of remelting in the mantle or mantle-crust or mantle with crustal contamination. However, auriferous intermediate-acid rocks are products of metasomatic-remelting in auriferous volcanic rocks or auriferous volcano-sedimentary rocks in the deep crust.

Three Alkali-Rich Intrusive Rock Belts Newly Discovered in the Mt.Kunlun-Mt. Altun Region, Xinjiang, China

The newly discovered three alkali\|rich intrusive rock belts in the Mt. Kunlun Mt. Altun region of southern Xinjiang are the Lapeiquan\|Yitunbulak alkali\|rich intrusive rock belt, the Gez\|Taxkorgan alkali\|rich intrusive rock belt and the Beilisai\|Abulash alkali\|rich intrusive rock belt. The former two belts were formed during the Yanshanian period, and the third one was formed during the Himalayan period, which is the youngest alkali\|rich intrusive rock belt in China. The discovery of the alkali\|rich intrusive rock belts is of great significance in shedding light on the history of tectono\|magmatic activities in this region.

Geochemistry of Alkali-rich Igneous Rocks of Northern Xinjiang and Its Implications for Geodynamics

Five nearly E-W-trending alkali-rich igneous rock belts are distributed from north to south in northern Xinjiang, and they are composed mainly of riebeckite, K-feldspar granite and high-K and medium-K calc-alkaline volcanic rocks and shoshonite. They were mainly emplaced or erupted between the Carboniferous and Permian. The compositions of Sr, Nd, Pb, and O isotopes imply that their principal resource materials are derived from the upper mantle or juvenile crust, indicating obvious continental growth in the Phanerozoic. The trace element association implies that their tectonic settings are within plate and volcanic arc for alkali-rich granites, and post-collisional are, late oceanic are and continental are for alkali-rich volcanic rocks. An archipelago model was suggested for the tectonic evolution in northern Xinjiang. It can be named the central-Asia-type orogeny, which is different from the so called circum-Pacific ocean-continent-type tectonics or the Alpine-Himalayan continent-continent-collisional orogeny.

Permian tectonic evolution and continental accretion in the eastern Central Asian Orogenic Belt:A perspective from the intrusive rocks

The tectonic evolution and history of continental accretion of the eastern Central Asian Orogenic Belt(CAOB)are not yet fully understood.In this study,we investigate Permian intrusive rocks from the Jiamusi Block of the eastern CAOB to constrain the tectonic evolution and continental accretion of this region during the late-stage evolution of the Paleo-Asian Ocean.Our new data show that Early Permian gabbro-diorites were derived from the partial melting of depleted mantle metasomatized by oceanic-slab-released fluids.Middle Permian adakitic granites have low Na2O and MgO and high K2O contents,indicating a thickened-lower-crust source.Late Permian S-type granites were derived from the partial melting of continental crust.A compilation of the available geochronological data for Permian intrusive rocks(including adakitic and A-,S-,and I-type granites and mafic rocks)from the eastern CAOB reveals that the A-type granites formed mainly during the Early–Middle Permian,S-type and adakitic granites mostly during the Middle–Late Permian,and I-type granites and mantle-derived mafic rocks throughout the Permian.The A-type granites,which are proposed to have been sourced from thinned continental crust,indicate an extensional setting in the eastern CAOB during the Early Permian.The Middle–Late Permian adakitic granites imply a thickened continental crust,which indicates a compressional setting.Therefore,the eastern CAOB underwent a transition from extension to compression during the Middle Permian,which was probably triggered by the late-stage subduction of Paleo-Asian oceanic crust.Considering the petrogenesis of the intrusive rocks and inferred regional tectonic evolution of the eastern CAOB,we propose that vertical underplating of mantle-and oceanic-slabderived magmas contributed the materials for continental crust accretion.

Geochemistry of Platinum Group Elements in Mafic-Ultramafic Rocks of Xinjie Intrusion

The platinum group elements (PGE) in the mafic ultramafic suite in the Xinjie layered intrusion and associated basalts and syenites were analyzed using neutron activation techniques after fire assay preconcentration. On this basis, the geochemistry of the platinum group during the magmatic stage is discussed. With respect to PGE distribution, the Xinjie layered intrusion is similar to the Bushveld ferruginous ultramafic series and is distinct from komatiite and Alpine type peridotite. It is also similar to the Emeishan basalt in PGE characteristics, implying that the original magmas of them may be of the same type.

Pre-collision Granites and Post-collision Intrusive Assemblage of the Kelameili-Harlik Orogenic Belt

The main types of intrusive rocks in the Kelameili-Harlik Hercynian orogenic belt include calc-alkaline granites, diabase dykes, kaligranites and alkaline granites. Investigation in field geology, petrology, mineralogy and geochemistry shows that the calc-alkaline granites belong to the syntexis-type (or I-type) and were formed in a pre-collisional magmatic arc environment. In consideration of the fact that kaligranites have many features of alkaline granites with higher consolidation temperatures than the calc-alkaline granites and show a discontinuity of minor element and REE evolution in respect to the calc-alkaline granites, they could not have been derived by differentiation of magmas for the calc-alkaline granites, but are likely to have been generated in an environment analogous to that for alkaline granites. The triplet of basic dyke swarms, kaligranites and alkaline granites could be regarded as a prominent indication of the initial stage of post-collisional delamination and extension. These rocks might have originated from underplating and intraplating of mantle-derived magmas at varying levels with varying degrees of partial melting, mixing, and interchange of crustal and mantle materials

Geochemical Trace of Silicon Isotopes of Intrusions and Ore Veins Related to Alkali-rich Porphyry Deposits in Western Yunnan, China

Western Yunnan is the well-known polymetallic province in China. It is characterized by copper-gold mineralization related to Cenozoic alkali-rich porphyry. This paper analyzes the silicon isotope data obtained from four typical alkali-rich porphyry deposits based on the dynamic fractionation principle of silicon isotope. The study shows that the ore materials should originate mainly from alkali-rich magmas, together with silicon-rich mineralizing fluids. The process of mineralization was completed by auto-metasomatism, i.e. silicon-rich mineralizing fluids (including alkali-rich porphyry and wall-rock strata) replaced and altered the country rocks and contaminated with crustal rocks during the crystallization of alkali-rich magmas. Such a process is essentially the continuance of the metasomatism of mantle fluids in crust's mineralization. This provides important evidence of silicon isotopic geochemistry for better understanding the mineralization of the Cenozoic alkali-rich porphyry polymetallic deposits

Effects of water intrusion and loading rate on mechanical properties of and crack propagation in coal–rock combinations

Tackling the problems of underground water storage in collieries in arid regions requires knowledge of the effect of water intrusion and loading rate on the mechanical properties of and crack development in coal–rock combinations. Fifty-four coal–rock combinations were prepared and split equally into groups containing different moisture contents(dry, natural moisture and saturated) to conduct acoustic emission testing under uniaxial compression with loading rates ranging from 0.1 mm/min to 0.6 mm/min. The results show that the peak stress and strength-softening modulus, elastic modulus, strain-softening modulus, and post-peak modulus partly decrease with increasing moisture content and loading rate. In contrast, peak strain increases with increasing moisture content and fluctuates with rising loading rate. More significantly, the relationship between stiffness and stress, combined with accumulated counts of acoustic emission, can be used to precisely predict all phases of crack propagation. This is helpful in studying the impact of moisture content and loading rate on crack propagation and accurately calculating mechanical properties. We also determined that the stress thresholds of crack closure, crack initiation, and crack damage do not vary with changes of moisture content and loading rate, constituting 15.22%, 32.20%, and 80.98% of peak stress, respectively. These outcomes assist in developing approaches to water storage in coal mines, determining the necessary width of waterproof coal–rock pillars, and methods of supporting water-enriched roadways, while also advances understanding the mechanical properties of coal–rock combinations and laws of crack propagation.

Petrogenesis and Tectonic Implications of the Late Silurian–Early Devonian Bimodal Intrusive Rocks in the Central Beishan Orogenic Belt,NW China:Constraints by Petrology,Geochemistry and Hf Isotope

A large number of Late Silurian–Early Devonian intrusive rocks are distributed in the central Beishan orogenic belt(BOB).Tectonic setting of these intrusive rocks is of great significance to the study of the subduction and accretion of the Paleo-Asian Ocean.Previous studies show that most of the intrusive rocks in this region are S-type or A-type granitoids.In this study,we firstly reported the Late Silurian–Early Devoniandia bases,granodiorites on the southside of the Baiyunshan ophiolitic mélanges belt,as a part of Hongliuhe-Xichangjing ophiolitic mélanges belt(HXOMB).Zircon LA-ICP-MS U-Pb dating yields emplacement ages between 418 and 397 Ma,REE distribution patterns exhibit enriched LREE and flat HREE in the diabases,the discriminant diagrams show that the diabases have geochemical characteristics of intraplate basalt.The granodiorites in this paper present more like S-and A-type granitoids reported,showing the geochemical characteristics of syn/post-collision granites.Actually,the bimodal magmatic rocks are developed during Late Silurian–Early Devonian on both sides of the HXOMB,which are related to the tectonic background of the post orogeny extension.The diabases are tholeiitic with relative strong depletedεHf(t)(+8.1 to+13.0),which are mainly from relative depleted mantle.The granodiorites are calc-alkaline with relative slightly depletedεHf(t)(+0.7 to+5.6)and the lower Mg#and MgO contents(34.6–36.9,0.50 wt.%–1.19 wt.%respectively),reflecting the source characteristics of meta-basalt.Therefore,the remelting of juvenile crust may be the main way of continental crust accretion during Late Silurian–Early Devonian in the central BOB.

Petrological characteristics,geochemical feature and metallogenetic relation of alkaline-rich rocks in northwest of Yunan Province,China

The alkali-rich rocks, spreading along the suture zone of Jingsha River, refer to the alkali-rich porphyry rocks, which emplace during the Himalaya epoch in northwest of Yunnan Province, and consist of syenit, syenit porphyry, monzonite porphyry and granite porphyry. Petrological chemical analysis results suggest that silica is poor and aluminum is rich, and high potassium large ion lithophile elements （LILE）, light rare earth element （LREE） and Sr are obviously detracted in these rocks. High field strength elements （HFSE） and heavy rare earth element （HREE） are depleted, especially Nb, Ta, P and Ti. 8Eu： 0.09--1.64 shows that plagioclase does not appear fractional crystallization during the formation of alkali-rich rocks, t^348, H and O isotopes and Pb isotopes suggest that ore-forming fluid is derived from the mantle, and Pb is possibly mixed by mantle, wall rock and crust. The age of Pb in alkali-rich rocks is about 250-220 Ma. The age of alkali porphyry rock （dykes） varies from 30 Ma to 50 Ma. Alkali rocks have strong metallogenetic relation. Au mineralization is associated to the alkali magrnatic activities with a relatively high temperature, low pressure and high oxygen fugacity. However, copper mineralization is mainly associated with alkali-sub-alkali magmatic activities in a process of relatively low temperature, high pressure and lower oxygen fugacity.

Fluid Mechanics of Intrusives

The fluid mechanics of dike emplacement are analyzed using the translatory wave theory. The stress strain relations in the host rock are assumed linear and the fracture resistance of the host rock is assumed small. The resulting model is a flowing dyke progressing upwards to the surface with constant speed and a very small side slope. Apart from the topmost section, the form of the dyke is very close to the static form corresponding to the magma pressure in a no-flow situation. Two scales are found that control the flow, a width scale and a composite stiffness parameter for the host rock, representing the properties of the rock and the magma such as elasticity and viscosity. The theory explains a number of special features for dykes that are already known by researchers. It also adds two new points, the most interesting being that the composite stiffness of the rock can be estimated from field observations of the downwards widening angle of the dyke.

Isla San Pedro Nolasco as a Late Miocene intrusive record at the eastern margin of the Gulf of California:Insights from geological,geochemical and geochronological studies

Isla San Pedro Nolasco(ISPN)is a structural high bounded by inactive dextral oblique-slip faults in the east-central part of the Gulf of California rift zone and is composed of intrusive rocks not exposed on other Gulf of California islands.Here we present the reconnaissance results from geological mapping,as well as first geochemical and geochronological data for the ISPN intrusive complex.The intrusive rocks compose a sheet-like body of intermediate and felsic composition intruded by an intermediate and acidic dike swarm.All intrusive rocks(host and dikes)range in age from ca.9 Ma to 10 Ma(^(40)Ar/^(39)Ar)and show a hydrous ferromagnesian mineral association(amphibole and biotite)with a calc-alkalic and transitional affinity.This hydrated mineralogical association has not been recognized in the coeval rocks along the onshore western margin of the North American plate(coastal Sonora).However,such hydrous mineralogical association is found in the coeval rift transitional volcanic rocks from the Baja California Microplate at Santa Rosalía and Bahía de LosÁngeles–Bahía de LasÁnimas.The ISPN continental block,at least 40 km long,has been pulled apart by transtensional faulting of the late Miocene Gulf of California shear zone before the westward migration of the North America-Pacific plate boundary at ca.3–2 Ma.Eventually,ISPN became isolated as an island during the late Miocene flooding of the Gulf of California seaway.

MODELLING OF COMPOSITION OF MANTLE SOURCE FOR THE JIJIE ALKALINE-ULTRABASIC INTRUSIVE COMPLEX, LUFENG, YUNNAN

Based on the data on petrology and geochemisty for the Jijie alkaline-ultrabasic intrusive rock complex, this paper, by means of correlation, suggested that the average composition of melteigites with 10% olivine added (Fo=86) can be considered as the composition of the primary magma of the Jijie complex. This magma, whose composition is estimated from the incompatible element P2O5, was produced by 3%±partial melting of pyrolites. The results of Petrological Mixing Calculating showed that the mantle-source rocks of the Jijie complex are obviously depleted in incompatible elements.