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Calc-alkaline Series (calc-alkaline + series)
Selected AbstractsGenesis and Mixing/Mingling of Mafic and Felsic Magmas of Back-Arc Granite: Miocene Tsushima Pluton, Southwest JapanRESOURCE GEOLOGY, Issue 1 2009Ki-Cheol Shin Abstract The Middle Miocene Tsushima granite pluton is composed of leucocratic granites, gray granites and numerous mafic microgranular enclaves (MME). The granites have a metaluminous to slightly peraluminous composition and belong to the calc-alkaline series, as do many other coeval granites of southwestern Japan, all of which formed in relation to the opening of the Sea of Japan. The Tsushima granites are unique in that they occur in the back-arc area of the innermost Inner Zone of Southwest Japan, contain numerous miarolitic cavities, and show shallow crystallization (2,6 km deep), based on hornblende geobarometry. The leucocratic granite has higher initial 87Sr/86Sr ratios (0.7065,0.7085) and lower ,Nd(t) (,7.70 to ,4.35) than the MME of basaltic,dacitic composition (0.7044,0.7061 and ,0.53 to ,5.24), whereas most gray granites have intermediate chemical and Sr,Nd isotopic compositions (0.7061,0.7072 and ,3.75 to ,6.17). Field, petrological, and geochemical data demonstrate that the Tsushima granites formed by the mingling and mixing of mafic and felsic magmas. The Sr,Nd,Pb isotope data strongly suggest that the mafic magma was derived from two mantle components with depleted mantle material and enriched mantle I (EMI) compositions, whereas the felsic magma formed by mixing of upper mantle magma of EMI composition with metabasic rocks in the overlying lower crust. Element data points deviating from the simple mixing line of the two magmas may indicate fractional crystallization of the felsic magma or chemical modification by hydrothermal fluid. The miarolitic cavities and enrichment of alkali elements in the MME suggest rapid cooling of the mingled magma accompanied by elemental transport by hydrothermal fluid. The inferred genesis of this magma,fluid system is as follows: (i) the mafic and felsic magmas were generated in the mantle and lower crust, respectively, by a large heat supply and pressure decrease under back-arc conditions induced by mantle upwelling and crustal thinning; (ii) they mingled and crystallized rapidly at shallow depths in the upper crust without interaction during the ascent of the magmas from the middle to the upper crust, which (iii) led to fluid generation in the shallow crust. The upper mantle in southwest Japan thus has an EMI-like composition, which plays an important role in the genesis of igneous rocks there. [source] Geo,tectonic Position of Tin Polymetallic Mineralization Zone in the Southern Da Hinggan Mountains Area, Inner Mongolia, China: An Introduction to This Special IssueRESOURCE GEOLOGY, Issue 4 2001Shihua SUN Abstract: As a part of the main activities of Japan-China technical cooperation project, a test survey area, approximately 5,000 km2, was established for the implement of its geological and geochemical research program. A major mineralization zone called Huanggang,Ganzhuermiao,Wulanhaote Sn-Cu polymetallic mineralization zone is recognized in the southern Da Hinggan Mountains area. The southern half of this zone is known as the sole Sn-mineralization zone in North China. The survey area lies in this prominent zone. As the most of the papers presented in this issue have concerns to the geology and mineralization in this survey area, this report was prepared to introduce geo-tectonic situation of the Sn-Cu polymetallic mineralization zone in the Inner Mongolia orogenic belt. The belt is divided into four tectonic facies (from NW to SE); I: Wuliyasitai volcano-plutonic zone, II: Hegenshan ophiolite mélange zone, III: Sunitezuoqi volcano-plutonic zone, IV: Wenduermiao ophiolite mélange zone. The subject Sn-Cu polymetallic mineralization zone is situated in the southeastern part of the Sunitezuoqi magmatic zone. About this Sunitezuoqi magmatic zone, three geo-tectonic characteristics are pointed out. In late Carboniferous to early Permian period, subduction of Hegenshan oceanic crust occurred, which accelerated volcano-plutonic activities and brought about basic to intermediate volcanic rocks of tholeiitic to calc-alkaline series represented by Dashizhai Group in the Sunitezuoqi magmatic zone. Late Jurassic to early Cretaceous acidic rocks representing the most culminated volcanism and plutonism in Mesozoic era in the Da Hinggan Moutains area are distributed very extensively in and around the Sn-Cu polymetallic mineralization zone. The Proterozoic metamorphic basement rocks called Xilinhaote complex are distributed close to the mineralized area in the Sunitezuoqi magmatic zone. Although the real mineralization was known associated with Mesozoic acidic to intermediate volcano-plutonic activities, it is thought that the lower Permian Dashizhai volcanic rocks and pre-Cambrian basement rocks might have played certain significant role in the process respectively of extraction of elements and formation of the magma favorable for such mineralization in the Sunitezuoqi magmatic zone. It would be necessary to give further considerations to these three geological units in relation to the Sn-Cu polymetallic mineralization. [source] Geological and Geochemical Characteristics of the Hydrothermal Clay Alteration in South KoreaRESOURCE GEOLOGY, Issue 4 2000Sang-Mo KOH Abstract: Hydrothermally altered areas forming pyrophyllite-kaolin-sericite-alunite deposits are distributed in Chonnam and Kyongsang areas, Cretaceous volcanic field of the Yuchon Group. The Chonnam alteration area is located within depression zone which is composed of volcanic and granitic rocks of late Cretaceous age. The clay deposits of this area show the genetic relationship with silicic lava domes. The Kyongsang alteration area is mainly distributed within Kyongsang Basin comprising volcanic, sedimentary and granitic rocks of Cretaceous and Tertiary age. Most of the clay deposits of this area are closely related to cauldrons. Paleozoic clay deposit occurs in the contact zone between Precambrian Hongjesa granite gneiss and Paleozoic Jangsan quartzite of Choson Supergroup. Cretaceous igneous rocks of the both alteration areas belong to high K calc-alkaline series formed in the volcanic arc of continental margin by subduction-related magmatism. Chonnam igneous rocks show more enrichment of crustal components such as K, La, Ce, Sm, Nd and Ba, higher (La/Yb)cn ratio, and higher initial 87Sr/86Sr ratio (0. 708 to 0. 712) than those of Kyongsang igneous rocks. This might be due to the difference of degree of crustal contamination during Cretaceous magmatism. The most characteristic alteration minerals of Chonnam clay deposits are alunite, kaolin, quartz, pyrophyllite and diaspore which were formed by acidic solution. Those of Kyongsang clay deposits are sericite, quartz and pyrophyllite which were formed by weak acid and neutral solution. The formation ages of the clay deposits of two alteration areas range from 70. 1 to 81. 4 Ma and 39. 7 to 79. 4 Ma, respectively. The Daehyun clay deposit in Ponghwa area of Kyongsang province shows the alteration age range from 290 to 336 Ma. This result shows the different alteration episode from the hydrothermal alteration of Cretaceous to early Tertiary in the Kyongsang and Chonnam alteration areas. These data indicate, at least, three hydrothermal activities of Tertiary (middle to late Eocene), late Cretaceous (Santonian to Maastrichtian) and Paleozoic Carboniferous Periods in South Korea. [source] Geochemistry and Genesis of the Late Jurassic Granitoids at Northern Great Hinggan Range: Implications for ExplorationACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 2 2010Guang WU Abstract: The Longgouhe and Ershiyizhan intrusions of the Late Jurassic, located in the Upper Heilongjiang Basin of the northern Great Hinggan Range, are closely related to porphyry Cu-Au mineralizations. In lithology the intrusions are quartz diorite, quartz monzodiorite and granodiorite of high-K calc-alkaline series, with minor aspects of shoshonite series. Their SiO2 and Al2O3 contents range from 61.37% to 66.59% and 15.35% to 17.06%, respectively. The MgO content ranges from 2.02% to 3.47%, with Mg# indices of 44,59. The (La/Yb)N and Eu/Eu* values range from 16.85 to 81.73 and 0.68 to 0.93, respectively, showing strong differentiation rare earth element (REE) patterns similar to those of adakites. The rocks are enriched in Ba, Sr and light REE (LREE), obviously depleted in Nb and Ta, slightly depleted in Rb and Ti, and poor in Yb and Y, with Yb and Y contents of 0.31,1.32 ppm and 4.32,12.07 ppm, respectively. As indicated by Sr/Y ratios of 67.74,220.60, the rocks are characterized by low-Y and high-Sr contents, which characterize the adakites in the world. Holistically, geochemical tracers suggest that the interested intrusions are adakitic rocks. Given that the Paleo-Asian Ocean and Mongol-Okhotsk Ocean were closed in the Late Paleozoic and Permian-Middle Jurassic, respectively, the interested intrusions should be formed by partial melting of delaminated crust, which had been thickened during collisional orogeny between the Siberian and Mongolian-Sinokorean continents. [source] Guandishan Granitoids of the Paleoproterozoic Lüliang Metamorphic Complex in the Trans-North China Orogen: SHRIMP Zircon Ages, Petrogenesis and Tectonic ImplicationsACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 3 2009Shuwen LIU Abstract: The Paleoproterozoic Lüliang Metamorphic Complex (PLMC) is situated in the middle segment of the western margin of the Trans-North China Orogen (TNCO), North China Craton (NCC). As the most important lithological assemblages in the southern part of the PLMC, Guandishan granitoids consist of early gneissic tonalities, granodiorites and gneissic monzogranites, and younger gneissic to massive monzogranites. Petrochemical features reveal that the early gneissic tonalities and granodiorites belong to the medium-K calc-alkaline series; the early gneissic monzogranites are transitional from high-K calc-alkaline to the shoshonite series; the younger gneissic to massive monzogranites belong to the high-k calc-alkaline series, and all rocks are characterized by right-declined REE patterns and negative Nb, Ta, Sr, P, and Ti anomalies in the primitive mantle normalized spidergrams. SHRIMP zircon U,Pb isotopic dating reveals that the early gneissic tonalities and granodiorites formed at ,2.17 Ga, the early gneissic monzogranites at ,2.06 Ga, and the younger gneissic to massive monzogranites at ,1.84 Ga. Sm,Nd isotopic data show that the early gneissic tonalities and granodiorites have ,Nd(t) values of +0.48 to ,3.19 with Nd-depleted mantle model ages (TDM) of 2.76,2.47 Ga, and early gneissic monzogranites have ,Nd(t) values of ,0.53 to ,2.51 with TDM of 2.61,2.43 Ga, and the younger gneissic monzogranites have ,Nd(t) values of ,6.41 to ,2.78 with a TDM of 2.69,2.52 Ga. These geochemical and isotopic data indicate that the early gneissic tonalities, granodiorites, and monzogranites were derived from the partial melting of metamorphosed basaltic and pelitic rocks, respectively, in a continental arc setting. The younger gneissic to massive monzogranites were derived by partial melting of metamorphosed greywackes within the continental crust. Combined with previously regional data, we suggest that the Paleoproterozoic granitoid magmatism in the Guandishan granitoids of the PLMC may provide the best geological signature for the complete spectrum of Paleoproterozoic geodynamic processes in the Trans-North China Orogen from oceanic subduction, through collisional orogenesis, to post-orogenic extension and uplift. [source] Permian High Ba-Sr Granitoids: Geochemistry, Age and Tectonic Implications of Erlangshan Pluton, Urad Zhongqi, Inner MongoliaACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 3 2009Hongling LUO Abstract: Erlangshan Pluton from Urad Zhongqi, central Inner Mongolia, is located in the middle segment of the northern margin of the North China Plate. The rocks consist mainly of diorites with gneissic structure. Petrochemical characteristics reveal that the diorites belong to metaluminous, high-potassium calc-alkaline series, with chemical signatures of I-type granites. They are characterized by low SiO2 contents (56.63%,58.53%) and A/CNK (0.90,0.96), high Al2O3 contents (17.30%,17.96%) and Na2O/K2O ratios (1.20,1.70), enrichment in large ion lithophile elements (LILE, e.g., Ba=556,915 ppm, Sr=463,595 ppm), and relative depletion in high field strength elements (HFSE, e.g., Nb, Ta, Ti) in primitive mantle-normalized spidergram, and right-declined rare earth element patterns with slightly negative Eu anomalies (,Eu=0.72,0.90). They have Sr/Y ratios (20,25) evidently less than Kebu Pluton (49,75) to its east. Sensitive high resolution ion micro-probe U-Pb zircon dating of the diorites has yielded an intrusive age of 270±8 Ma. This leads us to conclude that Erlangshan diorites were formed by mixing between the middle or lower crustal-derived magma and minor mantle-derived mafic magma, followed by fractional crystallization, which was trigged by crustal extension and fault activity in post-collisional setting. [source] Geochemistry, Nd Isotopic Characteristics of Metamorphic Complexes in Northern Hebei: Implications for Crustal AccretionACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 6 2006LIU Shuwen Abstract: The middle segment of the northern margin of the North China Craton (NCC) consists mainly of metamorphosed Archean Dantazi Complex, Paleoproterozoic Hongqiyingzi Complex and unmetamorphosed gabbro-anorthosite-meta-alkaline granite, as well as metamorphosed Late Paleozoic mafic to granitoid rocks in the Damiao-Changshaoying area. The ,2.49 Ga Dantazi Complex comprises dioritic-trondhjemitic-granodoritic-monzogranitic gneisses metamorphosed in amphibolite to granulite facies. Petrochemical characteristics reveal that most of the rocks belong to a medium- to high-potassium calc-alkaline series, and display Mg#less than 40, right-declined REE patterns with no to obviously positive Eu anomalies, evidently negative Th, Nb, Ta and Ti anomalies in primitive mantle-normalized spider diagrams, ,Nd(t)=+0.65 to ,0.03, and depleted mantle model ages TDM=2.78-2.71 Ga. Study in petrogenesis indicates that the rocks were formed from magmatic mixing between mafic magma from the depleted mantle and granitoid magma from partial melting of recycled crustal mafic rocks in a continental margin setting. The 2.44-2.41 Ga Hongqiyingzi Complex is dominated by metamorphic mafic-granodioritic-monzogranitic gneisses, displaying similar petrochemical features to the Dantazi Complex, namely medium to high potassium calc-alkaline series, and the mafic rocks show evident change in LILEs, negative Th, Nb, Ta, Zr anomalies and positive P anomalies. And the other granitiod samples also exhibit negative Th, Nb, Ta, P and Ti anomalies. All rocks in the Hongqiyingzi Complex show right-declined REE patterns without Eu anomaly. The metamorphic mafic rocks with ,Nd(t)= ,1.64 may not be an identical magmatic evolution series with granitoids that have ,Nd(t) values of +3.19 to +1.94 and TDM ages of 2.55-2.52 Ga. These granitic rocks originated from hybrid between mafic magma from the depleted mantle and magma from partial melting of juvenile crustal mafic rocks in an island arc setting. All the ,311 Ma Late Paleozoic metamorphic mafic rocks and related granitic rocks show a medium-potassium calc-alkaline magmatic evolution series, characterized by high Mg#, obviously negative Th, Nb, Ta anomalies and positive Sr anomalies, from no to strongly negative Ti anomalies and flat REE patterns with ,Nd(t)= +8.42, implying that the mafic magma was derived from the depleted mantle. However the other granitic rocks are characterized by right-declined REE patterns with no to evidently positive Eu anomalies, significantly low ,Nd(t)= ,13.37 to ,14.04, and TDM=1.97-1.96 Ga, revealing that the granitoid magma was derived from hybrid between mafic magma that came from ,311 Ma depleted mantle and granitoid magma from Archean to Early Paleoproterozoic ancient crustal recycling. The geochemistry and Nd isotopic characteristics as well as the above geological and geochronological results indicate that the middle segment of the northern margin of the NCC mainly experienced four crustal growth episodes from Archean to Late Paleozoic, which were dominated by three continental marginal arc accretions (,2.49, ,2.44 and 311 Ma), except the 1.76-1.68 Ga episode related to post-collisional extension, revealing that the crustal accretion of this segment was chiefly generated from arc accretion and amalgamation to the NCC continental block. [source] | ||||||||||