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1.
Early Yanshanian magmatic suites predominate absolutely in the Nanling granite belt. They consist mainly of monzogranite and K-feldspar granite. There occur associations of early Yanshanian A-type granitoids (176 Ma-178 Ma) and bimodal volcanic rocks (158 Ma-179 Ma) in southern Jiangxi and southwestern Fujian in the eastern sector of the granite belt and early Yanshanian basalts (177 Ma-178 Ma) in southern Hunan in the central sector of the belt. Both the acid end-member rhyolite in the bimodal volcanic rock association and A-type granitoids in southern Jiangxi have the geochemical characteristics of intraplate granitic rocks and the basic end-member basalt of the association is intraplate tholeiite, while the basaltic rocks in southern Hunan include not only intraplate tholeiite but also intraplate alkali basalt. Therefore the early Yanshanian magmatic suites in the Nanling region are undoubtedly typical post-orogenic rock associations. Post-orogenic suites mark the end of a post-collision or late orogenic event and the initiation of Pangaea break-up, indicating that a new orogenic Wilson cycle is about to start. Therefore it may be considered that the early Yanshanian geodynamic settings in the Nanling region should be related to post-orogenic continental break-up after the Indosinian orogeny and the break-up did not begin in the Cretaceous.  相似文献   

2.
Widespread Mesozoic magmatism occurs in the Korean Peninsula (KP). The status quo is poles apart between the northern and southern parts in characterizing its distribution and nature, with the nearly absence of any related information in North Korea. We have the opportunity to have conducted geological investigations in North Korea and South Korea during the past ten years through international cooperation programs. This led to the revelation of a number of granitoids and related volcanic rocks and thus facilitates the comparison with those in East China and Japan. Mesozoic granitoids in the KP can be divisible into three age groups: the Triassic group with a peak age of ~220 Ma, the Jurassic one of ~190–170 Ma and the late Early Cretaceous one of ~110 Ma. The Triassic intrusions include syenite, calc-alkaline to alkaline granite and minor kimberlite in the Pyeongnam Basin of North Korea. They have been considered to form in post-orogenic settings related to the Central Asian Orogenic Belt (CAOB) or the Dabie-Sulu Orogenic Belt (DSOB). The Jurassic granitoids constitute extensive occurrence in the KP and are termed as the Daebo-period magmatism. They correlate well with coeval counterparts in NE China encompassing the northeastern part of the North China Craton (NCC) and the eastern segment of the CAOB. They commonly consist of biotite or two-mica granites and granodiorites, with some containing small dark diorite enclaves. On one hand, Early Jurassic to early Middle Jurassic magmatic rocks are rare in most areas of the NCC, whilst Middle-Late Jurassic ones are not developed in the KP. On the other hand, both NCC and KP host abundant Cretaceous granites. However, the present data revealed contrasting age peaks, with ~130–125 Ma in the NCC and ~110–105 Ma in the KP. Cretaceous granites in the KP comprise the dominant biotite granites and a few amphibole granites. The former exhibit mildly fractionated REE patterns and zircon ε Hf(t) values from -15 to -25, whereas the latter feature strongly fractionated REE patterns and zircon ε Hf(t) values from -10 to -1. Both granites contain inherited zircons of ~1.8–1.9 or ~2.5 Ga. These geochemical characters testify to their derivation from re-melting distinct protoliths in ancient basement. Another Cretaceous magmatic sub-event has been entitled as the Gyeongsang volcanism, which is composed of bimodal calc-alkaline volcanic rocks of 94–55 Ma and granitic-hypabyssal granitic bodies of 72–70 Ma. Synthesizing the Mesozoic magmatic rocks across the KP, NCC and Japan can lead to the following highlights: (1) All Triassic granites in the NCC, KP and Japan have similar characteristics in petrology, chronology and geochemistry. Therefore, the NCC, KP and Japan tend to share the same tectonic setting during the Triassic, seemingly within the context of Indosinian orogensis. (2) Jurassic to earliest Cretaceous magmatic rocks in the NCC seem to define two episodes: episode A from 175 to 157 Ma and episode B from 157 to 135 Ma. Jurassic magmatic rocks in the KP span in age mainly from 190 to 170 Ma, whereas 160–135 Ma ones are rare. With the exception of ~197 Ma Funatsu granite, Jurassic magmatic rocks are absent in Japan. (3) Cretaceous granites in the KP have a peak age of ~110, ~20 Ma younger than those in the NCC, while Japan is exempt from ~130–100 Ma granites. (4) The spatial-temporal distribution and migratory characteristics of the Jurassic-Cretaceous magmatic rocks in Japan, KP, and NE China-North China indicate that the subduction of the Paleo-Pacific plate might not be operative before Late Cretaceous (~130–120 Ma). (5) Late Cretaceous magmatic rocks (~90–60 Ma) occur in the southwestern corner of the KP and also in Japan, coinciding with the metamorphic age of ~90–70 Ma in the Sanbagawa metamorphic belt of Japan. The magmatic-metamorphic rock associations and their spatial distribution demonstrate the affinities of sequentially subduction zone, island arc and back-arc basin from Japan to Korea, arguing for the Pacific plate subduction during Late Cretaceous. (6) This study raises another possibility that the Mesozoic cratonic destruction in the NCC, which mainly occurred during ~150–120 Ma, might not only be due to the subduction of the Paleo-Pacific Plate, but also owe much to the intraplate geodynamic forces triggered by other adjacent continental plates like the Eurasian and Indian plates.  相似文献   

3.
The Dabie-Sulu orogenic belt was formed by the Triassic continental collision between the South China Block and the North China Block. There is a large area of Mesozoic magmatic rocks along this orogenic belt, with emplacement ages mainly at Late Triassic, Late Jurassic and Early Cretaceous. The Late Triassic alkaline rocks and the Late Jurassic granitoids only crop out in the eastern part of the Sulu orogen, whereas the Early Cretaceous magmatic rocks occur as massive granitoids, sporadic intermedi- ate-ma...  相似文献   

4.
The Nanling metallogenic belt in South China is characterized by well-developed tungsten-tin mineralization related to multiple-aged granitoids. This belt is one of the 5 key prospecting and exploration areas among the 19 important metallogenic targets in China. Important progress has been made in recent years in understanding the Nanling granitoids and associated mineralization, and this paper introduces the latest major findings as follows: (1) there exists a series of Caledonian, Indosinian, and Yanshanian W-Sn-bearing granites; (2) the Sn-bearing Yanshanian granites in the Nanling Range form an NE-SW trending aluminous A-type granite belt that stretches over 350 km. The granites typically belong to the magnetite series, and dioritic micro-granular enclaves with mingling features are very common; (3) the Early Yanshanian Sn- and W-bearing granites possess different petrological and geochemical features to each other: most Sn-bearing granites are metaluminous to weakly peraluminous biotite (hornblende) granites, with zircon ?Hf(t) values of ca. ?2 to ?8, whereas most W-bearing granites are peraluminous two-mica granites or muscovite granites with ?Hf(t) values of ca. ?8 to ?12; (4) based on the petrology and geochemistry of the W-Sn-bearing granites, mineralogical studies have shown that common minerals such as titanite, magnetite, and biotite may be used as indicators for discriminating the mineralizing potential of the Sn-bearing granites. Similarly, W-bearing minerals such as wolframite may indicate the mineralizing potential of the W-bearing granites. Future studies should be focused on examining the internal relationships between the multiple-aged granites in composite bodies, the metallogenic peculiarities of multiple-aged W-Sn-bearing granites, the links between melt evolution and highly evolved ore-bearing felsic dykes, and the connections between granite domes and mineralization.  相似文献   

5.
The Dabieshan Orogenic belt is well known for the exhumation of early Mesozoic ultrahigh-pressure (UHP) metamorphic rocks and Jurassic–Cretaceous emplacement of voluminous granitoids. However, the tectonic evolution in the orogen during the Paleozoic, especially its magmatic response to tectonism has not received much attention. As indicated by published data, the Dabieshan orogenic belt contains different records of Paleozoic magmatic-tectonic association in different tectonic units. Occ…  相似文献   

6.
As the core block of the East Gondwana Land, the East Antarctic Shield was traditionally thought, before 1992, as an amalgamation of a number of Archaean-Paleoproterozoic nuclei, be-ing welded by Grenville aged mobile belts during 1400—900 Ma, while the …  相似文献   

7.
The relationships between the intrusion of gneissose granitoids and the attainment of regional high‐T conditions recorded in metamorphic rocks from the Ryoke belt of the Mikawa area, central Japan, are explored. Seven gneissose granitoid samples (tonalite, granodiorite, granite) were collected from three distinct plutonic bodies that are mapped as the so‐called “Older Ryoke granitoids.” Based on bulk‐rock compositions and U–Pb zircon ages obtained by laser ablation inductively coupled plasma mass spectrometry, the analyzed granitoids can be separated into two groups. Gneissose granitoids from the northern part of the area give weighted mean 206Pb/238U ages of 99 ±1 Ma (two samples) and 95 ±1 Ma (one sample), whereas those from the southern part yield 81 ±1 Ma (two samples) and 78–77 ±1 Ma (two samples). Regional comparisons allow correlation of the northern granitoids (99–95 Ma) with the Kiyosaki granodiorite, and mostly with the Kamihara tonalite found to the east. The southern granitoids are tentatively renamed as “78–75 Ma (Hbl)?Bt granite” and “81–75 Ma Hbl?Bt tonalite” (Hbl, hornblende; Bt, biotite). and seem to be broadly coeval members of the same magmatic suite. With respect to available age data, no gneissose granitoid from the Mikawa area shows a U–Pb zircon age which matches that of high‐T metamorphism (ca 87 Ma). The southern gneissose granitoids (81–75 Ma), although they occur in the highest‐grade metamorphic zone, do not seem to represent the heat source which produced the metamorphic field gradient with a low dP/dT slope.  相似文献   

8.
皖南谭山岩体的锆石定年及地质意义   总被引：1，自引：0，他引：1  
皖南地区广泛分布燕山期岩浆岩,但其年代学方面的工作较为薄弱。为厘定该地区燕山期岩浆岩年代学格架,本文利用LA-ICP-MS锆石U-Pb定年方法对皖南谭山岩体的正长花岗岩进行了锆石U-Pb年代学研究,两个样品的206Pb/238U加权平均年龄分别为128．5±1．7Ma和128．3±1．5Ma,基本一致,为早白垩世岩浆活动的产物。结合本地区高精度年代学数据,皖南地区中生代岩浆岩可划分为三个峰期：第一峰期为142～139Ma;第二峰期为133～130Ma;第三峰期为128～125Ma。  相似文献   

9.
The Nanling Mountain is an important Mesozoic orogenic belt in the south of China, its E-W-trending granites and adjacent sedimentary basins form a dis-tinctive basin-mountain landform. The Nanxiong basin and the Zhuguang granite, both located in the northern Nanling belt, make up a typical basin-mountain sys-tem. Since the 1970s, a systematical research on gran-ites and their deposit ores was carried out, from that the two main viewpoints were proposed[1—5], including (1) the polyphase gr…  相似文献   

10.
Researches over the last 20 years show that the orogenic belt remains rather active after plate colli-sion[1,2]. A complete orogenic cycle in the last period of the Wilson cycle can be defined by three stages of development[3]: (1) horizontal contraction and crustal thickening due to collision, as well as formation of topography and the crustal and lithospheric root; (2) eclogite facies metamorphism of the crustal root; and (3) delamination of the crustal root or lithospheric mantle, extension…  相似文献   

11.
The large-scale Huangshaping Pb-Zn-W-Mo polymetallic deposit is located in the central Nanling min- eralization zone, South China. Six molybdenite samples from the Huangshaping deposit were selected for Re-Os isotope measurement in order to define the mineralization age of the deposit. It yields a Re-Os isochron age of 154.8±1.9 Ma (2σ ), which is in accordance with the Re-Os model ages of 150.9― 156.9 Ma. This age is about 7 Ma younger than their host granite porphyry, which was dated as 161.6±1.1 Ma by zircon U-Pb method using LA-ICPMS. All these ages demonstrate that the Huang- shaping granite and related Pb-Zn-W-Mo deposit occurred in the middle Yanshanian period, when many other granitoid and related ore deposits emplaced and formed, e.g. the Qitianling granite and Furong tin deposit, the Qianlishan granite and giant Shizhuyuan W-Sn-Mo-Bi deposit and Jinchuantang Sn-Bi deposit in the nearby area. They constitute the main part of the magmatic-metallogenic belt of southern Hunan, and represent the large-scale metallogeny in middle Yanshanian in the area. The lower rhenium content in molybdenite of Huangshaping deposit suggests that the ore-forming material was mainly of crust origin.  相似文献   

12.
The Chiang Khong segment of the Chiang Khong–Lampang–Tak Volcanic Belt is composed of three broadly meridional sub‐belts of mafic to felsic volcanic, volcaniclastic, and associated intrusive rocks. Associated sedimentary rocks are largely non‐marine red beds and conglomerates. Three representative Chiang Khong lavas have Late Triassic (223–220 Ma) laser ablation inductively coupled mass‐spectroscopy U–Pb zircon ages. Felsic‐dominated sequences in the Chiang Khong Western and Central Sub‐belts are high‐K calc–alkaline rocks that range from basaltic to dominant felsic lavas with rare mafic dykes. The Western Sub‐belt lavas have slightly lower high field strength element contents at all fractionation levels than equivalent rocks from the Central Sub‐belt. In contrast, the Eastern Sub‐belt is dominated by mafic lavas and dykes with compositions transitional between E‐mid‐oceanic ridge basalt and back‐arc basin basalts. The Eastern Sub‐belt rocks have higher FeO* and TiO2 and less light rare earth element enrichment than basalts in the high‐K sequences. Basaltic and doleritic dykes in the Western and Central sub‐belts match the composition of the Eastern Sub‐belt lavas and dykes. A recent geochemical study of the Chiang Khong rocks concluded that they were erupted in a continental margin volcanic arc setting. However, based on the dominance of felsic lavas and the mainly non‐marine associated sediments, we propose an alternative origin, in a post‐collisional extensional setting. A major late Middle to early Late Triassic collisional orogenic event is well documented in northern Thailand and Yunnan. We believe that the paucity of radiometric dates for arc‐like lavas in the Chiang Khong–Lampang–Tak Volcanic Belt that precede this orogenic event, coupled with the geochemistry of the Chiang Khong rocks, and strong compositional analogies with other post‐collisional magmatic suites, are features that are more typical of volcanic belts formed in a rapidly evolving post‐collisional, basin‐and range‐type extensional setting.  相似文献   

13.
Geology of the Grove Mountains in East Antarctica   总被引：2，自引：0，他引：2  
Grove Mountains consists mainly of a series of high-grade (upper amphibolite to granulite facies) metamorphic rocks, including felsic granulite, granitic gneiss, mafic granulite lenses and charnockite, intruded by late tectonic gneissic granite and post-tectonic granodioritic veins. Geochemical analysis demonstrates that the charnockite, granitic gneiss and granite belonged to aluminous A type plutonic rocks, whereas the felsic and mafic granulite were from supracrustal materials as island-arc, oceanic island and middle oceanic ridge basalt. A few high-strained shear zones disperse in regional stable sub-horizontal foliated metamorphic rocks. Three generations of ductile deformation were identified, in which D1 is related to the event before Pan-African age, D2 corresponds to the regional granulite peak metamorphism, whereas D3 reflects ductile extension in late Pan-African orogenic period. The metamorphic reactions from granitic gneiss indicate a single granulite facies event, but 3 steps from mafic granulite, with P-T condition of M1 800°C, 9.3×105 Pa; M2 800–810°C, 6.4 × 105 Pa; and M3 650°C have been recognized. The U-Pb age data from representative granitic gneiss indicate (529±14) Ma of peak metamorphism, (534±5) Ma of granite emplacement, and (501±7) Ma of post-tectonic granodioritic veins. All these evidences suggest that a huge Pan-African aged mobile belt exists in the East Antarctic Shield extending from Prydz Bay via Grove Mountains to the southern Prince Charles Mountains. This orogenic belt could be the final suture during the Gondwana Land assemblage.  相似文献   

14.
The North Dabie complex unit(NDC)is a widely exposed petro-tectonic unit.To understand post-orogenic uplift history and mechanism of the Dabie orogenic belt,many samples of granite,granodiorite,diorite,and alkali feldspar granite with precise zircon U-Pb ages were collected for electron microprobe analysis of hornblende.Emplacement pressure values were then calculated by using an Al-in-hornblende geobarometer.The result shows that total Al(AlT)values in hornblende range from 1.17to 1.97 p.f.u.,XFe(=Fe/(Fe+Mg))from 0.4 to 0.65,and corresponding pressure values from 256.8 to 676.2 MPa for AlT greater than 1.17.It is suggested that although the main mechanism for the uplift is tectonic extension,inhomogeneous uplift related to the pluton emplacement is also important during post-orogenic evolution of the Dabie orogenic belt.Emplacement depth distribution of the plutons shows that uplift in the NDC is affected by horst-graben structures since 120 Ma.  相似文献   

15.
梅子坑钼矿位于九岭钨钼成矿带,为中型石英脉型钼矿床。矿区内地层和岩浆岩钼元素含量分别是克拉克值的43倍和21倍。矿体赋存于双桥山群修水组浅变质岩系中及北西向断裂控制的裂隙密集带中;矿石主要类型为石英脉型,矿石有益组分为辉钼矿,形成于石英-黄铁矿-辉钼矿-黄铜矿早期矿化阶段。矿床可能与隐伏的燕山期细粒花岗岩、花岗斑岩岩脉有成因关系,属与燕山期岩浆活动有关的中-高温热液矿床。北西向断裂密集带,硅化、云英岩化、黄铁矿化围岩蚀变,燕山期花岗岩类及双桥山群浅变质岩系,是其主要找矿标志。  相似文献   

16.
新疆阿尔泰成矿带花岗岩发育,其中很多花岗岩与成矿作用有着密切的联系,特别是400Ma左右的岩浆活动是阿尔泰地区一次重要的岩浆成矿活动,阿尔泰许多金属矿床与这一时期的岩浆构造作用有关。本次研究的出露于可可塔勒铅锌矿区的黑云母花岗岩体,其锆石LA-ICPMSU-Pb年龄为（401．8士1．5）Ma,表明可可塔勒花岗岩是阿尔泰成矿带400Ma左右发生的一次重要岩浆构造作用的产物,该黑云母花岗岩体侵入于矿区下泥盆统康布铁堡组火山岩地层中,岩体与围岩接触带附近的围岩蚀变明显,该黑云母花岗岩的侵入以及其后期的岩浆热液活动可能对区内成矿物质的活化、迁移、富集、成矿具有一定的贡献。  相似文献   

17.
We report precise 207Pb/206Pb single zircon evaporation ages for low-grade felsic metavolcanic rocks within the Onverwacht and Fig Tree Groups of the Barberton Greenstone Belt (BGB), South Africa, and from granitoid plutons bordering the belt. Dacitic tuffs of the Hooggenoeg Formation in the upper part of the Onverwacht Group yield ages between 3445 +/- 3 and 3416 +/- 5 Ma and contain older crustal components represented by a 3504 +/- 4 Ma old zircon xenocryst. Fig Tree dacitic tuffs and agglomerates have euhedral zircons between 3259 +/- 5 and 3225 +/- 3 Ma in age which we interpret to reflect the time of crystallization. A surprisingly complex xenocryst population in one sample documents ages from 3323 +/- 4 to 3522 +/- 4 Ma. We suspect that these xenocrysts were inherited, during the passage of the felsic melts to the surface, from various sources such as greenstones and granitoid rocks now exposed in the form of tonalite-trondhjemite plutons along the southern and western margins of the BGB, and units predating any of the exposed greenstone or intrusive rocks. Several of the granitoids along the southern margin of the belt have zircon populations with ages between 3490 and 3440 Ma. coeval with or slightly older than Onverwacht felsic volcanism, while the Kaap Valley pluton along the northwestern margin of the belt is coeval with Fig Tree dacitic volcanism. These results emphasize the comagmatic relationships between greenstone felsic volcanic units and the surrounding plutonic suites. Some of the volcanic plutonic units contain zircon xenocrysts older than any exposed rocks. These indicate the existence of still older units, possibly stratigraphically lower and older portions of the greenstone sequence itself, older granitoid intrusive rocks, or bodies of older, unrelated crustal material. Our data show that the Onverwacht and Fig Tree felsic units have distinctly different ages and therefore do not represent a single, tectonically repeated unit as proposed by others. Unlike the late Archaean Abitibi greenstone belt in Canada, which formed over about 30 Ma. exposed rocks in the BGB formed over a period of at least 220 Ma. The complex zircon populations encountered in this study imply that conventional multigrain zircon dating may not accurately identify the time of felsic volcanic activity in ancient greenstones. A surprising similarity in rock types, tectonic evolution, and ages of the BGB in the Kaapvaal craton of southern Africa and greenstones in the Pilbara Block of Western Australia suggests that these two terrains may have been part of a larger crustal unit in early Archaean times.  相似文献   

18.
INTRODUCTIONThe mafic-ultramafic complexesinthe Hongqilingarea were emplacedintothe metamorphic rocksof the Hulan Group. Age determination of the intrusion and metamorphism of the Hulan Groupmetamorphic rocks is crucial for the study of petrogenesis and evolution, orogenesis and itsdevelopment of the region. However ,so far it has been difficult to determine the geochronology ofmafic-ultramafic rocks inthe area ,thusthe age obtainedfromprevious data hadto be used.Inrecentyears ,withthe …  相似文献   

19.
Paleomagnetic characteristics of Carboniferous-Permian and Early Mesozoic geological complexes in Mongolia are studied. The studied rocks are shown to possess a multicomponent magnetization. Lowtemperature overprinting components of normal polarity discovered in nearly all of the studied strata were acquired after main deformation stages of the rocks, apparently in the Cenozoic. High-temperature overprinting components of reversed polarity identified in rocks of an active continental margin (ACM) were acquired when bimodal magma melts moved through ACM volcanic sequences. Late Carboniferous and Early Permian paleomagnetic poles of Mongolia calculated from directions of primary magnetization components are, respectively (Λ = 154.6, Φ = 32.2, A = 7.8) and (Λ = 95, Φ = 71, A = 8.7). Apparently, the territory of Mongolia in the Early Permian was a margin of the Siberian craton and was separated from the Northern China block by a basin extending for no less than 2000 km in the E-W direction. The strike of a marginal-continental volcanic belt was submeridional and a plate subducted under the continent from the east. Late Carboniferous-Permian intraplate magmatic complexes of Mongolia formed at various latitudes from various mantle sources during the northward movement of the Mongolian part of the Siberian continent. The oldest bimodal sequences of the Gobi-Tien Shan zone (318–314 Ma) formed at more southern latitudes (40°–47°–54°N) as compared with the 275-Ma complexes of the Gobi-Altai zone (51°–58°–67°N). Thus, sources of the Carboniferous-Permian intraplate magmatism in Central Asia either occupied a vast mantle region (up to 1000 km in the latitude direction) or moved together with the Asian continent.  相似文献   

20.
Major- and rare-earth-element (REE) concentrations and UThPb, SmNd, and RbSr isotope systematics are reported for Cenozoic volcanic rocks from northeastern and eastern China. These volcanic rocks, characteristically lacking the calc-alkaline suite of orogenic belts, were emplaced in a rift system which formed in response to the subduction of the western Pacific plate beneath the eastern Asiatic continental margin. The rocks sampled range from basanite and alkali olivine basalt, through olivine tholeiite and quartz tholeiite, to potassic basalts, alkali trachytes, pantellerite, and limburgite. These rock suites represent the volcanic centers of Datong, Hanobar, Kuandian, Changbaishan and Wudalianchi in northeastern China, and Mingxi in the Fujian Province of eastern China.The major-element and REE geochemistry is characteristic of each volcanic suite broadly evolving through cogenetic magmatic processes. Some of the outstanding features of the isotopic correlation arrays are as follows: (1) NdSr shows an anticorrelation within the field of ocean island basalts, extending from the MORB end-member to an enriched, time-averaged high Rb/Sr and Nd/Sr end-member (EM1), (2) SrPb also shows an anticorrelation, similar to that of Hawaiian and walvis Ridge basalts, (3) NdPb shows a positive correlation, and (4) the 207Pb/204Pb vs 206Pb/204Pb plot shows linear arrays parallel to the general trend (NHRL) for MORB on both sides of the geochron, although in the 208Pb/204Pb vs 206Pb/204Pb plot the linear array is significantly displaced above the NHRL in a pattern similar to that of the oceanic island basalts that show the Dupal signatures. In all isotope correlation patterns, the data arrays define two different mantle components—a MORB-like component and an enriched mantle component. The isotopic data presented here clearly demonstrate the existence of Dupal compositions in the sources of the continental volcanic rocks of eastern China. We suggest that the subcontinental mantle beneath eastern China served as the reservoir for the EMI component, and that the MORB component was either introduced by subduction of the Kula-Pacific Ridge beneath the Asiatic plate in the Late Cretaceous, as proposed by Uyeda and Miyashiro, or by upwellings in the subcontinental asthenosphere due to subduction.  相似文献   

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