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1.
Gold Deposits in the Sanandaj–Sirjan Zone: Orogenic Gold Deposits or Intrusion‐Related Gold Systems?
Most of the known large gold deposits in Iran are located along the Sanandaj–Sirjan Zone, western Iran, which hosts a wide range of gold deposit types. Gold deposits in the belt, hosted in upper Paleozoic to upper Mesozoic volcano‐sedimentary sequences of lower greenschist to lower amphibolite metamorphic grade, appear to represent mainly orogenic and intrusion‐related gold deposit types. The largest resource occurs at Muteh, with smaller deposits/occurrences at Zartorosht, Qolqoleh, Kervian, Qabaqloujeh, Kharapeh, and Astaneh. Although a major part of the gold deposits in the Sanandaj–Sirjan Zone are related to metamorphic devolatilization, some deposits including Muteh and Astaneh are related to short‐lived disruptions in an extensional tectonic regime and are associated with magma generation and emplacement. The age of gold ore formation in the orogenic gold deposits is Late Cretaceous to Tertiary, reflecting peak‐metamorphism during regional Cretaceous–Paleocene convergence and compression. The Oligocene to Pliocene age of most intrusion‐related gold systems is consistent with the young structural setting of the gold ore bodies; these deposits are sequestered along normal faults, correlated with Middle to Late Tertiary extensional tectonic events. This relationship is comparable to the magmatic‐metallogenetic evolution of the Urumieh‐Dokhtar magmatic arc, where the number of different types of gold‐copper deposits and the magnitude of the larger ones followed development of a magmatic arc. The appropriate explanation may be related to two different stages of gold mineralization consisting of a first compressional phase during the Late Cretaceous to Early‐Middle Tertiary, which is related to orogenic gold mineralization in the Qolqoleh, Kervian, Qabaqloujeh, Kharapeh, and Zartorosht deposits, and the extensional phase during the Eocene to Pliocene that is recognized by young intrusion‐related gold mineralization in the Muteh and Astaneh deposits. 相似文献
2.
内华达北中部的新月谷-独立金矿区线性构造(CVIL)是一个呈20°～30°走向、具多期变形、侵入及热液活动的构造带,该带从独立金矿区向南至科特兹矿山附近延伸达90 km,经过科特兹-派普来恩、卡林及独立三个主要的沉积岩型金矿区,含有罗伯茨山异地岩(可能是奥陶系Vinini组)的强烈构造岩,NE向的断层,白垩或第三纪的NE向的岩墙.变形带的组构具混杂岩的特点,但混杂岩中也显示有与晚三叠世和晚侏罗世之间形成的褶皱展布方向一致的定向组构.此外,沿CVIL带局部出现有第三纪的碧玉状岩石、角砾岩、方解石脉及脱钙蚀变作用.CVIL构造带南北两端成群出现的沉积岩型金矿床具有与卡林矿带金矿床相同的矿物特征.上述二个矿区都有NE向的断层,穿越罗伯茨山异地岩上盘中的构造窗和构造高地.CVIL可能是形成某些金矿床的主要热液通道. 相似文献
3.
《Geodinamica Acta》1999,12(2):113-132
The Aguilón Subbasin (NE Spain) was originated daring the Late Jurassic-Early Cretaceous rifting due to the action of large normal faults, probably inherited from Late Variscan fracturing. WNW-ESE normal faults limit two major troughs filled by continental deposits (Valanginian to Early Barremian). NE-SW faults control the location of subsidiary depocenters within these troughs. These basins were weakly inverted during the Tertiary with folds and thrusts striking E-W to WNW-ESE involving the Mesozoic-Tertiary cover with a maximum estimated shortening of about 12 %. Tertiary compression did not produce the total inversion of the Mesozoic basin but extensional structures are responsible for the location of major Tertiary folds. Shortening of the cover during the Tertiary involved both reactivation of some normal faults and development of folds and thrusts nucleated on basement extensional steps. The inversion style depends mainly on the occurrence and geometry of normal faults limiting the basin. Steep normal faults were not reactivated but acted as buttresses to the cover translation. Around these faults, affecting both basement and cover, folds and thrusts were nucleated due to the stress rise in front of major faults. Within the cover, the buttressing against normal faults consists of folding and faulting implying little shortening without development of ceavage or other evidence of internal deformation. 相似文献
4.
胶北地块与金成矿有关的郭家岭岩体和上庄岩体年代学及地球化学研究 总被引：4，自引：0，他引：4
胶东半岛是我国最主要的原生金矿矿集区,金矿的主要控矿围岩是郭家岭花岗岩,通过研究郭家岭花岗岩的地球化学特征对研究金矿的成因和物质来源具有指示性意义。本文研究的两个花岗岩岩体为上庄岩体和郭家岭岩体,两岩体同属郭家岭型花岗岩。通过对两岩体的花岗岩样进行岩相学矿相学观察、全岩主、微量元素和U-Pb同位素分析,获得胶东半岛中生代岩浆岩的成因机制与源区性质及自然金的产出形式等科学信息。LAICP MS锆石U-Pb年龄得出郭家岭岩体年龄125.4±2.2 Ma,上庄岩体U-Pb年龄128.8±2.0 Ma,都为中生代早白垩世,两岩体年龄相差3Ma,在年龄误差范围来看可以把两岩体作为同一期岩体,也在年龄角度证实两岩体都同属郭家岭花岗岩。两岩体的锆石组成都含有太古宙和晚侏罗纪的继承锆石,指示两岩体的成岩物质来源具相似性,都包含太古宙岩石成分和晚侏罗世花岗岩成分。两岩体具有相似的稀土元素和微量元素分配模式,表现出明显的LREE富集和HREE极度亏损,没有明显的铕负异常。郭家岭岩体和上庄岩体花岗岩都具有类似埃达克岩的特征,都具有高的Sr含量(913×10-6~1325×10-6),低的Y含量(2.2×10-6~8.4×10-6)和Yb含量(0.21×10-6~0.68×10-6),较高的(Dy/Yb)N比值1.62~2.28,暗示花岗岩岩浆形成时石榴石是一个重要的残留相,而没有斜长石作为残留相。两岩体具有较低的MgO、Cr、Ni含量和Mg#,反映郭家岭型花岗岩岩浆的形成可能是岛弧环境榴辉岩相压力条件下洋壳玄武质岩石的部分熔融。 相似文献
5.
A geochronological framework for orogenic gold mineralisation in central Victoria, Australia 总被引：3，自引：0，他引：3
Frank P. Bierlein Dennis C. Arne David A. Foster Peter Reynolds 《Mineralium Deposita》2001,36(8):741-767
New 40Ar/39Ar geochronological data support, and significantly expand upon, preliminary age data that were interpreted to suggest an episodic and diachronous emplacement of gold across the western Lachlan fold belt, Australia. These geochronological data indicate that mineralisation in the central Victorian gold province occurred in response to episodic, eastward progressing deformation, metamorphism and exhumation associated with the formation of the western Lachlan fold belt. Initial gold formation throughout the Stawell and the Bendigo structural zones can be constrained to a broad interval of time between 455 and 435 Ma, with remobilisation of metals into new structures and/or new pulses of mineralisation occurring between 420 and 400 Ma, and again between 380 and 370 Ma, linked to episodic variations in the regional stress-field and during intrusion of felsic dykes and plutons. This separation of ages is incompatible with the view that gold emplacement in the western Lachlan fold belt was the result of a single, orogen-wide event during the Devonian. A distinct phase of gold mineralisation, characterised by elevated Cu, Mo, Sb or W, is associated with both Late Silurian to Early Devonian (~420 to 400 Ma) and Middle to Late Devonian (~380 to 370 Ma) magmatism, when crustal thickening and shortening during the ongoing consolidation of the western Lachlan Fold Belt led to extensive melt development in the lower crust and resulted in widespread magmatism throughout central Victoria. These ~420 to 400 Ma and ~380 to 370 Ma occurrences, best exemplified by the Wonga deposit in the Stawell structural zone and many of the Woods Point deposits in the Melbourne structural zone, but also evidenced by occurrences at Fosterville and Maldon in the Bendigo structural zone, clearly formed synchronous with, or post-date, the emplacement of plutons and dykes, and thus are spatially (if not genetically) related to melt generation at depth. This later, magmatic-associated and polymetallic type of gold mineralisation is economically subordinate to the earlier, metamorphic-associated type of gold deposition in the Stawell and Bendigo structural zones, but tends to be the dominant style in the Melbourne Zone. These new geochronological constraints, together with zircon U-Pb data from felsic intrusive rocks of known relationship to gold mineralisation, demonstrate that initial hydrothermal alteration associated with gold emplacement in the western Lachlan fold belt was metamorphic-related, predating the emplacement of granite plutons by as much as 80 million years. This timing differs from other important orogenic gold districts where gold deposition is closely associated spatially with felsic magmatism. The early introduction of metamorphically derived fluids well before magmatism may reflect variations in the timing of peak metamorphic conditions at different crustal levels in an accretionary prism undergoing simultaneous deformation and erosion. Consequently, no genetic link exists between the main phase(s) of gold mineralisation and magmatism in the central Victorian gold province. With the exception of formation of a minor magmatism-related and geochemically-distinct mineralisation style at about 420 to 400 Ma, and again at about 380 to 370 Ma, the apparent spatial relationship between gold mineralisation and felsic intrusions is merely the result of melts and fluids being channelised along the same structures. 相似文献
6.
《Journal of Structural Geology》1987,9(7):859-867
The Hawasina complex consists of deformed slope to basinal sedimentary rocks of Mesozoic age, emplaced on the Arabian continental margin in the Late Cretaceous as a series of nappes. This complex is well exposed in the Sufrat ad Dawh range where it is represented by the Hamrat Duru Group and the Wahrah Formation. Two generations of imbricate faults are recognized in this area. The first is the imbrication of the Hamrat Duru and the Wahrah units into two separate nappes. These nappes were then folded and cross-cut by a second set of imbricate faults, resulting in the systematic tectonic repetition of the Wahrah-Hamrat Duru Nappe stratigraphy. The late-stage faulting event correlates with the origin of re-imbrication structures documented from other parts of the Oman orogen, interpreted to be of a post-emplacement, Early Tertiary age. This implies that Tertiary deformation of the Oman allochthons was expressed at least in part as a continuation of nappe development, initiated during the Late Cretaceous orogeny. 相似文献
7.
New geochronological and isotopic geochemical data are given, which make it possible to recognize two types of granitic rocks on the eastern Chukchi Peninsula. Early Cretaceous Tkachen and Dolina granitic plutons with zircon ages (U–Pb SIMS) of 119–122 and 131–136 Ma are related to the first type. They cut through Devonian–Lower Carboniferous basement rocks and are overlain by the Aptian–Albian Etelkuyum Formation. Basal units of the latter contain fragments of granitic rocks. Late Cretaceous Provideniya and Rumilet granitic plutons, which contain zircons with ages of 94 and 85 Ma (U–Pb SIMS), respectively, belong to the second type. They cut through volcanic–sedimentary rocks of the Etelkuyum and Leurvaam formations pertaining to the Okhotsk–Chukotka Volcanic Belt. In petrographic and geochemical features, the Early Cretaceous granitic rocks of the Tkachen Pluton are commensurable with I-type granites, while Late Cretaceous granite of the Rumilet Pluton is comparable to A2-type granite. The Sr–Nd isotopic data provide evidence that from the Early Cretaceous Tkachen and Dolina plutons to the Late Cretaceous Provideniya and Rumilet plutons, the degree of crustal assimilation of suprasubduction mantle-derived melts increases up to partial melting of heterogeneous continental crust enriched in rubidium. An unconformity and various degrees of secondary alteration of volcanic–sedimentary rocks have been established in the Okhotsk–Chukotka Volcanic Belt, and this was apparently caused by transition of the tectonic setting from suprasubduction to a transform margin with local extension. 相似文献
8.
该文是用地洼学说的观点论述整个青藏高原的大地构造性质,并从该区的构造层的结构、岩浆活动、沉积建造、构造型相、地震活动、地热、地球物理和现代地貌等特点来论证和分析它应归属地洼区。从地洼发展时期来看,它应归属“中亚期”地洼区。青藏高原北部进入地洼阶段较早,从侏罗纪时开始;而南部较晚,最晚是在渐新世时才进入地洼发展阶段。 相似文献
9.
安徽省铜陵地区是中国著名的以矽卡岩和斑岩型矿床为主的铜-金多金属矿集区,区内广泛产出的中酸性侵入岩与成矿关系十分密切。沙滩脚矿田位于该矿集区的东部,出露沙滩脚、桂花冲和姚家岭岩体及其不同规模、不同矿化类型的铜、金、锌等矿床,岩体对成矿起了重要的控制作用。本文在前人研究的基础上,对该矿田内的沙滩脚、姚家岭、桂花冲3个岩体进行了详细的岩石学、地球化学和锆石U-Pb年代学研究,以期查明沙滩脚矿田中酸性侵入岩的成因及成岩构造环境。岩石地球化学分析表明,3个岩体具有准铝质特征,均属于高钾钙碱性I型花岗岩类,轻稀土富集,重稀土亏损,具有弱的负Eu异常,富集Rb、Th等元素,亏损Nb、Ta等高场强元素。姚家岭岩体的锆石U-Pb年龄为140.4~140.9 Ma,沙滩脚岩体形成时代相对较早（141.4~144.1 Ma）,桂花冲岩体形成相对较晚（138.3Ma）。结合区域地质背景,笔者认为沙滩脚矿田的这些岩体形成于早白垩世伸展环境,是由来自于富集地幔的分异的碱性玄武质岩浆与地壳易熔组分部分熔融形成的花岗质岩浆混合后分期侵位形成的。 相似文献
10.
Models of continental crustal magmagenesis commonly invoke theinteraction of mafic mantle-derived magma and continental crustto explain geochemical and petrologic characteristics of crustalvolcanic and plutonic rocks. This interaction and the specificmechanisms of crustal contamination associated with it are poorlyunderstood. An excellent opportunity to study the progressiveeffects of crustal contamination is offered by the compositeplutons of the Alaska Range, a series of nine early Tertiary,multiply intruded, compositionally zoned (Peridotite to granite)plutons. Large initial Sr and Nd isotopic contrasts betweenthe crustal country rock and likely parental magmas allow evaluationof the mechanisms and extents of crustal contamination thataccompanied the crystallization of these ultra-mafic throughgranitic rocks. Three contamination processes are distinguishedin these plutons. The most obvious of these is assimilationof crustal country rock concurrent with magmatic fractionalcrystallization (AFC), as indicated by a general trend towardcrustal-like isotopic signatures with increasing differentiation.Second, many ultramafic and mafic rocks have late-stage phenocrystreaction and orthocumulate textures that suggest interactionwith felsic melt. These rocks also have variable and enrichedisotopic compositions that suggest that this felsic melt wasisotopically enriched and probably derived from crustal countryrock. Partial melt from the flysch country rock may have reactedwith and contaminated these partly crystalline magmas followingthe precipitation and accumulation of the cumulus phenocrystsbut before complete solidification of the magma. This suggeststhat in magmatic mush (especially of ultramafic composition)crystallizing in continental crust, a second distinct processof crustal contamination may be super imposed on AFC or magmamixing involving the main magma body. Finally, nearly all rocks,including mafic and ultramafic rocks, have (87Sr/86Sr)i thatare too high, and (T) Nd that are too low, to represent theexpected isotopic composition of typical depleted mantle. However,gabbro xenoliths with typical depicted-mantle isotopic compositionsare found in the plutons. This situation requires either anadditional enriched mantle component to provide the parentalmagma for these plutons, or some mechanism of crustal contaminationof the parent magma that did not cause significant crystallizationand differentiation of the magma to more felsic compositions.Thermodynamic modeling indicates that assimilation of alkali-andwater-rich partial melt of the metapelite country rock by fractionating,near-liquidus basaltic magma could cause significant contaminationwhile suppressing significant crystallization and differentiation. KEY WORDS: crustal contamination; Alaska Range; isotope geochemistry; zoned plutons; assimilation
*Corresponding author. e-mail: preiners{at}u.washington.edu; fax: (206) 543-3836. 相似文献
11.
《Journal of Structural Geology》1999,21(8-9):1131-1142
Using spatial relationships between individual plutons and faults to support genetic correlations between faulting and magmatism is meaningless since even random magmatic or tectonic processes will result in some plutons adjacent to faults. Our initial analyses of populations of faults and Carboniferous plutons in the Armorican Massif, France and faults and Alleghanian plutons in the southern Appalachians, USA indicate that plutons have broad distributions with respect to faults but with a tendency for plutons to occur away from faults. Maxima of integrated pluton areas occur at 1/4 (Appalachians) and 1/2 (Armorican) of the distance between the average fault spacing in these orogens. Although there is a great need for statistical evaluations of relationships between populations of igneous bodies and structures in a wide variety of settings and crustal depths, our initial studies suggest that faults do not preferentially channel magma during ascent or emplacement and that these are relatively unfocused processes within orogenic belts. 相似文献
12.
Sm–Nd ages of garnet from the northern Coast Mountains of south-eastern Alaska, USA, constrain the timing of thermal events in polyphase metamorphic rocks of the western metamorphic belt and provide new data on the spatial extent of Cretaceous regional metamorphism. Bulk garnet–whole-rock Sm–Nd ages for a sillimanite-zone amphibolite (Taku Inlet) and a biotite-zone metapelite (Tracy Arm) are 77±17 Ma and 59±12 Ma, respectively. Garnet core–whole-rock (80±9 Ma), core–matrix (84±9 Ma), rim–whole-rock (59±4 Ma) and rim–matrix (62±4 Ma) ages were obtained from a sample collected 200 m west of a Palaeocene Coast plutonic–metamorphic complex sill-like pluton that separates medium-grade metamorphic rocks from high-grade metamorphic rocks and voluminous Tertiary plutons in the core of the orogen. The garnet core ages of c. 80 Ma indicate that the regional metamorphic grade reached garnet zone prior to the intrusion of the plutons and high-grade metamorphism of rocks to the east. Similar ages for the younger plutons, the youngest garnets and the rim of a multistage garnet ( c. 59 Ma) indicate a later episode of contact metamorphic garnet growth. Documentation of pre-71 Ma garnet-zone metamorphism along the western edge of the Coast plutonic–metamorphic complex confirms that Albian to Late Cretaceous metamorphism associated with crustal thickening affected this part of the orogen. The similarity of garnet Sm–Nd ages to independent age estimates for metamorphic events confirms that this technique provides useful estimates for the timing of Late Cretaceous to Tertiary thermal events. The c. 20 Myr difference between garnet core and rim ages suggests that the Sm–Nd isotope systematics of a single garnet grain can be used for distinguishing between multiple metamorphic events. 相似文献
13.
A new database of 70 U–Pb zircon ages (mostly determined by SHRIMP) indicates that the South Patagonian batholith resulted from the amalgamation of subduction-related plutons from the Late Jurassic to the Neogene. Construction of the batholith began with a voluminous, previously undetected, Late Jurassic bimodal body mainly composed of leucogranite with some gabbro, emplaced along its present eastern margin within a restricted time span (157 to 145 Ma). This episode is, at least in part, coeval with voluminous rhyolitic ignimbrites of the Tobífera Formation, deposited in the deep Rocas Verdes Basin east of the batholith; this was the last of several southwestward-migrating silicic volcanic episodes in Patagonia that commenced in an Early Jurassic extensional tectonic regime. The quasi-oceanic mafic floor of the basin was also contemporaneous with this Late Jurassic batholithic event, as indicated by mutually cross-cutting field relationships. Changes in subduction parameters then triggered the generation of earliest Cretaceous plutons (Cretaceous 1: 144–137 Ma) west of the Late Jurassic ones, a westward shift that culminated at 136–127 Ma (Cretaceous 2) along the present western margin of the batholith. Most mid- to Late Cretaceous (Cretaceous 3: 126–75 Ma) and Paleogene (67–40 Ma) granitoids are represented by geographically restricted plutons, mainly emplaced between the previously established margins of the batholith, and mostly in the far south; no associated volcanic rocks of similar age are known at present in this area. During the final Neogene stage of plutonism (25–15 Ma) a recurrence of coeval volcanism is recognized within and east of the batholith. Typical εNdt values for the granitoids vary from strongly negative (− 5) in the Late Jurassic, to progressively higher values for Cretaceous 1 (− 4), Cretaceous 2 (− 0.7), Cretaceous 3 (+ 2) and the Paleogene (+ 5), followed by lower and more variable ones in the Neogene (− 1 to + 5). These variations may reflect different modes of pluton emplacement: large crustal magma chambers developed in the early stages (Late Jurassic to Cretaceous 1), leading to widespread emplacement of plutons with a crustal signature, whereas the Cretaceous 2, Cretaceous 3 and Palaeogene parts of the batholith resulted from incremental assembly of small plutons generated at greater depths and with higher εNdt. This does not in itself justify the idea of a reduction in crustal character due to progressive exhaustion of fusible material in the crust through which the magmas passed. 相似文献
14.
Elizabeth M. Truswell 《Australian Journal of Earth Sciences》2013,60(3-4):343-356
Fifty‐three sea‐floor samples close to Antarctica collected by Douglas Mawson during the Australasian Antarctic Expedition of 1911–1914 have beeen analysed for recycled palynomorphs. The distribution of the recycled microfossils provides a broad guide to the position of hidden sedimentary sequences on the Antarctic continental margin. The samples were dredged off the East Antarctic coast between 91°E and 146°E. In three distinct ‐areas, concentrations of recycled palynomorphs suggest the presence nearby of eroding sedimentary sequences. Near the western edge of the Shackleton Ice Shelf the recycled suite suggests Early to Late Permian, Late Jurassic to mid‐Cretaceous, and Late Cretaceous to Early Tertiary sediments, with evidence for marine influence only in the Tertiary. Samples from the outer edge of the continental shelf and slope east of Cape Carr indicate Early Cretaceous and Late Cretaceous to Early Tertiary sequences, and the same age span is suggested by samples from the western side of the Mertz Glacier Tongue; in this area radio echosounding has suggested that inland sedimentary basins intersect the coast. The sedimentary sequence predicted for the Shackleton Ice Shelf area probably faced the open Indian Ocean, at least since the Mesozoic. Cretaceous sequences predicted for the other localities occur at points on the Antarctic coast where they would be expected on the basis of most reconstructions. The area east of Cape Carr has as its conjugate’ coast part of the Great Australian Bight Basin; that off the Mertz Glacier, the area west of the Otway Basin. At both these areas on the southern Australian margin thick Cretaceous rift‐valley sequences occur. 相似文献
15.
花岗质岩浆的起源、迁移及就位是研究大陆岩石圈流变学特性的重要方面。然而,板内伸展背景下同构造花岗岩体的岩浆来源、就位机制和岩浆流动与区域应力场的关系等问题缺乏系统性的总结。晚中生代期间华北板块东部逐渐变为区域伸展体制,同时中浅部地壳形成一系列的韧性剪切带、变质核杂岩和拆离断层,这些伸展构造往往伴有同剪切变形的花岗岩体。因此,华北东部是系统研究板内伸展背景下同构造花岗岩体的最佳区域。本文选取多个典型的同构造花岗岩体,进行综合分析。通过归纳总结这些同构造岩体的岩石地球化学和年代学资料,发现多数同构造岩体具有多个岩浆源区,且较早就位的中性岩席(单元)往往来自壳幔混合岩浆或新生下地壳的部分熔融,而较晚的酸性岩席(单元)则主要来源于古老下地壳的部分熔融。这一特点反映了同伸展岩体岩浆源区由深至浅的演化规律,也揭示了区域伸展背景下源自地幔的流体和热量是触发地壳部分熔融的重要因素。通过分析岩浆就位过程中围岩和岩体中形成的定向及变形组构,发现华北东部同伸展岩体的就位模式可分为三大类:以扁平岩床或岩基形式就位于中部地壳的水平韧性剪切带内;岩浆以近直立运移的方式形成长轴平行拆离断层的岩基,就位于变质核杂岩核部或拆离断层下盘;岩浆就位于再活化的先存断裂,通过膨胀作用、挤压围岩获得就位空间并使围岩变形,形成类似底辟作用的就位方式。剪切应力和浮力是影响岩浆运移方向的重要力学参数。岩浆自源区上升的过程中浮力起着主要控制作用,就位于韧性剪切带时剪切应力起着控制作用,就位于浅部地壳的脆-韧性过渡带时浮力的作用再次凸显。 相似文献
16.
《Tectonophysics》1987,135(4):307-327
The Kutch-Saurashtra, Cambay and Narmada basins are pericontinental rift basins in the western margin of the Indian craton. These basins were formed by rifting along Precambrian tectonic trends. Interplay of three major Precambrian tectonic trends of western India, Dharwar (NNW-SSE), Aravalli-Delhi (NE-SW) and Satpura (ENE-WSW), controlled the tectonic style of the basins. The geological history of the basins indicates that these basins were formed by sequential reactivation of primordial faults. The Kutch basin opened up first in the Early Jurassic (rifting was initiated in Late Triassic) along the Delhi trend followed by the Cambay basin in the Early Cretaceous along the Dharwar trend and the Narmada basin in Late Cretaceous time along the Satpura trend. The evolution of the basins took place in four stages. These stages are synchronous with the important events in the evolution of the Indian sub-continent—its breakup from Gondwanaland in the Late Triassic-Early Jurassic, its northward drifting during the Jurassic-Cretaceous and collision with the Asian continent in the Early Tertiary. The most important tectonic events occurred in Late Cretaceous time. The present style of the continental margins of India evolved during Early Tertiary time.The Saurashtra arch, the extension of the Aravalli Range across the western continental shelf, subsided along the eastern margin fault of the Cambay basin during the Early Cretaceous. It formed an extensive depositional platform continuous with the Kutch shelf, for the accumulation of thick deltaic sediments. A part of the Saurashtra arch was uplifted as a horst during the main tectonic phase in the Late Cretaceous.The present high thermal regime of the Cambay-Bombay High region is suggestive of a renewed rifting phase. 相似文献
17.
华北燕山带:构造、埃达克质岩浆活动与地壳演化(英文) 总被引：19，自引：6，他引：19
GregoryA．DAVIS 《地学前缘》2003,10(4):373-384
埃达克质火成岩在中国东部,包括燕山带是很常见的,一般认为它们是下地壳不均匀的镁铁质岩石及/或富集的上地幔岩石在高压(≥1.5 GPa)下部分熔融的结果。在燕山带内埃达克岩浆的形成有一个很长的时间(约190～80 Ma),然而岩浆活动的峰期却与约170～130 Ma间有基底岩石卷入的陆壳收缩期相一致。尽管埃达克质岩浆活动的历史很长,但那种把岩浆活动与岩石圈的拆沉效应相联系的模式似乎是不适当的。在该带内,埃达克质与非埃达克质岩浆活动有一部分是同时的,而且在地理分布上也是相间的,这说明了在下地壳和上地幔岩石的部分熔融中成分是相当不均匀的。侏罗纪及白垩纪熔融作用的热源应当是与古太平洋板块俯冲相关的中生代板底垫托的玄武岩浆。除了局部例外,在燕山带,埃达克质岩浆活动的终结和碱性岩浆活动的开始约在130～120 Ma,在此时期收缩作用使东亚大达200万km~2以上的地区发生了NW—SE向的区域性伸展作用。强烈的地壳伸展仅局限于华北克拉通北缘分布的少数几个变质核杂岩中。陆壳的伸展减薄合理地解释了130～120 Ma间发生高压埃达克质熔融条件的终结,尽管还有局部年轻的埃达克火山活动(约120～80Ma)可以在伸展规模有限而厚的地壳依然存在的地区继续出现。燕山区早白垩世的碱性侵入体中的锆石不存在前寒武纪? 相似文献
18.
The Bahcecik prospect is located in the eastern Pontide tectonic province of the eastern Black Sea region of Turkey. It is one of the first low sulfidation epithermal systems to be described from this area of Turkey. Gold mineralization occurred within Late Cretaceous to early Tertiary volcanic rocks and is localized along east-trending normal faults and lithologic contacts. An early quartz–sericite alteration event was focused along the major fault in the area and resulted in precipitation of arsenian (?) pyrite with anomalous gold. A later, more spatially extensive, advanced argillic alteration event overprinted the quartz–sericite event. Native gold was precipitated during this event as disseminations and fracture fillings in quartz. Gold mineralization is restricted to the high-temperature portion of the alteration zone characterized by quartz veins with diaspore–pyrophyllite selvages. The prospect area was subjected to Tertiary to Holocene supergene alteration. 相似文献
19.
M. R. Handy 《International Journal of Earth Sciences》1996,85(4):832-851
The Zone of Samedan is part of a fossil, early Mesozoic rift system originally situated in the distal, Lower Austro-Alpine
domain of the Adriatic passive continental margin. An early Mesozoic configuration of asymmetrical rift basins bounded by
relative structural highs compartmentalized Late Cretaceous active margin tectonics; Jurassic half-grabens were folded into
arcuate synclines, whereas relative structural highs engendered thin, imbricated thrust sheets. West-directed thrusting and
folding initiated at the surface and continued to depths favoring mylonitization under lower greenschist-facies conditions.
At this time Liguria-Piemontese ophiolites were accreted to Lower Austro-Alpine units directly underlying the Zone of Samedan.
Late Cretaceous orogenic collapse of the Adriatic active margin involved the reactivation of west-directed thrusts as low-angle,
top-to-the-east, normal faults. These faults accommodated extensional uplift of Liguria-Piemontese ophiolites and Lower Austro-Alpine
units beneath and within the Zone of Samedan. During Paleogene collision, some Late Cretaceous faults in the Zone of Samedan
were reactivated under lower anchizonal conditions as north-directed thrusts. The latter stages of this early Tertiary thickening
were transitional to brittle, high-angle normal faulting associated with top-to-the-east extension and spreading above the
warm, uplifting Lepontine dome. 相似文献
20.
Magma mingling has been identified within the continental margin of southeastern China.This study focuses on the relationship between mafic and felsic igneous rocks in composite dikes and plutons in this area,and uses this relationship to examine the tectonic and geodynamic implications of the mingling of mafic and felsic magmas.Mafic magmatic enclaves(MMEs) show complex relationships with the hosting Xiaocuo granite in Fujian area,including lenticular to rounded porphyritic microgranular enclaves containing abundant felsic/mafic phenocrysts,elongate mafic enclaves,and back-veining of the felsic host granite into mafic enclaves.LA-ICP-MS zircon U-Pb analyses show crystallization of the granite and dioritic mafic magmatic enclave during ca.132 and 116 Ma.The host granite and MMEs both show zircon growth during repeated thermal events at-210 Ma and 160-180 Ma.Samples from the magma mingling zone generally contain felsic-derived zircons with well-developed growth zoning and aspect ratios of 2-3,and maficderived zircons with no obvious oscillatory zoning and with higher aspect ratios of 5-10.However,these two groups of zircons show no obvious trace element or age differences.The Hf-isotope compositions show that the host granite and MMEs have similar ε_(Hf)(t) values from negative to positive which suggest a mixed source from partial melting of the Meso-Neoproterozoic with involvement of enriched mantlederived magmas or juvenile components.The lithologies,mineral associations,and geochemical characteristics of the mafic and felsic rocks in this study area indicate that both were intruded together,suggesting Early Cretaceous mantle—crustal interactions along the southeastern China continental margin.The Early Cretaceous magma mingling is correlated to subduction of Paleo-Pacific plate. 相似文献