Tectonic setting and new division of evolution stages of Jiao-Liao-Ji belt: Implications from metagabbros in Jiaobei terrane
8
Citation
83
Reference
10
Related Paper
Citation Trend
Abstract:
祥山和于埠变质辉长岩是胶北地块上古元古代变质镁铁质岩石的典型代表,辉长岩侵入古元古代荆山群野头组,产有"祥山式"岩浆熔离型铁矿,成矿的专属性指示辉长岩属于层状侵入体类型,形成于大陆伸展构造背景。在祥山变质辉长岩中获得了1851±9Ma的变质年龄,在于埠变质辉长岩中获得了2052±23Ma的锆石U-Pb成岩年龄和1834±5Ma的变质年龄。~2.05Ga的岩浆结晶锆石的εHf(t)值均为正值(+1.87~+3.64),一阶段Hf模式年龄(tDM)为2292~2381Ma(平均为2327Ma),指示于埠变质辉长岩源自古元古代中期的亏损地幔。于埠变质辉长岩的成岩年龄制约了荆山群野头组的沉积上限,荆山群中至少有一部分形成于2.2~2.05Ga之间,沉积于大陆裂谷-稳定大陆边缘的构造环境。祥山和于埠变质辉长岩中有少量斜长花岗岩与之伴生,这些斜长花岗岩具有类似于大洋斜长花岗岩的岩石特征,低K、Ti、Sr,高Na、Yb,形成于低压背景;从斜长花岗岩中获得了1848±8Ma和1873±5Ma的锆石U-Pb年龄,斜长花岗岩中的锆石Th/U比值较低(0.01~0.29),具有初始熔体中结晶锆石特征。结合斜长花岗岩的地球化学特征,推测它们是辉长岩部分熔融的产物,并指示~1.87Ga已由挤压构造体制转变为伸展构造体制。综合前人研究成果,胶北地块已识别出2.18~2.15Ga、~2.10Ga、~2.05Ga的三期双峰式岩浆岩构造组合,指示2.2~2.05Ga期间总体为伸展构造背景。因此建议胶-辽-吉活动带的形成演化过程划分为两个阶段,早期为大陆裂解-稳定陆缘演化阶段(2.2~2.0Ga),沉积了巨量的陆缘碎屑岩-碳酸盐岩建造;晚期为俯冲-碰撞造山阶段(2.0~1.85Ga),胶-辽-吉活动带褶皱造山。First posted June 19, 2017 For additional information, contact: Geosciences and Environmental Change Science CenterU.S. Geological SurveyBox 25046, MS-980Denver, CO 80225-0046 The 7.5′ Strawberry Butte quadrangle in Meagher County, Montana near the southwest margin of the Little Belt Mountains, encompasses two sharply different geologic terranes. The northern three-quarters of the quadrangle are underlain mainly by Paleoproterozoic granite gneiss, across which Middle Cambrian sedimentary rocks rest unconformably. An ancestral valley of probable late Eocene age, eroded northwest across the granite gneiss terrane, is filled with Oligocene basalt and overlying Miocene and Oligocene sandstone, siltstone, tuffaceous siltstone, and conglomerate. The southern quarter of the quadrangle is underlain principally by deformed Mesoproterozoic sedimentary rocks of the Newland Formation, which are intruded by Eocene biotite hornblende dacite dikes. In this southern terrane, Tertiary strata are exposed only in a limited area near the southeast margin of the quadrangle. The distinct terranes are juxtaposed along the Volcano Valley fault zone—a zone of recurrent crustal movement beginning possibly in Mesoproterozoic time and certainly established from Neoproterozoic–Early Cambrian to late Tertiary time. Movement along the fault zone has included normal faulting, the southern terrane faulted down relative to the northern terrane, some reverse faulting as the southern terrane later moved up against the northern terrane, and lateral movement during which the southern terrane likely moved west relative to the northern terrane. Near the eastern margin of the quadrangle, the Newland Formation is locally the host of stratabound sulfide mineralization adjacent to the fault zone; west along the fault zone across the remainder of the quadrangle are significant areas and bands of hematite and iron-silicate mineral concentrations related to apparent alteration of iron sulfides. The map defines the distribution of a variety of surficial deposits, including the distribution of hematite-rich colluvium and iron-silicate boulders. The southeast corner of the quadrangle is the site of active exploration and potential development for copper from the sulfide-bearing strata of the Newland Formation.
Siltstone
Quadrangle
Dike
Conglomerate
Butte
Thrust fault
Cite
Citations (0)
The polygenetic Minas Geofracture separates the Meguma and Avalon Composite Terranes of the Maritime Appalachians. Dynamically recrystallized muscovite and biotite occur within D 3 shear zones which developed during dextral movement along the Geofracture. These record 40 Ar/ 39 Ar plateau ages between circa 360 and 370 Ma. Comparable plateau ages are recorded by micas within undeformed portions of granitic plutons and their low‐pressure, contact metamorphic aureoles. These are similar to U‐Pb ages previously reported for igneous monazite, therefore indicating relatively rapid postmagmatic cooling at shallow crustal levels. The D 3 fabrics were superimposed on earlier (S 1 ) structures which formed during initial amalgamation of the Meguma and Avalon Composite Terranes. Whole‐rock slate/phyllite samples collected outside high‐temperature portions of the plutonic contact aureoles yield 40 Ar/ 39 Ar plateau ages which correspond to groupings of circa 400–395 Ma, 390–385 Ma, and 380–375 Ma. These are interpreted to date diachronous formation of the S 1 fabrics and concomitant low‐grade regional metamorphism. In the circa 25 Ma between initial amalgamation and granitic plutonism, it is inferred that there was a slow rise of isotherms through the crust as a result of overthrust tectonic thickening. This led to crustal melting and the production of widespread granitic magmas which were emplaced immediately prior to D 3 dextral shearing.
Plutonism
Phyllite
Cite
Citations (101)
In its type area around Narooma, the Narooma Terrane in the Lachlan Orogen comprises the Wagonga Group, which consists of the Narooma Chert overlain by the argillaceous Bogolo Formation. Conodonts indicate that the lower, largely massive (ribbon chert) part of the Narooma Chert ranges in age from mid‐Late Cambrian to Darriwilian–Gisbornian (late Middle to early Late Ordovician). The upper Narooma Chert consists of shale, containing Eastonian (Late Ordovician) graptolites, interbedded with chert. Where not deformed by later faulting, the boundary between the Narooma Chert and Bogolo Formation is gradational. At map scale, the Narooma Terrane consists of a stack of imbricate thrust slices caught between two thrust faults that juxtaposed the terrane against the coeval Adaminaby Superterrane in Early Silurian time. These slices are best defined where Narooma Chert is thrust over Bogolo Formation. The soles of such slices contain multiply foliated chert. Late extensional shear bands indicate a strike‐slip component to the faulting. The Narooma Terrane, with chert overlain by muddy ooze, is interpreted to be an oceanic terrane that accumulated remote from land for ∼50 million years. The upward increase in the terrigenous component at the top of the Wagonga Group (shale, argillite, siltstone and sandstone of the upper Narooma Chert and Bogolo Formation) records approach of the terrane to the Australian sector of the Gondwana margin. Blocks of chert, argillite and sandstone reflect extensional/strike‐slip disruption of the terrane as it approached the transform trench along the Gondwana–proto‐Pacific plate boundary. Blocks of basalt and basalt breccia represent detritus from a seamount that was also entering the trench. There is no evidence that the Narooma Terrane or the adjacent Adaminaby Group formed in an accretionary prism/subduction complex.
Thrust fault
Siltstone
Cite
Citations (44)
Cite
Citations (0)
U-Pb isotopic analyses of monazite and zircon from six granitic plutons in the Meguma Terrane yield nearly concordant ages of 373+/-3 Ma, interpreted as the time of intrusion. U-Pb analyses of euhedral zircons with thick rims overgrowing cores, which were abraded to remove all or most of the rim, plot on chords between 370+/-3 and 628+/-33 Ma (Larrys River and Halfway Cove plutons), 372+/-3 and approximately 660 Ma (Shelburne pluton), and 373+/-2 and approximately 732 Ma (Barrington Passage pluton). The upper intercepts are interpreted as the age of magma source, correlatives of which are present in the Avalon Composite Terrane to the north. This basement may be either in depositional or tectonic contact with the overlying Cambro-Ordovician Meguma Group. Other zircons in the granites are generally irregular-euhedral with thin rims, and most U-Pb isotopic analyses fall between two chords from 373-2040 and 373-2300 Ma, with a few lying outside this field. These zircons are probably derived from the country rock (Goldenville Formation), which a previous study has shown contains detrital zircons with concordant U-Pb ages of 3000, 2000, and 600 Ma, and numerous intermediate discordant ages. These new ages, along with published data, document a relatively short (5-10 m.yr.) but voluminous period of magmatism. This age is approximately synchronous with intrusion of mafic rocks and lamprophyre dikes and regional low-pressure metamorphism and was followed by rapid denudation of 5-12 km. These observations may be interpreted in terms of shallowly dipping subduction and overriding of a mantle plume that eventually penetrates through the subducting plate to melt the overriding continental plate. Subsequent northward migration of the plume could explain both the approximately 360 Ma magmatism in the Cobequid Highlands (Avalon Composite Terrane) and the mid-Carboniferous plume-related intrusions around the Magdalen Basin.
Geochronology
Nova scotia
Devonian
Cite
Citations (54)
New geological and limited geochemical data indicate that the Kings Mountain belt forms part of the exotic Carolina arc terrane. The Carolina terrane and the fundamentally different Piedmont terrane are juxtaposed along the Kings Mountain shear zone and its extensions to the northeast and southwest. Ultramafic-mafic (ophiolitic?) rock bodies, melanges, and syn- or post-kinematic granitic plutons are present in or near the Kings Mountain shear zone and support its identification as a terrane suture.
Imbrication
Ultramafic rock
Cite
Citations (4)
The western flank of the Coast Mountains batholith between Cape Fanshaw and Taku Inlet is underlain primarily by Jura‐Cretaceous strata of the Gravina belt; pre‐Permian(?), Permian, and Triassic strata of the Taku terrane; and mid‐Proterozoic(?) to upper Paleozoic rocks of continental margin affinity. The continental margin rocks include mid‐Proterozoic(?) to lower Paleozoic(?) quartzite and marble of the Tracy Arm assemblage; mid‐Paleozoic metavolcanic and subordinate metasedimentary rocks of the Endicott Arm assemblage; and upper Paleozoic quartz‐rich metaturbidites and metaconglomerate of the Port Houghton assemblage. We suggest that these three assemblages are correlative with components of the Yukon‐Tanana terrane, which underlies a large region of Yukon and eastern Alaska. Rocks of the Gravina belt, Taku terrane, and Yukon‐Tanana terrane are juxtaposed along west‐vergent thrust faults of mid‐Cretaceous age and are internally deformed and disrupted along latest Cretaceous to early Eocene dip‐slip and possibly strike‐slip shear zones. These rocks and structures, together with mid‐Cretaceous to Eocene plutons of the Coast Mountains batholith, separate rocks of the Alexander‐Wrangellia terrane to the west from rocks of the Stikine terrane to the east. Mid‐Cretaceous thrust faults in the area belong to a system of thrusts that form the inboard margin of the Alexander‐Wrangellia terrane from central Alaska to northwestern Washington. The continental margin rocks in the northern Coast Mountains may be part of the in situ North American margin that has been overthrust by the Stikine and adjacent terranes. Alternatively, these rocks may have (1) rifted from and then returned to the North American margin, (2) moved >800 km along left‐lateral or right‐lateral faults from elsewhere along the North American margin, or (3) originated near a continent other than North America.
Batholith
Thrust fault
Continental Margin
Cite
Citations (69)
In the western Yarlung zangbo suture zone,there are widespread outcrops of Zhongba terrane between southern and northern tectonic melange.Petrology,detrital zircon geochronology and Hf isotope analysis were carried out on this strata,Zhongba terrane consists of low-grade metamorphic quartz sandstone,muscovite quartzite,muscovite calcite schist,argillaceous quartz siltstone and marble,this sedimentary succession was deposited on the coastal and shallow sea-shelf-outer shelf environments.U-Pb dating of detrital zircons from the quartz sandstone of Zhongba terrane yielded ages clustering at ～ 530Ma and ～ 950Ma,which can be compared with the counterpart from western Qiangtang terrane,Tethyan Himalaya and High Himalaya.They are remarkably similar with a wide but identical range of eHf(t) values of the ca.950Ma age population as well,at the same,the distinctive ca.1170Ma age population which is characteristic of zircons in the Lhasa terrane is absent in samples from Zhongba terrane.Our data suggests that Zhongba terrane were part of the Qiangtang-Greater India-Tethyan Himalaya continental margin system during the Paleozoic and had a probably different source and tectonic evolution with the Lhasa terrane.
Geochronology
Cite
Citations (14)