Geology and tectonic setting of Paleoproterozoic granitoid suites in the Island Harbour Bay area, Makkovik Province, Labrador

2001 ◽  
Vol 38 (3) ◽  
pp. 441-463 ◽  
Author(s):  
S M Barr ◽  
C E White ◽  
N G Culshaw ◽  
J WF Ketchum
Keyword(s):  
Earth Element ◽  
Tectonic Setting ◽  
Mafic Magma ◽  
Shear Zones ◽  
Magmatic Activity ◽  
Magmatic Arc ◽  
Bay Area ◽  
Granitoid Rocks ◽  
Andean Type ◽  
Variable Interaction

Paleoproterozoic granitoid rocks in the Island Harbour Bay area (Kaipokok domain, Makkovik Province, Labrador) are divided into four separate suites on the basis of field relations, petrology, and age. The redefined Island Harbour Bay plutonic suite consists of ca. 1895–1870 Ma dioritic to granitic (mainly granodioritic and granitic) units. The rocks are variably foliated as a result of emplacement under amphibolite-facies conditions in a dextral transpressive regime during Andean-type subduction. The dominant mafic mineral is biotite, and accessory epidote, allanite, and titanite are abundant. The suite is calc-alkalic, but with rare-earth element patterns similar to those of Archean tonalitic–trondhjemitic–granodioritic suites. It is interpreted to have formed deep in an Andean-type magmatic arc at the margin of the Nain continent. In contrast, the younger Hares Islands and Drunken Harbour granites (emplaced at ca. 1805 and 1790 Ma, respectively) were part of widespread late-orogenic magmatic activity in the Makkovik Province. In contrast to the Island Harbour Bay plutonic suite, these units retain igneous textures and are either unfoliated or display magmatic foliation, locally modified by emplacement in active shear zones. The ca. 1716 Ma Blacklers Bight granite varies from porphyritic to equigranular, is fluorite-bearing, and has chemical features approaching those of continental A-type granites. Similar granite occurs farther south in the Makkovik Province, reflecting widespread anorogenic magmatic activity at that time, perhaps related to mafic magma underplating. Variable interaction with Archean (Nain Province) crust by granitic magmas of all three ages is evidenced by εNd values ranging from –7.2 to –2.5.

scholarly journals Rhyacian evolution of the eastern São Luís Craton: petrography, geochemistry and geochronology of the Rosário Suite

2017 ◽  
Vol 47 (2) ◽  
pp. 275-299 ◽  
Author(s):  
Bruna Karine Correa Nogueira ◽  
Paulo Sergio de Sousa Gorayeb ◽  
Elton Luiz Dantas ◽  
Rafael Estumano Leal ◽  
Marco Antonio Galarza
Keyword(s):  
Shear Zones ◽  
Crustal Evolution ◽  
Calc Alkaline ◽  
Isotopic Data ◽  
Crust Formation ◽  
Magmatic Arc ◽  
Continental Arc ◽  
Amazonian Craton ◽  
Granitoid Rocks ◽  
Geochemical Studies

ABSTRACT: The São Luís Cráton comprises an area between northeast Pará state and northwest Maranhão that exposes Paleoproterozoic granitic suites and meta-volcanosedimentary sequences. In the east of this geotectonic unit, about 70 km south of São Luís, there is a portion of the São Luís Craton, represented by the intrusive Rosario Suite (RS). This work is focused on rocks of this suite, including petrographic, lithochemical and geochronological studies to understand the crustal evolution of these granitoid rocks. The rock spectrum varies from tonalitic to granodioritic, quartz dioritic and granitic compositions, and there are partial structural and mineralogical changes related to deformation along transcurrent shear zones. The geochemical studies show granitic metaluminous compositions of the calc-alkaline series with I-type affinity typical of magmatic arc. Rare earth elements show marked fractionation and slight Eu positive or negative anomalies (Eu/Eu* = 0.82 to 1.1). Zircon U-Pb data provided consistent ages of 2165 ± 7 Ma, 2170 ± 7 Ma, 2170 ± 7 Ma, 2161 ± 4 Ma and 2175 ± 8 Ma, dating emplacement of these granitoids as Paleoproterozoic (Rhyacian). Sm-Nd isotopic data provided model ages (TDM) of 2.21 to 2.31 Ga with positive values of εNd +1.9 to +3.2 (t = 2.17 Ga), indicating predominantly Rhyacian crustal sources for the parental magmas, similar to those ones found in other areas of the São Luís Craton. The data, integrated with published geological and geochronological information, indicate the occurrence of an important continental crust formation event in this area. The Paleoproterozoic evolution between 2.17 and 2.15 Ga is related to the Transamazonian orogeny. The granitoids of the Rosario Suite represent the main phase of continental arc magmatism that has continuity in other parts of the São Luís Craton and can be correlated with Rhyacian accretionary magmatism in the northwestern portion of the Amazonian Craton that amalgamated Archean terrains during the Transamazonian orogeny.

An early Paleozoic silicic large igneous province in NE Gondwana: a preliminary synthesis

2020 ◽  
Author(s):  
Wei Dan ◽  
J. Brendan Murphy ◽  
Gong-Jian Tang ◽  
Xiu-Zheng Zhang ◽  
Qiang Wang
Keyword(s):  
Tectonic Setting ◽  
Oceanic Lithosphere ◽  
Large Igneous Province ◽  
Early Paleozoic ◽  
Magmatic Rocks ◽  
Igneous Province ◽  
Granitoid Rocks ◽  
Andean Type ◽  
Almost All ◽  
The Relationship

<p>Five major oceans (Iapetus, Rheic, Proto-Tethys, Paleo-Tethys and Paleo-Asian) formed during or after assembly of the Gondwana continent. However, the relationship between them is poorly understood, largely due to the complex and disputed evolution of NE Gondwana in the early Paleozoic. Here we present a summary of early Paleozoic tectono-thermal events in the NE Gondwana and discuss their tectonic settings. Early Paleozoic magmatic rocks are widely distributed in the Himalaya, Lhasa, Southern Qiangtang, Baoshan, Sibumasu and Tengchong terranes, and their ages were loosely constrained to be ca. 530-430 Ma. However, after a critical review of these dating results, we propose the magmatic rocks were mostly formed between ca. 500-460 Ma. Although bimodal, they are dominated by granitoid rocks distributed over an area of >2500 km × 900 km. Thus, they constitute a typical silicic large igneous province. Almost all granitoid rocks were derived from partial melting of sedimentary rocks, but a few show A-type characteristics. Coeval amphibolite-facies metamorphic rocks yield ages of 490-465 Ma. A sedimentary hiatus marked by either a disconformity or angular unconformity coeval with the major magmatic flare-up period is evident in all terranes. Thus, present evidence doesn’t favor either the conventional Andean-type subduction model, in which these magmatic rocks reflect subduction of Proto-Tethys oceanic lithosphere beneath the northern Gondwanan margin, or a post-collision setting, in which extension is associated with the collapse of the Pan-African orogeny in NE Gondwana. The tectonic setting for this magmatic province is tentatively related to a plume in a far-field subduction zone.</p>

Late Cambrian – Early Ordovician magmatism in the Sierra de Pie de Palo, Sierras Pampeanas (Argentina): implications for the early evolution of the proto-Andean margin of Gondwana

2019 ◽  
Vol 157 (2) ◽  
pp. 321-339 ◽  
Author(s):  
Carlos D. Ramacciotti ◽  
César Casquet ◽  
Edgardo G. Baldo ◽  
Pablo H. Alasino ◽  
Carmen Galindo ◽  
...  
Keyword(s):  
Sedimentary Cover ◽  
Regional Metamorphism ◽  
Shear Zones ◽  
Magmatic Activity ◽  
Sierras Pampeanas ◽  
Mafic Magmatism ◽  
Magmatic Arc ◽  
Early Ordovician ◽  
Late Cambrian ◽  
Depleted Mantle

AbstractThe Sierra de Pie de Palo, in the Argentinean Sierras Pampeanas (Andean foreland), consists of a Mesoproterozoic basement and an Ediacaran – upper Cambrian sedimentary cover that underwent folding, thrusting and metamorphism during the Ordovician Famatinian orogeny. Mafic rocks and granitoids of the easternmost Sierra de Pie de Palo provide information about the magmatic activity at the proto-Andean margin of Gondwana during late Cambrian – Early Ordovician time. Magmatic activity began in the Sierra de Pie de Palo as dykes, sills and small intrusions of tholeiitic gabbros between 490 and 470 Ma, before shortening and regional metamorphism. Variable mantle sources (Nd depleted mantle age, TDM between 1.7 and 1.3 Ga) were involved in the mafic magmatism. Nd-isotope signatures were probably inherited from a Mesoproterozoic subcontinental mantle. Mafic magmatism was coincident with collapse of a Cambrian carbonate-siliciclastic platform that extended along SW Gondwana, and was probably coeval with the beginning of subduction. After mafic magmatism, peraluminous granitoids were emplaced in the Sierra de Pie de Palo along ductile shear zones during a contractional tectonic phase, coeval with moderate to high P/T metamorphism, and with the Cordilleran-type magmatic arc that resulted from a flare-up at c. 470 Ma. Granitoids resulted mainly from partial melting of metasedimentary rocks, although some hybridization with juvenile magmas and/or rocks cannot be ruled out. The evidence shown here further implies that the Pie de Palo block was part of the continental upper plate during the Famatinian subduction, and not an exotic block that collided with the Gondwana margin.

scholarly journals U-Pb geochronology, Sr-Nd geochemistry, petrogenesis and tectonic setting of Gandab volcanic rocks, northeastern Iran

2017 ◽  
Vol 44 (1) ◽  
pp. 269-286 ◽  
Author(s):  
Azam Entezari Harsini ◽  
Seyed A Mazaheri ◽  
Saeed Saadat ◽  
José F Santos
Keyword(s):  
Rare Earth ◽  
Rare Earth Elements ◽  
Rare Earth Element ◽  
Earth Element ◽  
Saturation Index ◽  
Tectonic Setting ◽  
Volcanic Rocks ◽  
Major Elements ◽  
Magmatic Arc ◽  
Heavy Rare Earth Elements

Abstract This paper addresses U-Pb geochronology, Sr-Nd geochemistry, petrogenesis and tectonic setting in the Gandab volcanic rocks. The Gandab volcanic rocks belong to the Sabzevar zone magmatic arc (northeastern Iran). Petrographically, all the studied volcanic rocks indicate porphyritic textures with phenocrysts of plagioclase, K-feldespar, hornblende, pyroxene, and magnetite which are embedded in a fine to medium grained groundmass. As well, amygdaloidal, and poikilitic textures are seen in some rocks. The standard chemical classifications show that the studied rocks are basaltic trachy andesite, trachy andesite, trachyte, and trachy dacite. Major elements reveal that the studied samples are metaluminous and their alumina saturation index varies from 0.71 to 1.02. The chondrite-normalized rare earth element and mantle-normalized trace element patterns show enrichment in light rare earth elements (LREE) relative to heavy rare earth elements (HREE) and in large ion lithophile elements (LILE) relative to high field strength elements (HFSE). As well they show a slightly negative Eu anomaly (Eu/Eu* = 0.72 – 0.97). The whole-rock geochemistry of the studied rocks suggests that they are related to each other by fractional crystallization. LA-MC-ICP-MS U-Pb analyses in zircon grains from two volcanic rock samples (GCH-119 and GCH-171) gave ages ranging of 5.47 ± 0.22 Ma to 2.44 ± 0.79 Ma, which corresponds to the Pliocene period. In four samples analysed for Sr and Nd isotopes 87Sr/86Sr ratios range from 0.704082 to 0.705931 and εNd values vary between +3.34 and +5. These values could be regarded to as representing mantle derived magmas. Taking into account the comparing rare earth element (REE) patterns, an origin of the parental magmas in enriched lithospheric mantle is suggested. Finally, it is concluded that Pliocene Gandab volcanic rocks are related to the post-collision environment that followed the Neo-Tethys subduction.

Mesozoic Tectonic Setting of SE Sundaland After Magmatism and Suture Evidences in JS-1 Ridge Area

2021 ◽  
Keyword(s):  
Early Cretaceous ◽  
Late Cretaceous ◽  
Tectonic Setting ◽  
Plate Boundary ◽  
Early Jurassic ◽  
The South ◽  
Magmatic Arc ◽  
Plate Convergence ◽  
Ridge Area ◽  
Cretaceous Subduction

Mesozoic plate convergence in SE Sundaland has been a source of debate for decades. A determination of plate convergence boundaries and timing have been explained in many publications, but not all boundaries were associated with magmatism. Through integration of both plate configurations and magmatic deposits, the basement can be accurately characterized over time and areal extents. This paper will discuss Cretaceous subductions and magmatic arc trends in SE Sundaland area with additional evidence found in JS-1 Ridge. At least three subduction trends are captured during the Mesozoic in the study area: 1) Early Jurassic – Early Cretaceous trend of Meratus, 2) Early Cretaceous trend of Bantimala and 3) Late Cretaceous trend in the southernmost study area. The Early Jurassic – Early Cretaceous subduction occurred along the South and East boundary of Sundaland (SW Borneo terrane) and passes through the Meratus area. The Early Cretaceous subduction occurred along South and East boundary of Sundaland (SW Borneo and Paternoster terranes) and pass through the Bantimala area. The Late Cretaceous subduction occurred along South and East boundary of Sundaland (SW Borneo, Paternoster and SE Java – South Sulawesi terranes), but is slightly shifted to the South approaching the Oligocene – Recent subduction zone. Magmatic arc trends can also be generally grouped into three periods, with each period corresponds to the subduction processes at the time. The first magmatic arc (Early Jurassic – Early Cretaceous) is present in core of SW Borneo terrane and partly produces the Schwaner Magmatism. The second Cretaceous magmatic arc (Early Cretaceous) trend is present in the SW Borneo terrane but is slightly shifted southeastward It is responsible for magmatism in North Java offshore, northern JS-1 Ridge and Meratus areas. The third magmatic arc trend is formed by Late Cretaceous volcanic rocks in Luk Ulo, the southern JS-1 Ridge and the eastern Makassar Strait areas. These all occur during the same time within the Cretaceous magmatic arc. Though a mélange rock sample has not been found in JS-1 Ridge area, there is evidence of an accretionary prism in the area as evidenced by the geometry observed on a new 3D seismic dataset. Based on the structural trend of Meratus (NNE-SSW) coupled with the regional plate boundary understanding, this suggests that both Meratus & JS-1 Ridge are part of the same suture zone between SW Borneo and Paternoster terranes. The gradual age transition observed in the JS-1 Ridge area suggests a southward shift of the magmatic arc during Early Cretaceous to Late Cretaceous times.

The petrological and geochemical study of granitoid rocks from Mashhad area, Iran: Evidence for the Late Triassic Collisional Belt Northeast of Iran

2021 ◽  
Author(s):  
Banafsheh Vahdati ◽  
Seyed Ahmad Mazaheri
Keyword(s):  
Subduction Zones ◽  
Tectonic Setting ◽  
Crustal Contamination ◽  
Oceanic Lithosphere ◽  
Late Triassic ◽  
Common Belief ◽  
Thrust Tectonics ◽  
Wide Range ◽  
Lree Enrichment ◽  
Granitoid Rocks

<p>Mashhad granitoid complex is part of the northern slope of the Binalood Structural Zone (BSZ), Northeast of Iran, which is composed of granitoids and metamorphic rocks. This research presents new petrological and geochemical whole-rock major and trace elements analyses in order to determine the origin of granitoid rocks from Mashhad area. Field and petrographic observations indicate that these granitoid rocks have a wide range of lithological compositions and they are categorized into intermediate to felsic intrusive rocks (SiO<sub>2</sub>: 57.62-74.39 Wt.%). Qartzdiorite, tonalite, granodiorite and monzogranite are common granitoids with intrusive pegmatite and aplitic dikes and veins intruding them. Based on geochemical analyses, the granitoid rocks are calc-alkaline in nature and they are mostly peraluminous. On geochemical variation diagrams (major and minor oxides versus silica) Na<sub>2</sub>O and K<sub>2</sub>O show a positive correlation with silica while Al<sub>2</sub>O<sub>3</sub>, TiO<sub>2</sub>, CaO, Fe<sub>2</sub>O<sub>3</sub>, and MgO show a negative trend. Therefore fractional crystallization played a considerable role in the evolution of Mashhad granitoids. Based on the spider diagrams, there are enrichments in LILE and depletion in HFSE. Low degrees of melting or crustal contamination may be responsible for LILE enrichment. Elements such as Pb, Sm, Dy and Rb are enriched, while Ba, Sr, Nd, Zr, P, Ti and Yb (in monzogranites) are all depleted. LREE enrichment and HREE depletion are observed in all samples on the Chondrite-normalized REE diagram. Similar trends may be evidence for the granitoids to have the same origin. Besides, LREE enrichment relative to HREE in some samples can indicate the presence of garnet in their source rock. Negative anomalies of Eu and Yb are observed in monzogranites. Our results show that Mashhad granitoid rocks are orogenic related and tectonic discrimination diagrams mostly indicate its syn-to-post collisional tectonic setting. No negative Nb anomaly compared with MORB seems to be an indication of non-subduction zone related magma formation. According to the theory of thrust tectonics of the Binalood region, the oceanic lithosphere of the Palo-Tethys has subducted under the Turan microplate. Since the Mashhad granitoid outcrops are settled on the Iranian plate, this is far from common belief that these granitoid rocks are related to the subduction zones and the continental arcs. The western Mashhad granitoids show more mafic characteristics and are possibly crystallized from a magma with sedimentary and igneous origin. Thus, Western granitoid outcrops in Mashhad are probably hybrid type and other granitoid rocks, S and SE Mashhad are S-type. Evidences suggest that these continental collision granitoid rocks are associated with the late stages of the collision between the Iranian and the Turan microplates during the Paleo-Tethys Ocean closure which occurred in the Late Triassic.</p>

Jurassic Arc: Reconstructing the Lost World of eastern Gondwana

Geology ◽  
2021 ◽  
Author(s):  
Elliot K. Foley ◽  
R.A. Henderson ◽  
E.M. Roberts ◽  
A.I.S. Kemp ◽  
C.N. Todd ◽  
...  
Keyword(s):  
Detrital Zircon ◽  
Tectonic Setting ◽  
Magmatic Arc ◽  
Continental Arc ◽  
Key Factor ◽  
Igneous Activity ◽  
Competing Models ◽  
Juvenile Crust ◽  
Sedimentary Fill ◽  
Continental Magmatic Arc

The tectonic setting of the Australian sector of the eastern Gondwanan margin during the Jurassic and Cretaceous is enigmatic. Whether this involved convergent tectonism and a long-lived continental magmatic arc or rift-related extension unrelated to subduction is debated. The paucity of Australian Jurassic–Cretaceous igneous outcrops makes resolving these competing models difficult. We used the detrital zircon record of the Jurassic–Cretaceous Great Australian Superbasin (GAS) as a proxy for igneous activity. We attribute the persistent magmatism recorded in GAS sedimentary fill throughout the Mesozoic to ca. 95 Ma to continuation of the established Paleozoic continental arc system. The detrital zircon record signals short (~10 m.y.) pulses of elevated Jurassic and Cretaceous magmatic activity and strongly positive εHf values, indicating juvenile crust or mantle-derived magmatism. Margin reconstruction indicates sustained continental growth at rates of at least ~55 km3 km–1 m.y.–1, mainly to the tract now represented by submerged northern Zealandia, due to the retreat of this arc system. We posit that arc retreat was a key factor in rapid crust generation and preservation, and that continental sedimentary systems globally may host cryptic records of juvenile crustal addition that must be considered in estimating crustal growth rates along convergent plate margins.

scholarly journals Permian Triassic geologic evolution in the southern Kitakami Belt, Japan

1992 ◽  
Vol 6 ◽  
pp. 155-155
Author(s):  
Kotaro Kamada
Keyword(s):  
Middle Triassic ◽  
Sedimentary Basin ◽  
Tectonic Setting ◽  
Japan Sea ◽  
Passive Margin ◽  
Middle Permian ◽  
Asian Continent ◽  
Transform Faults ◽  
Magmatic Arc ◽  
The Japan Sea

Before opening of the Japan Sea, the Japanese islands were attached to the eastern margin of the Asian continent. The Southern Kitakami Belt is regarded as a micro-continent in an accretional complex of the islands, that accreted before the Early Cretaceous. But its tectonic setting and location between the belt and the Asian continent is still an unresolved argument.Permo-Triassic sequences in the Southern Kitakami Belt are composed of shallow to off-shore deposits. These deposits are composed of clastics, carbonates with volcaniclastics. But there was no volcanic activity in the belt in the Middle to Late Permian. From the viewpoint of the sedimentary character and history, the Middle Permian to Middle Triassic sequences differ from their previous and their following successions in the belt. And the sedimentary basin of Middle Permian to Middle Triassic was bounded by transform faults. Magmatic arc was replaced by passive margin as hinterland of the Southern Kitakami Belt during the Middle Permian to Middle Triassic. It means that the sedimentary basin moved from the margin of Yangtze Platform to Sino-Korean Platform at that time.

New insights into the geologic evolution of the Grenvillian Trenton Prong inlier, Central Appalachian Piedmont, USA

2020 ◽  
Vol 57 (7) ◽  
pp. 840-854
Author(s):  
Richard A. Volkert
Keyword(s):  
Tectonic Setting ◽  
Hanging Wall ◽  
Sediment Source ◽  
Slow Cooling ◽  
Grenville Province ◽  
Magmatic Arc ◽  
Metamorphic History ◽  
Arc Setting ◽  
Appalachian Piedmont ◽  
Back Arc

New geochemical and 40Ar/39Ar hornblende and biotite data from the Grenvillian Trenton Prong inlier provide the first constraints for the identification of lithotectonic units, their tectonic setting, and their metamorphic to post-metamorphic history. Gneissic tonalite, diorite, and gabbro compose the Colonial Lake Suite magmatic arc that developed along eastern Laurentia prior to 1.2 Ga. Spatially associated low- and high-TiO2 amphibolites were formed from island-arc basalt proximal to the arc front and mid-ocean ridge basalt-like basalt in a back-arc setting, respectively. Supracrustal paragneisses include meta-arkose derived from a continental sediment source of Laurentian affinity and metagraywacke and metapelite from an arc-like sediment source deposited in a back-arc basin, inboard of the Colonial Lake arc. The Assunpink Creek Granite was emplaced post-tectonically as small bodies of peraluminous syenogranite produced through partial melting of a subduction-modified felsic crustal source. Prograde mineral assemblages reached granulite- to amphibolite-facies metamorphic conditions during the Ottawan phase of the Grenvillian Orogeny. Hornblende 40Ar/39Ar ages of 935–923 Ma and a biotite age of 868 Ma record slow cooling in the northern part of the inlier following the metamorphic peak. Elsewhere in the inlier, biotite 40Ar/39Ar ages of 440 Ma and 377–341 Ma record partial to complete thermal resetting or new growth during the Taconian and Acadian orogens. The results of this study are consistent with the Trenton Prong being the down-dropped continuation of the Grenvillian New Jersey Highlands on the hanging wall of a major detachment fault. The Trenton Prong therefore correlates to other central and northern Appalachian Grenvillian inliers and to parts of the Grenville Province proper.

scholarly journals The 1590-1520 Ma Cachoeirinha magmatic arc and its tectonic implications for the Mesoproterozoic SW Amazonian craton crustal evolution

2004 ◽  
Vol 76 (4) ◽  
pp. 807-824 ◽  
Author(s):  
Amarildo S. Ruiz ◽  
Mauro C. Geraldes ◽  
João B. Matos ◽  
Wilson Teixeira ◽  
William R. Van Schumus ◽  
...  
Keyword(s):  
Crystallization Process ◽  
Major And Trace Elements ◽  
Magmatic Arc ◽  
Rio Negro ◽  
Intrusive Rocks ◽  
Amazonian Craton ◽  
Granitoid Rocks ◽  
Geologic Setting ◽  
Fractional Crystallization Process ◽  
Tectonic Relationship

Isotopic and chemical data of rocks from the Cachoeirinha suite provide new insights on the Proterozoic evolution of the Rio Negro/Juruena Province in SW Amazonian craton. Six U-Pb and Sm-Nd analyses in granitoid rocks of the Cachoeirinha suite yielded ages of 1587-1522 Ma and T DM model ages of 1.88-1.75 Ga (EpsilonNd values of -0.8 to +1.0). In addition, three post-tectonic plutonic rocks yielded U-Pb ages from 1485-1389 Ma (T DM of 1.77-1.74 Ga and EpsilonNd values from -1.3 to +1.7). Variations in major and trace elements of the Cachoeirinha suite rocks indicate fractional crystallization process and magmatic arc geologic setting. These results suggest the following interpretations: (1) The interval of 1590-1520 Ma represents an important magmatic activity in SW Amazonian craton. (2) T DM and arc-related chemical affinity supportthe hypothesis that the rocks are genetically associated with an east-dipping subduction zone under the older (1.79-1.74 Ga) continental margin. (3) The 1590-1520 Ma age of intrusive rocks adjacent to an older crust represents similar geological framework along the southern margin of Baltica, corroborating the hypothesis of tectonic relationship at that time.

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