scholarly journals Sr and Nd isotopic characteristics of 1.77-1.58 Ga rift-related granites and volcanics of the Goiás tin province, central Brazil

2001 ◽  
Vol 73 (2) ◽  
pp. 263-276 ◽  
Author(s):  
MÁRCIO M. PIMENTEL ◽  
NILSON F. BOTELHO
Keyword(s):  
Continental Rift ◽  
Rift System ◽  
Isotopic Data ◽  
Sialic Crust ◽  
Central Brazil ◽  
T Values

Supracrustal rocks of the Araí Group, together with coeval A-type granites represent a ca. 1.77-1.58 Ga old continental rift in Brazil. Two granite families are identified: the older (1.77 Ga) group forms small undeformed plutons, and the younger granites (ca. 1.58 Ga) constitute larger, deformed plutons. Sr-Nd isotopic data for these rocks indicate that the magmatism is mostly product of re-melting of Paleoproterozoic sialic crust. Initial Sr ratios for both granite families are ca 0.726 and 0.720. Most TDM model ages are between 2.58 and 1.80 Ga. epsilonND(T) values are between +3.6 and -11.9. Araí volcanics are bimodal, with basalts and dacites/rhyolites interlayered with continental sediments. The felsic volcanics show Nd isotopic characteristics which are very similar to the granites, and are also interpreted as reworking of Paleoproterozoic crust. Detrital sediments of the Araí Group revealed T DM model ages between 2.4 and 2.16 Ga, indicating that they are the product of erosion of Paleoproterozoic crust. The data indicate that the Araí rift system was established on crust that had just become stable after the Paleoproterozoic orogeny.

scholarly journals Shrimp and conventional U-Pb age, Sm-Nd isotopic characteristics and tectonic significance of the K-rich Itapuranga suite in Goiás, Central Brazil

2003 ◽  
Vol 75 (1) ◽  
pp. 97-108 ◽  
Author(s):  
MÁRCIO M. PIMENTEL ◽  
ELTON L. DANTAS ◽  
REINHARDT A. FUCK ◽  
RICHARD A. ARMSTRONG
Keyword(s):  
Magma Mixing ◽  
Regional Metamorphism ◽  
Quartz Syenite ◽  
Sialic Crust ◽  
Central Brazil ◽  
Tectonic Significance ◽  
Mafic Magmas ◽  
End Members ◽  
T Values ◽  
Tectonic Origin

The Itapuranga alkali granite and Uruana quartz syenite are large K-rich EW-elongated intrusions, in the central part of the Neoproterozoic Brasília Belt, central Brazil. They are associated with Pireneus lineaments, which cut the regional NNW-SSE structures of the southern part of the belt. SHRIMP and conventional U-Pb data for the Itapuranga and Uruana intrusions indicate crystallization ages of 624 ± 10 Ma and 618 ± 4 Ma, respectively. Three zircon cores from the Itapuranga granite yielded U-Pb ages between 1.79 and 1.49 Ga. Sm-Nd T DM ages for both intrusions are 1.44 Ga and epsilonNd(T) values are -5.1 and -5.7, suggesting the input of material derived from older (Paleo- to Mesoproterozoic) sialic crust in the origin of the parental magmas. Magma mixing structures indicate co-existence of mafic and felsic end-members. The felsic end-member of the intrusions is dominantly represented by crust-derived melts, formed in response to the invasion of Paleo/Mesoproterozoic sialic crust by alkali-rich mafic magmas at ca. 620 Ma. These intrusions are roughly contemporaneous with, or perhaps slightly younger than, the peak of regional metamorphism in the southern Brasília Belt. Their emplacement along the Pireneus lineament suggest a syn-tectonic origin for them, most probably in transtensional settings along these faults.

scholarly journals U-Pb SHRIMP and Sm-Nd geochronology of the Silvânia Volcanics and Jurubatuba Granite: juvenile Paleoproterozoic crust in the basement of the Neoproterozoic Brasília Belt, Goiás, central Brazil

2001 ◽  
Vol 73 (3) ◽  
pp. 445-460 ◽  
Author(s):  
DANIELLE P. FISCHEL ◽  
MÁRCIO M. PIMENTEL ◽  
REINHARDT A. FUCK ◽  
RICHARD ARMSTRONG
Keyword(s):  
Central Brazil ◽  
Metavolcanic Rocks ◽  
Isotopic Analyses ◽  
T Values ◽  
Magmatic Event

U-Pb SHRIMP and Sm-Nd isotopic ages were determined for felsic metavolcanic rocks from the Silvânia Sequence and Jurubatuba Granite in the central part of the Brasília Belt. Zircon grains from a metavolcanic sample yielded 2115 ± 23 Ma and from the granite yielded 2089 ± 14 Ma, interpreted as crystallization ages of these rocks. Six metavolcanic samples of the Silvânia Sequence yielded a six-point whole-rock Sm-Nd isochron indicating a crystallization age of 2262 ± 110 Ma and positive epsilonNd(T) = +3.0 interpreted as a juvenile magmatic event. Nd isotopic analyses on samples from the Jurubatuba Granite have Paleoproterozoic T DM model ages between 2.30 and 2.42 Ga and epsilonNd(T) values vary between -0.22 and -0.58. The oldest T DM value refers to a sedimentary xenolith in the granite. These results suggest crystallization ages of Silvânia volcanics and Jurubatuba Granite are the first evidence of a ca. 2.14-2.08 juvenile magmatic event in the basement of the central part of the Brasília Belt that implies the presence of arc/suture hidden in reworked basement of the Brasília Belt.

Cenozoic high Sr/Y volcanic rocks in the Qiangtang terrane, northern Tibet: geochemical and isotopic evidence for the origin of delaminated lower continental melts

2008 ◽  
Vol 145 (4) ◽  
pp. 463-474 ◽  
Author(s):  
SHEN LIU ◽  
RUI-ZHONG HU ◽  
CAI-XIA FENG ◽  
HAI-BO ZOU ◽  
CAI LI ◽  
...  
Keyword(s):  
Subduction Zones ◽  
Volcanic Rocks ◽  
Mantle Peridotite ◽  
Calc Alkaline ◽  
Isotopic Data ◽  
Slab Melting ◽  
Northern Tibet ◽  
High K ◽  
T Values ◽  
Qiangtang Terrane

AbstractGeochemical and Sr–Nd–Pb isotopic data are presented for volcanic rocks from Zougouyouchaco (30.5 Ma) and Dogai Coring (39.7 Ma) of the southern and middle Qiangtang block in northern Tibet. The volcanic rocks are high-K calc-alkaline trachyandesites and dacites, with SiO2 contents ranging from 58.5 to 67.1 wt % The rocks are enriched in light REE (LREE) and contain high Sr (649 to 986 ppm) and relatively low Yb (0.8 to 1.2 ppm) and Y (9.5 to 16.6 ppm) contents, resulting in high La/Yb (29–58) and Sr/Y (43–92) ratios, as well as relatively high MgO contents and Mg no., similar to the compositions of adakites formed by slab melting in subduction zones. However, the adakitic rocks in the Qiangtang block are characterized by relatively low εNd(t) values (−3.8 to −5.0) and highly radiogenic Sr ((87Sr/86Sr)i=0.706–0.708), which are inconsistent with an origin by slab melting. The geochemistry and tectonics indicate that the adakitic volcanic rocks were most likely derived from partial melting of delaminated lower continental crust. As the pristine adakitic melts rose, they interacted with the surrounding mantle peridotite, elevating their MgO values and Mg numbers.

scholarly journals Geochronology and Geochemistry of the Zengudi and Tuobake Granite Porphyries in the Sanjiang Region, SW China: Petrogenesis and Tectonic Significance

Minerals ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 404
Author(s):  
Mao-Jun Tian ◽  
Huan Li ◽  
Landry Soh Tamehe ◽  
Zhen Xi
Keyword(s):  
Basaltic Magma ◽  
Volcanic Rocks ◽  
Isotopic Data ◽  
Tectonic Significance ◽  
Gondwana Margin ◽  
Granite Porphyries ◽  
Tethys Ocean ◽  
T Values ◽  
Crust Shortening ◽  
Representative Samples

The boundary between the Gondwana and Yangtze plate is still controversial. In southwest China, the Sanjiang region marks the collision zone which accreted several blocks coming from the northern Gondwana margin. In this region, subduction of the Paleo-Tethys Ocean and associated continental blocks during the Triassic Period led to the formation of an N–S trending complex involving intrusive and volcanic rocks. The intrusive rocks are important for constraining the evolution of the Paleo-Tethyan in southwestern China. This study presents new geochronological, geochemical, and Sr-Nd-Hf isotopic data of granite porphyries from northern Lancangjiang, in order to discuss the origin of these granites and their tectonic significance. Representative samples of the Zengudi and the Tuobake granite porphyries from the Yezhi area yielded weighted mean 206Pb/238U ages of 247–254 Ma and 246 Ma, respectively. The Zengudi granite porphyries display zircon ԐHf(t) values of −12.94 to −2.63, ԐNd(t) values of −14.5 to −9.35, and initial 87Sr/86Sr ratios of 0.708 to 0.716. The Tuobake granite porphyries have zircon ԐHf(t) values of −14.06 to −6.55, ԐNd(t) values of −10.9 to −9.41, and initial 87Sr/86Sr ratios of 0.716 to 0.731. Both the Zengudi and Tuobake granite porphyries exhibit strongly peraluminous signatures with high A/CNK nAl2O3/(K2O + Na2O + K2O) ratios (1.07–1.86 and 0.83–1.33, respectively). These granites are enriched in Rb and Th, and depleted in Ti, Nb, Ta, Sr, and P, with negative Eu anomalies (Eu/Eu* < 0.61). These geochemical and isotopic data indicate that the primary magma of the granite porphyries originated from partial melting of ancient continental crust as a result of basaltic magma underplating and underwent fractionation crystallization during their emplacement. We propose that the Triassic subduction of the Paleo-Tethys Ocean led to crust shortening and thickening in the Sanjiang region, while the northern Lancangjiang area was involved in the continental collision after the subduction of the Paleo-Tethys Ocean before 254 Ma.

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