Petrogenetic and geodynamic origin of the Neoarchean Doré Lake Complex, Abitibi subprovince, Superior Province, Canada

Abstract

The Neoarchean (ca. 2728 Ma) anorthosite-bearing Doré Lake Complex in the northeastern Abitibi subprovince, Quebec, was emplaced into an association of intra-oceanic tholeiitic basalts and gabbros known as the Obatogamau Formation. The Obatogamau Formation constitutes the lower part of the Roy Group, which is composed of two cycles of tholeiitic to calc-alkaline volcanic and volcaniclastic rocks, siliciclastic and chemical sedimentary rocks, and layered mafic to ultramafic sills. In this study, we report major and trace element results, and Nd, Sr, Pb and O isotope data for anorthosites, leucogabbros, gabbros and mafic dykes from the Doré Lake Complex and spatially associated basalts and gabbros of the Obatogamau Formation to assess their petrogenetic origin and geodynamic setting. Field and petrographic observations indicate that the Doré Lake Complex and associated volcanic rocks underwent extensive metamorphic alteration under greenschist facies conditions, resulting in widespread epidotization (20-40%) and chloritization (10-40%) of many rock types. Plagioclase recrystallized mainly to anorthite and albite endmembers, erasing intermediate compositions. Metamorphic alteration also led to the mobilization of many elements (e.g., LILE and transition metals) and to significant disturbance of the Rb-Sr and U-Pb isotope systems, resulting in 1935±150 Ma and 3326±270 Ma errorchron ages, respectively. The Sm-Nd isotope system was less disturbed, yielding an errorchron age of 2624±160 Ma. On many binary major and trace element diagrams, the least altered anorthosites and leucogabbros, and the gabbros and mafic dykes of the Doré Lake Complex plot in separate fields, signifying the presence of two distinct magma types in the complex. The gabbros and mafic dykes in the Doré Lake Complex share the geochemical characteristics of tholeiitic basalts and gabbros in the Obatogamau Formation, suggesting a possible genetic link between the two rock associations. Initial Nd (+2.6 to +5.0) and  18 O (+6.1 to +7.9‰) values for the Doré Lake Complex and gabbros of the Obatogamau Formation (Nd=+2.8 to +4.0;  18 O=+7.3 to 8.0‰) are consistent with depleted mantle sources. All rock types in the Doré Lake Complex and the Roy Group share the trace element characteristics of modern arc magmas, suggesting a suprasubduction zone setting for these two lithological associations. On the basis of regional geology and geochemical data, we suggest that the Doré Lake Complex and the Obatogamau Formation represent a dismembered fragment of a suture zone, like many Phanerozoic ophiolites, resulting from closure of a backarc basin between 2703-2690 Ma.

An Integrated Model for Ilmenite, Al-Spinel, and Corundum Exsolutions in Titanomagnetite from Oxide-Rich Layers of the Lac Doré Complex (Québec, Canada)

“…Moreover, these authors claim that the LDC shows geochemical resemblances to the Waconichi Formation tuffs (the felsic cap of the second Roy Group cycle; Figure 1), suggesting that it could represent the Waconichi's shallow magma chamber. More recently, Polat et al [5] proposed that the parental magma giving birth to gabbros and mafic dykes in the complex is genetically linked to the Obatogamau tholeiites, whereas the anorthositic rocks would involve a different magma source.…”

“…In the case of the LDC, Polat et al [5] recently proposed the presence of two different magma types, one generating gabbros and mafic dykes (genetically linked to the Obatogamau tholeiites), and the other anorthositic rocks. Along the same lines, we propose in the following section that the Layered Series of the LDC was built from successive magma injections with potential evidence of magma chamber inflation.…”

“…The Lac Doré Complex (LDC) in Québec, Canada, is a layered intrusion hosting a large deposit of vanadiferous titanomagnetite. Although the LDC has been well-documented since the 1960s from a lithological, structural, and petrogenetic perspective (e.g., [1][2][3][4][5]), no attempt has been made to investigate exsolution features in titanomagnetite and consider which parameters control their variation across the stratigraphy.…”

Origin of the Vanadiferous Serpentine–Magnetite Rocks of the Mt. Sorcerer Area, Lac Doré Layered Intrusion, Chibougamau, Québec

“…The LDC is also cut by a number of ultramafic to felsic dykes. Some of these intrusions are tonalite dykes related to the Chibougamau pluton, while most of the mafic dykes observed in the layered zone potentially represent feeders of the volcanic cycle 2 [9]. [1] and (b) in its NE limb [5].…”

“…The parental magma is generally viewed as tholeiitic [1,18,23] and, according to trace element modelling, may have coexisted with a calc-alkaline magma [24]. The rare earth elements (REE) and multi-element profiles of the LDC rocks are flat, can be more or less enriched in the most incompatible elements, and have abundances close to a N-MORB composition [9].…”