Geologic history of Martian regolith breccia Northwest Africa 7034: Evidence for hydrothermal activity and lithologic diversity in the Martian crust

The timing and mode of deposition for Martian regolith breccia Northwest Africa (NWA) 7034 were determined by combining petrography, shape analysis, and thermochronology. NWA 7034 is composed of igneous, impact, and brecciated clasts within a thermally annealed submicron matrix of pulverized crustal rocks and devitrified impact/volcanic glass. The brecciated clasts are likely lithified portions of Martian regolith with some evidence of past hydrothermal activity. Represented lithologies are primarily ancient crustal materials with crystallization ages as old as 4.4 Ga. One ancient zircon was hosted by an alkali-rich basalt clast, confirming that alkalic volcanism occurred on Mars very early. NWA 7034 is composed of fragmented particles that do not exhibit evidence of having undergone bed load transport by wind or water. The clast size distribution is similar to terrestrial pyroclastic deposits. We infer that the clasts were deposited by atmospheric rainout subsequent to a pyroclastic eruption(s) and/or impact event(s), although the ancient ages of igneous components favor mobilization by impact(s). Despite ancient components, the breccia has undergone a single pervasive thermal event at 500–800°C, evident by groundmass texture and concordance of ~1.5 Ga dates for bulk rock K-Ar, U-Pb in apatite, and U-Pb in metamict zircons. The 1.5 Ga age is likely a thermal event that coincides with rainout/breccia lithification. We infer that the episodic process of regolith lithification dominated sedimentary processes during the Amazonian Epoch. The absence of pre-Amazonian high-temperature metamorphic events recorded in ancient zircons indicates source domains of static southern highland crust punctuated by episodic impact modification

The geological history of the Latimojong region of western Sulawesi, Indonesia

We present an updated geological map and revised stratigraphy of the Latimojong region of central-western Sulawesi. This work includes new biostratigraphic ages from the Latimojong Metamorphic Complex, Toraja Group, Makale Formation and Enrekang Volcanics, together with whole-rock geochemical data and sensitive high-resolution ion microprobe (SHRIMP) U-Pb analyses from zircons extracted from igneous rocks in the region. Previous work on the study region and in other parts of Sulawesi have discussed the age and character of two different rock sequences with similar names, the Latimojong Complex and the Latimojong Formation. One would assume that the type location for these two sequences is in the Latimojong Mountains. However, there is considerable confusion as to the character and location of these sequences. We make a distinction between the Latimojong Formation and the Latimojong Complex, and propose that the Latimojong Complex be renamed the Latimojong Metamorphic Complex to minimise the confusion associated with the current nomenclature. The Latimojong Metamorphic Complex is an accretionary complex of low- to high-grade metamorphic rocks tectonically mixed with cherts and ophiolitic rocks, while the Latimojong Formation consists of Upper Cretaceous weakly deformed, unmetamorphosed sediments or very low-grade metasediments (previously interpreted as flysch or distal turbidites that unconformably overlie older rocks). Our work indicates that the Latimojong Formation must be restricted to isolated, unobserved segments of the Latimojong Mountains, or are otherwise not present in the Latimojong region, meaning the Latimojong Formation would only be found further north in western Sulawesi. Radiolaria extracted from chert samples indicate that the Latimojong Metamorphic Complex was likely assembled during the Cretaceous (Aptian-Albian) and was later metamorphosed. Ages obtained from benthic and planktonic foraminifera were used to differentiate and map the Toraja Group (Ypresian to Chattian: 56-23 Ma), Makale Formation (Burdigalian to Serravallian: 20.5-11.5 Ma) and Enrekang Volcanic Series (8.0-3.6 Ma) across the study area. U-Pb isotopic data collected from magmatic zircons record several phases of volcanism (∼38 Ma, ∼25 Ma and 8.0-3.6 Ma) in the region. Each phase of magmatism can be distinguished according to petrology and whole-rock geochemical data. The isotopic ages also show that dacites from the Enrekang Volcanic Series are contemporaneous with the emplacement of the Palopo Granite (6.6-4.9 Ma). Miocene to Proterozoic inherited zircons within these igneous rocks support earlier suggestions that Sulawesi potentially has a Proterozoic-Phanerozoic basement or includes sedimentary rocks (and therefore detrital zircons) derived from the erosion of Proterozoic or younger material. Some earlier work proposed that the granitic rocks in the region developed due to crustal melting associated with plate collision and radiogenic heating. Our observations however, support different interpretations, where the granites are associated with arc magmatism and/or crustal extension. The region was cross-cut by major strike-slip fault zones during the Pliocene. This deformation and the buoyancy associated with relatively young intrusions may have facilitated uplift of the mountains

The provenance of Borneo's enigmatic alluvial diamonds:A case study from Cempaka, SE Kalimantan

Gem-quality diamonds have been found in several alluvial deposits across central and southern Borneo. Borneo has been a known source of diamonds for centuries, but the location of their primary igneous source remains enigmatic. Many geological models have been proposed to explain their distribution, including: the diamonds were derived from a local diatreme; they were brought to the surface through ophiolite obduction or exhumation of UHP metamorphic rocks; they were transported long distances southward via major Asian river systems; or, they were transported from the Australian continent before Borneo was rifted from its northwestern margin in the Late Jurassic. To assess these models, we conducted a study of the provenance of heavy minerals from Kalimantan's Cempaka alluvial diamond deposit. This involved collecting U–Pb isotopic data, fission track and trace element geochemistry of zircon as well as major element geochemical data of spinels and morphological descriptions of zircon and diamond. The results indicate that the Cempaka diamonds were likely derived from at least two sources, one which was relatively local and/or involved little reworking, and the other more distal which records several periods of reworking. The distal diamond source is interpreted to be diamond-bearing pipes that intruded the basement of a block that: (1) rifted from northwest Australia (East Java or SW Borneo) and the diamonds were recycled into its sedimentary cover, or: (2) were emplaced elsewhere (e.g. NW Australia) and transported to a block (e.g. East Java or SW Borneo). Both of these scenarios require the diamonds to be transported with the block when it rifted from NW Australia in the Late Jurassic. The local source could be diamondiferous diatremes associated with eroded Miocene high-K alkaline intrusions north of the Barito Basin, which would indicate that the lithosphere beneath SW Borneo is thick (~ 150 km or greater). The ‘local’ diamonds could also be associated with ophiolitic rocks that are exposed in the nearby Meratus Mountains

Provenance of the Early Mesoproterozoic Radium Creek Group in the northern Mount Painter Inlier: Correlating isotopic signatures to inform tectonic reconstructions

New in situ zircon LA-ICPMS geochronologic and Hf-isotope data from the Radium Creek Group within the Mount Painter Inlier provide important temporal constraints on the Early Mesoproterozoic palaeogeography of eastern Proterozoic Australia. The entire Radium Creek Group was deposited in a single basin forming phase, and has a maximum depositional age of 1595. ±. 3.7. Ma. Detrital zircon from these metasedimentary rocks have U-Pb age populations at ca. 1595. Ma, 1660-1680. Ma, 1710-1780. Ma, ca. 1850. Ma and ca. 2500. Ma. These grains are characterised by isotopically diverse and evolved sources, and have crystallised within predominantly felsic igneous host-rocks. The relative age spectra and isotopic character has more similarity with the Gawler Craton than the Arunta Block, Curnamona Province or the Mount Isa Inlier. These observations suggest that the Mount Painter Province was adjacent to the Gawler Craton in the Early Mesoproterozoic. Our data supports a coherent South Australian Craton at ca. 1595. Ma and a contiguous continental mass that included the North and South Australian cratons. The Mount Painter Inlier occupied a complex plate tectonic setting in the overriding plate of two convergent margins. © 2014 Elsevier B.V

Archaean komatiitic and tholeiitic volcanics at Kambalda, Western Australia

Archaean metamorphosed mafic and ultramafic greenstone volcanics at Kambalda, W. Australia, divide into five stratigraphic and lithological groups: (a) lower footwall tholeiitic basalts with &sim;8&#37; MgO and spherulitic pyroxene textures; (b) upper footwall tholeiitic basalts with &sim;8&#37; MgO and subophitic textures; &sim;30&#37;-20&#37; MgO olivine spinifex textured komatiite lavas; (c) moderate to low MgO variolitic pillow basalts with felsic cores; (d) moderate to low MgO olivine - and pyroxene-phyric basalts. The lavas were erupted subaqueously, probably in deep water. The footwall basalts and komatiites share chondritic mantle ratios of Al/Ca/Ti/Zr/Y/REE, and geochemical trends suggest that the low-MgO basalts are minimum density cotectic lavas derived via olivine loss from komatiite parent magma. Spherulitic basal textures result from eruption as superheated liquids, subophitic textures from eruption at subliquidus temperatures. The parent magma of the footwall basalts was subsequently erupted as the Kambalda komatiite lavas, and the derivative nature of the footwall basalts implies the existence below Kambalda of an olivine cumulative body. High-Mg basalts overlying the komatiites are LREE-enriched, and cannot be related to LREE-depleted komatiite compositions by crystal fractionation. They either represent independent melts of enriched source compositions, or crustal contamination of komatiite magma. Felsic cores to variolitic pillows of high-Mg basalt probably result from metasomatic alteration, and do not represent immiscible igneous liquids. Geochemical trends thus directly link the high-Mg komatiite with the low-Mg tholeiite series. Pyroxene spinifex textured high-Mg basalts are not intermediate between the two and are not simply related to komatiites. Application of the term komatiitic to these basalts is therefore misleading. Conflicting evidence supports an eruption age of either &sim;3.2Ga, in which case the mantle was chemically but not isotopically differenitiated, or &sim;2.7Ga in which case either the mantle had gross Nd isotopic heterogeneities or LREE-enriched magmas are crustally contaminated. (D74037/87)</p