USGS Science⌕ Search
Home/Archive/USGS

USGS · 70030615

Cambrian nepheline syenite complex at Jabal Sawda, Midyan region, Kingdom of Saudi Arabia

W.K. Liddicoat·C.R. Ramsay·C. E. Hedge
View original source ↗Export metadata ↓

Abstract

The only nepheline syenite complex presently known in the Arabian Shield is at Jabal Sawda, about 30 km S of Haql in the extreme NW of Saudi Arabia. It is a post-tectonic, composite intrusion with a crudely concentric structure. A core of leuco-nepheline syenite, a partial ring of mela-nepheline syenite, and an almost complete outer ring of alkali-feldspar syenite are the main rock units. Several mega-inclusions of porphyritic nepheline syenite, nepheline monzosyenite, malignite and ijolite are present in the leuco-nepheline syenite. The chemical composition is notable for very high values of Al 2 O 3 , Na 2 O, Ba, La, Nb, Sr and Zr. U Pb isotope dating indicates an emplacement age of 553 ± 4 Ma, one of an increasing number of reliable Cambrian isotope dates in the northern Red Sea region.

Explore related subjects

Journal of African Earth SciencesArticle

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

W.K. Liddicoat, C.R. Ramsay, C. E. Hedge. 1986. Cambrian nepheline syenite complex at Jabal Sawda, Midyan region, Kingdom of Saudi Arabia. https://doi.org/10.1016/s0899-5362(86)80075-6

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related USGS reports

USGS2026

Sedimentological and geochemical characterization of lacustrine deposits of the Babouri-Figuil basin, northern Cameroon: Implications for source rocks distribution and petroleum exploration

The West and Central African Rift System (WCARS) refers to the series of Cretaceous rift basins where commercial hydrocarbon accumulations have been discovered. Some of the WCARS frontier basins are currently being investigated to increase our understanding of these basins in light of new commercial discoveries. The present study was performed in the Babouri-Figuil Basin (BFB), which is genetically related to the WCARS and constitutes an area of interest in terms of petroleum prospecting, where the distribution of petroleum source rocks and potential targets for petroleum exploration across the entire basin is poorly understood. For the current study, an integrated facies analysis along with organic and inorganic geochemical techniques were applied to the basin's Cretaceous deposits with the aim of reconstructing the paleodepositional environment, assessing factors that triggered the input of organic matter, and providing a spatial overview of the organic matter accumulation in the basin based on outcrop samples. An alluvial fan-lacustrine-braided river system is inferred from the facies analysis of the stratigraphic sequence consisting of conglomerate, sandstone, siltstone, limestone, marlstone, and claystone. Bulk analysis of organic matter reveals that black shale and massive claystone are the main prospective petroleum source rocks in the basin. Inorganic geochemical analyses reveal the influence of anoxic conditions, moderate to high primary productivity, and low terrigenous inputs in organic matter enrichment. The formations rich in organic matter are predominantly concentrated in the western and eastern parts of the basin which may represent areas with depressions, characterized by high accommodation space. In terms of the regional context of the WCARS rift basins, typical hydrocarbon exploration in the BFB may target basal-conglomerate, sandstone beds situated directly above or/and interbedded with the Lower Cretaceous source rocks, and the Upper Cretaceous sandstone beds. Basement rocks (granite, granodiorite, and gneisses) and oil shale deposits may represent potential unconventional hydrocarbon exploration. The current integrated study provides an insight that should guide future hydrocarbon exploration campaigns in the basin.

Babouri-Figuil basin↗
USGS2025

Geochemistry and spatial distribution of Neoproterozoic dike swarms from the northwestern tip of the Arabian-Nubian Shield: Implications for crustal extension

Ediacaran dike swarms in the Arabian-Nubian Shield (ANS) provide key insights into post-collisional tectonics and magmatism. This study presents new chemical data, two 40 Ar/ 39 Ar ages, and spatial distribution analysis for dike swarms in the northernmost ANS exposures in SW Jordan. Hornblende from a lamprophyre sill intruding the Saramuj Conglomerate yielded a plateau age of ∼592 ± 3 Ma, interpreted as the crystallization age of the sill. Micro-cores of sericite-rich domains in altered plagioclase phenocrysts from a dolerite dike intruding ∼586 Ma alkali granite produced ages of ∼580–570 Ma, interpreted as hydrothermal alteration ages, constraining dike emplacement to 586–580 Ma. The geochemistry of investigated dikes varies from alkaline to subalkaline and crosscuts calc-alkaline magmatic rocks. This transition reflects a shift from compression to extension (∼610-590 Ma), lithospheric thinning, and changes in mantle sources. After 590 Ma, magmatism became exclusively alkaline, forming A-type granitoids and dolerites, marking a shift to extensional magmatism. Dikes predominantly follow NE-SW and E-W orientations, with rare N-S, NW-SE, and WNW-ESE trends, suggesting a major horizontal extension direction from NW-SE to N-S. Dike density ranges from 5 to 13 %, averaging ∼9 %, with crustal extension estimates of 9–23 %, averaging 16 %. No correlation was found between dike composition, orientation, or order of emplacement, indicating consistent stress orientation during the final stage (605-580 Ma) of ANS evolution.

Journal of African Earth Sciences↗
USGS2014

A geological synthesis of the Precambrian shield in Madagascar

Available U–Pb geochronology of the Precambrian shield of Madagascar is summarized and integrated into a synthesis of the region’s geological history. The shield is described in terms of six geodynamic domains, from northeast to southwest, the Bemarivo, Antongil–Masora, Antananarivo, Ikalamavony, Androyan–Anosyan, and Vohibory domains. Each domain is defined by distinctive suites of metaigneous rocks and metasedimentary groups, and a unique history of Archean (∼2.5 Ga) and Proterozoic (∼1.0 Ga, ∼0.80 Ga, and ∼0.55 Ga) reworking. Superimposed within and across these domains are scores of Neoproterozoic granitic stocks and batholiths as well as kilometer long zones of steeply dipping, highly strained rocks that record the effects of Gondwana’s amalgamation and shortening in latest Neoproterozoic time (0.560–0.520 Ga). The present-day shield of Madagascar is best viewed as part of the Greater Dharwar Craton, of Archean age, to which three exotic terranes were added in Proterozoic time. The domains in Madagascar representing the Greater Dharwar Craton include the Antongil–Masora domain, a fragment of the Western Dharwar of India, and the Neoarchean Antananarivo domain (with its Tsaratanana Complex) which is broadly analogous to the Eastern Dharwar of India. In its reconstructed position, the Greater Dharwar Craton consists of a central nucleus of Paleo-Mesoarchean age (>3.1 Ga), the combined Western Dharwar and Antongil–Masora domain, flanked by mostly juvenile “granite–greenstone belts” of Neoarchean age (2.70–2.56 Ga). The age of the accretionary event that formed this craton is approximately 2.5–2.45 Ga. The three domains in Madagascar exotic to the Greater Dharwar Craton are the Androyan–Anosyan, Vohibory, and Bemarivo. The basement to the Androyan–Anosyan domain is a continental terrane of Paleoproterozoic age (2.0–1.78 Ga) that was accreted to the southern margin (present-day direction) of the Greater Dharwar Craton in pre-Stratherian time (>1.6 Ga), and rejuvenated at 1.03–0.93 Ga with the creation of the Ikalamavony domain. The Vohibory domain, an oceanic terrane of Neoproterozoic age was accreted to the Androyan–Anosyan domain in Cryogenian time (∼0.63–0.60 Ga). The Bemarivo domain of north Madagascar is a terrane of Cryogenian igneous rocks, with a cryptic Paleoproterozoic basement, that was accreted to the Greater Dharwar Craton in latest Ediacaran to earliest Cambrian time (0.53–0.51 Ga).

Journal of African Earth Sciences↗