Five hundred million years of punctuated addition of juvenile crust during extension in the Goochland Terrane, central Appalachian Piedmont Province

Research Article| August 01, 2003 Geochronology of the Mesoproterozoic State Farm gneiss and associated Neoproterozoic granitoids, Goochland terrane, Virginia Brent E. Owens; Brent E. Owens 1Department of Geology, College of William and Mary, Williamsburg, Virginia 23187, USA Search for other works by this author on: GSW Google Scholar Robert D. Tucker Robert D. Tucker 1Department of Geology, College of William and Mary, Williamsburg, Virginia 23187, USA Search for other works by this author on: GSW Google Scholar Author and Article Information Brent E. Owens 1Department of Geology, College of William and Mary, Williamsburg, Virginia 23187, USA Robert D. Tucker 1Department of Geology, College of William and Mary, Williamsburg, Virginia 23187, USA Publisher: Geological Society of America Received: 14 Sep 2002 Revision Received: 15 Jan 2003 Accepted: 07 Feb 2003 First Online: 02 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (2003) 115 (8): 972–982. https://doi.org/10.1130/B25258.1 Article history Received: 14 Sep 2002 Revision Received: 15 Jan 2003 Accepted: 07 Feb 2003 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Brent E. Owens, Robert D. Tucker; Geochronology of the Mesoproterozoic State Farm gneiss and associated Neoproterozoic granitoids, Goochland terrane, Virginia. GSA Bulletin 2003;; 115 (8): 972–982. doi: https://doi.org/10.1130/B25258.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The Goochland terrane is an isolated block of Mesoproterozoic crust in the Piedmont Province of central Virginia. We report U-Pb zircon dates and whole-rock major and trace element data for the State Farm gneiss, one of the main units in the terrane, and additional results for a newly recognized suite of Neoproterozoic granitoids that intrude the gneiss. The State Farm gneiss ranges in bulk composition from quartz monzodiorite to granite, and three samples yield U-Pb zircon dates of 1046 +7/–6 Ma, 1039 +18/–11 Ma, and 1023 ± 10 Ma. We interpret these dates as igneous crystallization ages, which indicate a maximum emplacement interval of ca. 1057–1013 Ma for these samples. Neoproterozoic granitoids (including the Fine Creek Mills and Flat Rock granites) are more alkaline than the State Farm gneiss and display all compositional characteristics of A-type granites (e.g., high Fe/Mg, Ga, Ga/Al, Nb, Zn, Y, Zr). U-Pb zircon analyses from five separate bodies indicate crystallization ages from ca. 654 to 588 Ma, but all results are complicated by Mesoproterozoic (ca. 1 Ga) inheritance, coupled, in some cases, with secondary Pb loss. We interpret the ages and compositions of the younger rocks to reflect Neoproterozoic rifting of the Goochland terrane, but its location during rifting is uncertain. The terrane may have been separated from Laurentia during the Neoproterozoic breakup of Rodinia and later reattached. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Research Article| November 01, 1996 Middle Proterozoic age for the Montpelier Anorthosite, Goochland terrane, eastern Piedmont, Virginia John N. Aleinikoff; John N. Aleinikoff 1U.S. Geological Survey, Box 25096, M.S. 963, Denver, Colorado 80225 Search for other works by this author on: GSW Google Scholar J. Wright Horton, Jr.; J. Wright Horton, Jr. 2U.S. Geological Survey, 926 National Center, Reston, Virginia 20192 Search for other works by this author on: GSW Google Scholar Marianne Walter Marianne Walter 1U.S. Geological Survey, Box 25096, M.S. 963, Denver, Colorado 80225 Search for other works by this author on: GSW Google Scholar Author and Article Information John N. Aleinikoff 1U.S. Geological Survey, Box 25096, M.S. 963, Denver, Colorado 80225 J. Wright Horton, Jr. 2U.S. Geological Survey, 926 National Center, Reston, Virginia 20192 Marianne Walter 1U.S. Geological Survey, Box 25096, M.S. 963, Denver, Colorado 80225 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1996) 108 (11): 1481–1491. https://doi.org/10.1130/0016-7606(1996)108<1481:MPAFTM>2.3.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation John N. Aleinikoff, J. Wright Horton, Marianne Walter; Middle Proterozoic age for the Montpelier Anorthosite, Goochland terrane, eastern Piedmont, Virginia. GSA Bulletin 1996;; 108 (11): 1481–1491. doi: https://doi.org/10.1130/0016-7606(1996)108<1481:MPAFTM>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Uranium-lead dating of zircons from the Montpelier Anorthosite confirms previous interpretations, based on equivocal evidence, that the Goochland terrane in the eastern Piedmont of Virginia contains Grenvillian basement rocks of Middle Proterozoic age. A very few prismatic, elongate, euhedral zircons, which contain 12–29 ppm uranium, are interpreted to be igneous in origin. The vast majority of zircons are more equant, subangular to anhedral, contain 38–52 ppm uranium, and are interpreted to be metamorphic in origin. One fraction of elongate zircon, and four fragments of a very large zircon (occurring in a nelsonite segregation) yield an upper intercept age of 1045 ± 10 Ma, interpreted as the time of anorthosite crystallization. Irregularly shaped metamorphic zircons are dated at 1011 ± 2 Ma (weighted average of the 207Pb/206Pb ages). The U-Pb isotopic systematics of metamorphic titanite were reset during the Alleghanian orogeny at 297 ± 5 Ma. These data provide a minimum age for gneisses of the Goochland terrane that are intruded by the anorthosite. Middle Proterozoic basement rocks of the Goochland terrane may be correlative with those in the Shenandoah massif of the Blue Ridge tectonic province, as suggested by similarities between the Montpelier Anorthosite and the Roseland anorthosite. Although the areal extent of Middle Proterozoic basement and basement-cover relations in the eastern Piedmont remain unresolved, results of this investigation indicate that the Goochland terrane is an internal massif of Laurentian crust rather than an exotic accreted terrane. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Unshaped basalt blocks from archaeological sites along the border of the Roman Empire (limes) in the lower Rhine area near Vleuten-De Meern (Utrecht) have been studied petrographically, analysed by XRF for major and trace elements, and dated by the 40Ar/39Ar method. The blocks are from a revetment in the bank of a fossil branch of the Rhine and a contiguous ship De Meern 4, both built around 100 AD. All nineteen blocks are alkali olivine basalt (AOB) with xenoliths of peridotite derived from the upper mantle and quartz xenocrysts from the continental crust; eighteen blocks contain resorbed plagioclase xenocrysts as well. Abundances of major and trace elements show that those eighteen samples form a chemically coherent group. The outlier, different in chemistry and without plagioclase xenocrysts, is from the ship. A basalt block from ship De Meern 1 (148 AD) conforms compositionally to the defined group. AOB lumps from a limes watchtower (2nd-3rd century) form a chemically distinct group.Low SiO2 contents (&lt;46 wt.%) and high abundances of Mg, Ti, Ni, and Sr indicate a within-plate origin, directly from primitive melts; proportions of selected trace elements point at a continental rift setting. In the archaeological context, the most likely source region for the blocks is the Cenozoic European Volcanic Province, upstream along the Rhine and its tributaries.The petrographic and analytical data of the blocks have been compared with 432 published analyses of German AOB. On petrographic grounds, the Eifel can be ruled out as a source area since typical Eifel basalt minerals, amphibole, biotite, K-feldspar and feldspatoids, are absent in the blocks. Applying seven geochemical criteria, based on abundances of major elements in the Roman blocks, twelve sites with matching AOB were found in the Siebengebirge, seven in the Vogelsberg, and one in the Westerwald.The ages of the blocks (26.3 - 28.5 Ma) are compatible with ages determined for AOB from the Siebengebirge (27.4 - 29.9 Ma), and preclude their provenance from the Vogelsberg (&lt; 18 Ma). The matching Westerwald sample is from 60 km beyond the limes, a prohibitive distance from the perspective of Roman logistics.AOB quarries of optimal logistic position are located adjacent to the Rhine, between Bonn and Remagen, a zone with significant Roman settlements from the first century AD. Geochemical correlation indicates AOB bodies at Rolandsbogen and Godesburg (S of Bonn) as potential sources of the blocks from the 100 AD revetment and ships. Similarly, the Erpeler Ley (E of Remagen) is indicated as the likely source for the blocks from a 2nd-3rd century AD watchtower.As the Godesburg basalt is at 1.6 km from the Rhine today, it is not obvious how the blocks were transported from there. However, it may be that the adjacent, now sanded, branch of the old Rhine river system, was navigable for flat-bottomed vessels in Roman times.Our study demonstrates that substantial detailed information regarding ancient mining and trading activities can be retrieved from seemingly indistinctive basalt blocks.

Genesis of the Angra dos Reis and other achondritic meteorites

Zircon age peaks are commonly interpreted either as crustal production peaks or as selective preservation peaks of subduction-produced crust selectively preserved during continent-continent collision. We contribute to this ongoing debate, using the Nd isotopic compositions of felsic igneous rocks and their distribution during the accretionary and collisional phases of orogens. The proportion of juvenile input into the continental crust is estimated with a mixing model using arc-like mantle and reworked continental crust end members. Orogen length and duration proxies for juvenile crustal volume show that the amount of juvenile crust produced and preserved at zircon age peaks during the accretionary phase of orogens is ≥3 times that preserved during the collisional phase of orogens. The fact that most juvenile crust is both produced and preserved during the accretionary phase of orogens does not require craton collisions for its preservation, thus favoring the interpretation of zircon age peaks as crustal production peaks. Most juvenile continental crust older than 600 Ma is produced and preserved before final supercontinent assembly and does not require supercontinent assembly for its preservation. Episodic destabilization of a compositionally heterogeneous layer at the base of the mantle may produce mantle plume events leading to enhanced subduction and crustal production. Our Nd isotope model for cumulative continental growth based on juvenile crust proxies for the past 2.5 b.y. suggests a step-like growth curve with rapid growth in accretionary orogens at the times of zircon age peaks.

We present an estimate for the composition of the depleted mantle (DM), the source for mid‐ocean ridge basalts (MORBs). A combination of approaches is required to estimate the major and trace element abundances in DM. Absolute concentrations of few elements can be estimated directly, and the bulk of the estimates is derived using elemental ratios. The isotopic composition of MORB allows calculation of parent‐daughter ratios. These estimates form the “backbone” of the abundances of the trace elements that make up the Coryell‐Masuda diagram (spider diagram). The remaining elements of the Coryell‐Masuda diagram are estimated through the composition of MORB. A third group of estimates is derived from the elemental and isotopic composition of peridotites. The major element composition is obtained by subtraction of a low‐degree melt from a bulk silicate Earth (BSE) composition. The continental crust (CC) is thought to be complementary to the DM, and ratios that are chondritic in the CC are expected to also be chondritic in the DM. Thus some of the remaining elements are estimated using the composition of CC and chondrites. Volatile element and noble gas concentrations are estimated using constraints from the composition of MORBs and ocean island basalts (OIBs). Mass balance with BSE, CC, and DM indicates that CC and this estimate of the DM are not complementary reservoirs.

Part I presents the results of a petrologic investigation of the Trinity peridotite, an enormous ultramafic massif in northern California. The Trinity is an easterly dipping sheet several km thick and composed of a diverse assemblage of ultramafic rocks including dunite, harzburgite, lherzolite, plagioclase lherzolite and clinopyroxene-rich dikes. Because of this diversity and the limited serpentinization, it is an excellent natural laboratory for studying the petrogenesis of ultramafic rocks. The structural history of the peridotite was outlined by detailed field mapping at scales of 1:31,250 and 1:240 at the northeast margin of the massif in the vicinity of Mount Eddy and China Mountain during the summers of 1977-1978. A combined petrographic and electron microprobe investigation was made on selected samples to determine their petrology, mineral chemistry and major element whole rock compositions. The Trinity peridotite is inferred to have originated in the upper mantle at a depth of not less than ~30 km and perhaps as deep as 100 km based on textural evidence for a transition from the spinel lherzolite (>10 kb) stability field to the plagioclase lherzolite (<10 kb) stability field, and on high equilibration temperatures (>1150° C.) preserved in cores of large pyroxene grains. During ascent through the mantle, the rocks deformed plastically, partially melted and reacted with transient melts derived from greater depth. Plastic deformation produced two generations of folds and a penetrative foliation. Pervasive partial melting of the plagioclase lherzolite produced feldspathic segregations, plagioclase-rich veins and resorption textures in pyroxenes and spinel; the composition of the veins suggests that this melt was essentially basaltic. Another melt, not in equilibrium with the peridotite, but also of basaltic affinity, passed through the peridotite, reacted with the ultramafic wall rocks to produce large tabular dunite bodies surrounded by zones of harzburgite and lherzolite, and crystallized clinopyroxene-rich dikes. The end of the ascent of the Trinity through the mantle is marked by intrusion of gabbro, hornblende diorite, diabase and albite granite, and the onset of brittle deformation circa 450-480 m.y. based on zircon ages of the granites (Mattinson and Hopson, 1972). The Trinity was subsequently thrust into the crust at about 380 m.y. based on Rb-Sr dates on rocks of the underlying Central Metamorphic Belt. It is suggested that the passage of the Trinity through the mantle may have occurred beneath an actively spreading back-arc basin. Part II of this thesis is a petrologic investigation of Lunar Rock 12013, one of the most significant lunar samples because of its extreme enrichments in incompatible elements (K, REE, U, etc.) and abundant material. Rock 12013 is best interpreted as a complex mixture of two polymict, impact generated breccias--one black, the other gray. The black breccia is a fragment-laden melt-rock formed by mixing cold, impact-derived mineral and lithic clasts with superheated impact melt of basalted composition. The melt is now crystallized to an aphanite of minute grain size. The gray breccia was also formed as a mixture of melt and impact-derived clasts, but the melt was granitic and crystallized to a fine grained felsite. The clasts in the breccias were derived from lithologies common in Highlands breccias, with the gray breccia dominated by feldspathic gabbro and basalt clasts and the black breccia dominated by quartzofeldspathic and norite clasts. A combined neutron activation, petrographie and electron microprobe analysis demonstrates that the incompatible elements in 12013 are concentrated in the melt-derived lithologies. The origin and relationships of the melts is problematic. Textural relations suggest that the two melts coexisted but did not mix, and some aspects of their major element abundances are compatible with a genetic relationship involving silicate liquid immiscibility (SLI). However, details of their trace element abundances are incompatible with SLI. It is suggested that 12013 is exotic to the Apollo 12 site and was formed by an impact(s) into a terrane of norite and quartofeldspathie plutonic rocks, gabbro and basalt hypabyssal or extrusive rocks, and a thin regolith cover. The two breccia were derived from different parts of this terrane and mixed violently in the ejecta cloud. Most of the radiometric clocks were reset by this event, and Rb-Sr, U-Th-Pb and 40Ar-39Ar yield ages of ~4.0 AE. Rb-Sr data, however, may be interpreted to suggest an age for the felsite protolith of ~4.5 AE. An alternative explanation, consistent with the petrography of the rock, is that the Rb-Sr data reflect mixing and partial equilibration at 4.0 AE of materials no older than 4.2 AE.

Archean greenstone belt magmatism and the continental growth–mantle evolution connection: constraints from Th–U–Nb–LREE systematics of the 2.7 Ga Wawa subprovince, Superior Province, Canada

The most important process affecting both major and trace-element concentrations in the mantle and crust is melting producing silicate liquids which then migrate. Another process whose effects are becoming more apparent is the transport of elements by CO 2 - and H 2 O-rich fluids. Due to the relatively small amounts of fluids involved they have but little effect on the major-element abundances but may severely affect minor- and trace-element abundances in their source and the material through which they travel. The Archaean crust was a density filter which reduced the possibility of komatiite or high FeO melts with relative densities greater than about 3.0 from reaching the surface. Those melts retained in the lower crust or at the crust-mantle boundary would have enhanced the possibility of melting in the lower crust. The high FeO melts may have included the Archaean equivalents of alkali basalt whose derivatives may form an important component in the Archaean crust. The occurrence of ultramafic to basic to alkaline magmas in some Archaean greenstone belts is an assemblage most typical of modern ocean-island suites in continental environments. The rock types in the assemblage were modified by conditions of higher heat production during the Archaean and thus greater extents of melting and melting at greater depths. If modern ocean-island suites are associated with mantle plumes, which even now may be an important way to transport heat upward from the deeper mantle, it is suggested that during the Archaean mantle plumes were an important factor in the evolution of the continental crust. It appears that the Archaean continental crust was of comparable thickness to that of the present based on geobarometeric data. If the freeboard concept applied then, this would suggest that plate tectonics was also an active process during the Archaean. If so, it is probably no more realistic to assume that all Archaean greenstone belts had a similar tectonic setting than to assume that all modern occurrences of basic rocks have a common tectonic setting.

Ancient rocks documenting early silicate Earth processes are only sparsely preserved on its modern surface. Some of the oldest known crustal lithologies (&amp;#8804;3.7 Ga) can be found within the Indian Shield. However, a substantial area of the western and central Indian basement has been covered by the ~66 Ma old Deccan flood basalts. Some Deccan-related mafic dykes in the Nandurbar-Dhule region of the Narmada-Tapi rift zone host xenolithic crustal material, which can be used to study the otherwise inaccessible basement. Textural and mineralogical heterogeneity amongst these xenoliths implies that they derive from different depths of a single column of crust and represent randomly sampled crustal rock types with possibly distinct heritages. Well studied examples of these dykes are the adjacent Rajmane and Talwade dykes south of Duhle, which host Neoarchean-aged [1] crustal xenoliths with highly variable 87Sr/86Sr ratios between 0.70935 and 0.78479 [2]. This led previous researchers to infer a genetic relationship of these xenoliths with rocks from the Dharwar Craton [1, 2].In this study, xenolith samples are used to investigate the evolution of sub-Deccan continental crust and evaluate whether randomly sampled crustal lithologies share a common Hadean heritage that is similar to published data for Dharwar granitic rocks. Our samples (n = 17) originate from two mafic dykes near Talwade and Ranala in the Nandurbar-Dhule region. We report major and trace element abundances and 142Nd isotopic compositions. The CIPW norms of xenoliths define a nearly continuous petrological evolution trend from tonalites to reworked, orthoclase-rich granites, with subordinate trondhjemitic compositions. The vertical cross-section of crust underlying the dykes therefore provides an opportunity to study the geochemistry of evolving primitive continental crust. Trace element abundance data also conform to a tonalite-trondhjemite-granodiorite-like (TTG) composition for a subset of the xenoliths, whereas others resemble younger granitoids, which might represent reworked TTG equivalents, or younger intrusions.The short-lived (t1/2 = 103 Ma) 146Sm-142Nd decay system is particularly sensitive to magmatic fractionation processes that occurred within the first ca. 500 Ma of Earth&amp;#8217;s history. Heterogeneous 142Nd/144Nd compositions (expressed as &amp;#956;142Nd = [(142Nd/144Nd)sample/(142Nd/144Nd)JNdi &amp;#8211; 1] * 106) are typically restricted to Archean-aged rocks and reveal information about the preservation of mantle heterogeneity over geological timescales. The &amp;#956;142Nd of dyke host lavas (n = 3) are heterogeneous (&amp;#956;142Nd = -2.0 &amp;#177;5.1 to +6.1 &amp;#177;5.1) but unresolved from the terrestrial standard. Such heterogeneity suggests that the parental magmas to the dykes experienced complex lithospheric and crustal assimilation during their ascent. Felsic xenoliths have homogeneous &amp;#956;142Nd compositions (&amp;#956;142Nd = -0.9 &amp;#177;2.3, 95% c.i., n = 7). Combined with the major and trace element data, this implies an extensively reworked crust underneath the Deccan Traps. The lack of recognizable &amp;#956;142Nd anomalies is consistent with data of younger Dharwar granitoids [3] and may reflect regional overprinting of mantle &amp;#956;142Nd heterogeneity at or before the Neoarchean emplacement age of the xenoliths.&amp;#160;[1] Upadhyay et al. (2015) J. Geol. 123(3), 295&amp;#8211;307.[2] Ray et al. (2008) Gondwana Res. 13, 375&amp;#8211;385.[3] Ravindran et al. (2022) Goldschmidt Abst. 10986.

The <i>ca</i>. 2.5 Ga as the time boundary between the Archean and the Proterozoic eons is a landmark, indicating the most important continental crust evolving stage of the Earth, that is, the global cratonization or the formation of supercraton(s) that was unseen before and is unrepeated in the following history of the Earth9s formation and evolution. The North China Craton (NCC) is one of the best recorders of the <i>ca</i>. 2.5 Ga event, and therefore studies in the thorough understanding of early Precambrian continental evolution are continuous. The period from 2.8 to 2.6 Ga is the major crustal growth period of the NCC and formed seven micro-blocks. All the micro-blocks in the NCC were surrounded by 2.6 to 2.54 Ga greenstone belts. The clear geological presentations are as follows: (1) Archaic basement rocks in North China (various micro-blocks) experienced strong partial melting and migmatization. The granitoid rocks derived from crustal partial melting include potassium, TTG and monzonitic granitoids, which come, respectively, from continental crust (sedimentary rocks with TTG gneisses), juvenile crust (mafic rocks with TTG gneisses) or mixed crust; (2) the BIF-bearing supracrustal rocks are mainly distribute in greenstone belts. The lithologic associations in the greenstone belts within the NCC are broadly similar, belonging to volcano-sedimentary sequences, with common bimodal volcanic rocks (basalt and dacite) interlayered with minor amounts of komatiites in the lower part, and calc-alkalic volcanic rocks (basalt, andesite and felsic rocks) in the upper part; (3) nearly all old rocks of &gt;2.5 Ga underwent ∼2.52 to 2.5 Ga metamorphism of amphibolite–granulite facies. Most metamorphosed rocks show high-temperature-ultra-high-temperature (HT–UHT) characteristics and record anticlockwise <i>P–T</i> paths, albeit a small number of granulites seemingly underwent high-pressure granulite facies metamorphism and record clockwise <i>P–T</i> paths; (4) ∼2.5 Ga mafic dikes (amphibolites), granitic dikes (veins) and syenitic–ultramafic dikes developed across these archaic basements and were strongly deformed or un-deformed; (5) the extensive 2.52 to 2.48 Ga low-grade metamorphic supracrustal covers has been recognized in eastern, northern and central parts of the NCC, which are commonly composed of bi-modal volcanic rocks and sedimentary rocks. The above mentioned ∼2.5 Ga geological rocks and their characters imply that the seven micro-blocks have been united through amalgamation to form the NCC. The metamorphosed late Neoarchean greenstone belts, as syn-formed mobile belts, welded the micro-blocks at the end of the Neoarchean. However, the metamorphic thermal grades of the greenstone belts are lower than those of the high-grade terranes within the micro-blocks, suggesting that the latter might have developed under a higher geothermal gradient than the former. Besides, the greenstone belts surround the various micro-blocks in the late Neoarchean when both the old continental crust and the oceanic crust were hotter. The subduction during the amalgamation, if it happened, must have been much smaller in scale as compared to those in the Phanerozoic plate tectonic regime, and all stages occurred at crust-scale instead of lithosphere-scale or mantle-scale. This is why most rocks record HT-UHT and anti-clockwise metamorphism, while only a few samples record high-pressure granulite facies metamorphism with clockwise <i>P–T</i> paths. The micro-block amalgamation was accompanied by extensive crust partial melting and granitization, which finally gave rise to the stabilization of the NCC. Except for the vast granitoid intrusions, mafic-syenitic dike swarms and sedimentary covers are also landmarks of cratonization. The <i>ca</i>. 2.5 Ga cratonization is a global epoch-making geological event, although the accomplishment of cratonization in various cratons is somewhat different in time. Cratonization declared the formation and stabilization of global-scale supercratons or cratonic groups coupling with lithosphere, which was followed by a “silent period” with rare tectonic-thermal action lasting 150 to 200 Ma (from 2.5 Ga – 2.3 or 2.35 Ga), and then followed by the Great Oxidation Event (GOE).

Highly siderophile element (HSE: Os, Ir, Ru, Pt, Pd, Re), major and trace element abundances, and 187Re–187Os systematics are reported for xenoliths and lavas from Aitutaki (Cook Islands), to investigate the composition of Pacific lithosphere. The xenolith suite comprises spinel-bearing lherzolites, dunite, and harzburgite, along with olivine websterite and pyroxenite. The xenoliths are hosted within nephelinite and alkali basalt volcanic rocks (187Os/188Os ∼0·1363 ± 13; 2SD; ΣHSE = 3–4 ppb). The volcanic host rocks are low-degree (2–5%) partial melts from the garnet stability field and an enriched mantle (EM) source. Pyroxenites have similar HSE abundances and Os isotope compositions (Al2O3 = 5·7–8·3 wt %; ΣHSE = 2–4 ppb; 187Os/187Os = 0·1263–0·1469) to the lavas. The pyroxenite and olivine websterite xenoliths directly formed from—or experienced extensive melt–rock interaction with—melts similar in composition to the volcanic rocks that host the xenoliths. Conversely, the Aitutaki lherzolites, harzburgites and dunites are similar in composition to abyssal peridotites with respect to their 187Os/188Os ratios (0·1264 ± 82), total HSE abundances (ΣHSE = 8–28 ppb) and major element abundances, forsterite contents (Fo89·9±1·2), and estimated extents of melt depletion (&amp;lt;10 to &amp;gt;15%). These peridotites are interpreted to sample relatively shallow Pacific mantle lithosphere that experienced limited melt–rock reaction and melting during ridge processes at ∼90 Ma. A survey of maximum time of rhenium depletion ages of Pacific mantle lithosphere from the Cook (Aitutaki ∼1·5 Ga), Austral (Tubuai’i ∼1·8 Ga), Samoan (Savai’i ∼1·5 Ga) and Hawaiian (Oa’hu ∼2 Ga) island groups shows that Mesoproterozoic to Neoproterozoic depletion ages are preserved in the xenolith suites. The variable timing and extent of mantle depletion preserved by the peridotites is, in some instances, superimposed by extensive and recent melt depletion as well as melt refertilization. Collectively, Pacific Ocean island mantle xenolith suites have similar distributions and variations of 187Os/188Os and HSE abundances to global abyssal peridotites. These observations indicate that Pacific mantle lithosphere is typical of oceanic lithosphere in general, and that this lithosphere is composed of peridotites that have experienced both recent melt depletion at ridges and prior and sometimes extensive melt depletion across several Wilson cycles spanning periods in excess of two billion years.

Abstract— Literature data on major and trace elemental abundances and water contents of the shergottite, nakhlite, and chassigny (SNC) meteorites are compiled and evaluated. The individual members of the SNC group are relatively homogeneous, and representative average compositions for each meteorite can be computed from multiple data reported in the literature. Major element abundances are used to calculate normative compositions and densities. The data survey shows that our knowledge of whole rock abundances in SNC meteorites is very limited for many elements and that more basic analytical work is needed.

Understanding the evolution of the mantle requires a knowledge of the relative variations of the major elements, trace elements and isotopes in the mantle. Most of the evidence for mantle heterogeneity is based on variations in the trace element and isotopic ratios of basaltic rocks. These ratios are presumed to reflect variations in the mantle sources. To compare major element heterogeneities with trace element and isotopic heterogeneities, it is necessary that the major element abundances in basalts also reflect variations in the mantle sources. Probably the only major element for which this is so is iron. If a basalt has only undergone fractional crystallization of olivine, then the abundance of FeO in the basalt reflects the FeO/MgO ratio of the mantle source, the degree of melting, and the pressure at which melting occurs. Relative pressures and degrees of melting can often be constrained, so that variations in the abundances of FeO can be used to obtain information about variations in the FeO/MgO ratio of the mantle sources of basalts. Comparison of FeO contents with trace element and isotopic contents of basalts shows some striking correlations and leads to the following conclusions. 1. Parental magmas for Kilauean basalts from Hawaii may be related by different degrees of melting of a homogeneous, garnet-bearing source. 2. Mid-ocean ridge basalts from the North Atlantic show a negative correlation of La/Sm with FeO, suggesting that the sources that are most enriched in incompatible trace elements are most depleted in FeO relative to MgO, and are probably also depleted in the other components of basalt. This correlation does not apply to the entire suboceanic mantle. 3. A comparison of tholeiites from near the Azores and from Hawaii shows that sources with similar Nd and Sr isotope ratios may have undergone distinctly different histories in the development of their major and trace element abundances. 4. Ocean island tholeiites tend to be more enriched in FeO than ocean floor tholeiites. Either the ocean island sources have greater FeO/MgO ratios, or melting begins at significantly greater pressures beneath ocean islands than beneath ocean ridges. 5. Major element variations in the mantle are controlled mainly by tectonics and the addition or removal of silicate melts. Trace element variations, however, may be controlled by the addition or removal of fluids as well. Thus major elements, trace elements and isotopes may each give a different perspective important to the understanding of the evolution of the mantle.

WE have determined major and trace element abundances for seven Ca,Al-rich aggregates, ten melilite chondrules, and an olivine chondrule and two olivine-rich aggregates from the Allende meteorite, a type III carbonaceous chondrite. Major element abundances were determined with the electron microprobe technique described by Reed and Ware1. An MS7 spark source mass spectrometer was used for the determination of trace element abundances. The technique used was that described by Taylor2 but with improved and extended data reduction techniques. The precision is about ±5% for the rare earth elements (REEs) and the accuracy about ±10%, but varies somewhat, being poorer for elements below mass number 105 than for those with higher mass numbers.