The Bowen Reaction Series in Geology

The Bowen Reaction Series in Geology The Bowen reaction series is a description of how magmas minerals change  as they cool. The petrologist Norman Bowen (1887-1956) carried out decades of melting experiments in the early 1900s in support of his theory of granite. He found that as a basaltic melt slowly cooled, minerals formed crystals in a definite order. Bowen worked out two sets of these, which he named the discontinuous and continuous series in his 1922 paper The Reaction Principle in Petrogenesis. The Bowen's Reaction Series The discontinuous series starts with olivine, then pyroxene, amphibole, and biotite. What makes this a reaction series rather than an ordinary series is that each mineral in the series is replaced by the next one as the melt cools. As Bowen put it, The disappearance of minerals in the order in which they appear ... is of the very essence of the reaction series. Olivine forms crystals, then it reacts with the rest of the magma as pyroxene forms at its expense. At a certain point, all the olivine is resorbed, and only pyroxene exists. Then pyroxene reacts with the liquid as amphibole crystals replace it, and then biotite replaces amphibole. The continuous series is plagioclase feldspar. At high temperatures, the high-calcium variety anorthite forms. Then as temperatures fall it is replaced by more sodium-rich varieties: bytownite, labradorite, andesine, oligoclase, and albite. As the temperature continues to fall, these two series merge, and more minerals crystallize in this order: Alkali feldspar, muscovite, and quartz. A minor reaction series involves the spinel group of minerals: chromite, magnetite, ilmenite, and titanite. Bowen placed them between the two main series. Other Portions of the Series The complete series is not found in nature, but many igneous rocks display portions of the series. The main limitations are the state of the liquid, the speed of cooling and the tendency of mineral crystals to settle under gravity: If the liquid runs out of an element needed for a particular mineral, the series with that mineral gets interrupted.If the magma cools faster than the reaction can proceed, early minerals can persist in partly resorbed form. That changes the evolution of the magma.If crystals can rise or sink, they stop reacting with the liquid and pile up somewhere else. All of these factors affect the course of a magmas evolution- its differentiation. Bowen was confident that he could start with basalt magma, the most common type, and build any magma from the right combination of the three. But mechanisms that he discounted- magma mixing, assimilation of country rock and remelting of crustal rocks- not to mention the whole system of plate tectonics he did not foresee, are much more important than he thought. Today we know that not even the largest bodies of basaltic magma sit still long enough differentiate all the way to granite.

Battle of Carillon in the French and Indian War

Battle of Carillon in the French and Indian War The Battle of Carillon was fought July 8, 1758, during the French Indian War (1754-1763). Forces Commanders British Major General James AbercrombieBrigadier General Lord George Howe15,000-16,000 men French Major General Louis-Joseph de MontcalmChevalier de Levis3,600 men Background Having suffered numerous defeats in North America in 1757, including the capture and destruction of Fort William Henry, the British sought to renew their efforts the following year. Under the guidance of William Pitt, a new strategy was developed which called for attacks against Louisbourg on Cape Breton Island, Fort Duquesne at the forks of the Ohio, and Fort Carillon on Lake Champlain. To lead this last campaign, Pitt desired to appoint Lord George Howe. This move was blocked due to political considerations and Major General James Abercrombie was given command with Howe as brigadier general (Map). Assembling a force of around 15,000 regulars and provincials, Abercrombie established a base at the southern end of Lake George near the former site of Fort William Henry. Opposing the British efforts was Fort Carillons garrison of 3,500 men led by Colonel Franà §ois-Charles de Bourlamaque. On June 30, he was joined by the overall French commander in North America, Marquis Louis-Joseph de Montcalm. Arriving at Carillon, Montcalm found the garrison insufficient to protect the area around the fort and possessing food for only nine days. To aid the situation, Montcalm requested reinforcements from Montreal. Fort Carillon Construction on Fort Carillon had begun in 1755 in response to the French defeat at the Battle of Lake George. Built on Lake Champlain, near the northern point of Lake George, Fort Carillon was situated on a low point with the La Chute River to the south. This location was dominated by Rattlesnake Hill (Mount Defiance) across the river and by Mount Independence across the lake. Any guns emplaced on the former would be in position to bombard the fort with impunity. As the La Chute was not navigable, a portage road ran south from a sawmill at Carillon to the head of Lake George. The British Advance On July 5, 1758, the British embarked and began moving over Lake George. Led by the industrious Howe, the British advance guard consisted of elements of Major Robert Rogers rangers and light infantry led by Lieutenant Colonel Thomas Gage. As the British approached on the morning of July 6, they were shadowed by 350 men under Captain Trà ©pezet. Receiving reports from Trà ©pezet regarding the size of the British force, Montcalm withdrew the bulk of his forces to Fort Carillon and began building a line of defenses on a rise o to the northwest. Beginning with entrenchments fronted by thick abatis, the French line was later strengthened to include a wooden breastwork. By noon on July 6, the bulk of Abercrombies army had landed at the northern edge of Lake George. While Rogers men were detailed to take a set of heights near the landing beach, Howe began advancing up the west side of the La Chute with Gages light infantry and other units. As they pushed through the wood, they collided with Trà ©pezets retreating command. In the sharp firefight that ensued, the French were driven off, but Howe was killed. Abercrombies Plan With Howes death, British morale began to suffer and the campaign lost momentum. Having lost his energetic subordinate, Abercrombie took two days to advance on Fort Carillon, which normally would have been a two-hour march. Shifting to the portage road, the British established a camp near the sawmill. Determining his plan of action, Abercrombie received intelligence that Montcalm possessed 6,000 men around the fort and that the Chevalier de Là ©vis was approaching with 3,000 more. Là ©vis was approaching, but with only 400 men. His command joined Montcalm late on July 7. On July 7, Abercrombie dispatched engineer Lieutenant Matthew Clerk and an aide to scout the French position. They returned reporting that it was incomplete and could be easily carried without artillery support. Despite a suggestion from Clerk that guns should be emplaced atop and at the base of Rattlesnake Hill, Abercrombie, lacking imagination or an eye for terrain, set upon a frontal assault for the next day. That evening, he held a council of war, but only asked whether they should advance in ranks of three or four. To support the operation, 20 bateaux would float guns to the base of the hill. The Battle of Carillon Clerk again scouted the French lines on the morning of July 8 and reported that they could be taken by storm. Leaving the majority of the armys artillery at the landing site, Abercrombie ordered his infantry to form with eight regiments of regulars in the front supported by six regiments of provincials. This was completed around noon and Abercrombie intended to attack at 1:00 PM. Around 12:30, fighting began when New York troops began engaging the enemy. This led a ripple effect where individual units began fighting on their fronts. As a result, the British attack was piecemeal rather than coordinated. Fighting forward, the British were met by heavy fire from Montcalms men. Taking severe losses as they approached, the attackers were hampered by the abatis and cut down by the French. By 2:00 PM, the first assaults had failed. While Montcalm was actively leading his men, sources are unclear as to whether Abercrombie ever left the sawmill. Around 2:00 PM, a second attack went forward. About this time, the bateaux carrying guns to Rattlesnake Hill came under fire from the French left and the fort. Rather than push forward, they withdrew. As the second assault went in, it met with a similar fate. Fighting raged until around 5:00 PM, with the 42nd Regiment (Black Watch) reaching the base of the French wall before being repulsed. Realizing the scope of the defeat, Abercrombie ordered his men to fall back and a confused retreat ensued to the landing site. By the next morning, the British army was withdrawing south across Lake George. Aftermath In the assaults at Fort Carillon, the British lost 551 killed, 1,356 wounded, and 37 missing against French casualties of 106 killed and 266 wounded. The defeat was one of the bloodiest battles of the conflict in North America and marked the only major British loss of 1758 as both Louisbourg and Fort Duquesne were captured. The fort would be captured the British the following year when Lieutenant General Jeffrey Amhersts advancing army claimed it from the retreating French. Following its capture, it was renamed Fort Ticonderoga.